UNIVERSITY OF WISCONSIN-LA CROSSE Graduate Studies BENEFITS, DISADVANTAGES, AND CHALLENGES OF RESPIRATORY GATING USED TO TREAT LEFT-SIDED BREAST CANCER PATIENTS RECEIVING RADIOTHERAPY A Research Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Medical Dosimetry Lisa Wojtowicz College of Science & Health Medical Dosimetry Program July 2012
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Benefits, Disadvantages, and Challenges of Respiratory Gating
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UNIVERSITY OF WISCONSIN-LA CROSSE
Graduate Studies
BENEFITS, DISADVANTAGES, AND CHALLENGES OF RESPIRATORY GATING USED
TO TREAT LEFT-SIDED BREAST CANCER PATIENTS RECEIVING RADIOTHERAPY
A Research Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Medical Dosimetry
Lisa Wojtowicz
College of Science & Health Medical Dosimetry Program
July 2012
2
July 23, 2012
BENEFITS, DISADVANTAGES, AND CHALLENGES OF RESPIRATORY GATING USED
TO TREAT LEFT-SIDED BREAST CANCER PATIENTS RECEIVING RADIOTHERAPY
By Lisa Wojtowicz
We recommend acceptance of this project report in partial fulfillment of the candidate's
requirements for the degree of Master of Science in Medical Dosimetry.
The candidate has met all of the project completion requirements.
Nishele Lenards, M.S. Date
Graduate Program Director
3
The Graduate School University of Wisconsin-La Crosse
La Crosse, WI
Author: Wojtowicz, Lisa
Title: Benefits, disadvantages, and challenges of respiratory gating used to treat left-
sided breast cancer patients receiving radiotherapy.
Graduate Degree/ Major: MS Medical Dosimetry
Research Advisor: Nishele Lenards, M.S.
Month/Year: July 2012
Number of Pages: 50
Style Manual Used: AMA, 10th edition
Abstract
Left-sided breast cancer patients receiving radiation therapy may experience long term
effects to their heart resulting in cardiac toxicities. Respiratory gating is used in an effort to
decrease the radiation delivered to the cardiac tissues of these patients during treatment. This
research discusses the applicable scientific literature and specifically examines the use of
respiratory gating in a retrospective study. In this study, 10 left-sided breast cancer patients
treated with respiratory gating were analyzed for mean dose of radiation to the heart, left
ventricle, and lung volume. The dosimetric plan with respiratory gating was compared to the
non-respiratory gating scan. The results showed a 15.5% decrease in the mean dose delivered to
the heart and a 17.7% decrease in mean dose delivered to the left ventricle in the plans where
gating was used. A 15.4% increase in the lung volume being treated was also recorded. The
results of this research, which support the literature reviewed, affirm that respiratory gating is an
appropriate and effective method of limiting radiation exposure in left-sided breast cancer
patients receiving radiation therapy.
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The Graduate School University of Wisconsin - La Crosse
La Crosse, WI
Acknowledgments
Thank you to my director, Nishele Lenards and my mentor, Kim Schmidt for the
guidance and helpful advice throughout this research project. Many thanks to the entire radiation
oncology staff at Gundersen Lutheran Medical Center in La Crosse, WI. Thank you Lindsey
Shields, for taking the time out of your day to proofread and edit my research paper. Mom, thank
you for being my number one fan for the duration of the medical dosimetry program. Grandma
Mills you taught me that determination and perseverance are two of the most important skills in
succeeding in life goals. Dad, thank you for taking the time to listen and for helping me move
across states so I could take my first professional job as a medical dosimetrist. Thank you Jessie,
for your laughter and bright attitude could always bring a smile to my face. My dear family and
friends thank you so much for the words of encouragement along the way. I sincerely appreciate
all of the support and cheer during the exciting challenges I encountered in the medical
(SIMRT), and beamlet IMRT (IMRT) to determine target coverage and dose to the normal
structures in relationship to respiratory motion. CWT method has been the technique of choice
for treating breast cancer in the past; however, patients that have larger breasts have an increase
in dose to the lung and heart while the breast tissue dose coverage is inhomogeneous.8 In order to
create a more optimal treatment plan, SIMRT or IMRT techniques are used to decrease the
amount of hot spots while delivering less dose to the normal structures. This study featured an
active breathing control (ABC) procedure.8 Active breathing control is a method that measures
breathing cycles and stops breathing at a specific phase of the respiratory cycle.7 Overall there
was not a significant change to the clinical target volume (CTV) in respect to respiratory motion
when using the planning techniques CWT and SIMRT. Although the IMRT plans were
conformal, respiratory motion modified target dose coverage. There were significant changes in
target coverage for the IMRT plans which led the researchers to recommend that respiratory
motion be accessed when the patient is simulated for treatment. If the medial marker motion is
less than 0.6 cm, a predetermined value, which can be measured from an end of expiration (EE)
and end of inspiration (EI) CT simulation scan or 4DCT, then the IMRT treatment modality is
appropriate for use. However, if the medial marker motion is greater than 0.6 cm respiratory
gating is needed to achieve adequate tumor coverage and limit the dose to the lungs and heart.8
A study performed by Borger et al26 examined the exposure to the heart when comparing
left and right-sided breast cancer. This is an important study to consider in terms of the use of
respiratory gating. This study concluded that left-sided breast cancer patients have an increased
risk for developing cardiovascular disease.26 This study included 1601 patients treated for breast
cancer during 1980 and 1993. Out of the 1601 patients 94% were compliant in follow-up. The
patients were treated using tangential beams at five different hospitals. Cardiovascular disease
was seen in 14.1%, ischemic heart disease 7.3%, and other forms of heart disease, 9.2%. Patients
started experiencing heart disease 10 to 11 years after radiation therapy. Patients who received
left-sided breast cancer radiotherapy had a greater incidence of cardiovascular disease (16%)
compared to those who had right-sided radiation (11.6%). This study measured the maximum
heart depth (MHD) to determine if the risk for developing cardiovascular disease increases when
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larger irradiated heart volumes are used in treatment. The study concluded that there was no
clinical significant increase in patients treated with larger heart volumes.26
Patients being treated for breast cancer by means of radiotherapy have been shown to
develop ischemic heart disease which may lead to death. After several studies reported the
elevated dose to the heart, numerous procedures were examined to decrease the heart dose.
Respiratory motion and intensity modulated planning were used to decrease the dose. A recent
study by Wang et al4 found it is important to monitor the patient’s cardiac motion, independently
of the patient’s respiratory cycle during deep-inspiration breath hold (DIBH). The researchers
looked at how much radiation was delivered during treatment of the breast to the posterior and
LAD coronary artery. Upon conclusion of the study, the researchers recommended that the LAD
coronary artery remain at least 5 mm from the field edge to decrease exposure to the heart.4
Left-sided breast cancer patients have been shown to experience more cardiac toxicity
after radiation therapy. Correa et al27 conducted a study to review the relationship that existed
between radiotherapy, cardiac markers, and clinical diagnosis of cardiac disease. The study
found a higher number of patients treated for left-sided breast cancer by the conventional
tangential beam method were experiencing latent heart tissue toxicities which were documented
by patient symptoms and abnormal laboratory values. The region of the heart damaged by the
radiation breast field was the LAD coronary artery. The research study stated 3DCRT, which is
currently the standard way of treating breast cancer patients, dramatically decreased dose to heart
and improved the survival rates of breast cancer patients.27
The heart is a known concern to radiation oncologists when prescribing radiation to the
breast region. The patient’s lungs are another normal structure included in the radiation field and
require additional attention to decrease the chances of the patient developing pneumonitis.
Korreman et al28 performed a retrospective study that included 33 patients. All of the patients in
the study had DIBH and free breathing (FB) scans, 17 of the patients had an inspiration gating
(IG) scan. The study evaluated cardiac damage and pneumonitis in patients receiving
radiotherapy after surgery. Researchers used radiobiological normal tissue complication
probability (NTCP) models to examine the probability of cardiac and pneumonitis complications.
This research showed a decrease in pneumonitis and cardiac mortalities after evaluating the
NTCP calculated values for patients treated with breast radiotherapy. The results demonstrated
that DIBH and IG make a significant impact on decreasing the patient’s chance of dying from
cardiac issues created by radiation and decreasing the likelihood of developing pneumonitis.28
24
The radiation treatment plan has evolved over several years to create an optimal plan that
covers the breast tissue accurately while decreasing the dose to the normal structures. McIntosh
et al 25 reviewed the reproducibility of patient setups for left-sided breast cancer patients during
deep inhalation breath hold treatments. Women treated for left-sided breast cancer were
documented as having increased cardiac symptoms. The symptoms included chest pain, coronary
artery disease, and myocardial infarction. Stress tests were done amongst right-sided and left-
sided breast cancer patients. The results from the stress tests showed abnormal results in 70% in
the patient’s LAD coronary artery of the left-sided breast cancer patients receiving radiation
therapy. The McIntosh et al 25 study used the Varian real-time position management (RPM)
system to examine the voluntary deep inhalation breath hold (VDIBH) method rather than the
ABC. The VDIBH and ABC method are used to decrease the radiation exposure to the heart
while maintaining the physician designated tumor volume. The LAD coronary artery and heart
radiation exposure is decreased when using the VDIBH because it increases the amount of space
between the breast target and heart. This study, which included 10 patients, examined the ability
to position a patient in the same position in the treatment appointment as was used in the
simulation appointment.25 This study was the first to examine VDIBH in the heart location in
three dimensions during treatment.25 In order to determine the patient setup accuracy for the
patient’s treatment the researchers co-registered orthogonal AP/LAT kV images. By measuring
these images the researchers were able to determine the relationship between the displacement of
the external RPM marker motion and the internal bony anatomy breath hold.25 Since the heart
dose was determined the heart volume used was shifted in alignment with the bony anatomy. The
researchers report that the shifts were minimal so they did not take into effect heterogeneity
differences in tissue.25
The McIntosh et al 25 study determined, that the VDIBH technique offered three positive
functions.
1)The heart moves inferiorly and posteriorly with respect to the left breast, distancing the
heart from the left anterior chest wall; 2) breath hold immobilizes the whole breast and
lumpectomy cavity, reducing PTV expansions for respiratory motion; and 3) it is relatively
inexpensive and can be widely adopted in most clinics.25
The radiation delivered to the heart was drastically reduced using the VDIBH technique. The
median heart dose volume getting more than 50% of the prescribed radiation dose went from
19.2% (FB technique) to 1.9% (VDIBH technique) The median LAD coronary artery volume
25
receiving more than 50% of the prescription dose went from 88.9% (FB technique) to 3.6%
(VDIBH technique).25 The overall difference in the ability to reproduce the patient setup during
treatment was a maximum of 3 millimeters. Through the research conducted, the team was able
to develop a standardized VDIBH radiation therapy procedure for left-sided breast cancer
patients. The standard procedure enabled the group to determine the amount of radiation
exposure to the heart and LAD coronary artery when using the VDIBH technique. The
evaluation of the results concluded that the VDIBH technique decreases the heart dose compared
to the FB technique and is an effective form of treatment because of the reproducibility level.25
In a study similar to McIntosh et al,25 Borst et al 29 evaluated the effect of image-guided
deep inspiration breath hold during breast radiotherapy. Borst et al29 examined 19 patients treated
with the deep inspiration breath hold (DIBH) procedure. Researchers determined the dose
delivered to the ipsilateral breast/thoracic wall, heart, (LV), and the LAD coronary artery. The
DIBH technique was compared to the FB technique. The reproducibility for the technique was
also measured during treatment. The patient position was modified during setup with the use of
cone-beam CT (CBCT) and observed by the 2D fluoroscopy and megavoltage electronic portal
imaging device (EPID) images.29 The Borst et al29 study demonstrated that the DIBH procedure
was simple to implement for treatment and decreased the dose to the heart, LV, and LAD
coronary artery without compromising the dose delivered to the target volume. Borst et al29
acknowledged limitations to the study, such as contrast not being used which impacted the LAD
coronary artery structure definition. Researchers contoured the first part of the LAD coronary
artery which was visible on all patients to develop consistency. The setup error was determined
for the breast and the organs at risk. Researchers found that the setup error did not have clinical
implications on the target volume and organs at risk.29
As the treatment modalities have improved over the years the longevity of breast cancer
patients has also increased. In order to decrease the cardiac toxicities associated with radiation
therapy in left-sided breast cancer patients, the dose to the heart needs to decrease to spare the
heart tissue. In addition to the radiation dose to the heart, the heart is also at an increased risk for
damage from the advanced, but severe cardiotoxic agents used in chemotherapy. There are
numerous studies that discuss how respiratory motion affects the dosimetric data treatment plans
and include the evaluation of respiratory motion and dose to target and avoidance structures in
terms of respiratory gating procedures.
26
Orlanzino et al30 selected 12 patients to evaluate the need for respiratory gating in
patients being treated for breast cancer with radiation therapy. Researchers were interested in the
relationship between the breast volume and chest wall interface since the target moves during
respiratory motion. The study was conducted to determine if the respiratory gating procedure
was necessary in radiation treatment of breast cancer. The study used a Varian Acuity simulator
to measure the movement between patient’s intact breast and chest wall. The distances between
the 2 volumes were measured using orthogonal anterior and lateral images. All 12 patients were
simulated in the supine position and utilized typical immobilization techniques for breast
patients. To quantify the distance between the breast target volume and chest wall during scans
BBs were placed at isocenter, and at 5 cm superior, inferior, lateral, and medial.30 The study was
interested in determining the patient’s normal respiratory pattern so patients were not given
guidelines for breathing during the scans.30 A typical breathing rate is 16-18 breaths per minute,
so the researchers obtained the images in 20 second intervals to measure the breathing pattern of
patients for 5-6 breathing cycles. The images were obtained for every one second period. The
results showed minimal movement between the target breast volume and chest wall. The average
maximum distance between the target breast volume and chest wall BBs were: 1.83 mm ± 1.08
mm sup-inf, 0.58 mm ± 0.21 mm lat-med, and 1.90 mm ± 1.04 mm ant-post axes.30 The study
concluded that the respiratory gating procedure used in breast cancer radiotherapy would not
have a large impact on the target volume in the efficacy of treatment. Researchers proposed that
improving image-guided localization as opposed to target motion may be more important in
improving the breast cancer radiotherapy.30
Aznar et al24 also studied breast cancer treatment in terms of efficacy of radiation therapy
similar to Orlanzino et al.30 The team of researchers was interested in the various respiration
patterns and the gating window range when using amplitude-gating when delivering radiation by
3DCRT and IMRT treatment plans. The study used the Varian Medical systems RPM method
and two-dimensional (2D)-array of ion chambers.24 The researchers devised specific methods to
evaluate the respiratory gating procedure.24 The breathing rate was quantified for two respiratory
cycle intervals, which were 4 and 6 seconds along with 5, 10, and 25 mm degrees in motion. The
gating window settings used were, 1.5, 2.4, and 5 mm. Researchers concluded that the
respiratory gating procedure improved the radiation delivery outcome.24 Aznar et al24
demonstrated that respiratory gating also improves the treatment delivery to the tumor volume
through the use of respiratory gating. Researchers used the gamma index (3%, 3 mm, dose range,
27
5-500% and 90-500%) in combination with determining the variance among the hot and cold
spots in the treatment plan.24 After analyzing the results, Aznar et al24 concluded that respiratory
gating gave a gamma pass rate and did not have hot and cold spots in the dosimetric plan from
the patient’s respiratory motion. The efficacy tumor volume results obtained by Aznar et al24
study contradicted the results found by Orlanzino et al.30
Accurate quality assurance (QA) is needed in all aspects of radiation therapy. QA for
respiratory gating has unique challenges because of the added temporal dimension.31 The goal of
the QA is to ensure clinically accurate treatment is delivered when respiratory gating is used.31
One main issue for respiratory gating and breath holding QA is determining treatment accuracy
when the internal target is indicated using external replacements. Testing of the software and
hardware is needed to ensure proper simulation, planning, patient localization, treatment, and
verification.31 Respiratory gating can be broken down into two different methods: internal and
external. The more common form of gating is external gating. In an external gating system the
box is placed on the patient’s abdomen. Fiducial markers are an example of an internal gating
system.31 Internal gating systems are not used often because they are only used in the real-time
tumor tracking (RTTT) system. An inaccuracy foreseen in respiratory gating is the determination
of tumor location from external breathing signals. Over time, the relationship between tumor
movement and the box signal change interfractionally and intrafractionally.31
In an effort to examine QA techniques for respiratory gating, Jiang et al31 used RPM by
Varian; this system uses the motion created by the abdomen as the signal. The following QA
procedure is recommended by Jiang et al.31 1.During treatment simulation, the reference home position should be accurately measured, using
techniques such as 4D CT. 2. During treatment planning, the patient and tumor geometry corresponding to
the gating window should be used. 3. During patient setup, the tumor home position at this fraction should
be matched to the reference home position. 4. During the treatment delivery, measures should be taken to
maintain a constant tumor home position, i.e. the tumor should always be at the same position when the
beam is turned on. 5. During the treatment delivery, tumor positions corresponding to the gating window
should be measured and compared with the reference tumor home position, either on- or offline.31
Jiang et al31 stated that steps one and two are simple while step three requires more effort and
they advise that image guidance techniques be used to ensure that the tumor home position and
the reference home position match. This is an important step because it will help decrease the
inter-fraction difference amid the external surrogate signal and the internal target location. Step
four states that the tumor should always be at the correct position when the beam is turned on. To
28
increase the accuracy, patient breath coaching is used. Massachusetts General Hospital
developed a system that requires a patient to wear video goggles in order to view their own
breathing pattern. The patient watches the video and aims to put their end of exhale position
between two lines; this additional QA step is necessary at simulation, patient setup, and
treatment delivery to ensure consistency. Step five is needed to monitor that the tumor location is
within the gating window. During treatment, the patient is monitored by watching the location of
the tumor in comparison to the reference position and tolerance zone. If the patient’s tumor
location does not lie within the tolerance zone, the therapist is able to stop treatment and adjust
the patient.
The treatment for left-sided breast cancer patients has been continuously evaluated in
order to decrease the dose to the heart which in turn would decrease the patient’s probability of
developing cardiac toxicities. Borer et al26 completed a retrospective study for left and right-
sided breast cancer patients to determine if there was an increased risk for patients treated on the
left-side. Researchers found that left-sided cancer patients were more likely to develop cardiac
problems later on.26 To track the dose to the heart and substructures, Feng et al21 developed an
atlas to help define these structures. Defining the OR with accurate consistency is an important
factor in measuring the normal structures in the field along with deciding the optimal OR for
treatment sites. Previous studies have documented the heart as an OR. Tan et al14 studied the
AMT in comparison to the heart in breast radiation therapy. The Tan et al14 study concluded that
when using the AMT as an OR the treatment plan did not compromise dose coverage while
decreasing dose to the heart. The patient’s lungs are also a concern during treatment. Korreman
et al28 determined that patients utilizing DIBH and IG during breast radiotherapy treatment
significantly decreased the chance of developing cardiac problems later on and lessening the
chance of developing pneumonitis. The combination of breast radiotherapy and chemotherapy
have shown to increase the probability that a patient will develop cardiac problems.14 The
anatomical location of the breast tumor and heart changes during the patient’s breathing cycle. It
is necessary to account for the physical displacement between the tumor and the heart in order to
increase the efficacy of the treatment and decrease the radiation exposure to the heart. To
decrease the dose to the heart 3DCRT has been used as a form of treatment planning to decrease
the amount of radiation delivered to the heart. Three dimensional computed tomography images
are used to develop radiation treatment plans. However, 3DCT is unable to capture the
movement of the tumor and normal structures in the radiation field. Qi et al5 used 4DCT images
29
to examine the MHD and DLAA to decide if respiratory gating would be suitable for treatment.
Cao et al8 studied SIMRT, beamlet IMRT, and CWT to decide how respiratory motion effected
target coverage in these treatment techniques. The study concluded that respiratory motion did
not significantly affect tumor coverage for the plans using the CWT and SIMRT. However,
significant changes were seen in the IMRT tumor coverage because of respiratory motion. The
treatment modalities have improved over the years for left-sided breast cancer patients. During
this development QA techniques have also been addressed for respiratory gating to ensure that
the treatment delivered is accurate. Jiang et al31 gave guidelines to follow during the patient
simulation and treatment process.
Several studies have researched breast cancer radiotherapy techniques and methods for
measurement to define and provide optimal treatment. Breast cancer patients are at an increased
risk for developing cardiovascular disease. Respiratory gating is used to decrease the dose to the
heart during left-sided breast cancer treatment. Accurate contours will help monitor the radiation
dose delivered to organs at risk in the field. The standard OR in left-sided breast cancer patients
have been the heart and lung volumes. To further decrease the damage done to the heart by
radiation researchers have investigated other OR. The AMT and LV have been documented as
pertinent OR during treatment plan optimization rather than the heart alone. Researching other
organs at risk provides direct links to the cause behind cardiovascular disease in left-sided breast
cancer patients. Researchers determined that patients treated using respiratory gating did not
have hot and cold spots that may normally be there from tumor respiratory movement. Quality
assurance is difficult for respiratory gating because of the added temporal dimension. Therefore,
researchers have focused on developing quality assurance standards to ensure the delivery of
treatment while using respiratory gating procedures.
30
Chapter III: Methodology
This research project examined left-sided breast cancer patients receiving radiation
therapy with the addition of respiratory gating technique. The study observed the dose to the
normal structures in a respiratory gating and non-respiratory gating plan. The interest in
performing the research stems from patients who were treated for breast cancer but later
developed cardiac toxicities due to the radiation the heart received during treatment. This chapter
will discuss the sample selection, instrumentation, data collected for analysis of the respiratory
gating study, and limitations of the research.
Sample Selection and Description
The patient population of left-sided breast cancer patients selected for this study was
compiled using a simple random sampling method. The study includes 10 patients chosen at
random who were treated for left-sided breast cancer at Gundersen Lutheran Medical Center for
radiotherapy with amplitude respiratory gating during January of 2011 to December of 2011. The
patient population was chosen at random to create a diverse group of patients with variable
breast, lung, and heart volumes. The research project consists of females who vary in age. This
study will compare the 2 data image sets (respiratory gating and non-respiratory gating) obtained
at simulation. The original treatment plan using the respiratory gating scan will be transferred to
the non-gating CT scan. The plan will be setup identical to the one used for treatment and
verified by checking the isocenter location via reference fields.
Instrumentation
The left sided breast cancer patients used for this research study were originally treated
with radiotherapy with the addition of respiratory gating. The CT images were captured with a
General Electric LightSpeed CT scanner. The respiratory gating system used for treatment was a
Varian RPM system. The RPM system is used to decrease the amount of artifact seen during a
patient’s breathing cycle and to measure motion.5 A Pinnacle3 Phillips version 8.0m treatment
planning computer was used to create the radiation treatment plans for both the respiratory gating
and non-respiratory image sets. The plans were computed with the heterogeneity correction
component turned on using the adaptive convolve algorithm. The patients were immobilized
with the use of a Vac-Lok and a wing board. Patients were scanned in the supine position with
their arms positioned above their head to decrease dose to normal structures and to ensure the
treatment volume would be covered effectively. The CT obtained did not include intravenous
contrast.
31
Data Collection Procedures
The data collected for the research study will come from the respiratory gating scan and
the non-respiratory gating scan obtained at the patient’s simulation. The plan created for the
patient’s treatment will be computed on each data set. The treatment plan will be transferred to
the non-respiratory gating scan and verified by checking that the location of the isocenter
matches that used in the respiratory gating scan. DRRs of the anterior and right lateral reference
fields of the original treatment plan on the gating scan will be compared to the anterior and right
lateral reference fields of the non-gating scan to make sure that isocenter is in the same location.
In order to evaluate the dose to the normal structures the following were contoured on
both data image sets: left lung, right lung, total lung, heart, and the left ventricle. The original
contours from the respiratory gating plan were used to record the research data. The left ventricle
was added to achieve more data for the analysis of respiratory gating in relationship to heart
tissue damage. Feng et al21 devised a cardiac atlas to aid in contouring the heart and
substructures. The Feng et al21 atlas was used to distinguish the left ventricle volumes in the
gating and non-gating scans. The total volume, the minimum, maximum and mean dose were
measured for the left lung, right lung, total lung, heart and left ventricle for the treatment plans
on the gating and non-gating scans.
Data analysis
After collecting the data from the gating and non-gating scan the analysis focused on the
dose to the heart and left ventricle. The dose to the left, right, and total lung was also monitored.
The percent volume of the lung receiving 20 Gy was measured and compared between the two
scans. The total lung volume between the gating and non-gating scans was measured. The
average mean dose for the total lung was recorded between scans. The average mean dose of the
heart and left ventricle were also compared amongst the gating and non-gating scan. After
evaluation of the dosimetric parameters, the results determined if respiratory gating for left-sided
breast cancer patients made a significant difference in treatment delivery.
Limitations
Ten left-sided breast cancer patients were randomly selected for this retrospective
research study that analyzed the effects of respiratory gating. The small sample size used in this
retrospective study gives limited research data. An increase in sample size would have given
more patient data and allowed for more accurate data analysis. The original treatment plan based
off of the respiratory gating scan was transferred to the non-respiratory gating scan. The patient
32
remained in the same supine setup as the gating scan; however, there might have been slight
movement in the patient’s position between scans. After the plan was transferred to the non-
gating scan the isocenter was verified by orthogonal DRRs for accuracy. Confirming the
placement of isocenter is done manually, which may result in slight human error. The structures
measured in the study consisted of the heart, left ventricle, left lung, right lung, and total lung.
These patient contours were performed by physicians, medical physicists, and medical
dosimetrists. Since the patients were contoured by different members of the radiation oncology
team there may be slight variations in the volumes studied. Patients selected for the study did not
receive intravenous contrast to highlight the left ventricle structure. Without intravenous contrast
the left ventricle was more difficult to contour.
Summary
For this retrospective study, 10 left-sided breast cancer patients were selected to analyze
the effects of respiratory gating during treatment. The radiation treatment plans were created on
respiratory gating and non-respiratory gating CT scans. Patients were treated in the clinic
according to the radiation treatment plan designed from the respiratory gating scan. A non-
respiratory gating scan was obtained at the initial CT-simulation. The respiratory gating
treatment plan was transferred to the non-respiratory gating scan. After contouring the normal
structures in the treatment field, heart, left ventricle, right lung, left lung, and total lung the
radiation exposure to the normal structures was recorded. The data was obtained to determine the
efficacy of respiratory gating in left-sided breast cancer patients.
33
Chapter IV: Results
Breast cancer patients are treated with radiation therapy to decrease the rate of
recurrence.5 Radiotherapy is a curative form of treatment for breast cancer patients. However,
radiotherapy recipients experience cardiac abnormalities that develop into heart disease later on
in life. In order to decrease the amount of radiation delivered to the heart during radiotherapy
treatment, respiratory gating is used. The purpose of this study was to determine the benefits of
respiratory gating in left-sided breast cancer patients. This research collected data from patient’s
treatment plans to evaluate the dosimetric treatment plan from the respiratory gating scan to a
treatment plan from a non-respiratory gating scan. The treatment plans compared the dose
distribution between the gating and non-gating treatment plan scans. To retrospectively analyze
the patients, the gating scan dosimetric plan was transferred to the non-gating scan treatment
plan, verified by orthogonal DRRs, and calculated. The data for this research was measured
through a comparison analysis of the dose delivered to the right and left lung, total lung, heart,
and left ventricle between the two treatment plan scans.
Item Analysis
Ten patients were used in the retrospective studies which are referred to as patients A
through J in the following results section. A total of 20 plans were reviewed, 10 dosimetric plans
on gating scans and 10 dosimetric plans on non-gating scans. The minimum dose, maximum
dose, mean dose, and percent dose received to specific volumes were compared to look at the
effects of radiation therapy. The primary focus of the study was to measure the amount of
radiation delivered to the heart and left ventricle. Additional areas of interest were the lung
volumes. Patients selected for the study had left-sided breast cancer so the dose to the recorded
dose to the right lung was minimal. The average mean dose delivered to the right lung for
patients A-J was 18.3 cGy for the dosimetric plan developed on the gating scan. The non-gating
scan dosimetric plan showed an average mean dose to the right lung for patients A-J as 17.5 cGy.
The percent difference between the gating and non-gating scan was 5% for the average mean
lung dose of the right lung volume.
The amount of dose delivered to the ipsilateral lung during breast radiotherapy is also
normally measured. The percent of lung volume receiving 20 Gy was recorded for both scans.
The percent of lung receiving 20 Gy in the gating scan for patients A-J was, 3.3%, 18.3%, 6.7%,
9.0%, 14.1%, 11.7%, 11.8%, 7.8%, 7.8%, 6.1%, and 25.9% respectively. The percent of lung
receiving 20 Gy in the non-gating scan for patients A-J was, 3.9%, 13.6%, 2.9%, 7.0%, 15.7%,
34
7.0%, 11.0%, 4.5%, 3.9%, and 25.7% respectively. The average percentage of the left lung
volume receiving 20 Gy for patients A-J in the gating scan was 11.5%. The average percentage
of the left lung volume receiving 20 Gy for patients A-J in the non-gating scan was 9.5%. Table
1 lists the values for the percent volume of ipsilateral lung receiving 20 Gy. Figure 1 is a graph
of the patient A- J demonstrating the difference between the gating and non-gating scan in terms
of the percent volume of the left lung receiving 20 Gy.
The respiratory and non-respiratory gating scan demonstrated a difference between the
total lung volumes. The respiratory gating scan showed an average total lung volume of 3500.81
cm3. The non-respiratory gating scan showed an average total lung volume of 2701.8 cm3. Table
3 lists the values of the average total lung volume (cm3) for the gating and non-gating scans. The
percent difference between the two scans is 30 percent. The average mean total lung dose for the
respiratory gating scan was 298.53 cGy. The average mean total lung dose for the non-
respiratory gating scan was 258.73 cGy. The percent difference for the mean total lung dose was
15.4% between the respiratory gating and non-respiratory gating scan. Figure 2 displays the
average mean total lung dose for the gating and non-gating scans. Table 2 lists the values for the
average mean total lung (cGy) for the gating and non-gating scans.
The heart and left ventricle volumes in the gating and non-gating scans were measured to
determine the amount of radiation delivered during patient treatment. The mean heart doses for
the gating and non-gating scans for patients A-J are shown in a graph format in Figure 3. The left
ventricle doses for the gating and non-gating scans for patients A-J are shown in a graph format
in Figure 4. The mean heart and left ventricle dose was higher in 7 out of 10 patients when gating
was not used in the radiation therapy planning. Table 4 lists the average mean dose for the heart
and left ventricle for the gating and non-gating scans.
To compare the different image data sets, the average mean dose to the heart and left
ventricle were calculated. The average mean heart dose for the respiratory gating scan was 99.87
cGy. The average mean heart dose for the non-respiratory gating scan was 115.34 cGy. The
average mean left ventricle dose for the respiratory gating scan was 161.08 cGy. The average
mean left ventricle dose for the non-respiratory gating scan was 203.24 cGy. The average mean
heart dose between the respiratory and non-respiratory gating scan results in a 15.5 percent
change. The average left ventricle heart dose between the respiratory and non-respiratory gating
scan results in a 17.7 percent change. Figure 5 depicts the values obtained for the average mean
dose of the heart and left ventricle in the gating and non-gating scan.
35
Overall, the retrospective study showed that the respiratory gating procedure decreased
the dose to the heart and left ventricle in the patients selected for the study. The total volume of
lung treated increased when respiratory gating was used. The ipslateral lung showed a slight
increase when measuring the percent volume of lung treated at 20 Gy. Dose to the right lung in
both the gating and non-gating scans was minimal because radiation was delivered to the left-
side only. Tables 5-24 list the volume (cm3), minimum dose (cGy), maximum dose (cGy), and
mean dose (cGy) for the right lung, left lung, total lung, heart, and left ventricle volumes.
36
Chapter V: Discussion
Breast cancer patients being treated with radiotherapy are at an increased risk for
developing cardiovascular disease after surviving breast cancer. Respiratory gating is a
procedure used to decrease the dose delivered to the heart during breast radiotherapy treatments.
Limiting the amount of radiation exposure to the patient’s heart decreases the likelihood a patient
will develop heart disease later on in life. Borger et al26 reported an increase in cardiovascular
disease in patients treated for left-sided breast cancer patients compared to right-sided breast
cancer patients. Researchers have employed different techniques to reduce the damage to the
heart during radiotherapy of left-sided breast cancer patients. McIntosh et al24 demonstrated how
VDIBH can be used to decrease the radiation exposure to the LAD coronary artery and the heart
by increasing the displacement between the breast target and heart. Different treatment planning
techniques have been explored to create the optimal treatment plan for left-sided breast cancer
patients. Tan et al14 studied IMRT planning objectives in order to develop treatment plans that
reduced the radiation exposure to the heart in left-sided breast cancer patients. The researchers
found that when the IMRT plan was optimized using AMT and H + LV as planning objectives
there was a decrease to the mean dose to the heart, LV, and AMT compared to using the heart
alone.14 Three dimensional conformal radiation therapy is another form of treatment planning
that has been shown to decrease the radiation exposure to the heart in left-sided breast cancer
patients.5 This research paper measured the effects of the organs at risk for breast radiotherapy
for plans created on respiratory gating and non-respiratory gating scans. This study evaluated the
radiation delivered to the right lung, left lung, total lung, heart and left ventricle. Data analysis
included measuring the amount of radiation delivered to the ipsilateral lung during radiation
treatment by recording the percent of lung volume that received 20 Gy. The average percentage
of the left lung receiving 20 Gy for treatment plans created on the gating scan was 11.5% and on
the non-gating scan was 9.5%. The heart and left ventricle volumes were also analyzed. The
average mean heart dose for the gating scan was 99.87 cGy whereas the average mean heart dose
for the non-gating was 115.34 cGy. The average mean left ventricle dose for the gating scan was
161.08 cGy where as the average mean left ventricle dose for the non-gating scan was 203.24
cGy. Seven out of 10 patients from the sample selection had a decrease in the amount of
radiation delivered to the heart and left ventricle.
37
Limitations
Ten left-sided breast cancer patients were randomly selected for this retrospective
research study that analyzed the effects of respiratory gating. The small sample size used in this
retrospective study gives limited research data. An increase in sample size would have given
more patient data and allowed for more accurate data analysis. The original treatment plan based
off of the respiratory gating scan was transferred to the non-respiratory gating scan. The patient
remained in the same supine setup as the gating scan; however, there might have been slight
movement in the patient’s position between scans. After the plan was transferred to the non-
gating scan the isocenter was verified by orthogonal DRRs for accuracy. Confirming the
placement of isocenter is done manually, which may result in slight human error. The structures
measured in the study consisted of the heart, left ventricle, left lung, right lung, and total lung.
These patient contours were performed by physicians, medical physicists, and medical
dosimetrists. Since the patients were contoured by different members of the radiation oncology
team there may be slight variations in the volumes studied. Patients selected for the study did not
receive intravenous contrast to highlight the left ventricle structure. Without intravenous contrast
the left ventricle was more difficult to contour.
Conclusions
After collecting the data and performing calculations, this study determined that left-
sided breast cancer patients may see positive benefits when being treated with respiratory gating
procedures. This study showed that seven out of 10 patients demonstrated a decrease in the
amount of radiation delivered to the heart and left ventricle. There was a 15.5% decrease in the
average mean dose of the heart. The left ventricle showed a 17.7% decrease in the average mean
dose. A study done by Korreman et al28 also confirmed the use of respiratory gating in left-sided
breast cancer patients to decrease the dose to the heart.
Although, there was a decrease in the mean dose to the heart and left ventricle the
respiratory gating treatment showed an increase of total lung volume treated. An increase of
15.4% of total lung volume was treated when using the respiratory gating procedure. These
results are contrary to a study done by Korreman et al28 which showed a decrease in pneumonitis
for patients that used the DIBH and IG methods and respiratory gating. The DIBH and IG
methods were used by Korreman et al28 to decrease the inspiration during the respiratory gating.
Although, there was an increase in total lung being treated in the respiratory gating scan the
radiation delivered to the lung was considered acceptable by the radiation oncologist treating the
38
patient. The heart and left ventricle were the main focus of this study because of the heart
toxicities a patient may experience later on in life due to the radiation treatment. On average,
there was a clear advantage to using respiratory gating in the left-sided breast cancer patients
used in the study.
Recommendations
The research study provided a limited sample size. In future studies involving respiratory
gating a larger sample size is needed to provide more accurate results. Another recommendation
to improve the study would include the addition of the target area. Including the target volume
would help determine if and how respiratory gating is affecting the target volume proximal
normal structures. Three of the 10 patients used in this retrospective study did not receive the
benefits of the respiratory gating procedure, which should be analyzed to determine if it was due
to the plan transfer performed between the 2 scans or if it was related to anatomical differences
among the patients chosen. Along with monitoring dose in 3DCRT plans it is also imperative to
determine how the use of IMRT in breast radiotherapy reduces the amount of dose delivered to
OR and increases the efficacy of the patient’s treatment plan. Analyzing planning objectives to
reach an optimal plan is an important part of developing the treatment planning process for left-
sided breast cancer patients.
39
Tables
Table 1. Percent volume of left lung receiving 20 Gy Patient Gating Scan Non-Gating Scan A 3.30% 3.90% B 18.30% 13.60% C 6.70% 2.90% D 9.00% 7.00% E 14.10% 15.70% F 11.70% 7.00% G 11.80% 11.00% H 7.80% 4.50% I 6.10% 3.90% J 25.90% 25.70% Average % 11.50% 9.50%
Table 2. Average mean total lung (cGy) gating vs. non-gating scan Scan Average Mean Total Lung (cGy) Gating 298.53 Non-Gating 258.73 % Difference 15.4%
Table 3. Average total lung volume (cm^3) gating vs. non-gating scan Scan Average Total Lung Volume (cm^3) Gating 3500.81 Non-Gating 2701.8 % Difference 0.3
Table 4. Average mean dose for the heart and left ventricle for the gating and non-gating scans. Average Mean Dose (cGy) Scan Heart Left Ventricle Gating 99.87 161.08 Non-Gating 115.34 189.53 % Difference 0.155 0.177
40
Table 5. Patient A gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 2006.16 5.9 204.5 25.1 Lt Lg 1545.35 13.4 5153.3 281.4 T Lg 3551.74 5.9 5153.3 136.6 Heart 736.83 21.4 1439.7 120.3 Lt Vent 190.1 45.1 1253 180.9
Table 6. Patient A non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1681.4 6.3 194.4 26.6 Lt Lg 1283.5 14.5 5123.4 303.3 T Lg 2965.03 6.3 5123.4 146.3 Heart 734.74 29.9 2503.4 135.4 Lt Vent 191.89 43.6 2109.2 188.6
Table 7. Patient B gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1946.99 4.1 1021.4 23.6 Lt Lg 1710.88 8.9 5504.4 992 T Lg 3658.02 4.1 5504.4 476.6 Heart 598.7 18.8 4377.1 134.1 Lt Vent 194.89 33.7 4019 220.5
Table 8. Patient B non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1487.95 4 139.2 21.2 Lt Lg 1245.87 9.4 5308 791.8 T Lg 2734.11 4 5308 372.4 Heart 603.24 15.1 3233.5 114 Lt Vent 214.19 30.8 2562.9 177.8
41
Table 9. Patient C gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 2149.29 1.8 215.2 14.3 Lt Lg 1886.78 6.5 4481.7 379.4 T Lg 4048.36 1.8 4481.7 185 Heart 668.69 15.5 2130 89.7 Lt Vent 185.3 18.6 2051 136.3
Table 10. Patient C non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1380.25 1.8 95.4 11.6 Lt Lg 1347.16 Not on DVH 4699.9 224.5 T Lg 2717.82 1.8 4699.9 117.2 Heart 645.04 10.6 1481.8 75.7 Lt Vent 177 24 1605.9 124.3
Table 11. Patient D gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1949.45 3.1 149.8 15.9 Lt Lg 1506.56 10.3 5055.9 502.1 T Lg 3456.6 3.1 5055.9 227.6 Heart 586.45 17.1 4491.5 123.5 Lt Vent 221.67 25.2 4339.5 174.1
Table 12. Patient D non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1645.86 3.8 134.9 16 Lt Lg 1241.38 12.8 4888.5 405.6 T Lg 2887.62 3.8 4888.5 183.5 Heart 616.1 20.2 4804 191.7 Lt Vent 224.64 31.9 4779.2 316.7
42
Table 13. Patient E gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 2015.66 1.5 335.7 15.2 Lt Lg 1818.12 3.7 5444.4 761.3 T Lg 3838.73 1.5 5444.4 369 Heart 605.3 10.7 1115.1 58.1 Lt Vent 171.91 17.2 1008.2 95.7
Table 14. Patient E non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1746.27 3 359.4 15.5 Lt Lg 1563.85 5.3 5439.1 830 T Lg 3310.38 3 5439.1 400.4 Heart 597.48 10.6 1511.4 65.3 Lt Vent 177.54 16.2 1794.2 115.2
Table 15. Patient F gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1487.91 3.7 353.7 18.7 Lt Lg 1300.93 7 5164.2 622.2 T Lg 2789.08 3.7 5164.2 300.3 Heart 637.54 16.3 4319.8 114.4 Lt Vent 196.5 27.8 4072.1 211.1
Table 16. Patient F non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1172.7 3.5 224.6 18.5 Lt Lg 1087.82 8.2 4819.6 426.6 T Lg 2260.79 3.5 4819.6 214.9 Heart 581.22 18.4 4590 134.9 Lt Vent 169.65 28.4 4660.7 252.3
43
Table 17. Patient G gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1876.64 2.3 187.8 16.3 Lt Lg 1465.24 6 5380.7 672.8 T Lg 3341.3 2.3 5380.7 304.3 Heart 573.15 17 3655 118.7 Lt Vent 148.39 29.7 3680.2 217.8
Table 18. Patient G non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1540.98 2.3 203.1 16.6 Lt Lg 1137.36 7.7 5281.6 621.3 T Lg 2678.47 2.3 5281.6 273.4 Heart 528.96 19.1 4434 158.1 Lt Vent 153.99 33.1 4501.6 283.8
Table 19. Patient H gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 946.93 4.2 233.9 11.7 Lt Lg 1270.34 9.5 5023.1 459.4 T Lg 2217.33 4.2 5023.1 205.6 Heart 405.81 15.9 2011.6 81.5 Lt Vent 143.12 26.1 1736.8 145.3
Table 20. Patient H non-gating scan treatment plan results Structure Volume (cm^3) Minimum Dose (cGy) Maximum Dose (cGy) Mean Dose (cGy) Rt Lg 759.14 3.6 147.9 10.5 Lt Lg 935.74 5.7 4780 311.8 T Lg 1694.91 3.6 4780 138.2 Heart 403.29 16.6 4051 104.1 Lt Vent 137.29 23.3 2843.6 167.5
44
Table 21. Patient I gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 2575.95 1.6 142.2 19.9 Lt Lg 2098.69 1.3 5102.9 375.9 T Lg 4684.28 1.3 5102.9 179.7 Heart 691.4 11.7 520.1 55.9 Lt Vent 189.89 16.4 479.6 80
Table 22. Patient I non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1625.03 4 89.4 18.3 Lt Lg 1441.66 0.2 5112.9 257.9 T Lg 3067.15 0.2 5112.9 130.9 Heart 686.77 16.3 4614.8 77.3 Lt Vent 193.44 19.7 3876.3 126.5
Table 23. Patient J gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1433.66 8.5 246.2 22.1 Lt Lg 610.1 24.5 5238.3 1288 T Lg 3422.61 8.5 5238.3 600.6 Heart 535.91 27.4 1034.8 102.5 Lt Vent 163.48 42.9 972.2 149.1
Table 24. Patient J non-gating scan treatment plan results
Structure Volume (cm^3)
Minimum Dose (cGy)
Maximum Dose (cGy)
Mean Dose (cGy)
Rt Lg 1105.1 9.3 194.2 19.9 Lt Lg 1596.21 26.6 5270 1285.7 T Lg 2701.49 9.3 5270 610.1 Heart 533.58 21.4 2549.1 96.9 Lt Vent 168.52 38.7 1531.4 142.6