Radiation Therapy

it is the use of high-energy ionizing rays to destroy a cancer cell's ability to grow and multiply.

goal

to deliver a precisely measured dose of irradiation to a defined tumor volume with minimal damage to surrounding healthy tissue. This results in eradication of tumor, high quality of life, prolongation of survival, and allows for effective palliation or prevention of symptoms of cancer,

with minimal morbidity.

General Considerations

Different irradiation doses are required for tumor control, depending on tumor type and the number of cells present. Varying radiation doses can be delivered to specific portions of the tumor (periphery versus central portion) or to the tumor bed in cases in which all gross tumor has been surgically removed.

Treatment portals must adequately cover all treatment volumes plus a margin.

Goals of Therapy

Curative: When there is a probability of long-term survival after adequate therapy; some adverse effects of therapy, although undesirable, may be acceptable.

Palliative: When there is no hope of survival for extended periods, radiation can be used to palliate symptoms, primarily pain. Lower doses of irradiation (75% to 80% of curative dose) can control the tumor and palliate symptoms without excessive toxicity

Principles of Therapy

Higher doses of irradiation produce better tumor control. For every increment of irradiation dose, a certain fraction of cells will be killed.

A boost is the additional dose administered through small portals to residual disease; it is given to obtain the same probability of control as for subclinical aggregates

Radiosensitivity is the degree and speed of response. This measure of susceptibility of cells to injury or death by radiation depends on cancer diagnosis and its inherent biologic activity. It is directly related to reproductive capability of the cell.

Role of oxygen

Oxygen must be present at the time of radiation's maximal killing effect. Poor circulation with resultant hypoxia can reduce cellular radiosensitivity. Giving multiple, daily doses allows reoxygenation and enhances radiosensitivity. The dose should allow for repair of normal tissues.

Cellular response can be modified by changing the dose rate, manipulating the process of cell repair, recruiting cells into replication cycle, and using hyperthermia (above 104° F [40° C]).

Radioresistance is the lack of tumor response to radiation because of tumor characteristics (slow-growing tumor, less responsive), tumor cell proliferation, and circulation. Radiation is most effective during the mitotic stage of the cell cycle

Radioresistant tumors

: Many tumors are resistant to radiation, such as squamous cell, ovarian, soft tissue sarcoma, and gliomas. Many other tumors can become resistant after a period of time. Normal radioresistant tissues include mature bone, cartilage, liver, thyroid, muscle, brain, and spinal cord

Beam energy and penetration : The majority of therapeutic radiation is

administered using the cobalt 60 source or high-energy photons from linear accelerators. The radiation beam decreases in intensity with increasing depth. The penetration of the radiation into the body is directly proportional to the generating energy.

Linear energy transfer (LET) is the rate at which energy is deposited per unit distance. High-energy electrons are used for tumors on or near the skin surface

Types of Radiation Therapy Two general types of radiation

techniques are used clinically: brachytherapy and teletherapy

brachytherapy

, the radiation device is placed within or close to the target tissue.

Radiation is delivered in a high dose to a small tissue volume with less radiation to adjacent normal tissue, but requires direct tumor access.

Interstitial therapy

utilizes solid radioactive material such as seed implants. These may be temporary (removed after several days) or permanent. The permanent type remains in place with gradual decay. Implant procedure is performed under local or general anesthesia. Used in breast and prostate disease

Intracavitary therapy

utilizes radioactive material that is inserted into a cavity such as the vagina, as in cancer of the uterine cervix.

Surface radiation is used in choroid cancer

Other forms of brachytherapy are systemic irradiation (parenteral or I.V.), oral 131I for thyroid cancer, or intraperitoneal radiation

Teletherapy

is external beam irradiation and uses a device located at a distance from the patient. It produces X-rays of varying energies and is administered by machines a distance from the body 31½ to 39 inches (80 to 100 cm).

Teletherapy is given almost exclusively with supervoltage equipment.

Most common use of radiation is local therapy

Chemical and Thermal Modifiers of Radiation Radiosensitization is the use of

medications to enhance the sensitivity of the tumor cells.

Radioprotectors increase therapeutic ratio by promoting repair of normal tissues.

Hyperthermia is combined with radiation. Uses a variety of sources (ultrasound, microwaves) and produces a greater effect than radiation alone. It is usually applied locally or regionally immediately after radiation.

Intraoperative radiation therapy involves placement of a targeting cone directly on the tumor site after surgical exposure.

Units for Measuring Radiation Exposure or Absorption

Gray (Gy) a unit to measure absorbed dose. One Gy equals 100 rads.

(Rad”term used in the past to measure absorbed dose.)

Joules/kg is also used to measure absorbed dose; 1 joule/kg = Gy

Roentgen (R)standard unit of exposure (usually applied to X-ray or gamma rays). Radiation dose equivalent (rem)â - unit of

measure that relates to biologic effectiveness (roentgen equivalent in human beings).

The recommendation for maximum permissible dose (MPD) for radiation workers is 5 rems for people over age 18; the maximum dose for women of reproductive capacity is 1.25 rems per quarter at an even rate

Clinical Considerations Nature and Indications for Use Used alone or in combination with

surgery or chemotherapy, depending on the stage of disease and goal of therapy

Adjuvant radiation therapy used when a high risk of local

recurrence or large primary tumor exists.

Curative radiation therapy - used in anatomically limited tumors (retina, optic nerve, certain brain tumors, skin, oral cavity). Course is usually longer and the dose higher

Palliative ”for treatment of symptoms. Provides excellent pain control for bone

metastasis. Used to relieve obstruction. Relief of neurologic dysfunction for brain

metastasis. Given in short, intensive courses

Radiosurgery (stereotactic) - usually given in single dose fractions. Indications for radiosurgery include the

presence of a radiographically distinct lesion that has the potential to respond to a single, large dose of radiation

The largest use has been in the treatment of arteriovenous malformations (AVMs) and primary and metastatic brain tumors.

A frame is attached to the patient's skull and used to target the treatment beam

Treatment Planning

Evaluation of tumor extent (staging), including diagnostic studies before treatment.

Define the goal of therapy (cure or palliation).

Select appropriate treatment modalities (irradiation alone or combined with surgery, chemotherapy, or both).

All patients undergo simulation and treatment planning. Simulation is used to accurately identify

target volumes and sensitive structures. CT simulation allows for accurate three-dimensional (3-D) treatment planning of target volume and anatomy of critical normal structures

Treatment aids (eg, shielding blocks, molds, masks, immobilization devices, compensators) are extremely important in treatment planning and delivery of optimal dose distribution. Repositioning and immobilization devices are critical for accurate treatment.

Lead blocks are made to shape the beam and protect normal tissues.

Skin markings are applied to define the target and portal. These are generally replaced later by permanent tattoos

Usual schedule is Monday through Friday.

Actual therapy lasts minutes. Most time is spent on positioning

Determine optimal dose of irradiation and volume to be treated, according to anatomic location, histologic type, stage, potential regional nodal involvement (and other tumor characteristics), and normal structures in the region.

Complications Complications depend on the site of

radiation therapy, type of radiation therapy (brachytherapy or teletherapy), total radiation dose, daily fractionated doses, and overall health of the patient. Adverse effects are predictable, depending on the normal organs and tissues involved in the field

Acute Adverse Effects Fatigue and malaise Skin: may develop a reaction as soon

as 2 weeks into the course of treatment (Skin erythema may range from mild to severe with possible dry-to-wet desquamation. Areas having folds, such as the axilla, under the breasts, groin and gluteal fold, are at an increased risk because of increased warmth and moisture.)

GI effects: nausea and vomiting, diarrhea, and esophagitis

Oral effects: changes in taste, mucositis, dryness, and xerostomia (dryness of mouth from lack of normal secretions)

Pulmonary effects: dyspnea, productive cough, and radiation pneumonitis (Usually occurs 1 to 3 months after radiation to the lung.)

Renal and bladder effects: cystitis and urethritis

Cardiovascular: damage to vasculature of organs, thrombosis (heart is relatively radioresistant)

Recall reactions: acute skin and mucosal reactions when concurrent or past chemotherapy (doxorubicin [Adriamycin], dactinomycin [Actinomycin D])

Bone marrow suppression: more common with pelvic or large bone radiation

Chronic Adverse Effects After 6 months with variability in time of

expression: Skin effects: fibrosis, telangiectasia,

permanent darkening of the skin, and atrophy

GI effects: fibrosis, adhesions, obstruction, ulceration, and strictures

Oral effects: permanent xerostomia, permanent taste alterations, and dental caries

Pulmonary effects: fibrosis Renal and bladder effects: radiation

nephritis, fibrosis Second primary cancer: patients who

have received combined radiation and chemotherapy with alkylating agents have a rare risk of developing acute leukemia

Nursing Assessment Assess skin and mucous membranes

for adverse effects of radiation. Assess GI, respiratory, and renal

function for signs of adverse effects. Assess patient's understanding of

treatment and emotional status

Nursing Diagnoses Risk for Impaired Skin Integrity

related to radiation effects Ineffective Protection related to

brachytherapy

Nursing Interventions Maintaining Optimal Skin Care Inform the patient that some skin reaction

can be expected, but that it varies from patient to patient. Examples include dry erythema, dry desquamation, wet desquamation, epilation, and tanning.

Do not apply lotions, ointments, or cosmetics to the site of radiation unless prescribed

Discourage vigorous rubbing, friction, or scratching because this can destroy skin cells. Apply ointments as instructed by health professionals.

Avoid wearing tight-fitting clothing over the treatment field; prevent irritation by not using rough fabric such as wool and corduroy.

Take precautions against exposing the radiation field to sunlight and extremes in temperature

Do not apply adhesive or other tape to the skin.

Avoid shaving the skin in the treatment field.

Use lukewarm water only and mild soap when bathing.

Ensuring Protection from Radiation To avoid exposure to radiation while

the patient is receiving therapy, consider the following: Time—exposure to radiation is directly

proportional to the time spent within a specific distance to the source

Distance—amount of radiation reaching a given area decreases as resistance increases.

Shield—sheet of absorbing material placed between the radiation source and the nurse decreases the amount of radiation exposure.

If exposed to penetrating radiation (X-ray or gamma rays), wear film badges on the front of the body.

Take appropriate measures associated with sealed sources of radiation implanted within a patient (sealed internal radiation). Follow directives on precaution sheet that is

placed on the charts of all patients receiving radiotherapy.

Do not remain within 3 feet (1 meter) of the patient any longer than required to give essential care

Know that the casing material absorbs all alpha radiation and most beta radiation, but that a hazard concerning gamma radiation may exist.

Do not linger longer than necessary in giving patient care, even though all precautions are followed

Be alert for implants that may have become loosened (those inserted in cavities that have access to the exterior); for example, check the emesis basin following mouth care for a patient with an oral implant.

Notify the radiation therapist of any implant that has moved out of position.

Use long-handled forceps or tongs and hold at arm's length when picking up any dislodged radium needle, seeds, or tubes. Never pick up a radioactive source with your hands.

Do not discard dressings or linens unless you are sure that no radioactive source is present

After the patient is discharged from the hospital, it is a good policy for the radiologist to check the room with a radiograph or survey meter to be certain that all radioactive materials have been removed.

Continue radiation precautions when a patient has a permanent implant, until the radiologist declares precautions unnecessary.

Evaluation: Expected Outcomes Skin without breakdown or signs of

infection Radiation precautions maintained