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Individually optimized contrast-enhanced 4D-CT for radiotherapy simulation in pancreatic adenocarcinoma
Wookjin Choi, Ming Xue, Barton Lane, Min Kyu Kang, Kruti Patel, William Regine, Paul Klahr, Jiahui Wang, Warren D'Souza, Wei Lu
Introduction•Pancreatic adenocarcinoma (PDA)–Radioresistant–Neighboring organs : highly sensitive to radiation
•Critical to accurately and precisely delineate target volume of PDA– Similar density and CT number to normal tissue –Move a large amount up to 1 – 2 cm due to respiration
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Introduction•Clinic: CE 3D-CT followed by a 4D-CT
•Contrast-enhanced (CE) 3D-CT– Enhance tumor-to-pancreas contrast– Increase the difference in CT numbers
•4D-CT–Quantify and compensate tumor respiratory motion
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Limitations of CE 3D-CT + 4D-CT• Geometrical discrepancy between the two scans– Due to variations in patient position and breathing pattern – On average 12% of GTVs fell outside ITV
{Li et al., 2013. J of Radiation Research 54: 950-956}.• Tumor-pancreas boundary– Barely detectable in 4D-CT without contrast
• Surrogates of motion have to be used.
• Solution: combine the two scans into a single CE 4D-CT scan
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CE 4D-CT• It is all about timing!
• Conventional fixed-delay CE 4D-CT– 50 s : from start of injection to scanning central pancreas during
pancreatic phase– Large variations in the contrast arrival time (10 – 35 s) and
injection duration (30 – 60 s)
• Individually optimized-delay CE 4D-CT
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Methods• Ten PDA patients enrolled.• CE 3D-CT followed by 4D-CT on simulation date– Bolus tracking for contrast timing, total 90 mL– When a threshold of 150 HU was reached, the CE 3D-CT scan was
started• CE 4D-CT on film date – Test injection for contrast timing, 10 mL– Full (140 ml) injection based on the estimated time to peak
enhancement
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ROI in aorta
Estimate Time to Peak Enhancement
{Bae 2010. Radiology 256: 32-61}
Using a test injection enhancement curve {Xue et al., 2012. Med. Phy. 39: 3903-3903}.
Enhancement (HU)
Time (Sec)
0 5 10 15 20 25 30 35 45
105100
959085807570656055
Typical transit time
Injection duration Typical arrival
time
𝑇 𝑝𝑒𝑎𝑘=T ID+15 s+(T arr−20 s )
Tarr = 24.2 s
Tpeak
Pancreas
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We can determine optimal delay time Tdelay
Determine the Delay Time
4D-CT Acquisition Contrast Injection
LO
4D-C
T Sc
an L
engt
h
Org
an
Tpeak
Tdelay = LO/V- Tpeak
ContrastEnhancem
ent Curve
Time (s)
Enhancement (HU)
a
c
b
de
Time when the organ is scanned over (Lo/V)
Time when organ reaches peak enhancement Tpeak
Synchronize
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Visual Evaluation
CE 3D-CT CE 4D-CT4D-CT• Three physicians visually scored image quality, and contoured
the tumor (red, T) and pancreatic tissue (blue, P).
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Tumor-to-Pancreas Contrast• Tumor-to-pancreas contrast (C) and contrast-to-noise ratio (CNR)– ROIs : Tumor-pancreas boundary
• Inter-observer variations in contouring the tumor– Simultaneous truth and performance level estimation (STAPLE)
{Yang et al., 2014. Int J Radiat Oncol Biol Phys 89: 214-21}.