To determine potential dosimetric benefits of image-guided adaptive radiation therapy treatment (IGART) strategies for
intermediate-risk prostate cancer. A 19 patient cohort with 8-13 CT-images was used to compare different IGART strategies.
The IMRT prescription was 46 Gy/23 fractions to the prostate and seminal vesicle PTVs, followed by a 40 Gy/20 fractions prostate
boost. For each patient, daily IGART imaging was simulated by random selection from available images. The three different
IGART-IMRT strategies are simuated; (A0) initial planning only with 5 mm PTV margins; (A1) daily re-planning without
considering prior dose; and (A2) online daily re-planning for each fraction considering prior dose obtained via deformable dose
mapping (A1 and A2, no PTV margin). For each strategy, daily dose was deformably mapped using Demons-based displacement
vector fields and accumulated to estimate the treatment dose. Strategies were compared via dosimetric adherence to constraints
and objectives. Results show A0 had larger doses to 20, 30, and 50% rectal (30?20%) and bladder (40?20%) volumes than A1
and A2 (p<0.001). Rectal and bladder D
?s were also respectively higher in A0 by 15?13% and 24?14% (p=0.002 and 0.00001
respectively). Comparing A1 and A2, no significant differences were found in prostate D98 (p=0.4) or bladder D
Significant differences were found for the rectum (D
, p=0.02). IGART utilizing daily re-planning (A1 and A2) has
dosimetric advantages over conventional-IMRT for critical structures, particularly high-dose regions, without compromising
PTV-coverage. Due to inherent deformation vector field inaccuracies, daily re-planning based on prior dose (A2) showed poor
rectal sparing than A1.
Manju Sharma completed her Ph.D. in Physics in 2006 from Panjab University, India. After the completion of her Ph.D., she worked at Roswell
Park Cancer Center on the development of nanocomposites for cancer detection. She did her postdoctoral studies at the University of Minnesota,
Minneapolis. The main focus was to study the impact of radiation treatment on bone health of cancer patients. Since 2010, she is working as a
postdoctoral fellow at the Virginia Commonwealth University on the development of image-guided adaptive radiation treatment techniques.
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