Coverage-Based Treatment Planning to Accommodate Deformable Organ Variations in Prostate Cancer Treatment
H Xu1*, D Vile1, M Sharma1, J Gordon2, J Siebers1, (1) Virginia Commonwealth University, Richmond, VA, (2) Henry Ford Health System, Detroit, MITU-E-141-2 Tuesday 2:00PM - 3:50PM Room: 141
Purpose: To (1) investigate the dosimetric impact of interfraction deformable organ motion for high-risk prostate cancer treatments and (2) compare two coverage-based planning (CP) techniques with the fixed margin-based planning (FM).
Methods:19 patients with 8-13 prostate CT images were used to model interfraction deformable organ changes using principal component analysis (PCA). Displacement vector fields (DVFs) that map from each of the 8-13 images to the reference image were analyzed with PCA to determine the dominant eigenmodes, which were then used to predict the synthetic patient geometries for virtual treatment course simulation. For each patient, an intensity modulated radiation therapy (IMRT) plan with zero PTV margin on target structures (CTVprostate and CTVseminalVesicles) was created, then evaluated by simulating 1000 30-fraction virtual treatment courses. Each fraction was prostate centroid aligned. Probabilistic metrics, including 5% and 95% percentile DVHs (pDVH) and TCP/NTCP distributions, were computed. Patients whose D98 failed to achieve 95% coverage probability objective D98,95>=78Gy (CTVprostate) or D98,95>=66Gy (CTVseminalVesicles) were replanned using (1) FM (PTVprostate = CTVprostate + 5mm, PTVseminalVesicles = CTVseminalVesicles + 8mm), (2) CPOM which optimized uniform margins for CTVprostate and CTVseminalVesicles to meet the CP objective, and (3) CPCOP which directly optimized coverage-based objectives for all structures of interest.
Results:For zero-PTV-margin plans, 0/19 patients satisfied objective D98,95 for both CTVprostate and CTVseminalVesicles. The selected margins used in FM failed to ensure target coverage for 8/19 patients. 11 CPOM plans and 8 CPCOP plans were favored over the other plans by achieving desirable D98,95 while sparing more normal tissues.
Conclusion:The dosimetric impact of deformable organ motions for prostate centroid alignment treatment is not insignificant. Coverage-based treatment planning techniques can produce better plans than FM, while relative advantages of CPOM and CPCOP are patient specific.
Supported by NIH P01-CA-116602 and Philips Medical Systems
Funding Support, Disclosures, and Conflict of Interest: NIH P01-CA-116602 and Philips Medical Systems