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SU‐FF‐T‐507: Radiobiology‐Guided IMRT for Dose‐Deficit Compensation in Permanent Interstitial Brachytherapy for Prostate Cancer
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3182005
Subject(s) - brachytherapy , medicine , nuclear medicine , prostate cancer , dosimetry , thermoluminescent dosimeter , medical physics , prostate , cancer , radiation therapy , radiology , dosimeter
Purpose: In permanent interstitial brachytherapy (PIB) for prostate cancer, dose deficits in excess 15% of prescription dose often occur as a result of poor implantation skill, post‐implant source migration and procedure‐induced prostate edema. Without intervention, these “cold” dose spots could lead to tumor recurrence and treatment failures. IMRT's dose‐painting capability is ideal for PIB dose‐deficit compensation. However, the temporal and spatial dose‐deposition patterns are distinctly different in PIB and IMRT. The aim of this work was to examine the radiobiological impact of using IMRT for PIB dose‐deficit compensation. Method and Materials: 3D PIB dose/dose‐rate distributions of actual patient plans were reconstructed from post‐implant CT using Varian BrachyVision3D system. Voxel‐specific IMRT compensation plans were generated using Varian Eclipse system. Biologically effective dose (BED) was used to capture the radiobiological interactions of PIB and IMRT dose‐delivery with the underlying cellular processes. Results: A method for determining voxel‐by‐voxel radiobiology‐based dose‐deficit was developed which consisted of 1) calculation of BED PIB ‐deficit distribution (from the nominal prescribed BED) in the PIB target volume, 2) determine the number (N) of 2‐Gy IMRT fractions needed to match the BED IMRT‐2Gy to the 90% of maximum BED PIB ‐deficit, and 3) determine the required dose‐per‐fraction (d) at each voxel for the N‐fraction IMRT dose‐compensation to match BED IMRT‐d to BED PIB ‐deficit at each voxel. To use the dose‐volume based Eclipse system for voxel‐specific IMRT plan, the target volume was partitioned into iso‐dose‐deficit sub‐volumes by turning the iso‐dose‐deficit lines into contours followed by Boolean subtraction of the volumes enclosed by successive iso‐dose‐deficit contours. This method was successfully demonstrated with actual patient PIB plans, showing the IMRT dose distribution filling the non‐uniform cold spots in PIB. Conclusions: A radiobiology‐guided IMRT technique for PIB dose‐deficit compensation has been developed that will enable detailed study of the radiobiological impact of combining treatments of PIB and IMRT.