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Adjoint Sensitivity Based Greedy Heuristic Treatment Planning Algorithm: Application To Multicatheter Interstitial High Dose Rate Brachytherapy For Accelerated Partial Breast Irradiation

V Chaswal*, B Thomadsen, University of Wisconsin, Madison, WI

SU-E-T-458 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Development of an automated, 3-D greedy heuristic optimization algorithm utilizing the adjoint sensitivity fields for treatment planning in multi-catheter interstitial high dose rate breast implants is presented. The optimization is based on maximizing the dose homogeneity in a breast implant.
Methods: Patient CT-scans were taken from the UW-hospitals and clinics and the ROI volumes were redrawn and catheters marked. CTV was defined as 1.5cm margin around the seroma. The CTV contour is limited 5mm inside the skin surface and near the pectoralis muscle. For ROI-adjiont maps skin and muscle are contoured. The contoured volumes were - Seroma: 5.7cc, CTV: 75.0cc, Skin: 79.5cc, Muscle: 55.9, Body: 1736.6cc. Prescribed dose was 3.4Gy to the CTV. Isodoses, dose volume histograms and a list of evaluation parameters were quantified to assess the quality of treatment plan generated.
Results: On all CT slices, the 150% isodoses were well separated from each other, the 100% isodose always stayed inside the skin surface with separation from the skin between 7mm-3mm, the 80% isodose covered the PTV entirely and stayed inside the outer skin surface. The V100, V150 and V200 for the PTV were 96%, 17.6% and 7.2%, respectively with DHI of 0.82 and CN of 0.68. The V100 and D100 for the seroma were 100% and 3.58Gy, respectively. The V100, V85 and D90 for the contoured skin were 0.85%, 4.46% and 0.15Gy, respectively. The V100 and D90 for the contoured muscle were 15.8% and 0.92Gy.
Conclusions: Our work demostrates development and use of new treatment planning engine based on adjoint sensitivity data, for breast brachytherapy. The treatment planning tool maximizes dose homogeneity in a breast implant and offers the capability of dose quantification and modulation in any number of contoured structures like the PTV, skin and pectoralis muscle doses.

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