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Cervical HDR Optimization Using Oncentra Masterplan's IPSA Algorithm

C Knill

C Knill1*, R Halford1, M Dominello1,2, S Miller1,2, (1) Karmanos Cancer Institute, Detroit, Michigan, (2) Wayne State University, Detroit, Michigan

SU-E-T-461 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Traditionally, cervical HDR planning was done using standard loading techniques, and prescription points defined in 2D. Currently, widespread availability of 3D imaging allows for structure contouring, inverse plan optimization, and structure based dose prescriptions. However, many institutions still use traditional techniques for some portion of HDR planning. The goal of this research is to compare inverse-optimized plans with structure based dose prescriptions, to forward-optimized plans with point A based prescriptions.

Methods: 41 clinical cervical HDR plans (12 patients), originally optimized using forward-planning techniques, were retrospectively optimized using Oncentra MasterPlans (Nucletron, Veenendal, the Netherlands) inverse planning simulated annealing (IPSA) algorithm. Dose objectives for the high risk CTV (HRCTV) and Organs at risk (OARs) were used in the inverse optimization. The inverse optimization plans were normalized to match the HRCTV D90 dose with their forward-planned counterparts. For each plan, the following values were recorded: the dose to Point A, D90 for intermediate risk CTV (IRCTV); D2cc, D0.1cc for OARs (rectum, bladder, sigmoid colon, small bowel) and total treatment time.

Results: Inverse optimization changed the dose to point A and IRCTV D90 by -12.77+/-32.86% and -17.17+/-31.52%, respectively. Changes in the OARs [D2cc, D0.1cc] were: [-15.89+/-27.10%,-12.87 +/-31.40%] for rectum, [-14.88+/-23.70%, -11.50+/-27.69%] for bladder, [-18.32+/-38.81%, -17.52+/-41.35%] for sigmoid colon, and [-24.10+/-36.61%,-22.47+/-39.64%] for small bowel. The treatment time changed by -25.49 +/-24.44%.

Conclusion: On average, the IPSA optimized plans decreased the dose to the IRCTV, point A, and OARs. However, the large standard deviations in the dosimetric changes indicate that the performance of the IPSA optimization is highly case dependent. Further IPSA studies are needed to determine whether dose can be increased to IRCTV and point A, while maintaining OAR sparing.

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