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Comparison of Forward-Planned and Inversely-Optimized Dose Distributions for Patients Treated Using An Hybrid Interstitial Gynecological Applicator Placed Under MRI Guidance for Treatment of Cervical Cancer

S Simiele1*, G Mcginnis2, M Cunningham1, C Starks1, L Colbert2, M Joyner2, L Lin2, A Jhingran2, P Eifel2, A Venkatesan3, A Klopp2, (1) Department of Radiation Physics, MD Anderson Cancer Center, Houston, TX, (2) Department of Radiation Oncology, MD Anderson Cancer Center, Houston, TX, (3) Abdominal Imaging Department, MD Anderson Cancer Center, Houston, TX


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To determine if inverse planning simulated annealing algorithm (IPSA) can improve HRCTV coverage and reduce dose to the OARs compared with forward planning for treatments with Elekta’s Venezia™ applicator.

Methods: Treatment plans from four patients enrolled on an IRB approved protocol investigating intraprocedural MRI-guided brachytherapy were evaluated. Each patient was treated with 45-50 Gy EBRT and two PDR fractions. One PDR fraction for each patient was treated using the Venezia™ applicator with applicator placement performed under MRI guidance. Two to eight intrauterine interstitial needles were used for each insertion. The treatment plans used clinically were optimized using forward planning with traditional source loading patterns in the tandem and lunar ovoids and by manually optimizing dwell times in the interstitial needles. Inversely-optimized plans were calculated for each patient with the goal of escalating dose to the HRCTV without exceeding the clinically-achieved OAR doses. The forward-planned and IPSA-optimized treatment plans were compared and evaluated based on HRCTV coverage, OAR sparing, and the source loading pattern.

Results: For the three patients treated with five or fewer needles, dose escalation to the HRCTV was not possible without exceeding the clinically-achieved OAR dose for the dose-limiting structure (DLS). For each plan, the non-DLS received less dose than delivered clinically. For the patient treated using eight needles, an increase of 4.9 Gy to the HRCTV was achieved without exceeding the clinically delivered OAR doses.

Conclusion: Use of IPSA for inverse optimization planning for the Venezia™ applicator can improve coverage of the HRCTV without compromising dose to the OARs with calculations taking several seconds. Inverse planning may decrease optimization times for brachytherapy planning and could be used as a method of real-time planning in an MRI-OR suite to determine the optimal needle arrangement to meet the planning objectives.


Interstitial Brachytherapy, Optimization, MRI


TH- Brachytherapy: Dose optimization and planning

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