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  4. Organs at Risk Anatomic Variations and Dosimetric Evaluations for Endometrial Cancer Treatment with the Fractionated High-Dose Rate GYN Brachytherapy

Organs at Risk Anatomic Variations and Dosimetric Evaluations for Endometrial Cancer Treatment with the Fractionated High-Dose Rate GYN Brachytherapy

M Shojaei1*, M RAHMAN2 , S Pella3 , G Kalantzis4 , (1),(2),(3),(4)Medical Physics, Department of physics, Florida Atlantic University, Boca Raton, Florida, (3) 21st Century Oncology, Boca Raton, FL

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: High dose rate brachytherapy has very sharp dose gradient; therefore, any internal volume variations of organs at risk can potentially result significant dose variation for the entire treatment. Organs anatomy has high-intensity variation in the pelvic region due to significant changes in the organ filling, weight loss, tumor shrinkage, etc.1 This retrospective study evaluates and analyzes inter-fractional volume variation and deformation of bladder and rectum for endometrial cancer treatment by calculating the mean volume, dice similarity coefficient (DSC), and coefficient of variance (CV) parameters.

Methods: A retrospective analysis of 118 HDR brachytherapy treatment plans of 30 patients that were generated in the treatment planning system Oncentra, and were imported into Eclipse for registration of the subsequent treatment plans into the initial CT-image guided plan. The “initial plan� was considered as the application of the “ideal plan� for all fractions during the entire treatment. The planning target volume, rectum, and bladder contours were compared, and the inter-fractional volume variations were calculated and analyzed.

Results: For all patients, volume variations were observed. The coefficient of variance varied noticeably. Furthermore, the dice similarity coefficient for the bladder has a range from 0.06 to 0.73, and for rectum has a range from 0.25 to 0.69. The mean dose difference for PTVi-Real between “Actual Plan� and “Registered Plan� for subsequent fractions, fraction 2, 3, 4, 5, is 5.9%, 7.8%, 5.1%, 6.5% respectively.

Conclusion: Two methods were followed: firstly, we considered that the initial plan was applied for each fraction as a standard plan and upon image registration we calculated the mean-volume values, DSC, and CV parameters. The mean dose difference for PTVi-Real between “Initial Plan� and “Registered Plan� for subsequent fractions were studied and reported.

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