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Inter-Fraction Variation of High Dose Regions of OARS in MR Image Based Cervix Brachytherapy Using Rigid Registration

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J Swamidas

Jamema Swamidas*, U Mahantshetty#, D Deshpande, S Shrivastava#,Department of Medical Physics, Radiation Oncology# Tata Memorial Hospital, Mumbai, Maharashtra

SU-E-T-424 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To quantify the inter fraction variation of spatial location of high dose regions of OARs in MR-image based cervix brachytherapy using rigid registration algorithm.

Methods: : Retrospective analysis of 27 previously treated patients under EMBRACE multi-centric trial was evaluated. Each patient had two applications, AP1 and AP2 with Vienna applicator. As part of the protocol, all patients underwent MR imaging for each application, followed by volume delineation (Oncentra v3.3) treatment planning & optimization (Plato sunrise, Nucletron), documentation of DVH parameters based on GEC-ESTRO recommendations. The volume receiving the dose D2cc from the plan with which the patient was treated was contoured in each of the image series for OARs rectum, bladder, sigmoid and small bowel region. Both the image series were exported to Eclipse planning system (v8.6.14, VMS) and were co-registered with applicator as the reference using rigid registration

Results: Out of 27 patients, the overlapping D2cc volumes were found in 21, 20, 10 and 4 patients for rectum, bladder, sigmoid and small bowel respectively between AP1 and AP2. The mean(SD) volume of overlap of D2cc was 0.20(0.23), 0.17(0.20), 0.07(0.14), and 0.09(0.11) for rectum, bladder, sigmoid and small bowel respectively. The overlap volume had a wide range which is evident from its standard deviation. The mean(SD) difference of the absolute volumes between AP1 and AP2 was 22(20), 5(6), and 11(11) for bladder, rectum and sigmoid respectively. The uncertainties include the calculation of small overlapping volumes of D2cc, co-registration and variation between applications.

Conclusions: The inter-fraction variation of spatial location of high dose regions were more consistent in rectum and bladder and less in sigmoid and much lesser in small bowel region

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