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Effect of Systematic Error of Ovoid Path Reconstruction in Cervical Cancer Brachytherapy Treatment Using Venezia Applicator

M Paudel1*, J Da Re2, A Shaaer3, E Leung1, A Ravi1, (1) Sunnybrook Odette Cancer Center, University of Toronto, Toronto, ON, CA, (2) McMaster University, Hamilton, ON, CA,(3) Ryerson University, Toronto, ON, CA

Presentations

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

Room: AAPM ePoster Library

Purpose: brachytherapy is a critical component of the therapeutic pathway for locally advanced cervical cancer. During the commissioning of intracavitary gynecological applicators, the accuracy of the source path modelled in the treatment planning system is validated. Systematic errors in the digitized source path may be possible through the following routes: uncertainties in source position during QA via autoradiography/fluoroscopy or error in the library model of the applicator itself. In this work, we have evaluated the dosimetric impact of systematic errors in ovoids source path for intracavitary cervical cancer treatment using the Venezia applicators (Elekta).

Methods: patient plans were retrospectively selected and anonymized. Systematic shifts (-3, -2, -1, 1, 2, and 3mm) in the ovoid paths along the length of the applicator path were applied and the plans were reevaluated in OncentraBrachyTM treatment planning system (Elekta). A percentage difference in clinically relevant dosimetric quantities for targets (GTVD98%, HRCTVD90%) and OARs (BladderD2cc and RectumD2cc) were reported between the shifted plans versus a reference plan with no offset. A p value<0.05 was considered statistically significant in the paired T-test for the mean.

Results: BladderD2cc and RectumD2cc but not the GTVD98% were significantly different from the reference plan for all the shifts studied. A trend of increase in GTVD98%, HRCTVD90% and RectumD2cc was found with increase in positive shift (i. e., when source positions were more distal from the connector end) whereas the trend was opposite for the BladderD2cc. The mean differences in (GTVD98%, HRCTVD90%, BladderD2cc, RectumD2cc) for the largest shifts of -3mm and 3mm were ( 1.6±2.5, -1.8±1.2, 2.8±1.2, -4.4±1.8%) and (0.8±2.4, 0.9±1.2, -2.8±0.9, 5.0±2.1%), respectively.

Conclusion: is a significant difference in HRCTVD90%, BladderD2cc and RectumD2cc with the systematic error in the source path along the length inside the ovoids of Venezia applicator used for intracavitary cervical cancer brachytherapy except for GTVD98%.

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Keywords

Brachytherapy, HDR, Treatment Planning

Taxonomy

TH- Brachytherapy: GYN Intracavity Brachytherapy

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