Abstract
In intracavitary radiotherapy (ICRT) for cancer cervix, applicator geometry has the potential to impact the doses to organs at risk (OARs) and the coverage of the target volume. At our centre two Varian made Fletcher-style applicator sets, namely defined (fixed) geometry and flexible geometry, are used for ICRT. In the present work, the two types of applicators were compared dosimetrically as per the recommendations of the International Commission on Radiation Units and Measurements (ICRU-38) while delivering high dose rate brachytherapy. Twenty four patients who underwent ICRT were considered for this study. Radiographic method was used for treatment planning on Abacus planning system. ICRU-38 recommended parameters were estimated and compared. Flexible geometry applicator showed 8.8% and 16% higher bladder and rectum point doses as compared to the fixed geometry one but the difference was statistically not significant. The thickness of the pear-shaped isodose volume was larger for the flexible geometry implant also indicating towards higher doses to OARs. The higher bladder and rectum point doses in the case of flexible applicator will need to be validated by a larger data set.
Highlights
Intracavitary radiotherapy (ICRT) is the most widely used form of brachytherapy in the treatment of cancer cervix.How to cite this paper: Singh, S., Sarin, A., Semwal, M.K., Singh, A.K., Goyal, P. and Kumar, A. (2015) Dosimetric Comparison of Fixed and Flexible Geometry ICRT Applicators in Patients Treated for Carcinoma Cervix
Our centre possesses two types of Varian make ICRT applicators namely Fletcher-style applicator set with defined geometry, and Fletcher-style applicator set with flexible geometry for Gammamed 12i high dose rate (HDR) Brachytherapy machines (Figure 1)
The ovoids seem to be reaching more in the posterior direction as compared to the fixed geometry applicator
Summary
Intracavitary radiotherapy (ICRT) is the most widely used form of brachytherapy in the treatment of cancer cervix. Our centre possesses two types of Varian make ICRT applicators namely Fletcher-style applicator set with defined (fixed) geometry, and Fletcher-style applicator set with flexible geometry for Gammamed 12i HDR Brachytherapy machines (Figure 1) Both these applicator types are based on the dosimetry of the conventional Fletcher-style application. These centres practice standard applicator geometry, as stored in their treatment planning system library, based on treatment planning It has been established by many studies that the 2D system of point dose prescription and reporting based on orthogonal radiographic reconstruction of applicators has limitations as compared to 3D volume dose prescription and reporting in terms of dose estimation to OARs and treated volume estimation [7][10]. It is believed that this study will be useful for clinicians in deciding the type of applicators depending on the clinical requirement
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