Abstract
Aim: To analyze the inter-fraction, intra-fraction uncertainties and to verify the delivered total dose with planned dose in the combined intracavitary-interstitial brachytherapy of gynaecological cancer patients using microMOSFET in-vivo dosimeter. Materials and Methods: Between May 2014 and March 2016, 22 patients who underwent brachytherapy treatments with an applicator combination of CT/MR compatible tandem, ring and Syed-Neblett template-guided rigid needles were included in this study. Specially designed microMOSFET, after calibration, was used to analyze the variations in dosimetry of combined intracavitary-interstitial application. Results: The standard deviation for Inter-fraction variation among 22 combined intracavitary interstitial applications ranged between 0.86% and 10.92%. When compared with the first fraction dose, the minimum and maximum dose variations were −9.5% and 26.36%, respectively. However, the mean doses varied between −5.95% and 14.49%. Intra-fraction variation, which is the difference of TPS calculated dose with first fraction microMOSFET-measured dose ranges from −6.77% to 8.68%. The variations in the delivered total mean dose in 66 sessions with planned doses were −3.09% to 10.83%. Conclusions: It is found that there was a gradual increase in microMOSFET measured doses as compared to the first fraction with that of subsequent fractions in 19 out of 22 applications. Tumor deformation and edema may be the influencing factors, but the applicator movements played a major role for the variations. We find that the microMOSFET is an easy and reliable system for independent verification of uncertainties during ICBT-ISBT treatments.
Highlights
Brachytherapy is used to deliver high doses limited to the accessible tumors, with minimal doses in the surrounding normal tissue regions
The inter-fraction variations of delivered doses for the combined Intracavitary Brachytherapy (ICBT) + Interstitial Brachytherapy (ISBT) of all patients are shown in Figure 3, keeping the first fraction dose as 100%
Percentage standard deviation (SD) of inter-fraction variations ranges from 0.86% to 10.92% (Figure 4)
Summary
Brachytherapy is used to deliver high doses limited to the accessible tumors, with minimal doses in the surrounding normal tissue regions. Though Intracavitary Brachytherapy (ICBT) is generally used in most of the gynaecological tumors, some patients with paravaginal and parametrial involvement, and with bulky and complex shaped tumour require Interstitial Brachytherapy (ISBT) as well [1]. ICBT + ISBT delivers better CTV coverage compared to the suboptimal doses from ISBT alone [2]. Syed-Neblett Template (SNT), Martinez Universal Perineal Interstitial Template (MUPIT) and Vienna applicator are used as implant templates for such treatments. The delivered dose has to be checked and verified with planned dose since precise and accurate dose delivery is essential in radiotherapy. In-vivo dosimeters like TLD, MOSFET, diodes, diamond detector and scintillation detector are used for dose delivery verifications in brachytherapy [3]
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