ABSTRACT
PURPOSE: The purpose of this study was to establish a dosimetric correlation between the bladder volume and its effects on the dose received by the organs at risk (OARs) (urinary bladder, rectum, and sigmoid) during computed tomography (CT)-guided high-dose-rate (HDR) brachytherapy in carcinoma cervix, and to determine an optimum bladder volume to limit the dose to OARs. MATERIAL AND METHODS: Seventy-five intracavitary applications in patients of carcinoma cervix (stage IIB, IIIA, IIIB, IVA) treated with external beam radiotherapy with concurrent chemotherapy followed by CT-based HDR intracavitary brachytherapy (tandem and ovoid type) at our institute between July 2014 to January 2016 were studied. The bladder volume at the time of imaging was noted and was correlated with the radiation dose received by bladder, rectum, and sigmoid colon. RESULTS: Dose volume histogram (DVH) parameters of the bladder increases by elevating the volume of the bladder. Rectum dose does not follow a continuous increasing trend. It increases up to a bladder volume of 110 cc and then starts decreasing. The highest rectal dose observed was in the bladder volume, range 70-110 cc. The minimum doses were recorded when the bladder volume was > 170 cc. Sigmoid colon DVH parameters follow a similar trend as that of the rectum. CONCLUSIONS: A relationship exists between the volume of the OARs and the dose received by them. A bladder volume of about 70 cm3 or less proved better for achieving the prescribed dose limits of bladder, rectum, and sigmoid. The correlations between the bladder volume and the doses received by the OARs were not significant.
ABSTRACT
BACKGROUND: Evaluation of a HDR- interstitial brachytherapy plan is a challenging job. Owing to the complexities and diversity of the normalization and optimization techniques involved, a simple objective assessment of these plans is required. This can improve the radiation dose coverage of the tumour with decreased organ toxicity. AIM: To study and document the various dose volume indices and parameters required to evaluate a HDR interstitial brachytherapy plan by Volume normalization and graphical optimization using MUPIT (Martinez Universal Perineal Interstitial Template) in patients of carcinoma cervix. SETTINGS AND DESIGN: Single arm, retrospective study. METHODS AND MATERIALS: 35 patients of carcinoma cervix who received EBRT and HDR brachytherapy using MUPIT, were selected. The dose prescribed was 4 Gray/Fraction in four fractions (16Gy/4) treated twice daily, at least 6 hours apart. CTV and OARs were delineated on the axial CT image set. Volume normalization and graphical optimization was done for planning. Coverage Index (CI), Dose homogeneity index (DHI), Overdose index (OI), Dose non-uniformity ratio (DNR), Conformity Index (COIN) and dose volume parameters i.e. D2cc, D1cc, D0.1cc of rectum and bladder were evaluated. STATISTICAL ANALYSIS: SPSS version 16 was used. RESULTS AND CONCLUSION: CI was 0.95 ± 1.84 which means 95% of the target received 100% of the prescribed dose. The mean COIN was 0.841 ± 0.06 and DHI was 0.502 ± 0.11. D2cc rectum and bladder was 3.40 ± 0.56 and 2.95 ± 0.62 respectively which was within the tolerance limit of this organs. There should be an optimum balance between these indices for improving the quality of the implant and to yield maximum clinical benefit out of it, keeping the dose to the OARs in limit. Dose optimization should be carefully monitered and an institutional protocol should be devised for the acceptability criteria of these plans.
