OC-42 INTERSTITIAL BRACHYTHERAPY VERSUS IMRT IN PATIENTS WITH CARCINOMA CERVIX UNSUITABLE FOR ICRT

Abstract

Purpose/Objective: IBT (interstitial brachytherapy) is the standard of treatment in patients with carcinoma cervix not suitable for ICRT (Intracavitary radiotherapy). We have designed this study to assess the role of IMRT (intensity modulated radiotherapy) in such patients and compare dose conformality, coverage of target and doses to OARs (Organ at risk) between IBT and IMRT. Materials and Methods: 12 patients were selected for this study. Target volume and OARs viz bladder, rectum and urethra were contoured on planning CT scans on brachytherapy treatment planning system(PLATO version 14.1 Nucletron®, Netherlands).The contoured images were then transferred to external beam planning system(Eclipse version 6.5).With IBT 20 Gy was prescribed in 2 fractions over 2 weeks (BED 40 Gy) and 33 Gy was prescribed with IMRT in 13 fractions over 2.5 weeks(BED 41 Gy).PTV D95%,PTV minimum, conformality index was used for comparison of target and dose maximum and dose to 5cm 3 and dose to 50% and 75% volume of rectum, bladder and urethra were used for comparison of doses to OARs. All doses were expressed in BED calculated by LQ-L formulae. For analysis a two-tailed paired t test was used with p value <0.05 considered as significant. SPSS version 16.0 was used Results: A total of 24 plans were generated; 12 for IMRT and 12 for IBT.IBT delivered higher mean doses to 95% volume of PTV 57.16+/5.54 Gy versus 41.47+/-0.19 Gy (p value 0.003) and also produced a more conformal plan as the mean conformity index was better with IBT 0.94+/-0.01 versus 0.908+/-0.02 for IMRT (p value 0.034).The hot spots were more inside the PTV with IBT as compared with IMRT. The mean maximum doses to the bladder and urethra were significantly reduced with IBT when compared with IMRT 50.64+/-7.2 Gy versus 66.31+/-2.79 (p value 0.004) and 34.90+/-13.01 versus 60.77+/-1.96 Gy (p value 0.009) respectively. In comparison, 5cm3 volume of bladder and urethra was better with IBT than IMRT:37.28+/-5.92 Gy versus 50.04+/-7.16 Gy(p value 0.05) and 21.04+/-8.24 Gy versus 24.08+/-8.06 Gy(p value 0.05).Though mean rectal dose maximum was statistically significantly lower with IBT as compared with IMRT 54.64+/-3.57 Gy versus 62.63+/-3.94 Gy (p value 0.02),the doses to 5 cm3 volume and dose to 50% and 75% volume of rectum were comparable and not statistically significant