Comparison of ICRU 38 Rectal Reference Point Dose Estimates with Measured Dose In-vivo in Cobalt-60 HDR Brachytherapy for Cervical Cancer

Abstract

The objective of this study was to compare the ICRU 38 calculated rectal dose with in-vivo dosimetry measured doses in Cobalt-60 HDR brachytherapy for cervical cancer. A total of 48 brachytherapy insertions done on 15 patients treated from January to March 2017 at our institution were included in this prospective cross sectional study. The results demonstrated no significant difference between the computed ICRU rectal point dose and in-vivo maximum measured rectal dose ((r) 0.6208, p <0.0001 [S]; t-test p=0.1578 [NS] 95%CI -0.78 to 0.46), but a significant difference between ICRU rectal point and in-vivo mean measured rectal dose ((r) 0.6033, p <0.0001[S]; t-test p<0.0001[S] 95%CI: -0.81 to 0.35). These findings were seen even when sub-analyzed for the two used fraction sizes of 7Gy and 8Gy. The results also showed no significant differences in the maximum ((r) 0.9029, p <0.0001[S]; t-test p=0.2576[NS], 95%CI -0.21 to 0.06) and mean ((r) 0.9766, p<0.0001[S]; t-test p=0.2786[NS], 95%CI -0.93 to 0.03) doses taken from treatment planning system assigned dose points coinciding with the imaged probes of the in-vivo dosimeter.  Over-all, this study was able to provide additional evidence that in-vivo dosimetry can be validly used in the clinical setting to estimate the dose to the rectum during Co60 HDR brachytherapy. Use of this technique allows for an additional quality assurance method that can contribute to reductions of errors in dose delivery.