3575 - A Randomized Crossover Trial to Compare Two Rectum Separation Techniques during High-Dose-Rate Intracavitary Brachytherapy with Tandem-Ring Applicators for Cancer Cervix

S. Vats¹, S. Thakur¹, V. Kumar², M. Gupta Sr¹, L. Chandrakant¹, M. Upadhyay¹, P. Sharma¹, and A. Azad¹; ¹Cancer Hospital, IGMC, Shimla, Himachal Pradesh, India, ²IGMC, Shimla, Himachal Pradesh, India

Purpose/Objective(s): Design of Tandem-ring (TR) applicators assembled with standard rectal retractor (RR) blades best conforms to the anatomy of a subset of patients with shallower/obliterated fornices and narrow vagina. A suboptimal rectum displacement achieved during the ICB procedure, especially in patients with roomy vagina, is less likely to be fully compensated with the process of treatment planning optimization. We indigenously developed a novel packing technique which allows for customized vaginal packing (VP) for the range of spaces, posterior and superior to RR blade in different patients. Novel technique is compared on classical International Commission on Radiation Units-38 (ICRU-38) rectal and bladder point doses with conventional technique of using RR alone.

Materials/

Methods: To respect contemporary dose constraints, we accept no more than 4.53 Gy (65% of 7Gy prescribed to point A) to ICRU rectal point per high-dose-rate (HDR)-ICB session. Any technique which further brings it down to 4.16 Gy (59.42% of 7Gy) or less, would lead to clinically significant reduction in the incidence of rectum toxicity. Hence, trial was designed to detect minimum 5% difference in the dose to ICRU rectal point per insertion. 47 patients who were assessed to be fit for ICB, after completion of external beam radiotherapy (EBRT) to a dose of 46 to 50Gy with concurrent weekly cisplatin, were enrolled in this trial to receive 3 to 4 HDR-ICB sessions of 7Gy each. First ICB session was randomized either in conventional or interventional arm. Each patient then crossed over to receive second session in the alternate arm. Tandem length, tandem angle, ring size, RR blade and a standard loading pattern to recapitulate the pear-shaped dose distribution were kept same during both the sessions. So, two consecutive sessions done on one patient differed only with regard to rectum separation method. Remaining ICB sessions were done as per physician preference and were not analyzed for this trial. 47 ICB sessions done using RR alone constitute conventional arm and 47 in which VP was combined with RR blade constitute interventional arm.

Results: The mean dose to the ICRU rectal point was 57.70% of the prescription dose (range, 44.81-73.6%; median 56.61%) in the conventional arm and 42.54% (range, 25.66-59.45%; median 41.77%) in the interventional arm, for same dose (100%) prescribed to point A in both arms. There was 15.16% (95%CI: 12.87-17.45) reduction in mean dose to the ICRU rectal point (p<0.001) per insertion in the interventional arm. The mean dose to the ICRU bladder point was 40.96% (range,13.89-98.07%; median 39.09%) in the conventional arm and 47.13% (range 15.47-90.48%; median 44.3%) in the interventional arm. There was 6.17% (95%CI: 2.64-9.70) increase in the mean dose to the ICRU bladder point (p=0.001). The point B dose, reference volumes and Total Reference Air Kerma (TRAK) values were similar between two arms.

Conclusion: Novel packing technique optimizes the rectum displacement achieved primarily with standard RR blades.