SU-E-T-515: Comparison of Two Dose-Specification Methods for the Treatment of Uterine Cervix Cancer with HDR Brachytherapy Using a Tandem and Ring Applicator.

PURPOSE

To compare the dose to the high-risk clinical target volume (HRCTV)-D90 and dose-limiting structures with the dose prescription to point A (Manchester system) using conventional methods to image-guided treatment planning with dose optimization and a dose prescription to D90 of the HRCTV.

METHODS

CT-MR-fused image sets for 16 patients (stage IA2-IIIB) with uterine cervix cancer were obtained for each of 5 fractions of HDR brachytherapy using tandem and ring applicators to generate 2 sets of plans. In the first set, the dose was prescribed to point A with a standard dwell weight pattern reflecting the Manchester system loading pattern. In the second set, the dose was prescribed to D90 of the HRCTV with graphical plan optimization. Parameters of clinical significance (HRCTV-D90 and dose received by 1.0, 2.0, and 5.0cc of the bladder, rectum, and sigmoid) were compared, as recommended by GEC-ESTRO.

RESULTS

HRCTV-V for 6 patients was =30cc (largest radius, <2.0cm) and >30cc (largest radius, =2cm) for the others. For the first set of plans, when HRCTV-V was <30cc, the ratio of doses HRCTV-D90/dose to point A varied from 1.10 to 1.40. When HRCTV-V was >30cc, it varied from 0.75 to 0.95. In the second set of plans, HRCTV-D90 always received the prescription dose. Doses to 2cc of one or more organs at risk exceeded >10% of the limiting doses for 9 patients in the first set of plans but remained <10% in all patients in the second set of plans. A 10-25% dose reduction to 2cc of the bladder and 15-35% to 2cc of the rectum and sigmoid occurred in the second set of plans.

CONCLUSIONS

Image-guided brachytherapy with dose optimization yields a prescribed dose to the HRCTV-D90 while maintaining doses to organs at risk close to their limiting value, offering a dosimetric benefit over the traditional method.