Preliminary results of a vaginal constraint for reducing G2 late vaginal complications after postoperative brachytherapy in endometrial cancer: a prospective analysis

Are 7.5 Gy×2 fractions more efficient than 6 Gy×3 in exclusive postoperative endometrial cancer brachytherapy? A clinical and dosimetrical analysis

PURPOSE

To compare two vaginal brachytherapy (VBT) schedules in postoperative endometrial carcinoma (PEC) patients considering vaginal-cuff relapses (VCR), late toxicities, dosimetry analysis and vaginal dilator use.

MATERIAL AND METHODS

110 PEC patients were treated with exclusive high-dose-rate VBT using two schedules. Group-1:44-patients received 6 Gy×3fractions (September-2011-April-2014); Group-2:66-patients were treated with 7.5 Gy×2fractions with a dose limit of equivalent total doses in 2-Gy fr (EQD2(α/β=3)) of 68 Gy in the most exposed 2 cm3 of clinical target volume (CTV) (July-2015-November-2021). The dose was prescribed at 5 mm from the applicator surface. Were evaluated the overall radiation dose delivered to 90% of the CTV (D90), the CTV receiving 100% of the prescription dose (V100) and the EQD2(α/β=3) received in the most exposed 2 cm3 to dose in CTV. Late toxicity was prospectively assessed using RTOG scores for bladder and rectum and objective LENT-SOMA criteria for late vaginal toxicity (LVT).

STATISTICS

Descriptive analysis, Chi-square, Student's t-tests and Kaplan and Meier method.

RESULTS

The median follow-up was 60 months (15.9-60). There were no VCR or late toxicities in bladder or rectum. LVT ≥ G1 appeared in 26/44 (59.1%) in Group-1 and 25/66 (37.9%) in Group-2. The mean EQD2(α/β=3) received by the most exposed 2 cm3 of CTV was 63.7 Gy ± 10.0 in Group-1 and 60.5 Gy ± 3.8 in Group-2 (p = 0.063). There were no differences in adherence to vaginal dilator use ≥9 months, overall D90 and V100.

CONCLUSION

Considering the lack of vaginal relapses and similar LVT over time, 7.5 Gy×2fractions seem more efficient in terms of patient comfort, workload, and cost. This is the first study using dosimetry parameters to compare effectivity of schedules. Larger series are needed to confirm the present results.

In Vivo Verification of Treatment Source Dwell Times in Brachytherapy of Postoperative Endometrial Carcinoma: A Feasibility Study

(1) Background: In brachytherapy, there are still many manual procedures that can cause adverse events which can be detected with in vivo dosimetry systems. Plastic scintillator dosimeters (PSD) have interesting properties to achieve this objective such as real-time reading, linearity, repeatability, and small size to fit inside brachytherapy catheters. The purpose of this study was to evaluate the performance of a PSD in postoperative endometrial brachytherapy in terms of source dwell time accuracy. (2) Methods: Measurements were carried out in a PMMA phantom to characterise the PSD. Patient measurements in 121 dwell positions were analysed to obtain the differences between planned and measured dwell times. (3) Results: The repeatability test showed a relative standard deviation below 1% for the measured dwell times. The relative standard deviation of the PSD sensitivity with accumulated absorbed dose was lower than 1.2%. The equipment operated linearly in total counts with respect to absorbed dose and also in count rate versus absorbed dose rate. The mean (standard deviation) of the absolute differences between planned and measured dwell times in patient treatments was 0.0 (0.2) seconds. (4) Conclusions: The PSD system is useful as a quality assurance tool for brachytherapy treatments.