PO38 Presentation Time: 4:45 PM

Purpose

To co-relate vaginal stricture with the radiotherapy dose at the posterior inferior border of symphysis (PIBS) points in the patients with locally advanced cervical cancer.

Material and Methods

A total of 45 untreated patients, with ECOG 0-2 registered from January 2020 to March 2021 with histopathologically proven carcinoma cervix from stage IIB to IVA were included in the study. All the patients received external beam radiation therapy (EBRT) on 6 MV Linear Accelerator with Volumetric modulated arc therapy (VMAT) to a dose of 45 Gy in 25 fractions to the pelvis and 55 Gy in 25 fractions to the positive nodal disease (Pelvic & Paraaortic) with simultaneous integrated boost (SIB) along with weekly concurrent cisplatin at 40 mg/m². Twenty-three patients were treated with Intracavitary Brachytherapy (ICRT) with a dose of 7 Gy per fraction for three weekly fractions. All the patients were scanned with 1 mm slice thickness & 3-D planning was done on Oncentra treatment planning system. The contouring of targets was done as per ICRU 89 in case of ISBT. Twenty-two patients were treated with interstitial brachytherapy (ISBT), with 6 Gy per fraction for four fractions. The dose was prescribed to HR CTV and point A for ISBT and ICRT respectively. The time gap between two fractions for patients treated with ISBT was at least six hours. Evaluation of disease status and treatment response was done with Functional MRI Pelvis before, during, and 3 months after completion of radiotherapy. Late vaginal morbidity was assessed as per CTCAE v5.0.

Results

The mean duration of follow-up was 12.17 months (1-24.3 months).35.6 % of patients had vaginal stricture with a mean duration of appearance at 7.55 months and a median duration of 8.0 months (3.9-12 months). 24.4% had grade 1 vaginal toxicity, 6.7% had grade 2 vaginal toxicity, 4.4% had grade 3 toxicity. Doses at PIBS 0, PIBS minus points had no correlation with vaginal toxicity, however, dose at PIBS plus 2 was significantly associated with vaginal stricture (p =0.03). Threshold doses and time of appearance of vaginal toxicity are shown in table 1.

Conclusion

Dose at PIBS + 2 is a strong predictor for vaginal stricture. Efforts during brachytherapy planning should be taken to reduce the dose to PIBS +2 so as to reduce the probability of vaginal stricture.