A Phase II Trial of Stereotactic Ablative Radiotherapy as a Boost for Locally Advanced Cervical Cancer.

Abstract

PURPOSE\nAssess the feasibility, safety and efficacy of Stereotactic ablative radiotherapy (SAbR) as alternative for intracavitary (ICBT) /interstitial brachytherapy (IBT) boost for locally advanced cervical cancer (LACC) after initial chemoradiation METHODS: A single arm institutional phase II study of SAbR as boost for LACC was conducted .Eligible patients had LACC FIGO 2009 stage IB2-IVB, performance status(PS) 0-3, and one of the following : medically unfit or refused ICBT or tumor extent required IBT for coverage . The cervix PTVboost volume received 28 Gy in 4 fractions.\n\n\nRESULTS\nStudy was closed with 15 of 21 patients completed due to concern for toxicity. Median follow up for this cohort is 19months. Patients had predominantly advanced stage (III-IV 53%) with median Charlson comorbidity score of 4. Most tumors were large with a median SAbR boost PTV size of 139 cc (range 51-268cc). Tumor size and patient co-morbidities probably contributed to the lower than expected 2 year local control (LC), progression free (PFS) and overall survival (OS) of 70.1% 46.7% and 53.3% respectively .The SAbR boost 2 year cumulative grade ≥ 3 toxicity of 26.7% was predominantly rectal (ulcer/fistula).The median SAbR PTV volume was 225 cc versus 95 cc for patients with and without grade ≥ 3 toxicity. On dosimetric analysis only the percentage of rectal circumference receiving 15Gy (PRC 15) for the SAbR boost was associated with development of grade 3 ulcer or rectovaginal fistula (p= 0.04), with PRC15 > 62.7% being strongest predictor of toxicity (AUC 0.93, sensitivity 100%, specificity 90%) CONCLUSION: In this SAbR boost series suboptimal outcomes were probably related to patient selection and very large tumor volume. This approach may still be warranted in patients with smaller tumors unable to undergo standard brachytherapy for cervix cancer.