Prospective Evaluation of Role of Hybrid Approach Brachytherapy with MRI Only at First Fraction Followed by CT Based IGBT in Subsequent Sessions in Cervical Cancer Patients

Abstract

<h3>Purpose/Objective(s)</h3> We evaluated target volume coverage and doses to organ at risks (OARs) using combined MRI and CT based intracavitary brachytherapy (hybrid approach) with MRI only at first fraction and CT in subsequent fractions for cervical cancer. <h3>Materials/Methods</h3> This is a single-arm, prospective, interventional trial (CTRI/2019/01/01691). 22 cervical cancer patients, after external beam radiotherapy (EBRT) by 3D-CRT, underwent IGBT planning at first fraction using MRI and CT in the second (CT-1) and third (CT-2) fractions (7Gy per fraction). The dose received by at least 90% of the volume (D90%) for high-risk clinical target volume (HR-CTV) and the doses to 0.1 cm³, 1 cm³, and 2 cm³ for the OARs were evaluated. <h3>Results</h3> Median age was 50 years. Stage distribution (FIGO 2009) was 6:8:8 for IIB:IIA:IIIB respectively. Median EBRT dose was 50Gy and all received weekly concurrent cisplatin at doses of 40mg/m² (median 5 cycles). HR-CTV volumes (mean ± SD) of MRI, CT-1 and CT-2 were 24.23 cc ± 9.26 cc, 27.82 cc ± 15.37 cc and 24.82 cc ± 11.14 cc respectively. No statistically significant differences in bladder (MRI, 99.0 cc ± 53.4 vs CT-1, 99.1 cc ± 54.2 vs CT-2, 105.6 cc ± 42.8), rectum (MRI, 42.6 cc ± 13.4 vs CT-1, 50.8 cc ± 23.8 vs CT-2, 47.0 cc ± 12.9) and sigmoid (MRI, 25.3 cc ± 12.1 vs CT-1, 25.2 cc ± 12.6 vs CT-2, 34.6 cc ± 16.9) volumes. D90% doses for HR-CTV were significantly higher in MRI based plans as compared to CT-1 (MRI, 108.86% vs CT-1, 98%, p=0.03) but not different than CT-2 (MRI, 108.86% vs CT-2, 106.86%, p=0.07). Doses OARs were not different (Table 1). At a median follow-up of 25 months, loco-regional control was 95.4% and any acute or late toxicities were limited to grade II. <h3>Conclusion</h3> MRI-based IGBT plans deliver higher doses to HR-CTV than CT-based plans and this can be further improved during subsequent fractions. Hybrid approach brachytherapy is feasible and cost-effective approach in limited resources constraint settings.