Spatially fractionated radiotherapy as an alternative to brachytherapy for cervical cancer with unfavourable dosimetry: An in-silico study.

PURPOSE: Brachytherapy is a critical component of cervical cancer treatment, but unfavourable anatomy or poor tumour response to external beam radiotherapy can make brachytherapy technically difficult or suboptimal, resulting in inadequate target coverage or unacceptable organ-at-risk doses. This study evaluated the dosimetric feasibility of spatially fractionated radiotherapy as an alternative boost option when brachytherapy cannot be optimally delivered. MATERIALS AND METHODS: An in-silico study was performed using volumetric-modulated arc therapy-based spatially fractionated radiotherapy on imaging data from ten patients who received brachytherapy between 2018 and 2021. These patients had suboptimal brachytherapy dosimetry due to unfavourable anatomy and/or large residual disease, or required advanced intracavitary-interstitial techniques. Before brachytherapy, magnetic resonance imaging was used to delineate the high-risk clinical target volume, and organs-at-risk were contoured on contrast-enhanced computed tomography. Two spatially fractionated radiotherapy plans were developed: (i) using straight virtual "rods" and (ii) using bending "rods". These virtual rods represented intentionally placed high-dose regions to recreate the heterogenous dose distribution characteristic of brachytherapy. Spatially fractionated radiotherapy plans were compared with clinically delivered brachytherapy plans. RESULTS: Both spatially fractionated radiotherapy approaches achieved high-risk clinical target D90 matching or exceeding brachytherapy across all patients. In cases with large residual tumours or unfavourable anatomy (n=7), spatially fractionated radiotherapy produced higher target coverage than brachytherapy. In patients with favourable intracavitary-interstitial brachytherapy dosimetry (n=3), spatially fractionated radiotherapy achieved comparable target doses. Bladder and rectum doses exceeded recommended constraints in seven of ten brachytherapy plans, whereas all spatially fractionated radiotherapy plans maintained organ-at-risk doses within recommended hard constraints. CONCLUSION: Spatially fractionated radiotherapy may offer a feasible alternative boost strategy for patients in whom brachytherapy is technically limited or yields suboptimal dosimetry. While not intended to replace brachytherapy, it may help bridge treatment gaps in challenging clinical scenarios.