Global Dose Optimization Strategy Integrating Spatially Fractionated Radiotherapy, External Beam Radiotherapy, and Brachytherapy for Cervical Cancer
Abstract
Purpose
To develop a global dose optimization strategy for organs at risk (OARs) in locally advanced cervical cancer (LACC) treated with combined spatially fractionated radiotherapy (SFRT), external beam radiotherapy (EBRT), and brachytherapy (BT), aiming to enable safe dose escalation for bulky tumors.
Methods
A retrospective analysis included 31 LACC patients treated with standard EBRT+BT. Patients were stratified into Group A (PTV only, 45 Gy) and Group B (simultaneous integrated boost to nodal PGTVN up to 55–57.5 Gy). Dosimetric parameters for targets and OARs from EBRT and BT were recorded. An innovative “Brachytherapy Influence Zone (BI)” was defined in EBRT planning by contouring the uterus and vagina with a 1 cm volumetric expansion, forming OAR-BI structures to explore potential optimization. Phase-specific OAR constraints and a BI-guided strategy were established for the integrated “SFRT+EBRT+BT” regimen. Feasibility was tested by implementing the full workflow in five patients, optimizing EBRT plans using OAR-BI.
Results
In EBRT, OAR D2cc was significantly higher in Group B (bladder: 49.35±4.36 Gy; sigmoid: 47.47±2.35 Gy) than in Group A (bladder: 45.36±0.48 Gy; sigmoid: 44.88±0.34 Gy; P<0.01). PGTVN volume did not correlate with original OAR doses, but PGTVN-BI volume strongly correlated with doses to Bladder-BI and Sigmoid-BI, and marginally with Rectum-BI. BT showed no significant intergroup differences in OAR EQD₂. All five patients completed SFRT-lattice boost with EBRT and BT. Cumulative doses to OARs met constraints in three patients; two with larger PGTVN-BI volume had OAR doses <2 Gy above constraints. Only two patients experienced grade 2 intestinal toxicity.
Conclusion
Using prior data and a BI-based optimization approach, SFRT-lattice boost can be safely integrated into standard LACC radiotherapy while maintaining OAR doses within acceptable limits, offering a practical framework for safe dose escalation in bulky tumors.