Dosimetric and Radiobiological Impact of Flattening Filter-Free Beam and Dose Calculation Algorithm Using RapidArc Plans for Cervical Cancer Treatment.

Abstract

Purpose: The aim of this study is to quantify the potential benefits of a flattening filter-free (FFF) beam and implement a dose-computation algorithm for cervical radiotherapy through dosimetric and radiobiological analyses using RapidArc.

Methods: Thirty-three patients were enrolled, and four RapidArc plans were created for each patient using a dual-arc flattening filter and 6-MV FFF photon beams for the two calculation algorithms. Homogeneity index (HI), conformity index (CI), target coverage, monitor units (MUs), and organ-at-risk (OAR) dosimetric characteristics were compared between the plans. Radiobiological characteristics and normal tissue complication probability (NTCP) scores were computed for the OAR using different biological models.

Results: No significant differences were observed in the D_max, D_98%, and CI in the planning target volume (PTV). Both computations estimated a significant difference in V_95%, D_2%, and HI for the PTV. Furthermore, the FFF beam showed a significant increase in the MUs and a significant reduction in V_30% for the femoral heads. The NTCP score showed a significant increase in the late effects on the bladder, rectum, and bowel with FFF beams.

Conclusion: The current study recommends FFF beams for better conformity, comparable dose coverage for the target, and OAR sparing invariable to the dose computation algorithm. The difference in the NTCP score for OAR was minimal with the FFF beam.