Author: Nobuki Imano, Daisuke Kawahara, Akito S Koganezawa, Yuji Murakami, Ikuno Nishibuchi, Takuya Wada 👨🔬
Affiliation: Department of Information and Electronic Engineering, Faculty of Science and Engineering, Teikyo University, Department of Radiation Oncology, Graduate School of Biomedical and Health Sciences, Hiroshima University 🌍
Purpose: Adaptive radiotherapy (ART) compensates for treatment plans based on anatomical changes while not considering biological effects such as interruptions during treatment. This study aims to develop a workflow for dose compensation during interruptions and to establish a comprehensive evaluation method for dose assessment with the biological adaptive radiotherapy (BART) system.
Methods: We analyzed 11 head-and-neck cases with a total of 29 planning target volumes (PTVs) treated with volumetric-modulated arc therapy (VMAT) that experienced interruptions during the treatment course. The decrease in biological effective dose (BED) due to the interruption was calculated using a modified linear-quadratic model considering the duration of the interruption and tumor regrowth. Three-dimensional compensating factor (CF) distributions were generated from physical dose (PD) distributions to compensate for the decrease in BED. CFs were designed to compensate for each PTV while minimizing dose increases to organs at risk (OARs). Compensated plans were generated using single-time optimization in the Eclipse treatment planning system (TPS). PTVs were evaluated using BED, while OARs were assessed using PD.
Results: Without compensation for interruptions, the BED at 2%, 50%, 95%, and 98% coverage for PTVs (∆BD2%, ∆BD50%, ∆BD95%, and ∆BD98%) decreased by -6.7%, -7.2%, -7.5%, and -7.7%, respectively. With compensation, the accuracy of BED compensation at ∆BD2%, ∆BD50%, ∆BD95%, and ∆BD98% was 1.8%, 1.8%, 2.0%, and 2.2%, respectively. The mean PD increases and 95% confidence intervals (CIs) for the brainstem, eye, mandible, optic nerve, parotid, and spinal cord were 1.7Gy (CI:0.9-2.5), 1.2Gy (CI:0.6-1.7), 2.2Gy (CI:1.2-3.3), 1.8Gy (CI:1.1-2.6), 1.4Gy (CI:0.8-2.0), and 1.8Gy (CI:0.7-3.0), respectively.
Conclusion: We successfully developed a biological compensation process for treatment interruptions that can be implemented in TPS. This approach compensates for BEDs to PTV while restricting the increases in PD to OARs. The proposed technique represents a novel strategy for integrating biological considerations into the ART workflow.