In vivo transit dosimetry methodology for whole breast intensity modulated radiation therapy

Background: In vivo transit dosimetry using an electronic portal imaging device (EPID-IVTD) is an important tool for verifying the accuracy of radiation therapy treatments. Despite its potential, the implementation of EPID-IVTD in breast intensity modulated radiation therapy (IMRT) treatments has not yet been standardized, limiting its clinical adoption. A standardized EPID-IVTD method could enhance treatment accuracy and improve patient safety in routine clinical practice. Purpose: This study aims to develop a method for EPID-IVTD for whole breast IMRT treatment. Methods: Gamma passing rates (GPRs) analysis was the basis of the work conducted on a dataset of 50 patients. The first phase of the work focused on the identification of the reference fraction. In the second phase a method for performing EPID-IVTD was implemented. Lower-tolerance and -action limits (l-TL and l-AL), as introduced by AAPM TG 218, were employed to determine the reference fraction and used as alert and alarm thresholds, respectively, in EPID-IVTD monitoring. Results: The first treatment fraction demonstrated the best dosimetric agreement with the theoretical plan and was therefore used as the reference in the second phase of the study. EPID-IVTD results showed that 75% of the GPRs ranged from 97.5% to 99.9%, 93.83% were above the l-TL, 4.31% fell between l-TL and l-AL, and 1.86% were below l-AL. Conclusions: A method for the implementation of an effective EPID-IVTD in whole breast IMRT treatment was developed and is now routinely applied at our center, enabling efficient monitoring in clinical practice.