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

## TL;DR

This paper introduces a standardized method for in vivo dosimetry in breast radiation therapy to improve treatment accuracy and patient safety.

## Contribution

The study develops a routine EPID-IVTD method for whole breast IMRT using AAPM TG 218 thresholds.

## Key findings

- 75% of gamma passing rates ranged from 97.5% to 99.9% in EPID-IVTD monitoring.
- 93.83% of results were above the lower-tolerance limit, indicating strong dosimetric agreement.
- The method is now routinely used at the authors' center for clinical monitoring.

## Abstract

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.

This study aims to develop a method for EPID‐IVTD for whole breast IMRT treatment.

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.

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.

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.