Combined Use of a Transmission Detector and an EPID-Based In Vivo Dose Monitoring System in External Beam Whole Breast Irradiation: A Study with an Anthropomorphic Female Phantom

Chiara Arilli,Angelo Piermattei,Yannik Wandael,Cinzia Talamonti,Livia Marrazzo,Stefania Pallotta,Mattia Grusio,Franco Fusi,Isacco Desideri,Silvia Calusi,Chiara Galeotti

doi:10.3390/app10217611

Abstract

We evaluate the combined usage of two systems, the Integral Quality Monitor (IQM) transmission detector and SoftDiso software, for in vivo dose monitoring by simultaneous detection of delivery and patient setup errors in whole breast irradiation. An Alderson RANDO phantom was adapted with silicon breast prostheses to mimic the female anatomy. Plans with simulated delivery errors were created from a reference left breast plan, and patient setup errors were simulated by moving the phantom. Deviations from reference values recorded by both monitoring systems were measured for all plans and phantom positions. A 2D global gamma analysis was performed in SoftDiso for all phantom displacements. Both IQM signals and SoftDiso R-values are sensitive to small MU variations. However, only IQM is sensitive to jaw position variations. Conversely, IQM is unable to detect patient positioning errors, and the R-value has good sensitivity to phantom displacements. A gamma comparison analysis allows one to determine alert thresholds to detect phantom shifts or relatively large rotations. The combined use of the IQM and SoftDiso allows for fast identification of both delivery and setup errors and substantially reduces the impact of error identification and correction on the treatment workflow.

Highlights

After breast conserving surgery, radiotherapy is the usual therapeutic strategy for breast cancer patients providing, with fewer toxicity effects, equivalent survival outcomes when compared with mastectomy [1,2]
Pre-treatment verification presents several drawbacks: (1) the actual patient geometry is never included in pre-treatment measurements, making it difficult to estimate the effect of observed dosimetric deviations on the actual patient; (2) deviations from intended treatment occurring during the dose delivery cannot be detected [9,10]; (3) pre-treatment verification requires additional measurement sessions, taking up valuable linac time and increasing workload
The first issue is usually addressed in commercial systems by reworking observed deviations on the patient anatomy [11,12,13]; the last two issues cannot be circumvented by using pre-treatment verification

Summary

Introduction

Radiotherapy is the usual therapeutic strategy for breast cancer patients providing, with fewer toxicity effects, equivalent survival outcomes when compared with mastectomy [1,2]. Patient quality assurance programs (QA) are performed in pre-treatment modality. The first issue is usually addressed in commercial systems by reworking observed deviations on the patient anatomy (using the planning CT scan) [11,12,13]; the last two issues cannot be circumvented by using pre-treatment verification. To solve these questions, in vivo dosimetry systems (IVDs) that perform dose measurements during the treatment and compare them to the intended dose are sometimes introduced into the clinical routine. All authors agreed that standard quality pre-treatment checks are not able to detect a large number of treatment errors, highlighting the need for IVDs

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Discussion

Conclusion