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

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.

IPEM topical report: guidance for the clinical implementation of online treatment monitoring solutions for IMRT/VMAT

“…Transmission detectors are not capable of true IVD because the measurement is not influenced by the patient. However, it has been demonstrated that online capabilities of transmission detectors can complement the use of EIVD, improving sensitivity to MU and collimator positioning variation (Arilli et al 2020). Furthermore, simultaneous measurement with both devices can help distinguish the root cause of errors i.e.…”

Applications of Medical Physics

“…Arilli et al [15] evaluate the combined use of the Integral Quality Monitor (IQM, iRT Systems GmbH, Koblenz, Germany) transmission detector and SoftDiso software (Best Medical Srl-Chianciano Terme, Italy) for in vivo dose monitoring for the simultaneous detection of delivery and patient setup errors in whole-breast irradiation. The authors show that the two devices provide complementary information and allow the fast detection of all types of errors.…”

Feasibility of using a transmission ion chamber for QA tests of medical linear accelerators

“…The IQM system is primarily developed to validate the accuracy of beam delivery both as a real‐time monitor (i.e., during treatment), as well as for pre‐treatment validation of patient specific treatment plans. The characteristics and performance of IQM system for IMRT and VMAT treatment patient‐specific QA has been investigated and compared to other devices 6–13 . Since the IQM detector is robustly mounted at the Linac collimator, and works with well‐understood ionization chamber principles, it is anticipated that the system's large transmission chamber may potentially be utilized as an efficient Linac QA device for a selected set of dosimetric parameters.…”

“…The characteristics and performance of IQM system for IMRT and VMAT treatment patient‐specific QA has been investigated and compared to other devices. 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 Since the IQM detector is robustly mounted at the Linac collimator, and works with well‐understood ionization chamber principles, it is anticipated that the system's large transmission chamber may potentially be utilized as an efficient Linac QA device for a selected set of dosimetric parameters.…”