AAPM Task Group Report 307: Use of EPIDs for Patient‐Specific IMRT and VMAT QA

Abstract

PurposeElectronic portal imaging devices (EPIDs) have been widely utilized for patient‐specific quality assurance (PSQA) and their use for transit dosimetry applications is emerging. Yet there are no specific guidelines on the potential uses, limitations, and correct utilization of EPIDs for these purposes. The American Association of Physicists in Medicine (AAPM) Task Group 307 (TG‐307) provides a comprehensive review of the physics, modeling, algorithms and clinical experience with EPID‐based pre‐treatment and transit dosimetry techniques. This review also includes the limitations and challenges in the clinical implementation of EPIDs, including recommendations for commissioning, calibration and validation, routine QA, tolerance levels for gamma analysis and risk‐based analysis.MethodsCharacteristics of the currently available EPID systems and EPID‐based PSQA techniques are reviewed. The details of the physics, modeling, and algorithms for both pre‐treatment and transit dosimetry methods are discussed, including clinical experience with different EPID dosimetry systems. Commissioning, calibration, and validation, tolerance levels and recommended tests, are reviewed, and analyzed. Risk‐based analysis for EPID dosimetry is also addressed.ResultsClinical experience, commissioning methods and tolerances for EPID‐based PSQA system are described for pre‐treatment and transit dosimetry applications. The sensitivity, specificity, and clinical results for EPID dosimetry techniques are presented as well as examples of patient‐related and machine‐related error detection by these dosimetry solutions. Limitations and challenges in clinical implementation of EPIDs for dosimetric purposes are discussed and acceptance and rejection criteria are outlined. Potential causes of and evaluations of pre‐treatment and transit dosimetry failures are discussed. Guidelines and recommendations developed in this report are based on the extensive published data on EPID QA along with the clinical experience of the TG‐307 members.ConclusionTG‐307 focused on the commercially available EPID‐based dosimetric tools and provides guidance for medical physicists in the clinical implementation of EPID‐based patient‐specific pre‐treatment and transit dosimetry QA solutions including intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatments.

Automation to facilitate optimisation of breast radiotherapy treatments using EPID-based in vivo dosimetry

“…The presence of the offset in our study led to the use of the change in standard deviation in dose instead of a gamma analysis and demonstrates the importance of assessing the metrics and tolerances needed for the specific local context to account for the limitations and performance of the IVD software and equipment in use. This is as recommended in Dogan et al (2023) and our novel tolerance metric is reported here in line with recommendations in the report that the sharing of clinical experience and tolerance levels should be encouraged to help inform others on likely performance ranges. Indeed, where the comparison is a 3D dose distribution based upon the planning CT scan instead of an ontreatment CBCT, gamma may not be an appropriate metric to use in any case because a change in dose measured at the EPID panel does not necessarily relate directly to an equivalent change in dose within the patient (for example in the case of significant shape change).…”

“…This can make it difficult to interpret IVD results in isolation or to set useful tolerances using standard dose comparison metrics such as gamma. This paper demonstrates the importance of using metrics that are appropriate to the particular IVD system in use, a topic which is discussed in AAPM TG307 (Dogan et al 2023), and reports our findings and tolerances in line with recommendations in that document.…”

Validation of an in vivo transit dosimetry algorithm using Monte Carlo simulations and ionization chamber measurements

“…We used a 20% threshold to exclude from the analysis the low‐dose region due to uncertainties in the dose conversion from EPID images. 22 No interpolation was applied to the PRIMO‐estimated dose.…”

“…They reported different examples of failing fractions related to deviations in treatment delivery. Both approaches are reported in the recently published report of the Task Group 307 22 on the use of EPID for transit dosimetry.…”

Wobbling nature of gamma passing rate as a function of calibration field sizes in patient-specific quality assurance

“…PSQA can be defined as a pre-treatment process involving measurements to confirm the deliverability and quality of the patient's treatment plan. 1 This ensures that the planned radiation dose aligns with the intended treatment and meets the required quality standards before the actual patient treatment begins. Various factors, such as the wrong position of the multi-leaf collimator (MLC), MLC speed and fluctuations in the linear accelerator (LINAC) output, beam stability, and planning grid size, may contribute to errors in treatment delivery.…”