Esposito, M; Baldoni, R; Bossuyt, E; Bresciani, S; Clark, C H; Jones, M; Kry, S; Perry, J; van de Kamer, J; Verellen, D; Jornet, N (2024) A commissioning protocol for portal imaging-based radiotherapy in vivo dosimetry systems. Physics and Imaging in Radiation Oncology, 32. 100666 ISSN 24056316

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Abstract

Background and Purpose
With the availability of commercial electronic portal imaging detector-based in vivo dosimetry (EPID-based IVD) solutions, many radiotherapy departments are adopting this technology. However, comprehensive commissioning guidance is lacking. This study aims to provide a protocol for testing the accuracy and sensitivity of EPID-based IVD systems.

Material and methods
The protocol was tested across four institutions using two different systems. Accuracy was evaluated with homogeneous slab phantoms using different square regular fields, and clinical plans in a CIRS lung phantom. Multiple forward and back-projected algorithm implementations were assessed for different energies. Sensitivity analysis in the lung phantom examined responses to setup errors, anatomical variations, and delivery errors.

Results
In homogeneous phantoms, over 85 % of pixels passed the 5 %/2mm gamma criteria, except for the 2x2 cm2 field. In the lung phantom, all systems and implementations achieved over 95 %-pixel pass rates at the 2 %/2mm criterion for volumetric modulated arc therapy (VMAT) plans. For conformal radiation therapy (3DCRT) plans, one system implementation showed poor accuracy, with over 90 % agreement only at the 5 %/2mm criterion. Considering all systems and implementations, average sensitivity and specificity for CRT plans ranged from 0.92 and 0.42 (at 2 %/2mm) to 0.71 and 0.52 (at 5 %/2mm), while for VMAT plans ranged from 0.41 and 0.81 (at 2 %2mm) to 0.37 and 0.81 (at 5 %/2mm).

Conclusion
We successfully developed a protocol to commission EPID IDV systems. It was found that not all systems and implementations achieved satisfactory accuracy and sensitivity, emphasising the need for thorough commissioning and benchmarking.

Item Type:	Article
Keywords:	“In vivo” dose measurements, EPID, QA, Dosimetry
Subjects:	Ionising Radiation > Dosimetry
Divisions:	Medical, Marine & Nuclear
Identification number/DOI:	10.1016/j.phro.2024.100666
Last Modified:	23 Mar 2026 15:38
URI:	https://eprintspublications.npl.co.uk/id/eprint/10352