A remote EPID-based dosimetric TPS-planned audit of centers for clinical trials: outcomes and analysis of contributing factors

Abstract

BackgroundA novel remote method for external dosimetric TPS-planned auditing of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for clinical trials using electronic portal imaging device (EPID) has been developed. The audit has been applied to multiple centers across Australia and New Zealand. This work aims to assess the audit outcomes and explores the variables that contributed to the audit results.MethodsThirty audits were performed of 21 radiotherapy facilities, 17 facilities underwent IMRT audits and 13 underwent VMAT audits. The assessment was based on comparisons between the delivered doses derived from images acquired with EPIDs and planned doses from the local treatment planning systems (TPS). Gamma pass-rate (GPR) and gamma mean value (GMV) were calculated for each IMRT field and VMAT arc (total 268 comparisons). A multiple variable linear model was applied to the GMV results (3%/3 mm criteria) to assess the influence and significance of explanatory variables. The explanatory variables were Linac-TPS combination, TPS grid resolution, IMRT/VMAT delivery, age of EPID, treatment site, record and verification system (R&V) type and dose-rate. Finally, the audit results were compared with other recent audits by calculating the incidence ratio (IR) as a ratio of the observed mean/median GPRs for the remote audit to the other audits.ResultsThe average (± 1 SD) of the centers’ GPRs were: 99.3 ± 1.9%, 98.6 ± 2.7% & 96.2 ± 5.5% at 3%, 3 mm, 3%, 2 mm and 2%, 2 mm criteria respectively. The most determinative variables on the GMVs were Linac-TPS combination, TPS grid resolution and IMRT/VMAT delivery type. The IR values were 1 for seven comparisons, indicating similar GPRs of the remote audit with the reference audits and > 1 for four comparisons, indicating higher GPRs of the remote audit than the reference audits.ConclusionThe remote dosimetry audit method for clinical trials demonstrated high GPRs and provided results comparable to established more resource-intensive audit methods. Several factors were found to influence the results including some effect of Linac-TPS combination.Electronic supplementary materialThe online version of this article (10.1186/s13014-018-1125-8) contains supplementary material, which is available to authorized users.

Validation of virtual water phantom software for pre‐treatment verification of single‐isocenter multiple‐target stereotactic radiosurgery

“…37 Therefore, the penumbra differences (≤1.1 mm) observed in Figures 4 cannot be attributed to a film limitation, and seems due to the modelling of the VIPER software, which has not been specifically optimized for small fields. 15 Hence, although there is margin for improvement in the VIPER modeling of the penumbra, it is still adequate for the purposes of this work.…”

“…Ansbacher described a method for rapid evaluation of IMRT plans, using EPID images for reconstruction of the dose delivered to a virtual 3D cylindrical phantom 13 . A similar method was used by the VIPER (VIrtual Phantom Epid dose Reconstruction) software developed at Calvary Mater Newcastle Hospital (CMNH) that has been used for remote EPID‐based external dosimetric auditing of IMRT and VMAT for clinical trials 14,15 . VIPER is not currently commercially available, but it can be made available on request for research purposes.…”

Verification of stereotactic radiosurgery plans for multiple brain metastases using a virtual phantom-based procedure

“…DVH calculation, however, is not currently available in the VIPER software. The implementation of a DVH approach in the VIPER software was also proposed by Miri et al [22]; 4. 3D dose distribution reconstruction on the patient's CT anatomy cannot be done by the VIPER software, as it is currently performed by other commercially-available systems [41,42]; 5.…”

“…3D dose distribution reconstruction on the patient's CT anatomy cannot be done by the VIPER software, as it is currently performed by other commercially-available systems [41,42]; 5. As pointed out by Miri et al [22], VIPER does not allow an end-to-end audit to be performed, for instance, absolute beam output, beam profile or inhomogeneity modelling cannot been assessed.…”

“…This approach was described by Ansbacher for verification of IMRT plans [20]. Audits of IMRT and VMAT for clinical trials have been done using the VIPER (VIrtual Phantom Epid dose Reconstruction) software that permits the 3D dose reconstruction from EPID images [21,22]. However, no SRS plans were included in those audits.…”