IMRT credentialing for prospective trials using institutional virtual phantoms: results of a joint European Organization for the Research and Treatment of Cancer and Radiological Physics Center project

Abstract

Background and purposeIntensity-modulated radiotherapy (IMRT) credentialing for a EORTC study was performed using an anthropomorphic head phantom from the Radiological Physics Center (RPC; RPCPH). Institutions were retrospectively requested to irradiate their institutional phantom (INSTPH) using the same treatment plan in the framework of a Virtual Phantom Project (VPP) for IMRT credentialing.Materials and methodsCT data set of the institutional phantom and measured 2D dose matrices were requested from centers and sent to a dedicated secure EORTC uploader. Data from the RPCPH and INSTPH were thereafter centrally analyzed and inter-compared by the QA team using commercially available software (RIT; ver.5.2; Colorado Springs, USA).ResultsEighteen institutions participated to the VPP. The measurements of 6 (33%) institutions could not be analyzed centrally. All other centers passed both the VPP and the RPC ±7%/4 mm credentialing criteria. At the 5%/5 mm gamma criteria (90% of pixels passing), 11(92%) as compared to 12 (100%) centers pass the credentialing process with RPCPH and INSTPH (p = 0.29), respectively. The corresponding pass rate for the 3%/3 mm gamma criteria (90% of pixels passing) was 2 (17%) and 9 (75%; p = 0.01), respectively.ConclusionsIMRT dosimetry gamma evaluations in a single plane for a H&N prospective trial using the INSTPH measurements showed agreement at the gamma index criteria of ±5%/5 mm (90% of pixels passing) for a small number of VPP measurements. Using more stringent, criteria, the RPCPH and INSTPH comparison showed disagreement. More data is warranted and urgently required within the framework of prospective studies.

On the sensitivity of TG‐119 and IROC credentialing to TPS commissioning errors

“…TG‐119 (2) and the IROC (3‐4) both utilize 1D and 2D measurements to evaluate agreement. Three‐dimensional dosimetry techniques that can sample an entire dose distribution with high spatial resolution have been applied to IMRT (16‐19) and may be well suited for TPS commissioning and credentialing procedures for a number of reasons.…”

“…Once the algorithm was commissioned with an intentional error, the dose for select clinical plans was recalculated using the altered algorithm and compared to the original plans to measure the clinical impact that the commissioning error would have. To measure the sensitivity of the IMRT commissioning process and IROC credentialing, the same was done with plans designed on the TG‐119 C‐shape (2) and IROC head and neck IMRT phantoms (3‐4) . The newly calculated plans were then compared to the original plans to determine the dosimetric effect of each error.…”

“…Another means to verify the TPS and IMRT commissioning process is through credentialing processes offered by outside institutions. The most common interinstitutional credentialing is through the Imaging and Radiation Oncology Core (IROC, formerly the RPC) which provides phantoms equipped with point measurement dosimeters and film planes to verify the proper dose delivery based on provided constraints (3‐4) …”

A system for remote dosimetry audit of 3D-CRT, IMRT and VMAT based on lithium formate dosimetry

“…It could be discussed whether one should have acceptance criteria for both PTV and OARs. IROC Huston has 7% as acceptance for measurement points in PTV (end-to-end IMRT, head and neck phantom), but only gamma criterion for measurement points in the OAR [18,19]. Even though it is important to verify the dose to OARs, it is normally more difficult to measure doses with high accuracy due to the dose gradients that normally appear in them.…”

Experimental evaluation of x‐ray acoustic computed tomography for radiotherapy dosimetry applications

“…IC profiles and profiles extracted from experimental XACT images were quantitatively compared using gamma analysis . A gamma criteria of 7%/4 mm was chosen based on the Radiology Physics Center complex dosimetry protocol recently used in a multi‐center IMRT credentialing study . The total gamma pass rate for a given profile was calculated for points in the jaw‐defined field size region.…”