Tolerance limits and methodologies for IMRT measurement‐based verification QA: Recommendations of AAPM Task Group No. 218

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143649/1/mp12810_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143649/2/mp12810.pd

IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119.

AAPM Task Group 119 has produced quantitative confidence limits as baseline expectation values for IMRT commissioning. A set of test cases was developed to assess the overall accuracy of planning and delivery of IMRT treatments. Each test uses contours of targets and avoidance structures drawn within rectangular phantoms. These tests were planned, delivered, measured, and analyzed by nine facilities using a variety of IMRT planning and delivery systems. Each facility had passed the Radiological Physics Center credentialing tests for IMRT. The agreement between the planned and measured doses was determined using ion chamber dosimetry in high and low dose regions, film dosimetry on coronal planes in the phantom with all fields delivered, and planar dosimetry for each field measured perpendicular to the central axis. The planar dose distributions were assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop confidence limits for the test results using the concept confidence limit = /mean/ + 1.96sigma. Other facilities can use the test protocol and results as a basis for comparison to this group. Locally derived confidence limits that substantially exceed these baseline values may indicate the need for improved IMRT commissioning

WE‐C‐BRB‐05: Results from 1005 IMRT Irradiations of an Anthropomorphic Head and Neck Phantom

Purpose: To credential institutions treating clinical trial patients with intensity modulated radiation therapy Methods: The credentialing body's anthropomorphic head and neck phantom was sent to institutions wishing to participate in multi‐institutional clinical trials. The phantom contained two PTV structures and an organ at risk (OAR). TLD and film dosimeters were imbedded in the PTV. Institutions were asked to image, plan and treat the phantom as they would a patient. The treatment plan should cover at least 95% of the primary PTV with 6.6 Gy and at least 95% of the secondary PTV with 5.4 Gy. The plan should limit the dose to the OAR to less than 4.5 Gy. The passing criteria were +/−7% for the TLD in the PTVs and a distance to agreement of 4 mm in the high dose gradient area between the PTV and the OAR. Results: The phantom was irradiated 1005 times by 689 institutions from 2001 through February 2011. 804 of the irradiations passed the criteria. 145 irradiations failed only the TLD criteria, 24 failed only the film criteria and 32 failed both sets of criteria. Only 61% of the irradiations passed a narrowed TLD criterion of +/− 5%. When possible, gamma calculations were made for an area around the primary PTV in the axial plane. The average percent of pixels meeting the gamma criteria was 89%. Conclusions: The head and neck phantom is a useful credentialing tool for multi‐institutional IMRT clinical trials. Tightening the criteria would significantly reduce the number of passing irradiations. Altering the criteria to use the gamma calculation instead of the DTA would slightly reduce the number of institutions passing, but would give a more comprehensive view of the fitness of the irradiation. The investigation was supported by PHS grants CA10953, CA81647 and CA21661 awarded by the NCI, DHHS