Radiotherapy deficiencies identified during on-site dosimetry visits by the IROC Houston QA Center

Publication date: Available online 24 August 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Stephen F. Kry, Lainy Dromgoole, Paola Alvarez, Jessica Leif, Andrea Molineu, Paige Taylor, David S. Followill
PurposeTo review the dosimetric, mechanical, and programmatic deficiencies most frequently observed during on-site visits of radiotherapy facilities by the Imaging and Radiation Oncology Core Houston office (IROC Houston).MethodsIROC Houston's findings between 2000 and 2014, including 409 institutions and 1020 linacs, were compiled. IROC Houston's on-site evaluation includes verification of absolute calibration (tolerance of ±3%), relative dosimetric review (tolerances of ±2% between TPS calculation and measurement), mechanical evaluation (including MLC and kV-MV evaluation against TG-142 tolerances), and general programmatic review (including institutional QA program versus TG-40 and TG-142).ResultsAn average of 3.1 deficiencies was identified at each institution visited, a number that has decreased slightly with time. The most common errors are tabulated, and include TG-40/TG-142 compliance (82% of institutions were deficient), small field size output factors (59% of institutions had errors ≥3%), and wedge factors (33% of institutions had errors ≥3%). Dosimetric errors of ≥10%, including in beam calibration, were seen at many institutions.ConclusionsThere is substantial room for improvement of both dosimetric and programmatic issues in radiotherapy, which should be a high priority for the medical physics community. Particularly relevant was suboptimal beam modeling in the treatment planning system and a corresponding failure to detect these errors by not including TPS data in the linac QA process.

Teaser

IROC Houston on-site visits of radiotherapy facilities includes an evaluation of beam calibration, relative dosimetry, mechanical checks, and other programmatic issues. The deficiencies identified over the past 15 years are compiled in this study, highlighting areas where problems are most often found (e.g., small field output factors, wedge factors, calibration, etc.). These areas should receive particular attention during beam modeling and machine QA by medical physicists to ensure optimal accuracy is achieved.


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