A revision of proton machine quality assurance for wobbled-proton-beam therapy.

Periodic checks for proton machine quality assurance (QA) are significant for machine users safely and accurately to provide proton-beam treatment for cancer. Our aim in this study was to describe a revision to proton machine QA procedures for wobbled-proton-beam therapy at the Shizuoka Cancer Center (SCC) in Japan. The previous daily, monthly, and annual QA procedures were determined by reference to our past operational experience and to QA papers for medical accelerators. The revised QA procedures were initiated in May 2011 after preliminary measurements to decide baselines for the QA procedures. This paper presents the proton machine QA procedures and the results of representative QA measurements. Three action levels were decided on by reference to the American Association of Physicists in Medicine Task Group 142 report. Tolerances of inspection action were decided on based on the provisional operational results and actual fluctuations of the QA measurement for a year, and those of scheduled action and stop-treatment action were determined by reference to the machine QA papers and those of the inspection action. No deviation from the tolerance of the scheduled action has been observed so far. Although a few QA procedures exceeded the tolerance of the inspection action, these excesses were resolved by inspection and improvement of the respective measuring procedure within the designated QA time. Hereafter, the proton machine QA procedures proposed in this study will be performed continuously at the SCC to assure patient safety and accurate operation of proton therapy.