Quality Assurance of the Multileaf Collimator for Intensity-Modulated Radiation Therapy with Flattening-Filter-Free Beams

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K19236
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Medical Physics and Radiological Technology
• Research Institution: Nara Medical University
• Principal Investigator: Wakai Nobuhide 奈良県立医科大学, 医学部, 助教 (50745338)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: FFFビーム / IMRT / MLC / 品質管理 / 医学物理

Outline of Final Research Achievements

We evaluated the impact of leaf gap error on target dose using intensity-modulated radiation therapy (IMRT) with flattening-filter-free (FFF) beams. IMRT plans with FFF and normal flattening-filtered (FF) beams were generated for 10 prostate cancer patients and 10 head and neck cancer patients were enrolled. In-house software was used to introduce three leaf gap errors (0.2, 0.6, and 1.0 mm) into each treatment plan, which were then recalculated. Changes in target dose with the three leaf gap errors were evaluated. Average leaf pair opening (ALPO) was calculated in all plans, and the relationship between ALPO and the changes in target dose were investigated. The changes in target dose for FFF beams were larger than those for the FF beams. The ALPO values for FFF beams were smaller than those for FF beams. For the three leaf gap errors, the changes in target dose negatively correlated with ALPO. The plan with a narrow ALPO showed weak robustness against leaf position error.

Free Research Field

医学物理学

Academic Significance and Societal Importance of the Research Achievements

近年、照射時間の短縮を目的として、フラットニングフィルターフリー(FFF)ビームの臨床応用が進んでいるが、FFFビームを用いたIMRTを行うときにMLCの位置精度が線量に与える影響についての研究は行われてこなかった。本研究では、FFFビームを用いたIMRTでは通常のビームと比べて、MLCの位置精度が線量に与える影響が大きくなることが分かった。各種ガイドラインでは通常のビームを用いた時のMLCの位置誤差の許容値は示されているが、本研究により、FFFビームを用いたIMRTでは、より厳しい許容値を設定する必要があることが示唆された。