A novel method for dose distribution registration using fiducial marks made by a megavoltage beam in film dosimetry for intensity-modulated radiation therapy quality assurance

作者：Nakayama Shinichi; Monzen Hajime^*; Oonishi Yuuichi; Mizote Rika; Iramina Hiraku; Kaneshige Souichirou; Mizowaki Takashi

来源：Physica Medica, 2015, 31(4): 414-419.

DOI：10.1016/j.ejmp.2015.02.003

• Film dosimetry
• Radiochromic film
• Quality assurance
• Dose distribution

Purpose: Photographic film is widely used for the dose distribution verification of intensity-modulated radiation therapy (IMRT). However, analysis for verification of the results is subjective. We present a novel method for marking the isocenter using irradiation from a megavoltage (MV) beam transmitted through slits in a multi-leaf collimator (MLC).
Methods: We evaluated the effect of the marking irradiation at 500 monitor units (MU) on the total transmission through the MLC using an ionization chamber and Radiochromic Film. Film dosimetry was performed for quality assurance (QA) of IMRT plans. Three methods of registration were used for each film: marking by irradiating with an MV beam through slits in the MLC (MLC-IC); marking with a fabricated phantom (Phantom-IC); and a subjective method based on isodose lines (Manual). Each method was subjected to local gamma-analysis.
Results: The effect of the marking irradiation on the total transmission was 0.16%, as measured by a ionization chamber at a 10-cm depth in a solid phantom, while the inter-leaf transmission was 0.3%, determined from the film. The mean pass rates for each registration method agreed within +/- 1% when the criteria used were a distance-to-agreement (DTA) of 3 mm and a dose difference (DD) of 3%. For DTA/DD criteria of 2 mm/3%, the pass rates in the sagittal plane were 96.09 +/- 0.631% (MLC-IC), 96.27 +/- 0.399% (Phantom-IC), and 95.62 +/- 0.988% (Manual).
Conclusion: The present method is a versatile and useful method of improving the objectivity of film dosimetry for IMRT QA.

• 出版日期2015-6