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J Korean Soc Ther Radiol Oncol > Volume 23(3); 2005 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 2005;23(3): 176-185.
Patient Specific Quality Assurance of IMRT: Quantitative Approach Using Film Dosimetry and Optimization
Kyung Hwan Shin, Sung Yong Park, Dong Hyun Park, Dongho Shin, Dahl Park, Tae Hyun Kim, Hongryull Pyo, Joo Young Kim, Dae Yong Kim, Kwan Ho Cho, Sun Nyung Huh, Il Han Kim, Charn Il Park
1Research Institute and Hospital, National Cancer Center, Korea. cool_park@ncc.re.kr
2Department of Radiation Oncology, Seoul National University College of Medicine, National Cancer Center, Gyeonggi, Korea.
ABSTRACT
PURPOSE:
Film dosimetry as a part of patient specific intensity modulated radiation therapy quality assurance (IMRT QA) was performed to develop a new optimization method of film isocenter offset and to then suggest new quantitative criteria for film dosimetry.
MATERIALS AND METHODS:
Film dosimetry was performed on 14 IMRT patients with head and neck cancers. An optimization method for obtaining the local minimum was developed to adjust for the error in the film isocenter offset, which is the largest part of the systemic errors.
RESULTS:
The adjust value of the film isocenter offset under optimization was 1 mm in 12 patients, while only two patients showed 2 mm translation. The means of absolute average dose difference before and after optimization were 2.36 and 1.56%, respectively, and the mean ratios over a 5% tolerance were 9.67 and 2.88%. After optimization, the differences in the dose decreased dramatically. A low dose range cutoff (L-Cutoff) has been suggested for clinical application. New quantitative criteria of a ratio of over a 5%, but less than 10% tolerance, and for an absolute average dose difference less than 3% have been suggested for the verification of film dosimetry.
CONCLUSION:
The new optimization method was effective in adjusting for the film dosimetry error, and the newly quantitative criteria suggested in this research are believed to be sufficiently accurate and clinically useful.
Key Words: IMRT QA, Film dosimetry, Optimization, Quantitative criteria
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