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Radiochromic film based transit dosimetry for verification of dose delivery with intensity modulated radiotherapy
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Purpose: To evaluate the transit dose based patient specific quality assurance (QA) of intensity
modulated radiation therapy (IMRT) for verification of the accuracy of dose delivered to the
Methods: Five IMRT plans were selected and utilized to irradiate a homogeneous plastic water phantom
and an inhomogeneous anthropomorphic phantom. The transit dose distribution was measured
with radiochromic film and was compared with the computed dose map on the same plane using a
gamma index with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit.
Results: While the average gamma index for comparisons of dose distributions was less than one
for 98.9% of all pixels from the transit dose with the homogeneous phantom, the passing rate was
reduced to 95.0% for the transit dose with the inhomogeneous phantom. Transit doses due to a 5 mm
setup error may cause up to a 50% failure rate of the gamma index.
Conclusions: Transit dose based IMRT QA may be superior to the traditional QA method since the
former can show whether the inhomogeneity correction algorithm from TPS is accurate. In addition,
transit dose based IMRT QA can be used to verify the accuracy of the dose delivered to the patient
during treatment by revealing significant increases in the failure rate of the gamma index resulting
from errors in patient positioning during treatment. ? 2013 American Association of Physicists in
Kwangzoo Chung
Proton Therapy Center, National Cancer Center, Goyang 410-769, Korea
Myonggeun Yoona) and Jaeman Son
Department of Radiological Science, College of Health Science, Korea University, Seoul 136-703, Korea
Sung Yong Park
Proton Therapy Center, McLaren Cancer Institute, Flint, Michigan 48532
Kiho Lee, Dongho Shin, Young Kyung Lim, and Se Byeong Lee
Proton Therapy Center, National Cancer Center, Goyang 410-769, Korea
Med. Phys. 40 (2), February 2013