title: Radiochromic film based transit dosimetry for verification of dose delivery with intensity modulated radiotherapy.
abstract: OBJECTIVE
  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 patient.
  
  
  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.
authors: Proton Therapy Center, National Cancer Center, Goyang, Korea.
authors: Kwangzoo
authors: K
authors: Chung
authors: Myonggeun
authors: M
authors: Yoon
authors: Jaeman
authors: J
authors: Son
authors: Sung
authors: S
authors: Yong Park
authors: Kiho
authors: K
authors: Lee
authors: Dongho
authors: D
authors: Shin
authors: Young
authors: Y
authors: Kyung Lim
authors: Se
authors: S
authors: Byeong Lee
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D019047:Phantoms, Imaging; D010969:Plastics; D011829:Radiation Dosage; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
chemical_list: D010969:Plastics