title: Measurements of patient's setup variation in intensity-modulated radiation therapy of head and neck cancer using electronic portal imaging device.
abstract: OBJECTIVE
  To measure the interfraction setup variation of patient undergoing intensity-modulated radiation therapy (IMRT) of head and neck cancer. The data was used to define adequate treatment CTV-to-PTV margin.
  
  
  METHODS
  During March to September 2006, data was collected from 9 head and neck cancer patients treated with dynamic IMRT using 6 MV X-ray beam from Varian Clinac 23EX. Weekly portal images of setup fields which were anterior-posterior and lateral portal images were acquired for each patient with an amorphous silicon EPID, Varian aS500. These images were matched with the reference image from Varian Acuity simulator using the Varis vision software (Version 7.3.10). Six anatomical landmarks were selected for comparison. The displacement of portal image from the reference image was recorded in X (Left-Right, L-R), Y (Superior-Inferior, S-I) direction for anterior field and Z (Anterior-Posterior, A-P), Y (S-I) direction for lateral field. The systematic and random error for individual and population were calculated. Then the population-based margins were obtained.
  
  
  RESULTS
  A total of 135 images (27 simulation images and 108 portal images) and 405 match points was evaluated. The systematic error ranged from 0 to 7.5 mm and the random error ranged from 0.3 to 4.8 mm for all directions. The population-based margin ranged from 2.3 to 4.5 mm (L-R), 3.5 to 4.9 mm (S-I) for anterior field and 3.4 to 4.7 mm (A-P), 2.6 to 3.7 mm (S-I) for the lateral field. These margins were comparable to the margin that was prescribed at the King Chulalongkorn Memorial Hospital (5-10 mm) for head and neck cancer.
  
  
  CONCLUSIONS
  The population-based margin is less than 5 mm, thus the margin provides sufficient coverage for all of the patients.
authors: Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
authors: N
authors: N
authors: Naiyanet
authors: S
authors: S
authors: Oonsiri
authors: C
authors: C
authors: Lertbutsayanukul
authors: S
authors: S
authors: Suriyapee
references: Med Phys. 2004 Nov;31(11):2978-88
references: 15587650
references: Int J Radiat Oncol Biol Phys. 2000 Jul 1;47(4):1121-35
references: 10863086
references: Int J Radiat Oncol Biol Phys. 1999 Mar 1;43(4):905-19
references: 10098447
references: Radiother Oncol. 2001 Feb;58(2):155-62
references: 11166866
references: Int J Radiat Oncol Biol Phys. 1999 Jul 15;44(5):1165-70
references: 10421551