title: Analysis of changes in dose distribution due to respiration during IMRT.
abstract: OBJECTIVE
  Intensity modulated radiation therapy (IMRT) is a high precision therapy technique that can achieve a conformal dose distribution on a given target. However, organ motion induced by respiration can result in significant dosimetric error. Therefore, this study explores the dosimetric error that result from various patterns of respiration.
  
  
  METHODS
  Experiments were designed to deliver a treatment plan made for a real patient to an in-house developed motion phantom. The motion pattern; the amplitude and period as well as inhale-exhale period, could be controlled by in-house developed software. Dose distribution was measured using EDR2 film and analysis was performed by RIT113 software. Three respiratory patterns were generated for the purpose of this study; first the 'even inhale-exhale pattern', second the slightly long exhale pattern (0.35 seconds longer than inhale period) named 'general signal pattern', and third a 'long exhale pattern' (0.7 seconds longer than inhale period). One dimensional dose profile comparisons and gamma index analysis on 2 dimensions were performed
  
  
  RESULTS
  In one-dimensional dose profile comparisons, 5% in the target and 30% dose difference at the boundary were observed in the long exhale pattern. The center of high dose region in the profile was shifted 1 mm to inhale (caudal) direction for the 'even inhale-exhale pattern', 2 mm and 5 mm shifts to exhale (cranial) direction were observed for 'slightly long exhale pattern' and 'long exhale pattern', respectively. The areas of gamma index >1 were 11.88%, 15.11%, and 24.33% for 'even inhale-exhale pattern', 'general pattern', and 'long exhale pattern', respectively. The long exhale pattern showed largest errors.
  
  
  CONCLUSIONS
  To reduce the dosimetric error due to respiratory motions, controlling patient's breathing to be closer to even inhaleexhale period is helpful with minimizing the motion amplitude.
authors.affiliation: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Jung Suk
authors.initials: JS
authors.lastname: Shin
authors.forename: Eunhyuk
authors.initials: E
authors.lastname: Shin
authors.forename: Youngyih
authors.initials: Y
authors.lastname: Han
authors.forename: Sang-Gyu
authors.initials: SG
authors.lastname: Ju
authors.forename: Jin Sung
authors.initials: JS
authors.lastname: Kim
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Ahn
authors.forename: Tae Gyu
authors.initials: TG
authors.lastname: Kim
authors.forename: Bae Kwon
authors.initials: BK
authors.lastname: Jeong
authors.forename: Hee-Chul
authors.initials: HC
authors.lastname: Park
authors.forename: Young-Chan
authors.initials: YC
authors.lastname: Ahn
authors.forename: Doo Ho
authors.initials: DH
authors.lastname: Choi