title: Anterior-posterior treatment localization in pelvic radiotherapy: tattoos or fixed couch-to-isocentre distance.
abstract: The methods of determining the anterior-posterior isocentre location in pelvic radiotherapy are either by aligning lateral localization lasers to tattoo marks on skin, or by setting a constant daily couch-to-isocentre distance. While using the former method the day-to-day vertical couch movement was recorded and combined with measurements of day-to-day anterior-posterior patient movement made with an electronic portal imaging device to determine whether couch vertical movement contributes to anterior-posterior setup variation. Seven unimmobilized patients were studied, four supine prostate and three prone rectum patients. The two motions were found to be highly correlated (correlation coefficient = 0.82) which supports the constant couch-to-isocentre distance approach. When the day-to-day couch vertical movement was subtracted from the anterior-posterior movement results the setup variation was reduced in six of the seven patients.
authors.affiliation: Oncology Department, Auckland Hospital, New Zealand. pgreer@ahsl.co.nz
authors.forename: P B
authors.initials: PB
authors.lastname: Greer
authors.forename: T M
authors.initials: TM
authors.lastname: Mortensen
mesh_terms: D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D013653:Tattooing; D013679:Technology, Radiologic