Time trend of patient setup deviations during pelvic irradiation using electronic portal imaging.
An electronic portal imaging device (EPID) was used to detect patient setup displacement during the course of a 3-field pelvic irradiation of two groups of patients: 10 rectal and 10 prostate carcinomas. These patients were irradiated with conventional treatment techniques in routine clinical practice. A total of 469 portal images and 60 simulator films were used to determine the values of setup deviations in the X- Y- and Z-directions of a fixed coordinate system, corresponding to the medio-lateral, cranio-caudal and antero-posterior direction, respectively. The absolute displacement averaged over all setups and patients ranged between 0.4 mm and 1.4 mm with a standard deviation (S.D.) of 1.6-3.9 mm. The overall distribution along each direction could be separated into a distribution of random deviations (S.D.s ranging from 1.2 to 2.8 mm) around the mean deviation of each patient and a distribution of the means themselves: the distribution of systematic deviations (S.D.s ranging from 1.0 to 2.6 mm). Significant gradual displacement as a function of time was detected in 5 out of the 20 patients, 2 in the rectum and 3 in the prostate group. This "time trend" was found along each of the 3 directions specified. The magnitude of the time-dependent displacement throughout the course of treatment ranged between 4 and 11 mm. It can be concluded that for treatments requiring a high level of precision, portal images should be made and analyzed during the whole treatment course in order to detect and correct significant time trends.
el-Gayed
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Department of Radiotherapy, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis), Amsterdam.
Bel
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Vijlbrief
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Bartelink
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Lebesque
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D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy*; D004582:Electronics, Medical / Q000295:instrumentation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D010388:Pelvis / Q000033:anatomy & histology / Q000528:radiation effects*; D016684:Prone Position; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D011882:Radiotherapy, High-Energy / Q000295:instrumentation; D012004:Rectal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D012399:Rotation; D012542:Scattering, Radiation; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D016683:Supine Position; D013997:Time Factors