title: Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments.
abstract: The adequacy of setup margins for various sites in patients treated with helical tomotherapy was investigated. A total of 102 patients were investigated. The breakdown of the patients were as follows: Twenty-five patients each in brain, head and neck (H and N), and pelvis, while 12 patients in lung and 15 in craniospinal irradiation (CSI). Patients were immobilized on the institutional protocol. Altogether 2686 megavoltage computed tomography images were analyzed with 672, 747, 622, 333, and 312 fractions, respectively, from brain, H and N, pelvis, lung, and CSI. Overall systematic and random errors were calculated in three translational and three rotational directions. Setup margins were evaluated using van Herk formula. The calculated margins were compared with the margins in the clinical use for various directions and sites. We found that the clinical isotropic margin of 3 mm was adequate for brain patients. However, in the longitudinal direction it was found to be out of margin by 0.7 mm. In H and N, the calculated margins were well within the isotropic margin of 5 mm which is in clinical use. In pelvis, the calculated margin was within the limits, 8.3 mm versus 10 mm only in longitudinal direction, however, in vertical and lateral directions the calculated margins were out of clinical margins 11 mm versus 10 mm, and 8.7 mm versus 7.0, mm respectively. In lung, all the calculated margins were well within the margins used clinically. In CSI, the variation was found in the middle spine in the longitudinal direction. The clinical margins used in our hospital are adequate enough for sites H and N, lung, and brain, however, for CSI and pelvis the margins were found to be out of clinical margins.
authors: Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Bhagyalakshmi Akkavil
authors: BA
authors: Thondykandy
authors: Department of Medical Physics, Advanced Center for Treatment, Research, and Education in Cancer, Navi Mumbai, Maharashtra, India.
authors: Jamema V
authors: JV
authors: Swamidas
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Jayprakash
authors: J
authors: Agarwal
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Tejpal
authors: T
authors: Gupta
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Sarbani G
authors: SG
authors: Laskar
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Umesh
authors: U
authors: Mahantshetty
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Shrinivasan S
authors: SS
authors: Iyer
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Indrani U
authors: IU
authors: Mukherjee
authors: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Shyam K
authors: SK
authors: Shrivastava
authors: Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors: Deepak D
authors: DD
authors: Deshpande
keywords: Image guidance; margins; setup error