title: Couch height-based patient setup for abdominal radiation therapy.
abstract: There are 2 methods commonly used for patient positioning in the anterior-posterior (A-P) direction: one is the skin mark patient setup method (SMPS) and the other is the couch height-based patient setup method (CHPS). This study compared the setup accuracy of these 2 methods for abdominal radiation therapy. The enrollment for this study comprised 23 patients with pancreatic cancer. For treatments (539 sessions), patients were set up by using isocenter skin marks and thereafter treatment couch was shifted so that the distance between the isocenter and the upper side of the treatment couch was equal to that indicated on the computed tomographic (CT) image. Setup deviation in the A-P direction for CHPS was measured by matching the spine of the digitally reconstructed radiograph (DRR) of a lateral beam at simulation with that of the corresponding time-integrated electronic portal image. For SMPS with no correction (SMPS/NC), setup deviation was calculated based on the couch-level difference between SMPS and CHPS. SMPS/NC was corrected using 2 off-line correction protocols: no action level (SMPS/NAL) and extended NAL (SMPS/eNAL) protocols. Margins to compensate for deviations were calculated using the Stroom formula. A-P deviation > 5mm was observed in 17% of SMPS/NC, 4% of SMPS/NAL, and 4% of SMPS/eNAL sessions but only in one CHPS session. For SMPS/NC, 7 patients (30%) showed deviations at an increasing rate of > 0.1mm/fraction, but for CHPS, no such trend was observed. The standard deviations (SDs) of systematic error (Σ) were 2.6, 1.4, 0.6, and 0.8mm and the root mean squares of random error (σ) were 2.1, 2.6, 2.7, and 0.9mm for SMPS/NC, SMPS/NAL, SMPS/eNAL, and CHPS, respectively. Margins to compensate for the deviations were wide for SMPS/NC (6.7mm), smaller for SMPS/NAL (4.6mm) and SMPS/eNAL (3.1mm), and smallest for CHPS (2.2mm). Achieving better setup with smaller margins, CHPS appears to be a reproducible method for abdominal patient setup.
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan; Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Ohira
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan; Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ueda
authors.affiliation: Department of Radiation Oncology, Yao Municipal Hospital, Yao, Japan.
authors.forename: Kinji
authors.initials: K
authors.lastname: Nishiyama
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Miyazaki
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Isono
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Katsutomo
authors.initials: K
authors.lastname: Tsujii
authors.affiliation: Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Takashina
authors.affiliation: Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Koizumi
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Kiyoto
authors.initials: K
authors.lastname: Kawanabe
authors.affiliation: Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan. Electronic address: teshima-te@mc.pref.osaka.jp.
authors.forename: Teruki
authors.initials: T
authors.lastname: Teshima
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D056888:Patient Positioning / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000295:instrumentation
keywords: Abdominal cancer; Couch; Setup; Skin mark