title: Multivariate analysis of factors predicting prostate dose in intensity-modulated radiotherapy.
abstract: We conducted a multivariate analysis to determine relationships between prostate radiation dose and the state of surrounding organs, including organ volumes and the internal angle of the levator ani muscle (LAM), based on cone-beam computed tomography (CBCT) images after bone matching. We analyzed 270 CBCT data sets from 30 consecutive patients receiving intensity-modulated radiation therapy for prostate cancer. With patients in the supine position on a couch with the HipFix system, data for center of mass (COM) displacement of the prostate and the state of individual organs were acquired and compared between planning CT and CBCT scans. Dose distributions were then recalculated based on CBCT images. The relative effects of factors on the variance in COM, dose covering 95% of the prostate volume (D95%), and percentage of prostate volume covered by the 100% isodose line (V100%) were evaluated by a backward stepwise multiple regression analysis. COM displacement in the anterior-posterior direction (COMAP) correlated significantly with the rectum volume (δVr) and the internal LAM angle (δθ; R = 0.63). Weak correlations were seen for COM in the left-right (R = 0.18) and superior-inferior directions (R = 0.31). Strong correlations between COMAP and prostate D95% and V100% were observed (R ≥ 0.69). Additionally, the change ratios in δVr and δθ remained as predictors of prostate D95% and V100%. This study shows statistically that maintaining the same rectum volume and LAM state for both the planning CT simulation and treatment is important to ensure the correct prostate dose in the supine position with bone matching.
authors.affiliation: Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Tsuneyuki
authors.initials: T
authors.lastname: Tomita
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan. Electronic address: m_nkmr@kuhp.kyoto-u.ac.jp.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Hirose
authors.affiliation: Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kitsuda
authors.affiliation: Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Notogawa
authors.affiliation: Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Katsuhito
authors.initials: K
authors.lastname: Miki
authors.affiliation: Department of Radiation Oncology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Kiyonao
authors.initials: K
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology, Osaka Red Cross Hospital, Osaka, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishigaki
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003627:Data Interpretation, Statistical; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
keywords: Interfraction displacement; Multivariate analysis; Prostate cancer