title: Assessment of daily needle applicator displacement during high-dose-rate interstitial brachytherapy for prostate cancer using daily CT examinations.
abstract: To improve treatment conformity for prostate cancer, we investigated daily applicator displacement during high-dose-rate interstitial brachytherapy (HDR-ISBT). Thirty patients treated with HDR-ISBT as monotherapy were examined. All patients received a treatment dosage of 49 Gy per 7 fractions over 4 days. For dose administration, we examined 376 flexible applicators (1128 points) using our unique ambulatory implant technique. Using CT images with a 3-mm slice thickness, we calculated the relative coordinates of the titanium markers and the tips of the applicators. We calculated the distance between the center of gravity of the markers and the tips of the catheters, and compared the distances measured on the day of implantation and the second, third, and fourth treatment days. The mean displacement distance for all applicators was 4.3 ± 3.4 mm, 4.6 ± 4.1 mm, and 5.8 ± 4.5 mm at 21, 45, and 69 hours after initial planning CT. We used a 15-mm margin for needle displacement and only 2 points of 2 patients (16 mm and 18 mm at 69 hours, 2/1128 = 0.2%) exceeded this range. Almost patients (87%) showed the largest displacement within the first 21 hours. The relative doses that covered 100% of CTV (D100(CTV)) values compared with the initial treatment plan were reduced to 0.96 ± 0.08, 0.96 ± 0.08 and 0.94 ± 0.1 at 21, 45 and 69 hours. However, the relative D90(CTV) values kept acceptable levels (1.01 ± 0.02, 1.01 ± 0.03 and 1.01 ± 0.03). Cranial margin of 15 mm seems to be effective to keep D90(CTV) level if we do not do corrective action.
authors.affiliation: Department of Radiology, National Hospital Organization Osaka National Hospital, Osaka, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Takenaka
authors.forename: Ken
authors.initials: K
authors.lastname: Yoshida
authors.forename: Mari
authors.initials: M
authors.lastname: Ueda
authors.forename: Hideya
authors.initials: H
authors.lastname: Yamazaki
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Miyake
authors.forename: Eiichi
authors.initials: E
authors.lastname: Tanaka
authors.forename: Mineo
authors.initials: M
authors.lastname: Yoshida
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yoshimura
authors.forename: Toshitsugu
authors.initials: T
authors.lastname: Oka
authors.forename: Kazuya
authors.initials: K
authors.lastname: Honda
mesh_terms: D000368:Aged; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D061106:Radiotherapy Setup Errors; D014057:Tomography, X-Ray Computed