Assessment of Daily Needle Applicator Displacement during High-Dose-Rate Interstitial Brachytherapy for Prostate Cancer using Daily CT Examinations

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  • TAKENAKA Tadashi
    Department of Radiology, National Hospital Organization Osaka National Hospital
  • YOSHIDA Ken
    Department of Radiation oncology, National Hospital Organization Osaka National Hospital Institute for Clinical Research, National Hospital Organization Osaka National Hospital
  • UEDA Mari
    Department of Radiology, National Hospital Organization Osaka National Hospital
  • YAMAZAKI Hideya
    Department of Radiology, Kyoto Prefectural University of Medicine
  • MIYAKE Shunsuke
    Department of Radiology, National Hospital Organization Osaka National Hospital
  • TANAKA Eiichi
    Department of Radiation oncology, National Hospital Organization Osaka National Hospital
  • YOSHIDA Mineo
    Department of Radiation oncology, National Hospital Organization Osaka National Hospital
  • YOSHIMURA Yasushi
    Department of Radiology, National Hospital Organization Osaka National Hospital
  • OKA Toshitsugu
    Department of Urology, National Hospital Organization Osaka National Hospital
  • HONDA Kazuya
    Department of Radiology, National Hospital Organization Osaka National Hospital

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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.

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