Search

To expand the indications for high-dose-rate interstitial brachytherapy (HDR-ISBT) for deep-seated pelvic tumors, we investigated the usefulness of Doppler transrectal ultrasonography (TRUS) guidance and virtual planning. The patient was a 36-year-old female. She had right internal iliac lymph node oligometastasis of vaginal cancer 12 months after radical radiotherapy. The tumor could not be found by gray-scale TRUS and physical examination. Virtual planning was performed using computed tomography with template and vaginal cylinder insertion. We uploaded the images to our treatment planning software and reconstructed the contours of the clinical target volume (CTV) and right internal iliac vessel. Virtual needle applicators were plotted using the template holes for virtual planning. At the time of implantation, Doppler TRUS was used to prevent vessel injury by needle applicators. Applicators were implanted in accordance with virtual planning and Doppler TRUS could detect the right iliac vessel. The percentage of CTV covered by the prescribed dose was 99.8%. The minimum dose received by the maximally irradiated 0.1-cc volume for the right internal iliac vessel was 95% prescribed dose. Complete response was achieved, however, radiological findings showed marginal recurrence at 15 months after HDR-ISBT. Post-radiation neuropathy occurred as a late complication four months after treatment; however, the pain was well controlled by medication. We consider that virtual planning and Doppler TRUS are effective methods in cases where it is difficult to detect the tumor by physical examination and gray-scale TRUS, thereby expanding the indications for ISBT.

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.

We investigated daily needle applicator displacement during multifractionated high-dose-rate interstitial brachytherapy (HDR-ISBT) for postoperative recurrent uterine cancer. Eight patients with postoperative recurrent uterine cancer received HDR-ISBT with or without external beam radiotherapy using our unique ambulatory technique. To analyze displacement, we obtained daily computed tomography (CT) images for 122 flexible needle applicators at 21, 45, 69, and 93 hours after implantation. Displacement was defined as the length between the center of gravity of titanium markers and the needle applicator tips along the daily CT axis. For cases in which displacement was not corrected, we also calculated the dose that covered 90% of the clinical target volume (D90(CTV)) using a dose-volume histogram (DVH). Median caudal needle applicator displacement at 21, 45, 69, and 93 hours was 3, 2, 4, and 5 mm, respectively. More than 15 mm displacement was observed for 2% (2 of 122) and 17% (10 of 60) of needle applicators at 21 and 93 hours, respectively. Cases in which dwell positions were not changed to correct the treatment plan, 2 of 8 patients showed more than 10% reduction in D90(CTV) values compared with the initial treatment plan. Correction of dwell positions of the treatment source improves treatment DVH for multifractionated HDR-ISBT.