Needle applicator displacement during high-dose-rate interstitial brachytherapy for prostate cancer

Purpose

To introduce an effective ambulatory technique in high-dose-rate interstitial brachytherapy (HDR-ISBT) for prostate cancer, we investigated the displacement distance using our novel calculation method.

Methods and Materials

Sixty-four patients treated with HDR-ISBT as monotherapy were examined. Of these, 4, 17, and 43 patients were administered treatment doses of 38Gy (3 days), 49Gy (4 days), and 54Gy (5 days), respectively. For dose administration, we used 776 flexible applicators with a removable template (ambulatory technique).

Using CT images, we calculated the relative coordinates of the metal markers and applicators. From these coordinates, to analyze displacement during treatment, we measured the distance between the tip of the needle applicator and the center of gravity of the markers along the average applicator vector.

Results

The median displacement distance for all applicators was 7mm (range, −14 to 24), and that of each treatment schedule was 4, 6, and 9mm for 38, 49, and 54Gy, respectively. Of the 776 applicators, displacement of >10mm was seen in 198 (26%) applicators and >15mm in 57 (7%) applicators.

Body height (p<0.0001) and anticoagulant usage (p<0.0001) were significant factors influencing displacement.

Conclusions

We investigated needle applicator displacement using our unique method. Additional cranial margins are necessary if there is no repositioning of the dwell position. CT scanning should be performed daily during treatment for checking the position of the applicator to detect and rectify the issue of displacement.