ESTRO 2024 - Abstract Book

S396

Brachytherapy - Urology

ESTRO 2024

All erroneously reconstructed needles were visually evaluated in the Oncentra-Prostate treatment planning system using transverse TRUS images to determine the underlying reasons leading to these reconstruction errors.

Figure 1 – View of the clinical setup for EMT measurements with the hybrid EMT/BT afterloader in intraoperative TRUS based prostate HDR-BT.

Results:

The median (range) relative displacement of the reference sensor during measurements was 0.2 (0.0 – 1.6) mm, which is below the sensitivity of the EMT sensor defined in [3]. Therefore, it was concluded that the EMT measurements were an accurate representation of the real needle position. A total of 265 needles were evaluated. Over all patients median (range) ED between measured and reconstructed dwell positions was 1.0 (0.1 – 9.4) mm. Out of the 265 needles, 61 (23%) had at least one dwell position with an ED greater than 2 mm. When categorizing the needles with errors based on severity, 24/61 were classified as minor, 13/61 as moderate, 15/61 as major, and 9/61 as severe. Based on visual evaluation, EMT measurements revealed reconstruction errors due to user errors (25/61), poor needle visibility (13/61), reconstruction on artifacts (13/61), erroneous catheter depth definition (7/61), reconstruction on fixation needles (2/61), reconstruction on wrong needles (1/61) (Figure 2).