[Evaluation of Exposure Dose Reduction Effect for Cone-beam Computed Tomography with Bismuth Sheet in Image-guided Radiation Therapy of Prostate Cancer].

Abstract

Purpose: Image-guided radiation therapy using cone-beam computed tomography (CBCT) for prostate cancer is problematic due to the increasing exposure dose at each treatment session. This study aimed to evaluate the effect of exposure dose reduction using bismuth sheets for pelvic CBCT.

Methods: Using a radiophotoluminescence dosimeter (GD-352M) and CBCT imaging conditions with three X-ray tube rotation angles (292°-88°, 92°-248°, and 92°-88°), absorbed doses were measured in the rectum, anterior and posterior bladder walls, right and left pelvic subcutaneous at 5 cm superior the prostate center of the pelvic phantom and in a testis. Next, the same measurements were performed when these measurement points were covered with a bismuth sheet.

Results: The absorbed doses at 92°-248° with the bismuth sheets were reduced by 31.3% from 16.3±0.2 mGy to 11.2±0.2 mGy for the rectum and by 57.1% from 45.0±2.7 mGy to 19.3±1.0 mGy for the testis, which were the lowest among the imaging conditions. Although the anterior and posterior bladder walls were the highest dose at 48.7±11.5 and 20.2±0.4 mGy, the high reduction rates of 42.0% and 36.9%, respectively.

Conclusion: From the viewpoint of the exposure risk to the bladder, rectum, and testis, using bismuth sheets and the X-ray tube rotation angle of 92°-248° effectively reduced the exposure dose.