Effect of hydrogel-spacer implantation and uneven positioning on rectal dose in intensity-modulated radiotherapy for prostate cancer.

Objectives: Implanting a hydrogel spacer in radiation therapy for prostate cancer is effective in reducing rectal dose. Hydrogel spacer can be unevenly distributed. we often encountered in which the hydrogel spacer was not in place at the prostatic apex. This study had two objectives. The first was to analyze whether the rectal dose could be reduced in patients who underwent hydrogel-spacer implantation at our hospital. The second was to analyze whether the rectal dose could be reduced in cases where the hydrogel spacer was unevenly distributed and not in place at the prostatic apex, as compared with cases without hydrogel-spacer implantation. Methods: We retrospectively reviewed the records of patients who underwent intensity-modulated radiation therapy for prostate cancer at our hospital between March 2020 and June 2022. Initially, the rectal dose parameters were compared between patients who underwent hydrogel-spacer implantation and those who did not. Additionally, the same parameters were compared between patients who did not undergo hydrogel-spacer implantation and those who did, but in whom the spacer was not in place at the apex. Results: 45 patients did not undergo hydrogel-spacer implantation and 36 patients did. A comparison of rectal dose parameters between patients with and without hydrogel-spacer implantation showed a reduction in all parameters in those with implantation. The 36 patients with hydrogel-spacer implantation included 16 patients in whom the hydrogel spacer was not in place at the apex. A comparison of rectal dose parameters between the 45 patients without hydrogel-spacer implantation and the 16 patients with the hydrogel spacer not in place at the apex showed a reduction in all parameters in the latter group. Conclusion: Hydrogel-spacer implantation was effective in reducing the rectal dose. The rectal dose could be reduced even in cases with uneven distribution of the spacer, as compared with cases without spacer implantation.