Patient factors affecting the distribution of hydrogel spacers in combination with permanent prostate brachytherapy

Abstract

Uniform placement of SpaceOAR is useful in radiation therapy because it reduces the radiation dose to the rectum. We evaluated the placement patterns of the SpaceOAR system along with permanent prostate brachytherapy in patients with prostate cancer and investigated patient factors that influenced placement morphology. We examined 360 cases of prostate cancer to identify patient factors that affected the distribution of SpaceOAR injections in our hospital between April 2018 and April 2021. The uniformity of placement morphology （homogeneous or heterogeneous） was assessed based on T2-weighted magnetic resonance images obtained the day after SpaceOAR implantation. We identified the following as influencing factors: age, initial prostate-specific antigen level, prostate volume, clinical T stage, Gleason score, National Comprehensive Cancer Network risk classification, and duration of neoadjuvant hormonal therapy. Multivariate analysis of patient characteristics and SpaceOAR placement morphology showed statistically significant differences in the National Comprehensive Cancer Network risk classification （p＝0.02） and neoadjuvant hormonal therapy duration （p＝0.004）. The cutoff value of the receiver operating characteristic curve for SpaceOAR homogeneity and neoadjuvant hormonal therapy duration, performed as a subgroup analysis, was 3 months, with a sensitivity of 0.83 and specificity of 0.52. Patients classified as high risk according to the National Comprehensive Cancer Network guidelines and those with a longer neoadjuvant hormonal therapy period may exhibit less uniform SpaceOAR system placements. Furthermore, a neoadjuvant hormonal therapy duration of 3 months seems to be a suitable duration for achieving uniformity.