Session Item

This study aimed to evaluate the influence of hydrogel spacer (HS) on the seminal vesicle (SV) displacement in prostate radiotherapy.

Twenty patients with prostate cancer who received intensity modulated radiation therapy (IMRT) were enrolled. Computed tomography (CT) and magnetic resonance (MR) images were taken before and after HS insertion within the peripheral space for the IMRT planning, and the SV before and after HS insertion were delineated. The amount of SV displacement between before and after HS insertion were evaluated.

Large SV cranio-caudal displacements (≥0.50 cm) was observed in 25% of all patients (one patient; 1.00cm, four patients; 0.50-1.00cm). All slices (inferior vs. midgland vs. superior) with ≥1.00cm HS lateral distribution influenced the SV cranio-caudal displacement (p=0.005) and associated with large cranial SV displacement (≥0.5cm) (p=0.004). HS displacement of cranio-caudal side (inferior vs. midgland vs. superior) (p=0.386) and any HS displacement of inferior axial slices did not lead SV cranio-caudal displacement. In addition, all slices (inferior vs. midgland vs. superior) with ≥1.00cm HS lateral distribution did not influence the medial-lateral displacement, and anterior-posterior displacement (p=0.499 and 0.697, respectively), and HS thickness did not associate with cranio-caudal, medial-lateral, and anterior-posterior SV displacement (p=0.507, 0.989, and 0.750, respectively).

The SV cranio-caudal displacement was influenced by the position of inserted HS. When sigmoid colon or small bowel depressed in rectovesical excavation and the SV needs to be included in the target volume, the HS insertion needs to be performed carefully.