ESTRO 2023 - Abstract Book

S1252

Digital Posters

ESTRO 2023

Treatment was generally well tolerated. PROMs showed that SMART has high level of patients satisfaction and grade 2 and above toxicities are relatively low. Conclusion Our experience indicates that SMART is a safe and well tolerated system for delivery of SBRT in localised prostate cancer.

PO-1542 Seminal vesicle displacement with Hydrogel spacer insertion on prostate radiotherapy

K. Makita 1 , Y. Hamamoto 1 , H. Kanzaki 1 , K. Nagasaki 1 , K. Hashine 2

1 National Hospital Organization Shikoku Cancer Center, Department of Radiation Oncology, Matsuyama, Japan; 2 National Hospital Organization Shikoku Cancer Center, Department of Urology, Matsuyama, Japan Purpose or Objective This study aimed to evaluate the influence of hydrogel spacer (HS) on the seminal vesicle (SV) displacement in prostate radiotherapy. Materials and Methods 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. Results 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). Conclusion 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. Purpose or Objective The objective of this study was the comparison of acute gastrointestinal (GI) and genitourinary (GU) toxicity, as, well as late GI and GU toxicity after moderately hypofractionated (HF) or conventionally fractionated (CF) primary whole pelvis radiotherapy (WPRT). Materials and Methods Patients with primary prostate cancer treated between 2009 and 2021 were investigated. Applied doses were either 60 Gy in 3 Gy per fraction to the prostate and 46 Gy in 2.3 Gy to the whole pelvis (VMAT technique), or 78 Gy in 2 Gy per fraction to the prostate and 50/50.4 Gy in 1.8 to 2 Gy per fraction (VMAT or IMRT technique) to the whole pelvis. Acute and late GI and GU toxicities according to RTOG were assessed. Results 106 patients treated with HF and 157 patients treated with CF were included. Median follow-up in the HF and the CF group was 12 and 57 months, respectively. Regarding acute GI toxicity, grade 0 was reported in 13.3 % (HF) vs. 6.4 % (CF), grade 1 in 40.0 % vs. 54.8 %, grade 2 in 46.7 % vs. 37.6 % and grade 3 in 0 % vs. 1.3 % showing no significant difference (p = 0.71). Regarding acute GU toxicity, grade 0 was reported in 20 % (HF) vs. 10.8 % (CF), grade 1 in 57.1 % vs. 57.3 %, grade 2 in 20.0 % vs. 31.8 %, and grade 3 in 2.9 % vs. 0 %, showing a significant difference in favor of HF (p = 0.04). The maximal rate of late GI toxicity was grade 0 in 76.4 % (HF) vs. 61.8 % (CF), grade 1 in 16.0 % vs. 21.7 %, grade 2 4.7 % vs. 13.8 %, and grade 3 1.9 % vs. 2.6 %. The maximum rate of late GU toxicity was grade 0 in 62.3 % (HF) vs. 45.4 % (CF), grade 1 in 26.4 % vs. 26.3 %, grade 2 in 11.3 % vs. 23.0 %, and grade 3 0 % vs. 5.3 %. However, as follow-up time differs between both groups, we compared late GI and GU toxicity between both groups after 3, 12, and 24 months and did not find any significant differences (p = 0.59, 0.22 and 0.71 for GI toxicity and 0.39, 0.58, and 0.90 for GU, respectively). Table 1: Maximum Acute Gastrointestinal and Genitourinary Toxicity after moderate hypofractionation (HF) and conventional fractionation (CF). PO-1543 Assessing the Toxicity After Moderately Hypofractionated Whole Pelvis Radiotherapy M. Moll 1 , G. Goldner 1 1 Medical University of Vienna, Radiation Oncology, Vienna, Austria