ESTRO 38 Abstract book

S589 ESTRO 38

Conclusion There is a place for salvage HDRBT in the efficient treatment of localised prostate cancer relapse after prior radiotherapy due to its ability to deliver the significant radiation dose to the prostate while minimising normal tissue exposure. The toxicity rates of the procedure are acceptable although the selection of candidates for salvage HDRBT should be carried out carefully with the consideration of the individual risk of distant failures. PO-1058 Long-term outcomes of LDR compared to hypofractionated EBRT for intermediate-risk prostate cancer N. Sanmamed Salgado 1 , L. Joseph 1 , J. Crook 2 , J. Borg 1 , P. Chung 1 , P. Warde 1 , A. Di Tomasso 1 , A. Berlin 1 , M. Patel 1 , A. Bayley 1 , C. Catton 1 , J. Helou 1 1 Princess Margaret Cancer Center, Radiation oncology, Toronto, Canada ; 2 BC Cancer Center for the Southern Interior, Radiation oncology, Kelowna, Canada Purpose or Objective Low dose-rate brachytherapy (LDR) and hypofractionated external beam radiotherapy (EBRT) are accepted standard treatments in the setting of intermediate-risk (IR) prostate cancer. As yet, none of these options have been tested against one another in a randomized trial. We aim to compare the long-term oncologic outcomes of IR prostate cancer patients treated with LDR or EBRT at a single institution. Material and Methods Between January 2005 and December 2013, 248 patients diagnosed with IR prostate cancer (≤T2c, Gleason ≤7 and PSA ≤20 ng/mL) were treated with LDR or EBRT; 123 patients received a permanent implant of iodine-125 seeds prescribed to 145 Gy as a minimum peripheral dose and 125 patients were treated with EBRT to a total dose of 60 Gy in 20 fractions. The ‘‘nadir +2 ng/mL’’ PSA threshold (Phoenix definition) was used to define biochemical relapse (BR). To account for the competing risk of death, the cumulative incidence function (CIF) of BR and metastases for each group, and the 95% confidence intervals were reported. To test whether the difference between the groups is significant, Gray’s method was applied. The Kaplan-Meier (KM) method was used to estimate overall survival (OS) and prostate cancer specific survival (PCSS), and log-rank test was used to compare treatment groups. A two-tailed p-value ≤0.05 was considered statistically significant. Results Median follow-up was 95 [interquartile range (IQR): 79- 118] and 96 (IQR: 63-123) months in the LDR and EBRT groups, respectively. In the LDR group, mean age was 65 (±7) with a median PSA at baseline of 6.8 ng/mL (IQR: 5.3- 9.6); for the EBRT group, mean age was 71 (±5) years and median PSA at baseline was 7.4 ng/mL (IQR: 5.9-9.7). Neoadjuvant androgen deprivation therapy was used for cytoreduction in 4 patients treated with LDR and none with EBRT. BR was observed in 5 patients treated with LDR and 34 treated with EBRT. At 60 months and 90 months, the CIF of BR was 0.9% (0.1-4.4) and 3.5% (0.9-9.2) vs.16.6% (95% CI: 10.3-24.2) and 23.7% (16.0-32.3) ( p <0.001) in the LDR and EBRT groups (Figure 1). The median time to develop metastases was 99 months (IQR: 70-121) in the entire cohort with no statistical significant difference between groups. At 90 and 108 months, the CIF of metastases was 0% and 1.6% (95% CI: 0.1-7.5) compared to 3.4% (95% CI: 0.9-8.9) and 9.1% (95% CI: 3.5-18.2) in the LDR and EBRT groups ( p =0.003), respectively. At the last follow-up, 24 patients were deceased in the cohort. Amongst those, 3 died from their cancer in the EBRT group [PCSS of 96.4% (95% CI: 89.3- 98.8)] and none died in the LDR group ( p= 0.09 ).

Conclusion Permanent iodine-125 seed implant was associated with higher biochemical and distant failure control in our cohort when compared to moderately hypofractionated EBRT. In the absence of a randomized trial, LDR when feasible should be offered to patients with a life expectancy of >7 years. PO-1059 Separation and rectal dosimetry with a hydrogel spacer inserted during prostate HDR brachytherapy R. DAVDA 1 , D. Pendsé 2 , A. Mitra 1 , M. Prentice 1 , L. Melcher 3 , N. Rosenfelder 4 , M. Singhera 3 , R. Patel 5 , M. Boutros 5 , C. Allen 2 , H. Payne 1 1 University College London Hospitals NHS Foundation Trust, Oncology, London, United Kingdom ; 2 University College London Hospitals NHS Foundation Trust, Radiology, London, United Kingdom ; 3 North Middlesex University Hospital NHS Trust, Oncology, London, United Kingdom ; 4 Royal Free London NHS Foundation Trust, Oncology, London, United Kingdom ; 5 University College London Hospitals NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom Purpose or Objective Pre-rectal spacers have been shown to reduce high dose radiation to the rectum and late patient reported toxicity for men trated with external beam radiation (EBRT). The ICEMAN trial is investigating the insertion of a pre-rectal spacer in men with high risk localised or locally advanced prostate cancer undergoing high dose rate (HDR) brachytherapy boost followed by EBRT to the pelvis. We report initial findings using a novel technique to insert hydrogel spacer (SpaceOAR) during the HDR procedure. Material and Methods Trial participants underwent multi-parametric prostate MRI < 2 weeks prior to the HDR brachytherapy and spacer insertion procedure, with a second MRI 5 days after the procedure. Brachytherapy procedures were via a transperineal approach under transrectal ultrasound guidance. Immediately prior to brachytherapy catheter implantation, a 15 cm Kellett needle was inserted in the midline between Denonvillier’s fascia and the anterior rectal wall to the prostate midgland and the 5Fr Kellett sheath left in-situ. After HDR implant catheter placement hydrodissection of the pre-rectal space was achieved by injecting saline via this sheath with subsequent injection of 10 cc hydrogel spacer. A CT planning scan was used to contour PTV, organs at risk and spacer. Brachytherapy plans were produced using graphical (GRO) and inverse planning by simulated annealing (IPSA). HDR prescription was 15 Gy to the prostate and seminal vesicles followed by 46 Gy in 23 fractions EBRT to the pelvis. Separation between posterior prostate and anterior rectal wall was measured by a Uro- radiologist on the MRI prior to, and MRI after the procedure on T2 axial 3 mm slices using sagittal planes for reference at the apex, mid-gland, base and seminal