ESTRO 38 Abstract book

S141 ESTRO 38

M. Peters 1 , M.J. Van Son 1 , M.A. Moerland 1 , J.J.W. Lagendijk 1 , J.R.N. Van der Voort van Zyp 1 1 UMC Utrecht, Radiation Oncology Department, Utrecht, The Netherlands Purpose or Objective Radiorecurrent prostate cancer is conventionally treated with palliative androgen deprivation therapy (ADT) or curative whole-gland salvage, both with a high risk of significant side-effects and a detrimental impact on quality of life (QoL). MRI-guidance has made focal salvage high-dose-rate (HDR) brachytherapy (BT) possible. Focal treatment could postpone or prevent ADT and substantially reduce side effects. Tumor control, toxicity and QoL of MRI-guided focal salvage HDR-BT are described here. Material and Methods From July 2013 to July 2018, 96 patients with locally recurrent, non-metastatic prostate cancer after primary radiotherapy were treated with MRI-guided focal salvage HDR-BT. Multiparametric-MRI and PSMA or Choline-PET/CT were used for intraprostatic disease assessment and exclusion of metastases. A single dose of 19Gy was prescribed. MRI compatible catheters allowed MRI-guided treatment planning after insertion. Biochemical failure was defined by the Phoenix-definition (nadir+2ng/ml). Prospective data collection included genitourinary (GU) toxicity, gastro-intestinal (GI) toxicity and erectile dysfunction (ED) with the Common Terminology Criteria for Adverse Events (CTCAE) 4.0. Urinary symptoms and erectile function were further assessed with IPSS and IIEF questionnaires. RAND-36, EORTC QLQ-C30 and EORTC QLQ-PR25 were used for QoL assessment. Results Median age pre-focal salvage was 72 years (interquartile range [IQR] 67-74). Median PSA was 5 (3-7), median PSADT 17 months (12-25). Tumor (rT)-stages were T2 (64%), T3 (34%), T4 (2%). Primary treatment was mostly EBRT (55%) and I-125 BT (42%). D95 was median 19Gy (18-20), urethral D10 16Gy (11-18), D1cc bladder 8Gy (5-11) and D1cc rectum 10Gy (8-12). Median follow-up was 11 months (5- 23). Two patients had grade 3 urethral stricture, at 6 and 24 months (Figure 1). There was no grade 3 GI toxicity. IPSS scores increased until 12 months (8.3 to 11.1, p=0.001), after which they normalized (10.6 and 9.2 at 24 and 36 months [p=0.07, and p=0.26], respectively). IIEF decreased from 10.9 at baseline to 8.1 at 12 months (p<0.001) and 7.6 at 24 months (p=0.004). Corrected for multiple testing, QoL only deteriorated in the first month due to urinary complaints. At 2 years, biochemical disease-free survival was 77% (95% CI 65-91%), metastases- free survival 84% (95% CI 73-92%) (Figure 2) and overall survival 98% (95% CI 93-100%).

Material and Methods From Nov 2010 to July 2017, there were 178 patients treated with HDR monotherapy of 19Gy in a single fraction using the urethra dose constraints of D10% <22Gy, D30% <20.8Gy and maximum dose <28.5Gy.There were a total of five ≥grade2 strictures as defined by CTCAE v4.0 as being symptomatic, requiring dilatation or catheterization strictures (confirmed on cystoscopy). A matched pair analysis used one control for each stricture case matched for pre-treatment IPSS score, number of needles used and clinical target volume (CTV) size . For all data sets, pre-treatment T2-weighted MRI images were used to define regions-of-interests as urethra and the whole prostate gland.The urethra was divided into membranous urethra and inferior, mid and superior thirds of the prostatic urethra for the dosimetric analysis. MRI textural radiomic features associated with prostate cancer response in the literature of energy, contrast and homogeneity were selected. Pyradiomics was used to extract textural features on the whole prostate gland volumes. Wilcoxon signed-rank test was performed to investigate significant differences in dosimetric parameters and MRI radiomic feature values between cases and controls. Results There were no statistically differences in pre-treatment IPSS score, number of needles used CTV and urethra volume size between the two groups of patients with and without strictures. As suggested in table 1, the urethral dosimetric parameters investigated were not statistically different between cases and controls (p>0,05). With regards to MRI radiomics feature analysis, significant differences were found in contrast and homogeneitybetween cases and controls (p<0.05). However, this did not apply to the energy feature.

Conclusion In this matched pair analysis, no association between post- treatment stricture and urethral dosimetry was identified. The MRI radiomic features of homogeneity and contrast of the prostate gland identified patients who develop strictures after HDR monotherapy. Although sample size is small, this warrants further investigation. OC-0285 Clinical outcomes of focal salvage high-dose- rate brachytherapy for radiorecurrent prostate cancer.