ESTRO 38 Abstract book

S823 ESTRO 38

only were spared from ADT for 3 years. Prospective trials with sufficiently long follow-up are needed evaluate the potential of ADT and its duration in addition to radical radiotherapy for PSMA-PET detected oligorecurrent prostate cancer. EP-1523 Predictors of severe late urinary toxicity after curative radiotherapy for localised prostate cancer K. Takeda 1 , Y. Takayama 2 , N. Kadoya 2 , H. Takagi 1 , K. Ito 2 , T. Chiba 2 , K. Sato 3 , S. Dobashi 1 , R. Umezawa 2 , T. Yamamoto 2 , Y. Ishikawa 2 , K. Takeda 2 , H. Matsushita 2 , Y. Kawasaki 4 , K. Mitsuduka 4 , K. Jingu 2 1 Tohoku University School of Medicine, Health Sciences- Course of Radiological Technology, Sendai, Japan ; 2 Tohoku University Graduate School of Medicine, Department of Radiation Oncology, Sendai, Japan ; 3 Tohoku University Hospital, Department of Radiation Technology, Sendai, Japan ; 4 Tohoku University Graduate School of Medicine, Department of Urology, Sendai, Japan Purpose or Objective We aimed to assess the difference between planned and accumulated doses in prostatic urethra (PU) and bladder and to investigate the relationship between these differences and coexistent clinical status on severe late urinary toxicity following curative radiotherapy for patients with localised prostate cancer (PLPC). Material and Methods Overall, 302 PLPC were treated with image-guided intensity-modulated radiation therapy (IMRT) between 2008 and 2015 in our institution. All PLPC had fiducial markers (FM) implanted in the prostate for daily set-up correction. For each PLPC, urethral catheter (UC) was temporarily used for the PU identification and delineation on planning CT (pCT) images. Moreover, cone-beam CT (CBCT) image was acquired on the first IMRT day and then approximately every 4 days, following daily set-up correction, throughout IMRT course (total 9–10 scans per PLPC). A radiation oncologist (RO) contoured the PU based on UC and the prostate, rectum, bladder, and seminal vesicles on pCT images. Among 302 PLPC, 8 who experienced grade 3 late urinary toxicities (according to the Common Terminology Criteria for Adverse Events version 4.0) within median follow-up period of 53 months (range, 6–118) were enrolled in the present study; the total dose administered was 80Gy in 40 fractions for 6 PLPC and 76Gy in 38 fractions for the remaining 2. Their median age was 65 years (range 59–73). Coexistent clinical status in the eight PLPC included antithrombotic therapy (AT) in four, diabetes mellitus in three, and prior transurethral prostate resection and high intensity focused ultrasound in two. All CBCT images were rigidly registered in the corresponding pCT images via matching FM and were exported to RayStation (version 4.5.1). Thereafter, the RO delineated the bladder on all CBCT images. The PU delineation conducted in each of the eight PLPC was transferred from pCT images to corresponding CBCT images. All CBCT images were then deformed to the corresponding pCT images using deformable image registration. Dose distributions were deformed and summed to estimate the following accumulated dosimetric factors: D 98 , D 95 , D mean , D 50 , D 2 , V 75 and D max of PU; and D 98 , D 95 , D mean , D 50 , D 2 , V 35 , V 55 , V 65 , V 70 , V 75 and V 80 of bladder. Mann–Whitney test was used to evaluate the difference of these dosimetric factors between planned and accumulated doses and to assess relationship between differences of dosimetric variables and coexistent status. Results Marginally significant difference between planned and accumulated doses in D 98 and D 95 of PU were observed (p = 0.05). For PLPC treated with and without AT, the differences between both doses in D 98 , D 95 , D mean , D 2 and D max of PU were significant (p = 0.029). Differences of the

Munich, Germany ; 5 University of Freiburg, Radiation Oncology, Freiburg, Germany ; 6 University Hospital Tübingen, Radiation Oncology, Tübingen, Germany ; 7 University Hospital LMU Munich, Radiation Oncology, Munich, Germany ; 8 University Hospital Zürich, Radiation Oncology, Zürich, Switzerland Purpose or Objective Based on 68 Ga-PSMA-PET imaging, approximately 20-40% of early biochemical recurrent prostate cancer after radical prostatectomy are oligometastatic and located outside the prostate bed, challenging the current standards of care. Definitive radiotherapy (RT) of these recurrences plays an increasingly important role, but it remains unknown whether patients benefit from the addition of antihormonal therapy (ADT) in this situation. This study aims to compare the efficacy of definitive radiotherapy (RT) of 68 Ga-PSMA-positive oligorecurrences (ORT) with or without additive antihormonal therapy (ADT). Material and Methods Retrospectively, data of 305 patients who underwent definitive radiotherapy (RT) of 647 oligorecurrent 68 Ga- PSMA -positive metastatic sites were evaluated. Patients were treated between 04/2013 and 01/2018 in 6 academic centers. All oligorecurrent patients were treatment-naïve. PSA-progression free survival (PFS) and ADT-free survival was analyzed using Kaplan-Meier survival curves and log rank testing. Toxicity were analyzed with the CTCAE v4 score. Uni-, and multivariate analyses were performed to determine patient, disease and treatment factors influencing PFS. Results Median age of patients was 70 (46-95) years, 96% were initially high-, or very high risk. Median PSA at time of 68 Ga-PSMA-PET was 1.05 (0.04-47.5) ng/ml and PSA-DT was 6.3 (1-56) months. A median of 1 (1-19) nodal, and 1 (1-5) distant metastatic lesions were irradiated. Overall, 93% of patients showed a PSA-decrease to median 0.07 (range 0-13.7) ng/ml after median FU of 16 (1-57) months. 37% of patients received additional ADT. Additional ADT resulted in a significantly improved PFS compared to RT alone, which remained significant in multivariate analysis (p=0.0001). However, the addition of ≤6 mo ADT did not significantly improve PFS compared to patients not receiving ADT (fig. 1). Other independent significant factors for better PFS were nodal-only metastases and biochemical recurrence ≥ 1 year. Patients without additional ADT required second salvage therapies more frequently (4% vs. 33%, p<0.001), but 1- and 3y ADT-free survival was 93% and 59%. Grade ≥3 acute toxicity was observed in 0.9% of patients, late toxicity in 2.3%.

Conclusion Definitive RT in this large cohort of mainly very high-risk, treatment-naïve oligorecurrent PCa patients was feasible and safe. Immediate addition of ADT improved PFS significantly, but two-third of patients treated with RT