Abstract Book

S856

ESTRO 37

Material and Methods 44 localized prostate adenocarcinoma patients (33 low and 11 intermediate risk) without hormonal therapy, were irradiated using the CyberKnife Radiosurgical System. The prescription dose was 36,25 Gy in five fractions. During the 2-year follow-up all the patients had at least eight PSA measurements – before the treatment (1-2 months before), during RT (after the 4 th fraction) and 1, 3, 6, 12, 18 and 24 months after RT. Additional measurements were made if necessary. Results The mean initial PSA value among the patients was 6,25 ng/ml (range from 3,02 to 17,46 ng/ml). During the treatment, we observe the PSA increase – the mean value 11,89 ng/ml (4,13-30,68ng/ml, 155% of the initial PSA in average). In 14 cases we noticed the PSA nadir 12 months after the treatment. The rest of the patients achieved their nadirs after 24 months with a mean value of 0,80 ng/ml (0,10- 3,21 ng/ml). The mean slope of the PSA was 0,56 ng/ml/month (median 0,46 ng/ml/month). In 10 cases we observed PSA bounce (3 of them met a biochemical failure criteria). No true biochemical failure was observed. Conclusion The PSA kinetics after treatment can reflect the biological effect of radiation on prostate cancer and potentially correlate with a clinical outcome. Especially the lower value of PSA nadir (<0,5 ng/ml) is considered to associate with an increased freedom from biochemical failure. The interpretation of PSA slope is more controversial however some studies indicates a correlation with clinical outcome. What is more we need to remember about a typical PSA bounce (similar to brachytherapy) which can mimic a biochemical failure. It is also probable that some patients will achieve a nadir later than 24 months after RT. Our results are similar to other SBRT studies. The further follow-up is still necessary. EP-1591 Three years experience of moderate hypofractionated Helical Tomotherapy for Prostate Cancer F. Cuccia 1 , V. Figlia 1 , M. Gueci 1 , G. Napoli 1 , N. Luca 1 , A. Palmeri 1 , A. Lo Casto 2 , D. Cespuglio 3 , G. Evangelista 3 , G. Mortellaro 3 , G. Ferrera 3 1 Radiation Oncology School- University of Palermo, Department of Radiation Oncology- ARNAS-Civico Hospital, Palermo, Italy 2 Radiation Oncology School- University of Palermo, Section of Radiology-Di.Bi.Med., Palermo, Italy 3 ARNAS-Civico Hospital, Department of Radiation Oncology, Palermo, Italy Purpose or Objective To evaluate biochemical control and toxicity after moderate hypofractionated IMRT-IGRT by means of Helical Tomotherapy (HT) in prostate cancer (PC) From December 2012 to October 2015, 94 patients (pts) were treated with curative intent for PC using HT. 32% were low risk (LR), 29% intermediate risk (IR), 39% high risk (HR). Median age was 74 years (range, 58-88); Median iPSA was 9,47 ng/ml (1,35-170). Androgen deprivation was prescribed according to NCCN recommendations. All pts received 70 Gy in 28 fractions to the prostate. Through the simultaneous integrated boost (SIB) technique, in the IR group 61.6 Gy were delivered to the seminal vesicles; for HR pts, whole pelvis irradiation with definitive treatment. Material and Methods

a total dose of 50.4 Gy was added. Daily megavoltage computed tomography (MVCT) image guidance was performed. For pts enrolled in the first year of this series, PTVs were generated by adding a margin of 0,8 cm posteriorly and 1 cm in all other directions. Subsequently, we adopted a tighter margin policy using 0,5 cm posteriorly and 0,8 cm in all other directions. Toxicity was prospectively evaluated basing on CTCAE V4.0 criteria, biochemical failure was defined following Phoenix criteria of Nadir PSA value + 2 ng/ml. Overall survival (OS) and biochemical failure-free survival (BFFS) were assessed using Kaplan-Meier analysis. Results Median follow-up was 36 months (range 12-56). Acute G1 and G2 gastrointestinal (GI) toxicity rates were 15,9% and 10,6%; acute G1 and G2 genitourinary (GU) were 40,4% and 11,7%; no ≥G3 was detected. 1-year GI and GU rates were G1 in 20,2%, G2 in 4,2%, G1 in 13,8% and G2 in 1,06% respectively. 2-yrs rates were G1 in 12,9%, G≥2 in 8,2% for GI; G1 in 5,8%, G≥2 in 2,2% for GU. 3-yrs rates were G1 in 14,5% and G2 in 4,1% for GI, G1 in 6,25% and G2 in 12,5% for GU. 4-yrs rates were both G1 in 4,76% for GI and GU. Most common acute and late side effects were respectively diarrhea and proctitis for GI, dysuria and urgency for GU. At the time of final assessment, 3- and 4-yrs BFFS were both 96,4% for LR disease, 82,1% and 70,3% for IR disease , 89% and 84,3% for HR disease; 3- and 4-yrs OS of the entire population were 84,6% and 79,5%. Twelve patients experienced a biochemical relapse, including 3 nodal recurrences, successfully treated with SBRT, and 2 bony recurrences who underwent palliative RT. Conclusion Our data support the 70 Gy/2.5 Gy/fx schedule as a well tolerated regimen with excellent rates of acute and late toxicity, reporting BFFS rates comparable to other experiences of moderate hypofractionation for PC available in literature. A longer follow-up is advocated for further evaluation of clinical outcomes to analyze the impact of predictive factors in different risk subgroups. EP-1592 Impact of 68Ga-PSMA PET/CT in prostate cancer patients with biochemical recurrence after surgery S. Bartoncini 1 , D. Nicolotti 2 , D. Deandreis 2 , A. Guarneri 1 , A. Zitella 3 , R. Passera 2 , R. Parise 4 , M. Bellò 5 , B. Lillaz 3 , G. Bisi 2 , P. Gontero 3 , U. Ricardi 4 1 A.O.U. Città della Salute e della Scienza, Department of Oncology- Division of Radiation Oncology, Torino, Italy 2 University of Turin- A.O.U. Città della Salute e della Scienza, Department of Medical Sciences- Nuclear Medicine Unit, Torino, Italy 3 University of Turin- A.O.U. Città della Salute e della Scienza, Department of Surgical Sciences- Division of Urology, Torino, Italy 4 University of Turin- A.O.U. Città della Salute e della Scienza, Department of Oncology - Division of Radiation Oncology, Torino, Italy 5 A.O.U. Città della Salute e della Scienza, Nuclear Medicine Unit, Torino, Italy Purpose or Objective The aim of this study is to evaluate the impact of 68 Ga- PSMA PET/CT in patients with persistent or recurrence prostate cancer after radical prostatectomy (RP) elegible to salvage radiotherapy (SRT). Material and Methods From November 2016 and October 2017, we prospectively included patients with persistent or recurrence prostate