ESTRO 36 Abstract Book

S710 ESTRO 36 2017 _______________________________________________________________________________________________

was observed in 7 patients (30%) with a G2 urinary frequency observed in two of these patients (9%); in only one patient a G2 urinary retention was observed and it was treated with transient catheterization and oral and rectal medications. No acute gastrointestinal ≥ G2 or genito- urinary ≥ G3 toxicity was found. No other toxicities were observed. At a median FUP of 16 months (range 7-27, from the time of diagnosis), only one patient presented an outfield relapse of disease, that was treated with androgen deprivation therapy (ADT). No other biochemical recurrence or progression of disease was observed. Conclusion Preliminary findings show that our schedule of hypofractionated radiotherapy, delivered with FFF- VMAT and gated using beacon transponders, is a valid option for intermediate risk PC. Early results in terms of feasibility, toxicity profile and disease control are encouraging to warrant the pursuance of the study. EP-1338 High precision radiotherapy for early prostate cancer with concomitant boost to the dominant lesion. G. Riva 1 , G. Timon 1 , D. Ciardo 1 , A. Bazani 2 , D. Maestri 2 , D. De Lorenzo 3 , F. Pansini 2 , R. Cambria 2 , F. Cattani 2 , G. Marvaso 1 , D. Zerini 1 , D.P. Rojas 1 , S. Volpe 1 , F. Golino 1 , V. Scroffi 1 , C. Fodor 1 , G. Petralia 4 , O. De Cobelli 5 , R. Orecchia 6 , B.A. Jereczek-Fossa 7 1 Istituto Europeo di Oncologia - IEO, Radiotherapy, MIlan, Italy 2 Istituto Europeo di Oncologia - IEO, Medical Physics, MIlan, Italy 3 Istituto Europeo di Oncologia - IEO, Scientific Direction, MIlan, Italy 4 Istituto Europeo di Oncologia - IEO, Radiology, MIlan, Italy 5 Istituto Europeo di Oncologia - IEO, Urology, MIlan, Italy 6 Istituto Europeo di Oncologia - IEO, Medical Imaging and Radiation Sciences, MIlan, Italy 7 Istituto Europeo di Oncologia - IEO- Università degli Studi di Milano, Radiotherapy, MIlan, Italy Purpose or Objective To report preliminary results, in terms of acute toxicity, of an innovative hypofractionated treatment with concomitant boost to the dominant lesion for patients with early stage prostate cancer (PCa). Material and Methods This prospective phase II trial, supported by AIRC (Associazione Italiana per la Ricerca sul Cancro), started in June 2015. Patients with low- and intermediate-risk PCa who met the inclusion criteria underwent hypofractionated radiotherapy (RT) to the prostate with a total dose of 36.25 Gy in 5 fractions (biologically equivalent to a 90.6 Gy, considering a α/β ratio of 1.5 Gy) and a simultaneous integrated boost (SIB) to the dominant intraprostatic lesion (DIL) of 37.5 Gy in 5 fractions (biologically equivalent to a 96.4 Gy, considering a α/β ratio of 1.5 Gy). The DIL was identified by a multiparamentric magnetic resonance imaging (mpMRI) co-registered with planning CT. The treatment was delivered using a Varian Trilogy TM with RapidArc ® technology. Toxicity was assessed according to CTCAE v4.0 and RTOG/EORTC criteria. The preliminary evaluation of the first 13 patients was required to assess the feasibility of the treatment before completing the enrollment of 65 patients. Results The first 13 patients completed the treatment between June 2015 and February 2016. Patients’ characteristics are reported in Table 1. An example of dosimetric distribution is shown in Figure 1. With a median clinical follow-up of 5.9 months, ranging from 1 to 6 months, no grade 3 or 4 acute toxicity was reported. At the end of RT, only one patient experienced G2 gastrointestinal (GI) toxicity, and 4 patients had G1 genitourinary (GU) events. After one

month, G1 GI toxicity was reported in 2 patients and G1 GU in 4 patients; no toxicity higher than G2 has been recorded. At 6 months from the end of treatment, 8 patients have been evaluated and no events higher than G2 have been experienced: 1 patient had G1 GI toxicity and 3 patients had G1 GU toxicity.

Conclusion Up to October 2016, 42 patients have completed the treatment. More mature results seem to confirm the presented preliminary ones. Our preliminary data show the feasibility of an extremely hypofractionated schedule with concomitant boost on the mpMRI-identified DIL. The higher number of patients expected for the trial and a longer follow-up are needed to confirm these results. The secondary endpoints of the study, namely the evaluation of late toxicity, patient free survival, overall survival, quality of life and pattern of failure will be investigated when more mature follow-up data will be available. EP-1339 Feasibility and efficacy of moderately hypofractionated radiotherapy in high risk prostate cancer G. Marvaso 1 , G. Riva 2 , C. Bassi 2 , C. Fodor 2 , D. Ciardo 2 , D. Zerini 2 , G. Timon 2 , A. Surgo 3 , A. Maucieri 3 , F. Pansini 4 , P. De Marco 5 , F. Cattani 6 , O. De Cobelli 7 , R. Orecchia 8 , B. Jereczek-Fossa 9 1 European Insitute of Oncology, radiation oncologist, Milan, Italy 2 European Institute of Oncology, Radiotherapy, Milan, Italy 3 IEO-University of Milan, Radiotherapy, Milan, Italy 4 European Insitute of Oncology, Medical Physics, Milan, Italy 5 IEO- University of Milan, Medical Physics, Milan, Italy 6 European institute of Oncology, Medical Physics, Milan, Italy 7 IEO- Univesity of Milan, Urology, Milan, Italy 8 IEO, Scientific Direction, Milan, Italy 9 IEO- University of Milan, Radiotherapy, Milan, Italy Purpose or Objective Prostate cancer (PCa) is the second most common male cancer. The prognosis for patients with a diagnosis of high- risk PCa is poor. No consensus exists on the most effective treatment. In the last decade, hadrontherapy with carbon ions has been considered a suitable strategy for high-risk PCa, in terms of the dose delivery with a resulting