ESTRO 38 Abstract book

S822 ESTRO 38

benefit of metastasis-directed therapy. However, specific response criteria for PSMA-PET/CT are urgently needed. Also, an interval of more than 6 months may be required to fully estimate the local efficacy of SABR in control PSMA-PET/CT in some patients. EP-1520 Acute and late toxicity of hypofractionated RT for localized prostate cancer: IMRT vs Tomotherapy A. Rese 1 , F. Pastore 1 , G. Panelli 1 , A. Pepe 1 , D. Toledo 1 , F. Francomacaro 1 , V. Iorio 1 1 Emicenter, Radiotherapy, Casavatore NA, Italy Purpose or Objective To evaluate the incidence of acute and late toxicity after hypofractionated radiotherapy using Linac intensity- modulated radiotherapy (IMRT) compared with helical Tomotherapy. Material and Methods From September 2016 to March 2018, 110 consecutive patients with localized prostate cancer (cT1-2, GS< 8, PSA<10 ng/ml) were randomized to Linac IMRT and to helical Tomotherapy. 55 patients were treated with Linac IMRT and 55 with TOMO. Patients were monitored before therapy, weekly during therapy, 2 weeks, three and six months after radiotherapy was completed, using RTOG GI and genitourinary toxicity grading scale. Patients received radiotherapy schedule according to histology reports following international guidelines. Doses were prescribed to planning target volumes (PTVs) as the followings: 72 Gy (2.4 Gy/fx) to PTV-whole prostate and 64.5 Gy (2.15 Gy/fx) to PTV-prostate and seminal vescicles in 30 fractions with SIB technique. Dose to abdominal cavity, both femoral heads, bladder and rectum were constrained below each tissue tolerance. Results Median age of the patients was 72.5 (range 55-86 years). At the end of the treatment (6 weeks), 16/55 (29%) patients in the TOMO group vs. 19/55 (34.5%) patients in the Linac IMRT group had G1-G2 grade of GI toxicity (p=0.009), while 2/55 (4%) patients in the TOMO group vs. 4/55 (7.3%) patients in the Linac IMRT group had G3 grade of GI toxicity. 27/55 (49%) patients in the TOMO group vs. 31/55 (56%) patients in the Linac IMRT group had G1-G2 grade of GU toxicity (p=0.04), while 1/55 (1.8%) patients in the TOMO group vs. 3/55 (5.5%) patients in the Linac IMRT group had G3 grade of GU toxicity. No G4 grade of GI and GU toxicity was showed. After 6 months from the end of the treatment, no patients in the TOMO group vs. 2/55 (3.6%) patients in the Linac IMRT group had G1-G2 grade of GI toxicity, while 1/55 (1.8%) patients in the TOMO group vs. 2/55 (3.6%) patients in the Linac IMRT group had G3 grade of GU toxicity. Conclusion Acute toxicity is very low. Most of the recorded symptoms decrease over time. A small increase in mild toxicity, statistically significant, was observed in the Linac IMRT group when compared with TOMO group. Our study confirmed that Tomotherapy allows for safe moderate hypofractionation, offering a shorter overall treatment time, a lower rate of acute and late toxicities and providing potentially more economic health care. EP-1521 IMRT for prostate cancer with seminal vesicle involvement : A multicentric retrospective analysis F. Goupy 1 , S. Supiot 2 , D. Pasquier 3 , I. Latorzeff 4 , U. Schick 5 , E. Monpetit 6 , G. Martinage 3 , C. Hervé 1 , B. Le Proust 7 , J. Castelli 1 , R. De Crevoisier 1 1 Centre Eugène Marquis, Radiotherapy, Rennes, France ; 2 CLCC René Gauducheau, Radiotherapy, Nantes- Saint- Herblain, France ; 3 CLCC Oscar Lambret, Radiotherapy, Lille, France ; 4 Clinique Pasteur, Radiotherapy,

Toulouse, France ; 5 University Hospital Cavale Blanche, Radiotherapy, Brest, France ; 6 Centre Saint-Yves, Radiotherapy, Vannes, France ; 7 Centre Eugène Marquis, Medical Imaging, Rennes, France Purpose or Objective MRI can detect with high specificity prostate cancer with seminal vesicle involvement (ISV), classifying the tumor stage as T3b. Delivering high curative dose (> 70 Gy) in the ISV is particularly challenging, when respecting the dose constraints in the OARs. No studies have reported data of external beam radiotherapy for specifically T3b prostate cancer. The objective of this study was to analyze the dose distribution and the clinical outcome in a large series of patients having received IMRT for T3b prostate cancer. Material and Methods This retrospective analysis included all patients having received IMRT and androgen deprivation therapy for T3b prostate cancer, between 2008 and 2017 in six French institutions, with available MRI images and dosimetric data. A dosimetric analysis was performed, in particular regarding the ISV, divided in three thirds in the cranio- spinal axis. Recurrences, survivals and toxicities (CTCAE v4.03) were analyzed. Results A total of 276 T3b patients was included. The mean follow- up was 35 months. Only the first proximal thrid of seminal vesicle was involved for 64% of patients, and the entire for 16% of patients. Lymph node involvement was present for 26% of patients. The mean (range) prescribed doses to the prostate and to the ISV were 77 Gy (70-80) and 68 Gy (46- 80), respectively. The prescribed doses to the ISV and the not-involved SV were equal to or greater than 70 Gy for 64% and 22% of patients, respectively. The pelvic lymph nodes without lymph node involvement were treated at a prophylactic dose in 90% of cases. The mean prescribed dose to the involved lymph node was 52 Gy (46-74), and equal to or greater than 60 Gy for 30%. The dose constraints recommendations were exceeded in less than 12% of patients for the rectum and the bladder. The 5 year risks of biochemical and clinical recurrences and cancer specific death were 24.8%, 21.7% and 10.3% respectively. The 5 year risks of local, pelvic lymph node and metastatic recurrences were 6.4%, 11.3% and 15%, respectively. Lymph node involvement was the only significant prognostic factor on clinical recurrence (HR 2.90, p=0.005) and cause specific survival (HR 4.45, p=0.017). Grade > 2 acute and 5 year late toxicity rates were 13.2% and 12% for digestive toxicity, and 34% and 31.5% for urinary toxicity. The dose to the pelvic lymph node was predictive of late digestive toxicity (HR 1.13, p=0.002). Conclusion We reported the most important series of IMRT for T3b prostate cancer. IMRT combined with IGRT allows delivering a high curative dose (> 70 Gy) in the ISV, while rarely exceeding dose constraints. Late digestive toxicity was low but urinary toxicity was slightly increased. Local control appears high and the main pattern of recurrence is metastasis, mostly related to lymph node involvement at diagnosis. More follow-up is needed to confirm the results due to the relative recent use of MRI allowing characterizing ISV. The combined MRI Linac may even more improves the results by a better IGRT targeting. EP-1522 Radiotherapy with or without antihormonal therapy for PSMA-positive oligorecurrent prostate cancer S. Kroeze 1 , C. Henkenberens 2 , N. Schmidt-Hegemann 3 , M. Vogel 4 , S. Kirste 5 , J. Becker 6 , H. Christiansen 2 , C. Belka 7 , S. Combs 4 , A. Grosu 5 , A. Müller 6 , M. Guckenberger 8 1 University Hospital Zürich, Radiation Oncologý, Zurich, Switzerland ; 2 Medical School Hannover, Radiotherapy and Special Oncology, Hannover, Germany ; 3 University Hospital LMU, Radiation Oncology, Munich, Germany ; 4 Technical University Munich, Radiation Oncology,