ESTRO 36 Abstract Book

S723 ESTRO 36 _______________________________________________________________________________________________

acute GI toxicity grade I was observed in 6 patients (17.1%) and grade II in 3 patients (8.6%). No late grade III-IV GU or GI toxicity was detected. For one patient a TURP was planned at 8 months after treatment, for urethral stricture. Only 1 patient (3%) developed biochemical recurrence after a follow-up of 27 months. Conclusion Hypo-RT (63,4 Gy/20 fractions) with a high equivalent BED (EQD2Gy_tumor = 85 Gy) produces aceptable acute and sub-acute toxicity rates with excellent outcomes of biochemical control for intermediate risk prostate cancer. Longer term follow-up should be analyzed to confirm these data. EP-1348 Set-up errors in prostate cancer radiotherapy based on cone-beam computed tomography. M. Trignani 1 , G. Caponigro 1 , M. Di Biase 1 , P. Bagalà 1 , M.D. Falco 1 , A. Vinciguerra 1 , A. Augurio 1 , M. Di Tommaso 1 , L. Caravatta 1 , D. Genovesi 1 1 Ospedale Clinicizzato S.S. Annunziata, Radiotherapy, Chieti, Italy Purpose or Objective To evaluate set-up accuracy using cone-beam computed tomography (CBCT) in patients with prostate cancer receiving VMAT (volumetric modulated arc therapy) or IMRT (intensity modulated radiation therapy) techniques. Material and Methods From January 2015 to September 2016, 1199 CBCT referred to 98 prostate cancer patients received radiation treatment at our Institution using Elekta Synergy Agility Linear Accelerator were acquired, recorded and evaluated. All patients underwent to planning computed tomography (CT) in supine position; knees and ankles were placed in a steady and comfortable position using a footrest. CT scans with slices at 5 mm were acquired at 2 mm in condition of fully bladder (0.75 liter of water, 45 minutes prior to CT scan) and empty rectum. Planning CT was sent to Oncentra Master Plan planning system and then via DICOM to XVI software for co-registration with the CBCT scans. For the CBCT acquisition we used the “pelvis M15”; the Grey level algorithm was employed to obtain 3D-3D co- registration with CT planning. An internal protocol was adopted to reduce interfraction set-up errors and to correct systematic errors. This protocol consisted in the execution of 5 consecutively CBCT during first week of treatment and once weekly CBCT during RT course. On the basis of literature data an on-line correction protocol was adopted: the tolerance level was 3 mm for translation displacements and 3° for rotations; translation displacements were applied in case of values >3 mm, while for rotation >3° patients were repositioned. Then an offline correction was applied with the mean of first 5 scans used to correct systematic errors with 3 mm. Means (m) and standard deviations (SD) of all translational (x, y, z) and rotational displacements were calculated in relation to the first 5 and the following CBCTs. The Wilxocon test was used to evaluate statistically significant differences between displacements related to first 5 CBCTs and to the following CBCTs. Results Results are summarized in Table 1. Median values were <3 mm for all CBCTs, for both the first five and following CBCTs, mean values were within 5mm. Greater shifts were observed on z axis. Wilcoxon test showed a statistically significant correlation only for the x (p value = 0.001). Conclusion In our study, we have analyzed translational set-up uncertainties in prostate cancer treatments using CBCT and we found that all the displacements were within 5 mm, well within the offset established. The action level

of 3 mm currently adopted at our center results safe and it constitutes a good start point to reduce margin CTV- PTV. EP-1349 Adjuvant hypofractionated radiotherapy for prostate cancer: acute toxicity S. Saldi 1 , R. Bellavita 2 , I. Palumbo 3 , C. Mariucci 1 , E. Arena 1 , M. Lupattelli 2 , M. Mendichi 1 , M. Tenti 1 , F. Tamburi 2 , V. Bini 4 , C. Aristei 3 1 University of Perugia, Radiation Oncology Section, Perugia, Italy 2 Perugia General Hospital, Radiation Oncology Section, Perugia, Italy 3 University of Perugia and Perugia General Hospital, Radiation Oncology Section, Perugia, Italy 4 Perugia General Hospital, Internal Medicine Endocrin and Metabolic Sciences Section, Perugia, Italy and preliminary outcome of hypofractionated adjuvant radiotherapy (Hypo-ART) with helical tomotherapy after radical prostatectomy (RP). Material and Methods From February 2014 to July 2016, 30 prostate cancer patients received Hypo-ART for pT2-3 N0-1 and/or R1disease. Median age was 67 years (range 53-74). The surgical Gleason score was: <7 in 8 patients (27%), 7 in 10 (33%) and >7 in 12 (40%). Before RP the median PSA was 7.74 (range: 1.13-44.48) which dropped to 0.025 ng/ml (range: 0 -0.53) before Hypo-ART. RT schedule: all 30 patients received 2.25 Gy in 29 fractions (total dose: 65.25 Gy) to the prostate/seminal vesicle bed; 15 (50%) patients also received 1.8 Gy in 29 fractions to the pelvic lymph nodes (total dose: 52.2 Gy). A simultaneous integrated boost (SIB) technique was used. Hormone therapy (LHRH analogue and/or anti-androgen) was administered to 15 (50%) patients with high risk features. Toxicity was graded according to the Common Terminology Criteria for Adverse Events version v4.0. Biochemical failure was defined by ASTRO criteria. The Kaplan-Meier method determined time-to-acute toxicity events. The Mann-Whitney tested compared clinical and dosimetric variables in groups with and without acute toxicity. Results Median follow-up was 26.5 months (range: 3-31). The median duration of HT was 21 months (range 4-33). Only G1-G2 acute genitourinary (GU) and intestinal (GI) toxicities occurred. Acute grade 1 GU toxicity occurred in 14/30 patients (56%), with 13 (43%) developing cystitis and 1 (3%) hematuria. Acute grade 2 GU toxicity (cystitis) developed in 3/30 (10%) patients, with 1 also affected by urinary retension (3%). Acute grade 1 GI toxicity (proctitis) occurred in 14/30 patients (47%), which was associated with rectal bleeding in 2 (7%) and diarrhoea in 5 (17%). Acute grade 2 GI toxicity (proctitis) developed in 3/30 (10%) patients, which was associated with rectal bleeding in 1 (3%) and diarrhoea in 1 (3%). Post Hypo-ART the median PSA was 0.01 ng/ml (range:0-0.22) and the nadir was 0.005 ng/ml (range: 0-0.2). At the last follow-up no patient presented evidence of biochemical or loco- regional recurrence. The probability of developing acute GU on day 44 and GI toxicity on day 43 was 50% (95% CI 41- 46; 95% CI 39-46 respectively ). No differences emerged in clinical and dosimetric variables in group with or without acute toxicity. Conclusion These results suggest that moderate Hypo -ART is safe, effective and well-tolerated. A longer follow-up is needed to assess late toxicity and disease-free survival. Purpose or Objective To evaluate acute toxicity