Abstract Book

S865

ESTRO 37

to consider the likelihood of finding the CTV/OAR in a given point. The variable weight factors derive from the probabilities of systematic organ displacement, as assessed from the repeated CTs, and systematic 3D-setup errors. IMRT was given in 39 fractions to 78Gy. Short- term androgen deprivation was recommended and given in 78.6% of patients. Results Long-term toxicity was evaluated in 26/28 patients after a median follow-up of 7.1 years. Late bladder toxicity (RTOG G1) was observed in 14.3% of patients. Late rectal toxicities (RTOG) of G1 (7.1%) and of G2 (3.6%) were observed. No higher graded toxicity occurred. Two patients developed a recurrence. The Prostate Cancer Specific Survival and the Distant Metastasis Free Survival after 7 years was 100%. Conclusion Probabilistic dose prescription-based IMRT was feasible in a clinical study. Dose escalation with the CovP concept was associated with a low rate of toxicity and a high efficacy regarding local and distant control. EP-1607 Balloon Device for Prostate Cancer SBRT - Increased Spacing helps to Overcome Rectal Toxicities P. Costa 1 , G. Fonseca 1 , A. Costa 1 , C. Calçada 2 , J. Conde 2 , C. Fardilha 2 , J. Gonçalves 2 , J. Vale 1 , F. Ponte 1 , G. Campos 1 , P. Genésio 1 , F. Rodrigues 1 , R. Oliveira 1 , B.W. Corn 3 1 Instituto CUF Porto, Radiation Oncology, Porto, Portugal 2 Braga Hospital, Radiation Oncology, Braga, Portugal 3 Shaare Zedek Medical Center, Radiation Oncology, Jerusalem, Israel Purpose or Objective To evaluate the dosimetric impact and toxicity outcomes of the increased separation distance between the prostate and the anterior rectal wall among prostate cancer patients treated with SBRT. The ideal regimen for extreme hypofractionation in prostate cancer is still to be determined. Higher radiation regimens are related to additional tumor control outcomes. Although evolving technologies allowed further dose escalation with acceptable toxicities, the rectum still represents the primary organ at risk (OAR) in this setting. Lower doses to the rectum potentially allows further dose escalation to the prostate while reducing the dose levels to the rate-limiting OAR. The BioProtect ® balloon implant indicated for spacing between the prostate and the rectum, made of a biodegradable polymer, enables dose escalation while maintaining lower 13 patients were treated in our department for prostate cancer with extreme hypofractionated radiotherapy between December 2015 and July 2017. All underwent BioProtect ® balloon implantation. A total dose of 3750 cGy in 5 consecutive days was performed. For dosimetric comparison, additional CT scans were performed pre balloon implantation. Maximum and average dose to the rectum, Vol(cc)>3440cGy, D10, D20 and D50 were calculated pre and post balloon implantation. EPIC QoL scoring index questionnaire for bowel habits and urinary function at the outset and at the end of the treatment course was obtained. Results A statistically significant reduction in the max and average dose to the rectum as well as in the Vol (cc)>3440cGy, D10 and D20 dosimetric parameters with toxicity to the rectum. Material and Methods

p value <0,005 was obtained. D50 parameter had no statistical difference between pre and post balloon implant p value >0,08. No balloon placement related toxicities were observed in this study. EPIC QoL for bowel habits and urinary symptoms had no statistical difference between pre and post balloon implant. Conclusion Increased separation with a balloon spacer between rectum and prostate appears to be a safe and effective tool allowing for lower dose to the anterior rectal wall. Acute and late effects to the rectum with extreme hypofractionation may be underestimated, as limited data are available for these new regimens. The BioProtect ® balloon spacer has advantageous characteristics compared with other spacing solutions, in particular the amount of spacing achieved and the related homogeneity. This balloon spacer presents the possibility of adjustable placement (including deflation and repositioning) during the procedure, avoiding any asymmetric deployment, allowing for optimal spacing. A low level of toxicity for bowel habits and urinary function was observed for this cohort. Dosimetric improvements observed with lower doses to the rectum allows for extra dose to the prostate without exceeding this OAR tolerance, opening new possibilities for dose escalation and disease control. EP-1608 Prostate cancer radiotherapy in elderly patients : Does it make a difference in acute toxicities? M. Wafa 1 , N. Fourati 1 , K. Hajeur 1 , F. Leila 1 , S. Tarek 1 , K. Mouna 1 , S. Wicem 1 , D. Jamel 1 1 Hopital Habib Bourguiba, Radiation Oncology, Sfax, Tunisia Purpose or Objective The aim of our study was to retrospectively compare, the incidence of acute toxicities occurred during conformal radiotherapy, with curative intent in patients aged over 70 years and the younger population. Material and Methods From 2011 to 2016, 84 patients were treated with conformal radiotherapy for localized prostate cancer including 42 patients (50%) older than 70 years (group 1) and 42 patients younger than 70 years (group 2). For group 1, the median age was 74 years (70-81 years), the median PSA was 18.5 ng / ml (1-219 ng / ml). According to D'Amico classification, 29 patients (69%) were at high risk group. One patient (2.4%) had postoperative radiotherapy and 2 patients (4.8%) had lymph node involvement. For group 2, the median age was 64 years (50-69 years), the median PSA level was 11 ng / ml (1-192 ng / ml). Twenty five patients (59.5%) were at high risk group. Five patients (11.9%) had postoperative radiotherapy and 3 patients (7.1%) had lymph node involvement. Treatment consisted on 3D conformal radiation therapy (n=46) or intensity modulated radiotherapy (n=38), at a dose of 66 Gy for postoperative irradiation and at a dose ≥ 70 Gy for the definitive treatment. Patients were followed up weekly during treatment to determine the acute toxicities which were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) v.4. Khi-Deux test was used to compare the two groups and a p < 0.05 was considered statistically significant.