ESTRO 37 Abstract book

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ESTRO 37

Material and Methods This retrospective study includes 137 patients who received primary radiation therapy in our center between 2010 and 2014. All patients were treated with IMRT technique with IGRT including cone beam CT and daily 2D2D imaging. Before treatment 4 gold fiducials were implanted in the prostate in all patients. Treatment planning was done by MRI and/or PET-CT imaging. Patients with a large prostate volume and/or high risk disease were prescribed neoadjuvant and concomitant hormonal therapy. The total dose in the prostate was 74- 76 Gy. In case of node positive cancer up to 54 Gy were given to pelvic lymph nodes. Biochemical recurrence was defined as PSA >= 2ng/ml (or +2ng/ml from PSA nadir). Kaplan-Meier analysis was performed for biochemical recurrence free survival (bRFS) and overall survival (OS). Results Median follow-up was 48 months (2 – 81). In total 20 out of 137 patients developed a recurrence (10 biochemical recurrence only, 6 lymph node recurrences outside the radiation field, 2 distant metastases, 1 lymph node recurrence outside the radiation field and distant metastases and 1 recurrence inside radiation field). The 4 year bRFS was 82 %. 4 year OS was 92 %. Acute grade 3 genitourinary toxicity was observed in two patients (1,5 %). No patient had late grade 3 genitourinary toxicity. Acute grade 3 gastrointestinal toxicity was observed in five patients (3,6 %), late grade 3 gastrointestinal toxicity was observed in 6 patients (4,4 %). Factors that influenced bRFS were lymph node status, irradiation dose (cont.), concomitant and adjuvant hormonal therapy in univariate analysis. The following cox regression analysis showed significant influence of lymph node status and concomitant hormonal therapy. Conclusion Primary image-guided radiation therapy leads to very good local tumor control rates with low acute and late toxicity. We observed only 1 local recurrence in the radiation area. EP-1606 Probabilistic Planning Concept instead of Target Volume Margins - Prospective evaluation D. Wegener 1 , B. Berger 2 , Z. Outaggarts 1 , D. Zips 1 , F. Paulsen 1 , M. Bleif 3 , D. Thorwarth 4 , M. Alber 5 , O. Dohm 6 , A.C. Müller 1 1 Eberhard Karls University Tübingen, Department of Radiation Oncology, Tübingen, Germany 2 Oberschwabenklinik Ravensburg- Academic Hospital of Eberhard Karls University Tübingen, Department of Radiation Oncology, Ravensburg, Germany 3 Alb Fils Kliniken Göppingen- Academic Hospital of Eberhard Karls University Tübingen, Department of Radiation Oncology, Göppingen, Germany 4 Eberhard Karls University Tübingen, Department of Radiation Oncology- Research Section of Biomedical Physics, Tübingen, Germany 5 Ruprecht Karls University Heidelberg, Department of Radiooncology and Radiotherapy, Heidelberg, Germany 6 Eberhard Karls University Tübingen, Department of Radiation Oncology- Section of Medical Physics, Tübingen, Germany Purpose or Objective Cure- and toxicity rates after IMRT of prostate cancer can both suffer from ill-chosen PTV margins. We studied the potential for Organ at Risk (OAR) sparing of the probabilistic dose prescription concept i.e. the coverage probability concept (CovP) for compensation of tumor

movement. Furthermore, outcome parameters of patients were evaluated. Material and Methods Twenty-eight prostate cancer patients (median age 70) with localized disease (cT1c-2c, N0, M0) and intermediate risk features (PSA<20, Gleason score ≤7b) were treated in a prospective study with the CovP. CTs were acquired on three subsequent days to capture form changes and movement of prostate and OAR. The clinical target volume (CTV, prostate) and the OARs (bladder and rectum) were contoured in each CT. The union of CTV1-3 was encompassed by an isotropic margin of 7mm to define the PTV (planning target volume). The CovP concept employs spatially variable weight factors for the target- and OAR cost functions that allow the optimizer 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

toxicity to the rectum. Material and Methods

13 patients were treated in our department for prostate cancer with extreme hypofractionated radiotherapy