Abstract Book

S843

ESTRO 37

Material and Methods 20 patients (pts) with intermediate-high PCa treated with radical RT were enrolled in this study. The prescribed dose was 78 Gy to prostate (CTV1) and 60 Gy to prostate plus seminal vesicles (CTV2) delivering 2 Gy/fraction (fr). The CBCTs were acquired according to our IGRT protocol during the first 5 frs, then once a week for the remaining of the treatment. The CBCTs were imported in the Raystation treatment planning system (TPS) and coregistered with the planning CT using the on-line match rigid transformations provided by the OBI system on the treatment unit (Varian Trilogy TX). Then the deformable image registration (DIR) algorithm ANACONDA was applied to propagate the CTV1 and CTV2 volumes from the reference planning CT to the first 5 CBCTs. The reliability of the DIR mapped ROIs was assessed by a radiation oncologist and the contours were used to generate the ITV used to adapt the plan. The original plan was re-optimized using robust algorithm based on the worst scenario optimization assuming an isotropic 5 mm maximum setup error. Then CTV coverage and OAR sparing achieved with the robust plan (RP) were analyzed and compared with the original standard plan (SP) calculating the dose distributions on the residual CBCTs. Results Based on 10 pts preliminary data analysis, a robustness simulation showed that RP achieved optimal coverage of CTV also in the worst scenario (geometric error up to 5 mm) with D99>95% of prescribed dose with significant less dose to rectum and bladder. The analysis on all the residual CBCT acquired during the treatment showed that CTV coverage of RP was optimal and not significantly different from SP. Statistically (Wilcoxon test), significant dose reduction was noted for rectum (p<0.001) and for empty bladder (p<0.01). Moreover, RP appeared to be less sensitive to bladder and rectal filling and to decrease the integral dose. Conclusion Robust optimization is a feasible and safe approach in prostate treatment. It may be successfully used to adapt the treatment with better target coverage and OAR sparing than standard PTV based planning during the treatment course. EP-1564 The comparison of treatment outcome between fiducial-based and bone-based IGRT for prostate cancer W. Majewski 1 , A. Napieralska 1 , R. Kulik 2 , G. Głowacki 3 , L. Miszczyk 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Department, Gliwice, Poland 2 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Department of Radiotherapy and Brachytherapy Panning, Gliwice, Poland 3 Nu-Med Health Center, Radiotherapy Department, Tomaszów Mazowiecki, Poland Purpose or Objective The aim of the study is to compare the clinical outcome: acute and late toxicity, progression-free survival (PFS) and overall survival (OS) in patients with prostate cancer treated with radiotherapy using two forms of image guidance: bone – based (BB) or fiducial – based (FB). Material and Methods The retrospective study group consisted of 180 consecutive patients treated with radical conventionally fractionated radiotherapy between 2008 and 2011 with daily kV–kV image guidance. A total of 89 patients were

positioned to pelvic bones (Group BB) and 91 patients were positioned to a fiducial (GoldAnchor) implanted into the prostate gland (Group FB). There were no statistical differences between groups with regard to clinical factors like: T-stage, PSA concentration, Gleason score etc. The low- (LR), intermediate- (IR) and high-risk groups (HR) were observed in group BB and FB in: 21% and 14%; 36% and 46%; 43% and 40%, respectively (p=ns). Patients were treated with 6-20 MV photons with a total dose of 76 in 38 fractions to the prostate. Patients in a high-risk group were initially treated with an elective pelvic lymph nodes irradiation. Treatment outcome was assessed with regard to PFS (including any clinical or biochemical progression or death) or OS. The overall survival (OS) was evaluated using the Kaplan-Meier method. Acute and late toxicity was evaluated based on RTOG/EORTC criteria. Results The median follow-up was 5 years. The 5-year PFS was 76% in Group FB and 73% in Group BB (p=0.72). The 5- years PFS by the risk groups were: LR- 91% (FB) 82% (BB) p=0.81; IR- 78% (FB) 76% (BB) p=0.55; HR- 66% (FB) 66% (BB) p=0,46. The 5-year OS was 80% in BB Group and 91% FB Group (p=0.20), however the survival curves started to diverge after 4 years, favoring FB IGRT. The difference was the biggest in the IR group - 5-year OS of respectively of 92% (FB) and 75% (BB) p=0.06, respectively, and no difference in low-risk group 91% (FB) and 89% (BB) p=0.50 as well as high-risk group 88% (FB) and 76% (BB) p=0.48. There was some slight benefit in terms of acute toxicity in patients having fiducial based IGRT. The incidence of severe acute G3 GU toxicity was lower in FB Group – 1 (1%) compared to 5 (5%) in group BB (p=0.035). Also more patients in FB Group had no acute GI toxicity: 40 (44%) vs 26 (29%) (p=0.019), however the incidence of acute G2/G3 GI toxicity was not statistically different between groups (p=0.2). The actuarial 5-year incidence of late G2+ GU and GI toxicity was similar: 13% in both groups (p=0.98) and 19% vs 15% (p=0.55), respectively. Conclusion Despite some benefit in terms of acute toxicity in FB group, there is no clear advantage of one IGRT method over another in terms of OS or PFS. However, intermediate risk prostate cancer patients are those who might benefit the most from implementation of fiducial- based IGRT. Further studies with longer follow-up are needed to confirm that hypothesis. G. Fanetti 1 , G. Marvaso 1 , A. Rese 2 , R. Ricotti 1 , D. Ciardo 1 , E. Rondi 3 , S. Comi 3 , F. Cattani 3 , D. Zerini 1 , C. Fodor 1 , O. De Cobelli 4 , R. Orecchia 5 , B. Jereczek-Fossa 1 1 European Institute of Oncology, Division of Radiation Oncology, Milano, Italy 2 Federico II University Hospital, Division of Radiation Oncology, Napoli, Italy 3 European Institute of Oncology, Unit of Medical Physics, Milano, Italy 4 European Institute of Oncology, Division of Urology, Milano, Italy 5 European Institute of Oncology, Department of Medical Imaging and Radiation Sciences, Milano, Italy Purpose or Objective To evaluate outcome in patients (pts) treated with Stereotactic Body Radiotherapy (SBRT) with or without androgen deprivation therapy (ADT) to bone EP-1565 Stereotactic Body Radiotherapy For Castration-Sensitive Prostate Cancer Bone Oligometastases