ESTRO 36 Abstract Book

S141 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective Prostate cancer is the most frequent malignancy in African-Caribbean men, a population sharing common genetic traits with African-American (AA) but presenting also genomic and epidemiologic specificities. Despite socio-economic disparities with French mainland, all patients were treated within the French state-financed equal-access healthcare system. In this study, we report biochemical outcomes of patients treated by brachytherapy in our department from 2005 to 2014 in an African-Caribbean population Material and Methods 370 consecutive patients receiving I125 brachytherapy as a curative treatment for early-stage (localized) disease between 2005 and 2014 were recorded. Selected patients presented with low risk disease: initial PSA (iPSA) < 10 ng/mL, clinical stage <= T2a, Gleason <7. Patients with intermediate risk of recurrence were also included on a case to case basis with PSA <15 or Gleason 7 (3+4). Biochemical failure free-survival (BFFS) was defined according to the ASTRO nadir+2 definition. Results The 3-year and 5-year BFFS for the entire cohort were 98.3% and 91.6% respectively. For patients with low and intermediate-risk disease, the 5-year BBFS rates were 92.1 and 90.8%, respectively. In univariate and multivariate analysis, only Gleason score ( ˂ 7 vs 7; P = 0.030 ˂ 0.05) was a significant predictor of biochemical failure. The overall rate of late and acute grade 2 or higher Genito-urinary toxicity was 12.6% and 10.3 %. Conclusion In this large single-center series, brachytherapy achieved excellent rates of medium-term biochemical control in both low- and selected intermediate-risk localized prostate cancer in African-caribean patients. Brachytherapy seems to be an excellent choice of treatment, with excellent outcomes and limited morbidity for African-Caribbean populations. To our knowledge, our series is the first presenting brachytherapy results in this specific population. OC-0274 Comparison of MRI/CT fusion and CT for prostate post-implant dosimetry using sector analysis N. Katayama 1 , M. Takemoto 2 , A. Takamoto 3 , S. Sugiyama 1 , K. Hisazumi 1 , K. Watanabe 1 , H. Ihara 1 , K. Katsui 1 , Y. Nasu 3 , S. Kanazawa 3 1 Okayama University Graduate School of Health Sciences, Department of Radiology, Okayama, Japan 2 Himeji Red Cross Hospital, Department of Radiotherapy, Himeji, Japan 3 Okayama University Graduate School of Health Sciences, Department of Urology, Okayama, Japan Purpose or Objective Anatomical structures are well defined, so MRI/CT fusion is considered the best method for postimplant dosimetry of permanent prostate brachytherapy. We compared the results obtained from MRI/CT fusion-based dosimetry with those of CT-based dosimetry using sector analysis, and analyzed the factors associated with the difference of the whole prostate dose between the two dosimetry. This is the first report which evaluated those factors using 3- Tesla MRI in which contouring and fusion are thought to be more accurate than in 1.5-Tesla MRI. Material and Methods The subjects were 81 consecutive patients treated with 144 Gy of brachytherapy alone using loose I-125 radioactive seeds. For postimplant analysis, CT and MRI scans were obtained at 1 month after implantation. CT and 3-Tesla T2-weighted MR images were fused and aligned on the basis of seed distribution in MRI/CT fusion- based dosimetry. Dosimetry was computed for the whole prostate and for the prostate divided into anterior and posterior sectors of the base, mid-gland, and apex (Fig. 1). The volumetric and dosimetric results were compared

between MRI/CT fusion-based and CT-based dosimetry using a paired t test. Factors associated with the absolute value of the difference of D90 between the two dosimetry (|D90MRI/CT - D90CT|) were analyzed by multiple regression. P values of <0.05 were defined to be significant.

Results D90 (176.7 Gy vs 173.0 Gy; p = 0.003) and V100 (97.2% vs 96.5%; p = 0.013) were significantly higher in MRI/CT fusion-based dosimetry than in CT-based dosimetry. Prostate volume (28.5 mL vs 30.8 mL; p < 0.001) was significantly lower in MRI/CT fusion-based dosimetry than CT-based dosimetry. Sector analysis showed a decrease in MRI/CT fusion D90 at the anterior base (154.9 Gy vs 166.5 Gy; p < 0.001) and the posterior apex (169.7 Gy vs 177.6 Gy; p < 0.001), and increase in MRI/CT fusion D90 in the anterior mid-gland (195.2 Gy vs 181.7 Gy; p < 0.001), the posterior mid-gland (196.1 Gy vs 193.9 Gy; p = 0.030), and the anterior apex (198.7 Gy vs 175.0 Gy; p < 0.001). |D90MRI/CT - D90CT| was largest at the anterior apex sector among 6 sectors (27.2 Gy). On multivariate analysis, |D90MRI/CT - D90CT| of whole prostate are associated with |prostate volume (PV)MRI/CT - PVCT| (p = 0.036), |D90MRI/CT - D90CT| at the posterior base sector (p = 0.035), |D90MRI/CT - D90CT| at the anterior mid-gland sector (p = 0.011), and |D90MRI/CT - D90CT| at the anterior apex sector (p = 0.004) (Table 1).

Conclusion Several postimplant dosimetric variables were significantly different on MRI/CT fusion vs CT. The differences between the two methods of PV, D90 at the posterior base, anterior mid-gland, and anterior apex sectors may greatly influence the difference of D90 of the whole prostate.

Proffered Papers: Physics treatment verification

OC-0275 Testing an MR-compatible afterloader for MR- based source tracking in MRI guided HDR brachytherapy E. Beld 1 , P.R. Seevinck 2 , J. Schuurman 3 , F. Zijlstra 2 , M.A. Viergever 2 , J.J.W. Lagendijk 1 , M.A. Moerland 1 1 UMC Utrecht, Department of Radiotherapy, Utrecht, The Netherlands 2 UMC Utrecht, Image Sciences Institute, Utrecht, The Netherlands 3 Elekta NL, Veenendaal, The Netherlands

Purpose or Objective