G. Gibbard1, T. Perrenec2, D. de Jong1, K. A. Al Feghali1, O. M. Oderinde1,3, A. Maniyedath1, A. Moignier2, C. Rousseau2, L. Ferrer2, G. Delpon2, M. Hatt4, Y. Seroux2, M. Doré2, and S. Supiot2; 1RefleXion Medical, Inc., Hayward, CA, 2Institut de Cancérologie de lOuest René Gauducheau, Saint-Herblain, France, 3Advanced Molecular Imaging in Radiotherapy (AdMIRe) Research Laboratory, Purdue University, West Lafayette, IN, 4LaTIM, UMR 1101 INSERM, University of Brest, Brest, France
Purpose/Objective(s): The PAIR prostate study aims to demonstrate the dosimetric feasibility of tumoral and hypoxia-guided dose escalated radiation therapy in prostate cancer on a novel ring gantry system TPS, based on conventionally fractionated and hypofractionated regimens. Materials/
Methods: The GTV was delineated on MRI and the hypoxic region (biological tumor volume [BTV]) within the PTV on F-MISO PET uptake was delineated on pre-therapeutic F-MISO PET scans of 7 patients showing uptake in the tumor before undergoing external-beam RT for intermediate-risk prostate cancer. IMRT planning was performed using three different prescriptions regimen 1) Standard fractionation (SF) 77Gy/35 fractions (fx) to PTV, with a boost to 95Gy and 118Gy in 35 fx to the GTV and to the hypoxic region defined by F-MISO PET, respectively, 2) moderate hypofractionation (MH) 60 Gy/20 fx with a boost to 67Gy and 91Gy in 20 fx to the GTV and to the hypoxic region, respectively, and 3) high hypofractionation (HH) 40 Gy/5 fx with a boost to 50Gy in 5 fx to the GTV and as high as possible to the hypoxic region (SBRT). Planning was performed on atreatment planning system. Results: The average size of the GTV and BTV was 11.4±11.3 cc, and 1.30±1.20 cc, respectively. For the SF regimen, the average D98% and D2% to the PTV, GTV and BTV were 71.3±11.7 Gy and 105.0±7.6 Gy; 90.3±6.9 Gy and 113.2± 6.9 Gy; and 107.4±5.6 Gy, and 116.0±5.6 Gy, respectively. For the MH and HH techniques, the average D98% to the PTV was 54.3±2.5 Gy, and 31.7± 5.3 Gy, and the average D2% was 83.6±7.0 Gy, and 55.8±2.9 Gy. In addition, the average D98%, and D2% to the GTV was 61.2±6.2 Gy, and 89.8±5.9 Gy using the MH treatment technique, while the average D98%, and D2% to the BTV was 85.2±4.1 Gy, and 92.3±3.2 Gy, respectively. Also, for the HH treatment planning method, the average D98%, and D2% to the GTV was 45.7±4.9 Gy, and 59.2±3.2 Gy, while the average D98%, and D2% to the BTV was 53.6±4.2 Gy and 60.6±2.5 Gy, respectively. The average D50% of the bladder, rectum, and femoral heads was 12.6±5.4 Gy, 24.8±9.9 Gy, and 9.6±2.5 Gy, while the average V15Gy was 43.0±11.5%, 59.4±12.5 %, and 12.5±14.1%, respectively. Conclusion: This study showed the dosimetric feasibility of dose-escalating the tumor and the hypoxic region in patients with prostate cancer using standard, moderate and high hypofractionated regimen on a treatment planning system while keeping the doses within acceptable limits for the organs at risk.
