ESTRO 38 Abstract book

S1024 ESTRO 38

fluoride, a material obtained by an original procedure based on powder sintering. Dosimetric results obtained with the final beam design show that BNCT can deliver high doses to tumour respecting the dose constraints in the critical organs. Conclusion As the selectivity of BNCT is due to boron uptake more than to the neutron beam itself, BNCT can be an option to treat tumours that are too large or infiltrated into the normal tissues or too close to very radiosensitive organs. Moreover, it could be exploited for metastatic spreads. Clinical experience show that a favorable dose distribution is possible also for tumours that have no other treatment options, and treatment planning simulations with this neutron beam demonstrate that clinical BNCT is possible with this technology. EP-1886 Efficacy of a hydrogel spacer in 3D-CRT for prostate cancer M. Ogita 1 , H. Yamashita 1 , S. Sawayanagi 2 , W. Takahashi 1 , K. Nakagawa 1 1 The University of Tokyo Hospital, Radiology, Tokyo, Japan ; 2 Teikyo University Hospital, Radiology, Tokyo, Japan Purpose or Objective Intensity-modulated radiotherapy (IMRT) can reduce the toxicity of prostate RT, but three-dimensional conformal radiotherapy (3D-CRT) is still used in many facilities. Insertion of a hydrogel spacer creates the space between prostate and rectum. We aimed to evaluate the 3D-CRT plan using a hydrogel spacer can fulfill the dose constraints of IMRT for prostate cancer. Material and Methods From April 2017 to July 2018, the planning computed tomography (CT) scans of 39 consecutive prostate cancer patients received stereotactic body radiotherapy in our institution were used in this analysis. All patients inserted a hydrogel spacer before the treatment and underwent CT scans before and after the hydrogel insertion. The planning CT scan was taken with a full bladder and empty rectum. The 3D-CRT plan was made based on three types of risk groups based on NCCN classification; low, intermediate, and high risk. CTV included prostate + seminal vesicle (SV) 2cm for high risk, prostate + SV 1cm for intermediate, and prostate only for low risk. PTV margin of 7 mm except for 5 mm posterior around the CTV were added. The 3D-CRT plan included 10 MV of coplanar seven photon beams, and 76 Gy/38fr delivered to iso- center. Dose constraints for rectum and bladder were V70 Gy ≤ 15%, V65 Gy ≤ 30%, V40 Gy ≤ 60%, and V50 ≤ 50% for femoral head. Results Thirteen (33%), 19 (49%) and 35 (90%) patients before the spacer insertion fulfilled the rectum dose constraints, and 34 (87%), 38 (97%), and 38 (97%) after the spacer fulfilled rectum dose constraints for high, intermediate, and low risk planning, respectively. A hydrogel spacer use significantly increased the dose constraints fulfilment rate in high risk (P < 0.001) and intermediate risk (P = 0.004), but no difference was found in low risk planning (P = 0.25). The mean rV70 Gy, rV50 Gy, and rV40 Gy were 12% vs 23%, 17% vs 29%, and 52% vs 62% in high risk group (with vs without spacer, P < 0.001, P < 0.001, P < 0.001, respectively). Thirty-three (85%) vs 23 (59%) in high risk, 35 (90%) vs 29 (74%) in intermediate risk, and 38 (97%) vs 36 (92%) in low risk planning fulfilled bladder dose constrains, (with vs without spacer, P = 0.006, P=0.03, P = 0.25, respectively). Mean PTV D95 was 72 Gy, 72 Gy and 71 Gy in high, intermediate and low risk with a spacer, respectively. The patient who had a large prostate had difficulty to fulfill the dose constraints even with a spacer. Conclusion Most of the 3D-CRT plan fulfilled IMRT dose constraints by using a hydrogel spacer. If IMRT is not available, a

Conclusion FRED was commissioned and validated against the experimental data acquired during the start-up of PBT centre in Krakow. A fast procedure for phase space library implementation was developed. FRED passed clinical acceptance tests required to admit certified TPS for clinical use. Once commissioned and tested with patient CT data, FRED can be used for fast recalculation of clinical treatment plans. EP-1885 Neutron beam design and dosimetric evaluation for accelerator-based Boron Neutron Capture Therapy S. Bortolussi 1 , I. Postuma 2 , N. Protti 2 , S. Fatemi 2 , C. Magni 1 , S. Gonzalez 3 , S. Altieri 1 1 University of Pavia and INFN, Department of Physics, PAVIA, Italy ; 2 INFN, Unit of Pavia, Pavia, Italy ; 3 CNEA, Computationl Dosimetry and Treatment Planning group, Buenos Aires, Argentina Purpose or Objective Boron Neutron Capture Therapy (BNCT) is a form of hadrontherapy based on the administration of a drug able to concentrate adequate quantities of 10B into the tumour and on the subsequent irradiation with low-energy neutrons. At these energies, the neutron capture reaction in 10B occurs with a cross section of almost 4000 b. The reaction produces two high-LET, short-range particles (alpha particle and 7Li ion) that cause non-reparable damage only to the cell where they are created. If 10B concentration is higher in the tumour than in normal cells, it is possible to deliver a therapeutic dose to the malignancy while sparing the healthy tissues. A project to build a clinical BNCT facility in Italy based on a proton accelerator is underway. The proton beam produces neutron by (p,n) reaction in a Be target and a Beam Shaping Assembly (BSA) has been designed to obtain an epithermal neutron beam to treat deep-seated tumours. To optimize the beam, the geometry of BSA was first set- up to comply with physical in-air figures of merit, traditionally used to evaluate the suitability of a neutron facility for BNCT. The beam has been then improved according to its dosimetric performance in real cases of deep-seated tumours and taking into account peripheral dose in-patient and in the environment. Material and Methods The clinical neutron beam has been designed by MCNP. The BSA geometry and materials have been selected among different possibilities according to the in-air physical characteristics of the beam, such as epithermal flux and contaminations from thermal and fast dose components and from gamma. The selected beams have been tested on a real case of limb osteosarcoma to evaluate the potentiality to deliver a high radiation dose with a uniform distribution in the tumour while keeping the dose to the most radiosensitive organ below the tolerance limit. The treatment planning system NCTPlan, already used for clinical BNCT, has been employed. Finally, radioprotection calculation in the treatment room and peripheral dose in a human model in the irradiation position has been used to further optimize the beam. Results An epithermal beam peaked around 1 keV has been obtained with a BSA whose main component is alluminum