Calorimetric approach for 3D dosimetry of high intensity therapeutic electron beams

The technique of High Dose Rate Intra-Operative Radiation Therapy (HDR-IORT) consists in the delivery ofirradiation immediately after the removal of a cancerous mass, where the same incision is used to focalize theradiation to the tumour bed. Given its particular characteristics, IORT requires dose measurements that aredifferent from those requested in external radiotherapy treatments. The main reason lies in the fact that in thiscase a single high dose must be delivered to a target volume whose extension and depth will be determined directlyduring the operation. Because of this peculiar characteristics, until now there is not a dosimetric system able todetect the electron beam giving at once a realtime response and an extensive spatial measure of the absorbeddose.Within the framework of a research project of the INFN (Italian National Institute of Nuclear Physics), weproposed a new system to overcome the problems, Dosiort. The final set-up is a solid phantom having a densityapproximately 1 g/cm3 with sensitive layers of scintillating fibres at fixed positions in a calorimetric configurationfor the containment of electrons of energy 4-12 MeV. The prototype will be able to define the physical andgeometrical characteristics of the electron beam (energy, isotropy, homogeneity, etc) and to measure the parametersneeded to select the energy, the intensity and the Monitor Units (MU) for the exposition: percentage Depth Dose;beam profiles; isodose curves; values of dose per MU.In this work we present the results obtained by using two orthogonal layers of the calorimetric phantom Dosiort,in particular we report the measurement of the dynamic range of the read-out system and the first qualitativestudy of the results which can be extracted from the measurements taken in a test beam.