Ponente
Abstract
The number of protontherapy facilities has grown exponentially in the last years. By 2019, about 90 proton therapy facilities are running worldwide and it is planned that Spain will join the list in the incoming year. The use of protons presents substantial clinical advantages compared to conventional radiotherapy with photons. Protons deliver most of the energy in a narrow well-defined area at the end of its range (the so-called Bragg peak) after which dose sharply falls off to zero. This enables a better tumour covering while minimizing the damage to the surrounding healthy tissue. However, uncertainties in the proton range lead to increased treatment margins which in turn limit the maximum potential of this technique. In the last decades,several methods have been proposed to monitor the proton range and control the dose deposition within the patient in vivo, i.e, during the treatment. Hereof we focus on those based on the detection of the secondary radiation originated during the nuclear reactions of protons in tissue: (1) Positron Emission Tomography (PET) for the positron emitters and (2) Prompt gamma Imaging in the case of prompt gamma-rays. In this context we propose in our group the use of contrast agents, elements that are activated by the incoming protons, to enhance the feasibility of both techniques as a possible solution to the problem of range uncertainty in protontherapy.
In this work we have studied the proton activation on two elements: Iodine and Zinc, by means of the reactions 127I(p; n)127mXe and 64Zn(p; n)64Ga respectively.The short half-life of these isotopes, being69.2(9) s for the 127mXe excited sate and 158(4)for the 64Ga, makes them suitable to be used for in-vivo range verification. Both targets have been bombarded with protons in the 2-10 MeV energy range using the beam delivered by the 5MV- CMAM tandetron accelerator.
In the case of the 127I(p; n)127mXe we report the first experimental measured values for the thick target yields and cross sections in this energy range. For the 64Zn(p; n)64Ga, we confirm that our measurements are in very good agreement with the literature data. The low energy threshold and large cross-sections for the 127mXe are more favourable than in the case of the 64Ga.
