Particle Therapy (PT) is potentially the most conformal and selective form of radiotherapy, but its clinical outcome is still limited, mainly because of the numerous sources of uncertainties affecting both treatment planning and delivery. The objective technical complexity of predicting and verifying the ion path in the patient has led to conservative treatments that, in order to increase safety, sacrifice efficacy. Having the full control of the dose gradient within the patient in real time would allow to fully exploit the ballistic advantage of PT. The healthy-tissue sparing effect can be enormous, further encouraging the use of PT for paediatric malignancies. Alternatively, the target dose could be increased to achieve better tumour control, and dose escalation procedures could be envisaged to treat radio-resistant tumours.
With the aim of increasing both safety and efficacy, this project proposes a new medical-imaging modality, Prompt Gamma Time Imaging (PGTI), and the development of a dedicated fast gamma detector, TIARA (Time-of-flight Imaging ARrAy), to monitor PT treatments in real-time. They exploit the signal of the secondary prompt gamma-rays emitted from nuclear interactions in the patients to recover information on ion range, tissue density and dose.
TIARA will be composed of 30 gamma detection modules based on monolithic Cherenkov radiators uniformly distributed around the patient, and read in temporal coincidence with a dedicated beam monitor, to allow the measurement of the total Time-Of-Flight (TOF) of the incident ion and the PG with a temporal resolution of the order of 100 ps rms. The resolution of an inverse problem (the PGTI algorithm) makes it possible to determine the spatial distribution of the PG vertices, which is strongly correlated with the particle path in the patient, but also to the densities of tissues intersected by the beam. This will allow to correlate the images provided by PGTI to real-time dose distributions, in order to enable the use of this technique for adaptive dosimetry. PGTI will be also explored as a potential approach to proton tomography. If this project is successful, it will allow, for the first time, to control the uncertainties affecting both treatment planning and treatment delivery with a unique device. PGTI may be the missing step towards the birth of image-guided particle therapy.
