PGTI · Prompt Gamma Time Imaging: a new medical-imaging modality for adaptive Particle Therapy

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, I propose a new medical-imaging modality to monitor PT treatments in real-time. It exploits the signal of secondary prompt gamma-rays emitted from nuclear interactions in the patients to recover information on ion range, tissue density and dose. I refer to this technique as Prompt Gamma Time Imaging (PGTI). An original reconstruction algorithm and a dedicated detector will be developed to prove the clinical advantages of PGTI, and bring this technique at the doorsteps of its clinical application. I will develop models 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. For the first time, it would be possible 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.