The particle therapy (PT) is a technique for cancer treatment that exploits hadron beams, mostly protons and carbon ions. The characteristic profile of the energy deposition along the beam track, with the peculiar maximum at the end of the range (Bragg Peak) that is moved inside the patient with the increase of the beam energy, allows this techique to precisely deposit the dose on the tumor volume and to spare the surrounding healthy tissue. Due to this spatial selectivity in dose deposition, a critical issue is the monitoring of the beam range so to check the correct dose delivery to the tumor and surrounding tissues. The information needed to use the correct patterns of beam direction, energies and intensities is provided by the planning CT. Possible changes in the beam range are often due to the morphological changes of the patient tissue with respect to the planning imaging along the beam track during the entire treatment time (order of thirty fractions in a two monthes period).
A innovative tracking device, named Dose Profiler (DP) for inter-fractional monitoring in pencil beam carbon ion therapy has been designed and built by our group, and is now in clinical testing phase at the CNAO (Centro Nazionale di Adroterapia Oncologica) center in Pavia. Its scope is to quantitatively molitor the inter-fractional motion so that a re-planning imaging CT can be done in case of detected changes.
The DP detects and reconstruct the direction of the secondary charged particles (mainly protons) produced by beam interactions in the patient tissue and excaping the patient. The point of closest approach of the tracked protons with the emitting pencil beam provides the emission point of the secondary.
The 3D map of the proton emission points provides the info used to monitor the patient morphology. Different sets of statistical analysis of the 3D mapos coming from subsequent treatments are studied to design a statistical robust method to assess the moment for a re-planning CT
The research project will provide a clinical technique that will increase the quality of the carbon ion treatment of the tumors. During the many fraction of the treatment (thirty, one each two days) the patient may change morphology. The changes can be due to several reason, one among the others, the changing of the tumor size along the treatment. Nowadays there is no standard protocol to take care of these changes, but if not taken into account can completely spoil the accuracy of the dose deposition in the patient. In many cases a new imaging and a new treatment planning should be done to ensure the typical selectivity of the particle therapy after the morphological changes. However the replanning CT will give additive dose to the patient and cannot be repeated blindly after each fraction not only for radioprotection but also to avoid to make the clinical workflow longer.
This research project is embedded in this landscape and aims to quantitative evaluate the internal morphological changes of the patient between irradiation fractions by means of the secondary charged particles produced by the beams inside the patient and escaping from the patient. The main outcome of the project then will allow to safely replan the treatment and to keep the particle therapy therapeutic efficiency.