Particle Therapy is a technique for radioresistant tumors performed with protons or light ions, aiming to deliver a high precision treatment. Compared to conventional radiotherapy, ions allow for a higher dose deposition in the tumor region while sparing the surrounding healthy tissue.
In this field, Monte Carlo (MC) simulations are the most accurate tool for reproducing the dose deposition. Standard MC calculations are not routinely used in clinical practice because they typically demand substantial computational resources and they are usually only used to check treatment plans for a restricted number of difficult cases.
The code FRED (Fast paRticle thErapy Dose evaluator) has been developed to allow a fast optimization of the treatment plans of particle therapy while profiting from the dose release accuracy of a MC tool. Within FRED, the proton and ion interactions are described with the precision level available in leading edge MC tools used for medical physics applications, with the advantage of reducing the simulation time up to a factor 1000.
Presently electrons are not transported in the code. A necessary improvement is to introduce the most important interaction processes of electrons with human tissue. This will allow accurate dose prediction in high density-gradient regions were the transport of secondary electrons (delta rays) is expected to be significant.
We intend to also model electron beams (up to 10 MeV) which are used in Intra-Operative Radiation Therapy (IORT). In this energy range, also production of high energy photons is expected. Aim of the project is to include the most relevant photon interactions, e.g. photoelectric effect, Compton scattering and pair production.
The project will significantly improve the capabilities of the Fred code, opening up the possibility to use it at the clinical level for lung and pelvis treatments in particle therapy. It will also allow the investigation of MeV electron beam treatments for the IORT.
The novel strategy of fast MC tools is to implement only the most relevant interaction models needed for an accurate dose recalculation. Presently just a few projects worldwide have taken this long route, rewriting from scratch a MC transport code running on GPU hardware.
At the moment, Fred is one of the fastest and most accurate dose engines available to the scientific community. The most refined model is that of proton beam transport, which allows to use Fred as a third party dose calculator for quality assurance protocols in proton treatment centres.
Head and neck plans can be also reproduced with accuracy using Fred, but lung irradiation or pelvis treatment require the transport of secondary electrons (delta rays). Once this feature will be introduced in the code, treatment centres collaborating with our research group could use Fred to also check patient plans for the most complex and difficult cases. This procedure is rarely followed presently due to the high-computational cost and to the long times needed to obtain a recalculation by a standard MC code. The use of Fred as a fast recalculation tool will give the possibility to routinely check TPS plans against MC recalculation, helping the medical physicists in optimizing their treatment planning strategy.