Beamlines for Medical Applications

Cancer is a critical societal issue. Worldwide, in 2018 alone, 18.1 million cases were diagnosed, 9.6 million people died and 43.8 million people were living with cancer. Current projections anticipate an increase with approximatively 24,6 million newly diagnosed patients and 13 million related deaths by 2030.
RT is now a fundamental component of effective cancer treatment and control. The most frequently used modality of RT uses high-energy (6 to 10 MeV) photon, and in a small proportion low to intermediate energy (3 to 25 MeV) electron beams. The main challenge of RT is that the dose delivered to a tumour is limited by the dose that can be tolerated by the surrounding normal tissues. A most interesting and unexplored possibility is the use of RT with higher energy electrons ( VHEE, 50-250 MeV) which recently has gained interest. The main advantages of VHEE beams over photons are related to the fact that 1) small diameter VHEE beams can be scanned and focused easily, thereby producing finer resolution for intensity modulated treatments than photon beams. 2) VHEE beams operate at very high dose rate possibly compatible with the generation of the "FLASH effect" (i.e. to elicit normal tissue sparing). With the help of the more recent developments of the electron linear accelerator technology, the high current electron beams can be accelerated to the energies of 100s of MeV with the accelerating structures of just several meters of length. This allows the development of very high-energy electron (VHEE) irradiation facilities at the size of conventional facilities for proton therapy, with even lower cost of construction and operation. Several fundamental challenges remain in regards to the implementation of VHEE beams for cancer treatment. Firstly, the precision of the treatment planning systems for the VHEE beams is very limited. The demand for those systems is high in the RT community, and the reliable database for interaction cross-sections with different tissue types are necessary. Secondly, the dose distribution in the patient tissue is a crucial aspect. The dose needs to be homogenously distributed within the tumour (with a typical dose requirement of about 60 Gy) and to remain as low as possible outside of the tumour tissue. Thirdly, there are strict requirements on the speed and precision of the beam intensity measurement for the use in RT. The student would study the production of the secondary particles (in particular neutrons) generated by the electron beams and propagating into the direction of the patient. These values will need to be compared with the corresponding values for the proton and ion therapy, assuming the same overall dose. This is a challenging goal, given that the photonuclear processes have very low cross sections and are not included in some simulation codes. The study can be extended to make recommendations on the radiation protection guidelines and shielding requirements for the future VHEE facilities.
The student is also to examine the dose deposition in the patient tissue and the options to influence it. Different techniques for the dose optimization, including beam collimation, scanning and beam shape modification with help of a compensator or other methods, need to be evaluated. Finally, student would examine the options for the reliable and quick beam diagnostics available for VHEE treatments, in particular in regards to beam intensity measurement and dose verification. Novelty of the research methodology RT with VHEE is a new topic with very little experimental data for deep tissue dose deposition. CERN would contribute with its expertise of high gradient accelerators, in particular based on CLIC technology. CERN would also contribute with its expertise in beam-matter interaction, with CERN STI group managing the largest and extremely well calibrated database of beam interaction cross sections. CERN has also expertise on beam diagnostics for the high-energy electron beams.