Innovative radio guided surgery of brain tumors exploiting β- decays

• Elena Solfaroli (Istituto Italiano di Tecnologia)

Room: Aula Conversi The radio-guided surgery (RGS) represents a significant surgical adjunct to intraoperatively detect millimetric tumor residues by administering to the patient a radio-marked tracer that is preferentially taken up by the tumor. It is crucial for those tumors where the surgical mass removal is the only possible therapy. The main innovation of the RGS exploiting β- emitters is the higher tumor to non-tumor activity ratio (TNR) compared to the established techniques using γ radiation. The reduced penetration power of electrons allows the extension of the technique to clinical cases that would be otherwise prevented by the presence of nearby healthy organs taking up the tracer, as for abdominal and brain tumors and in case of pediatric neoplastic disease. The lower background rate is also correlated to both a smaller radiopharmaceutical activity to be administered to the patient to detect cancerous remnants and a lower exposure for the medical team. To test the feasibility of the β- RGS technique on brain tumors, we created a collaboration that joins together experimental particle physicists, electronic and bio- engineers, nuclear medicine physicians, oncologists and neurosurgeons, covering a wide range of specializations. Such collaboration has identified as first clinical case of interest the meningioma brain tumors because of their sensitivity to DOTATOC, well documented in literature, that can be marked with 90Y and the relatively large number of cases, but the goal is to apply the technique to gliomas. We developed prototypes of the intraoperative β- detecting probe with millimetric scintillator core made of para-terphenyl, adopted due to its high light yield and low density. Pre-clinical tests showed that with a radiotracer activity on the tumor of 5 kBq/ml and a TNR of 10 a 0.1 ml cancerous residual can be detected in 1s. From these measurements we extrapolated with a detailed simulation the expected exposure of the surgeon, resulted in ~0.1 μSv/h on the whole body, ~1 μSv/h on the hands, well below the corresponding values for established RGS with gamma radiation (99mTc).

New on line methods to monitor dose profiling in particle therapy treatments

• Michela Marafini (Centro Fermi)

Room: Aula Conversi ParticleTherapy (PT) uses accelerated charged ions for cancer treatment. The high irradiation precision and conformity achievable with heavy ions, enhance the Radio Biological Effectiveness (RBE) of such therapy while helping sparing the surrounding healthy tissues and Organs At Risk (OAR). To fully profit from the improved therapy spatial selectiveness, a novel monitoring technique, capable of providing a high precision in-treatment feedback on the dose release position, is required. We propose a novel approach based on the simultaneous detection of secondary protons and prompt photons that are emitted at large angles and are correlated with the Bragg Peak position and the related dose release. We will review the measured flux and energy spectra for secondary particles produced by 12C, 4He and 16O ion beams of therapeutical energies impinging on PMMA phantoms. Such measurements shows that the rate of produced particles is large enough to supply the sample needed for online monitor operating providing the required O(mm) spatial resolution. The novel dual mode PT monitor, named DoseProfiler, will be presented. The DoseProfiler, whose final layout has been optimized using a dedicated MonteCarlo simulation based on the aforementioned experimental results, combines a tracker detector made of scintillating fibers and a calorimeter built with pixelated LYSO crystals. Six tracker layers (x-y planes) of squared scintillating fibers, will provide the particle direction information, while the crystals will measure the particle energy.