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).
