KEY POINTS
- The investigators treated a mouse osteosarcoma model using therapeutic carbon-11 radioactive ion beams monitored with the SIRMIO in-beam positron emission tomography scanner.
- Three penetration depths were tested: a short range stopping before complete tumour coverage, an optimal “Goldilocks” range covering the tumour while sparing normal tissue and a long range traversing the tumour and adjacent structures.
- A collimated 5 Gy monoenergetic probing beam was used before treatment. Positron emission tomography images were generated approximately every 25 seconds to identify the beam range.
- Beam penetration was adjusted during the same irradiation session using a remotely controlled range shifter. The maximum depth discrepancy between probing and treatment configurations was 0.40 mm.
- After range verification, a 20 Gy spread-out Bragg peak treatment was delivered to the planned volume.
- Optimal-range and long-range irradiation controlled tumour growth, whereas short-range irradiation resulted in continued tumour growth from insufficient target coverage.
- Treatment-related toxicity occurred only in the long-range group, directly linking excessive beam penetration with normal-tissue injury.
CLINICAL TAKEAWAY
This is the first demonstration that radioactive ion beam imaging can guide range correction during irradiation in a living organism. Clinical translation will require human-scale beam production, imaging hardware, automated decision rules and rigorous validation of the additional probing dose and adaptation workflow.