Range verification in heavy-ion therapy using a hadron tumour marker

Objective. Anew method to estimate the range of an ion beam in a patient during heavy-ion therapy was investigated, which was previously verified for application in proton therapy. Approach. The method consists of placing a hadron tumour marker (HTM) close to the tumour. As the treatment beam impinges on the HTM, the marker undergoes nuclear reactions. When theHTMmaterial is carefully chosen, the activation results in the emission of several delayed, characteristic gamma rays, whose intensities are correlated with the remaining range inside the patient. When not just one but two reaction channels are investigated, the ratio between these two gamma ray emissions can be measured, and the ratio is independent of any beam delivery uncertainties. Main results. A proof-of-principle experiment with an 16Oion beam and Ag foils asHTMwas successfully executed. The Ag-107(O-16, (x))Sb-112 and the Ag-107(O-16, x)(114) Sb reaction channels were identified as suitable for theHTM technique. When only one gamma-ray emission is measured, the resulting range-uncertainty estimation is at the 0.5mmscale. When both channels are considered, a theoretical limit on the range uncertainty of a clinical fiducal marker was found to be +/- 290 mu m. Significance. Range uncertainty of a heavy-ion beam limits the prescribed treatment plan for cancer patients, especially the direction of the ion beam in relation to any organ at risk. An easy to implement range-verification technique which can be utilized during clinical treatment would allow treatment plans to take full advantage of the sharp falloff of the Bragg peak without the risk of depositing excessive dose into healthy tissue.