Quality assurance method for monitoring of lateral pencil beam positions in scanned carbon‐ion radiotherapy using tracking of secondary ions

Purpose Ion beam radiotherapy offers enhances dose conformity to the tumor volume while better sparing healthy tissue compared conventional photon radiotherapy. However, increased gradient also makes it more sensitive uncertainties. While most important uncertainty source is patient itself, delivery subject Most of proton therapy centers used cyclotrons, which deliver typically a stable over time, allowing continuous extraction beam. Carbon-ion (CIRT) in contrast uses synchrotrons and requires larger energy-dependent extrapolation nozzle-measured positions obtain lateral isocenter, since nozzle-to-isocenter distance than for cyclotrons. Hence, control pencil at isocenter CIRT uncertainties Therefore, an independent monitoring actual close would be very valuable provide additional information. techniques capable do so are scarce, they limited precision, accuracy effectivity. Methods The detection secondary ions (charged nuclear fragments) has previously been exploited Bragg peak position C-ion beams. In our previous work, we investigated first time feasibility beams CIRT. reported precision were not sufficient potential implementation into clinical practice. this shown how performance method improved point relevance. To minimize observed uncertainties, mini-tracker based on hybrid silicon pixel detectors was repositioned downstream anthropomorphic head phantom. secondary-ion fluence rate rises up 1.5 × 105 ions/s/cm2, causing strong pile-up signals. solve problem, performed hardware changes, optimized detector settings, adjusted setup geometry developed new algorithms resolve ambiguities track reconstruction. studied two treatment plans delivered with realistic 3 Gy (RBE) averaged 0.27 Gy/s Heidelberg Ion-Beam Therapy Center (HIT) Germany. measured reference obtained either from nozzle or multi-wire proportional chamber positioned room isocenter. Results presented simultaneously monitor both coordinates entire during delivery, using only 2-cm2 mini-tracker. effectivity (defined as fraction analyzed beams) 100%. reached (0.6 1.5) mm (0.5 1.2) line clinically accepted QA measurements positions. Conclusions It demonstrated that non-invasive implementation. next step evaluate group patients future observational study.