Ion-beam radiotherapy is an advanced cancer treatment modality offering steep dose gradients and a high biological effectiveness. These gradients make the therapy vulnerable to patient-setup and anatomical changes between treatment fractions, which may go unnoticed. Charged fragments from nuclear interactions of the ion beam with the patient tissue may carry information about the treatment quality. Currently, the fragments escape the patient undetected. Inter-fractional in-vivo treatment monitoring based on these charged nuclear fragments could make ion-beam therapy safer and more efficient. We developed an ion-beam monitoring system based on 28 hybrid silicon pixel detectors (Timepix3) to measure the distribution of fragment origins in three dimensions. The system design choices as well as the ion-beam monitoring performance measurements are presented in this manuscript. A spatial resolution of 4 mm along the beam axis was achieved for the measurement of individual fragment origins. Beam-range shifts of 1.5 mm were identified in a clinically realistic treatment scenario with an anthropomorphic head phantom. The monitoring system is currently being used in a prospective clinical trial at the Heidelberg Ion Beam Therapy Centre for head-and-neck as well as central nervous system cancer patients.

ADVACAM s r o Prague Czech Republic

Clinical Cooperation Unit Radiation Oncology German Cancer Research Centre Heidelberg Germany

Department of Physics and Astronomy Heidelberg University Heidelberg Germany

Department of Radiation Oncology Heidelberg University Hospital Heidelberg Germany

Division of Medical Physics in Radiation Oncology German Cancer Research Centre Heidelberg Germany

Heidelberg Institute for Radiation Oncology Heidelberg Germany

Heidelberg Ion Beam Therapy Centre Department of Radiation Oncology Heidelberg University Hospital Heidelberg Germany

National Center for Tumor Diseases NCT Heidelberg A Partnership Between DKFZ and University Medical Center Heidelberg Heidelberg Germany

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