Dosimetric precision of an ion beam tracking system

Abstract

Background: Scanned ion beam therapy of intra-fractionally moving tumors requires motion mitigation. GSI proposed beam tracking and performed several experimental studies to analyse the dosimetric precision of the system for scanned carbon beams. Methods:A beam tracking system has been developed and integrated in the scanned carbon ion beam therapy unit at GSI. The system adapts pencil beam positions and beam energy according to target motion.Motion compensation performance of the beam tracking system was assessed by measurements with radiographic films, a range telescope, a 3D array of 24 ionization chambers, and cell samples for biological dosimetry. Measurements were performed for stationary detectors and moving detectors using the beam tracking system. Results:All detector systems showed comparable data for a moving setup when using beam tracking and the corresponding stationary setup. Within the target volume the mean relative differences of ionization chamber measurements were 0.3% (1.5% standard deviation, 3.7% maximum). Film responses demonstrated preserved lateral dose gradients. Measurements with the range telescope showed agreement of Bragg peak depth under motion induced range variations. Cell survival experiments showed a mean relative difference of -5% (-3%) between measurements and calculations within the target volume for beam tracking (stationary) measurements. Conclusions:The beam tracking system has been successfully integrated. Full functionality has been validated dosimetrically in experiments with several detector types including biological cell systems.

Comparison of photon volumetric modulated arc therapy, intensity-modulated proton therapy, and intensity-modulated carbon ion therapy for delivery of hypo-fractionated thoracic radiotherapy

“…Although active tumor tracking may lead to the smallest high dose volume, this approach places a high demand on scanning speed, which must allow for rapid alteration of beam energy to adjust the Bragg peak in depth in relation to tumor motion [ 43 ]. This longitudinal compensation may be achieved through the use of wedges [ 44 , 45 ]. However, tumor tracking remains an area of active research in thoracic particle therapy.…”

Advances in 4D Treatment Planning for Scanned Particle Beam Therapy — Report of Dedicated Workshops

“…Previous studies concentrated on simple phantom geometries and had the goal of feasibility checks since the application and therapy control needs are challenging. With respect to system performance ( 98 ) but also dosimetrically ( 49 , 99 , 100 ), beam tracking works precisely. In case of non-translational motion, e.g., rotations, adjustment of the pencil beam position is insufficient since the pre-irradiation mainly of proximal parts of the target by distal iso-energy layers changes.…”

Particle therapy for noncancer diseases

“…2 for a lung tumor. 99 Motion monitoring could either be achieved by one of the established motion detection systems (e.g., ANZAI belt, VARIAN RPM, and Cyberknife Synchrony correlation model) but kidney motion is also detectable via ultrasound, 97 which would provide internal motion rather than a surrogate. NIRS in Japan performs treatment of renal cell carcinoma with a passively scattered carbon beam since 1997.…”