Management of organ motion in scanned ion beam therapy

Abstract

Scanned ion beam therapy has special demands for treatment of intra-fractionally moving tumors such as lesions in lung or liver. Interplay effects between beam and organ motion can in those settings lead to under-dosage of the target volume. Dedicated treatment techniques such as gating or abdominal compression are required. In addition 4D treatment planning should be used to determine strategies for patient specific treatment planning such as an increased beam focus or the use of internal target volumes incorporating range changes.Several work packages of the Clinical Research Units 214 and 214/2 funded by the German Research Council investigated the management of organ motion in scanned ion beam therapy. A focus was laid on 4D treatment planning using TRiP4D and the development of motion mitigation strategies including their quality assurance. This review focuses on the activity in the second funding period covering adaptive treatment planning strategies, 4D treatment plan optimization, and the application of motion management in pre-clinical research on radiation therapy of cardiac arrhythmias.

A single ion discriminator ASIC prototype for particle therapy applications

“…However, their sensitivity is limited to O(10 3 ) protons [19], while the charge collection time can be as large as hundreds of µs. These drawbacks prevent their use in emerging new dose delivery modalities aiming to mitigate uncertainties due to organ motion [7], like volumetric rescanning and line scanning [6], where faster beam movements and small doses need to be accurately monitored.…”

“…. Charge sensitive amplifier (1), low-pass filter (2), leading edge discriminator (3,4), single ended to differential converter (5), current mode logic driver (6), pulser (7), recovery (8), inverters for signal shaping ( 9), test pulse circuit (10).…”

“…Indeed, the sensitivity of ionization chambers (ICs), the state-of-the-art beam monitors in charged particle therapy, limits the minimum number of particles that can be safely delivered to the order of thousands per spot, while their slow collection time (hundreds of microseconds) precludes the use of ICs on fast beam delivery strategies like, for example, volumetric rescanning and line scanning [6] to mitigate interplay effects between beam and organ motion [7]. To overcome these drawbacks, the project aims at exploring the use of thin silicon sensors (50 µm) based on the Low Gain Avalanche Diode (LGAD) design [8] with an internal gain of 10-15, achieved through a thin p+ layer implanted just beneath the n++ electrode.…”

Extension of RBE-weighted 4D particle dose calculation for non-periodic motion

“…For the purpose of treatment planning, the motion was assumed to be periodic. The motion used during treatment planning was split into ten phases of equal length with a mean displacement corresponding to the simulated CTs 7,8,11,15,19,19,15,11,8 and 7. This corresponds to a maximum tumor displacement of 9.83 mm in cranio-caudal direction, − 3.82 mm in antero-posterior direction and − 0.18 mm in left-right direction. The union of the tumor contours in these 10 states was defined as the ITV.…”

“…Tumors in the thorax and abdomen are strongly affected by respiratory motion and its variability [6,7]. Therefore, treatment methods have been developed in attempt to handle tumor motion during radiotherapy including gating, ITVs, rescanning, tumor tracking [3,8] and 4D optimization [9], as well as robust optimization [10][11][12].…”