A novel algorithm for the calculation of physical and biological irradiation quantities in scanned ion beam therapy: the beamlet superposition approach

Abstract

The calculation algorithm of a modern treatment planning system for ion-beam radiotherapy should ideally be able to deal with different ion species (e.g. protons and carbon ions), to provide relative biological effectiveness (RBE) evaluations and to describe different beam lines. In this work we propose a new approach for ion irradiation outcomes computations, the beamlet superposition (BS) model, which satisfies these requirements. This model applies and extends the concepts of previous fluence-weighted pencil-beam algorithms to quantities of radiobiological interest other than dose, i.e. RBE- and LET-related quantities. It describes an ion beam through a beam-line specific, weighted superposition of universal beamlets. The universal physical and radiobiological irradiation effect of the beamlets on a representative set of water-like tissues is evaluated once, coupling the per-track information derived from FLUKA Monte Carlo simulations with the radiobiological effectiveness provided by the microdosimetric kinetic model and the local effect model. Thanks to an extension of the superposition concept, the beamlet irradiation action superposition is applicable for the evaluation of dose, RBE and LET distributions. The weight function for the beamlets superposition is derived from the beam phase space density at the patient entrance. A general beam model commissioning procedure is proposed, which has successfully been tested on the CNAO beam line. The BS model provides the evaluation of different irradiation quantities for different ions, the adaptability permitted by weight functions and the evaluation speed of analitical approaches. Benchmarking plans in simple geometries and clinical plans are shown to demonstrate the model capabilities.

Accuracy assessment of the CNAO dose delivery system in the initial period of clinical activity and impact of later improvements on delivered dose distributions

“…Secondly, these quantities have been used to create two 3D physical dose maps, one for the prescription and one for measured data, by using a validated dose computation software. 12 The correspondence of the two dose distributions has been evaluated with the gamma-index method using a 2 mm grid spacing with 0.2 mm resolution, 2 mm distance-toagreement (DTA) and 2% dose difference. 13 The analysis of the maximum gamma value and of the percentage of points with gamma ≤ 1 (passing volume, in the following) was performed as a function of the day of the treatment.…”

“…To evaluate the impact on dose distributions of deviations between prescribed and measured quantities, TPS reference values and corresponding values measured by monitor chambers were used as input of a validated dose calculation tool. 12 The correspondence between the 3D dose maps has been quantified by means of the gamma-index criterion, 13 and the results have been reported for one representative patient treated with protons. Finally, to study the effect on delivery quality of the implementation of a feedback algorithm for the correction of small position deviations, delivered dose distributions of the same treatment plans before and after feedback implementation have been compared.…”

Control Of The Dose Distribution In Charged Particle Therapy

“…It exploits the duty cycle of the CNAO synchrotron, which has a spill of 1 second and a dead time of 3-4 seconds during which RIDOS is able to evaluate a fast forward planning and a fast gamma index [33] to compare the actual delivered dose with the original planning. This is made by a deep exploitation of the graphic processing unit (GPU) calculation, which allows, in our case, to gain a factor 800 with respect to the existing single core CPU calculation [34]. Moreover, RIDOS is also able to manage the patient 4D-CT together with the information of the real-time respiratory phase, in order to account for intra-fraction target deformation.…”

Feasibility study of a plastic scintillating plate‐based treatment beam fluence monitoring system for use in pencil beam scanning proton therapy

“…These studies showed that scintillator‐based dosimetry systems offered a fast response and could be used as high‐resolution dosimeter tools if the quenching effects were corrected. A commercially available scintillator‐based dosimeter tool, Lynx (IBA Dosimetry, Louvain‐la‐Neuve, Belgium), has been used in proton beam measurements . The Lynx detector is suitable for 2D relative dosimetry in ion beams with short‐term stability, dose linearity, and good image quality.…”

“…A commercially available scintillator-based dosimeter tool, Lynx (IBA Dosimetry, Louvain-la-Neuve, Belgium), has been used in proton beam measurements. [31][32][33] The Lynx detector is suitable for 2D relative dosimetry in ion beams with short-term stability, dose linearity, and good image quality. Although these detectors are suitable for ordinary proton QA, they cannot be used to monitor patient treatment because they are too bulky to place between the patient and the nozzle.…”