Purpose
Radiation therapy with ion beams provides a better conformation and effectiveness of the dose delivered to the tumor with respect to photon beams. This implies that a small uncertainty or ...variation in the crossed tissue shape and density may lead to a more important underdosage of the tumor and/or an overdosage of the surrounding healthy tissue. Although the online control of beam fluence and transverse position is well managed by an appropriate beam delivery system, the online measurement of the longitudinal position of the Bragg peak inside the patient is still an open issue. In this paper we propose a proof‐of‐concept study of a technique that would allow the online verification of the patient thickness along the beam direction, which could permit detecting a subset of possible range error causes, such as morphological variations.
Methods
The nuclei 12C and 4He have the same magnetic rigidity: the two species could be accelerated together in an accelerator and a mixed particle beam delivered to the patient. In the same medium and with the same energy per nucleon, the range of 4He2+ is about three times the 12C6+ one. It is, thus, conceivable to achieve a dual goal with a single mixed beam: carbon, stopping into the tumor, is appointed to cure, while helium, emerging from the patient, to control: by detecting and measuring the residual range and position of He, it would be possible to determine the integrated relative stopping power of the patient and prove that it is the expected one. For the detection of helium particles, a plastic scintillator and an optical sensor are proposed. Being helium ions not available at CNAO, the detection system has been characterized using a proton beam. Nevertheless, since the light emitted by a proton is less than the one produced by a helium ion, the helium signal is expected to be more pronounced than the proton one (for the same number of particles). To predict the magnitude of the light signal measured by the sensor, two Monte Carlo models have been setup and validated by measuring the photons per pixel impinging on the sensor. To deal with the many optical issues and to reliably describe the physical process, some corrections have been included into the models.
Results
The predictions of both the models are in good agreement with the measurements (within the 20% in terms of absolute photons per pixel). The proposed detection system is able to measure the range of a proton beam with sub‐millimetrical precision also in the presence of the background produced by carbon ion fragments and discrepancies in the expected range were detected with a resolution better than 1 mm.
Conclusions
Although many technical issues have still to be addressed for a real implementation in a clinical environment, the preliminary results of this study suggest that a surrogate of real‐time verification of the beam range inside the patient during a treatment with carbon ions is possible by adding a small fraction of helium ions to the primary beam.
Energetic carbon ions are promising projectiles used for cancer radiotherapy. A thorough knowledge of how the energy of these ions is deposited in biological media (mainly composed of liquid water) ...is required. This can be attained by means of detailed computer simulations, both macroscopically (relevant for appropriately delivering the dose) and at the nanoscale (important for determining the inflicted radiobiological damage). The energy lost per unit path length (i.e., the so-called stopping power) of carbon ions is here theoretically calculated within the dielectric formalism from the excitation spectrum of liquid water obtained from two complementary approaches (one relying on an optical-data model and the other exclusively on
calculations). In addition, the energy carried at the nanometre scale by the generated secondary electrons around the ion's path is simulated by means of a detailed Monte Carlo code. For this purpose, we use the ion and electron cross sections calculated by means of state-of-the art approaches suited to take into account the condensed-phase nature of the liquid water target. As a result of these simulations, the radial dose around the ion's path is obtained, as well as the distributions of clustered events in nanometric volumes similar to the dimensions of DNA convolutions, contributing to the biological damage for carbon ions in a wide energy range, covering from the plateau to the maximum of the Bragg peak.
The advent of Graphics Processing Units (GPU) has prompted the development of Monte Carlo (MC) algorithms that can significantly reduce the simulation time with respect to standard MC algorithms ...based on Central Processing Unit (CPU) hardware. The possibility to evaluate a complete treatment plan within minutes, instead of hours, paves the way for many clinical applications where the time-factor is important. FRED (Fast paRticle thErapy Dose evaluator) is a software that exploits the GPU power to recalculate and optimise ion beam treatment plans. The main goal when developing the FRED physics model was to balance accuracy, calculation time and GPU execution guidelines. Nowadays, FRED is already used as a quality assurance tool in Maastricht and Krakow proton clinical centers and as a research tool in several clinical and research centers across Europe. Lately the core software has been updated including a model of carbon ions interactions with matter. The implementation is phenomenological and based on carbon fragmentation data currently available. The model has been tested against the MC FLUKA software, commonly used in particle therapy, and a good agreement was found. In this paper, the new FRED data-driven model for carbon ion fragmentation will be presented together with the validation tests against the FLUKA MC software. The results will be discussed in the context of FRED clinical applications to
C ions treatment planning.
The Superconducting Ion Gantry (SIG) project aims to design, construct, and test a curved superconducting dipole demonstrator magnet for an ion gantry (up to a rigidity of 6.6 Tm). The main ...demonstrator magnet parameters are a dipolar field of 4 T generated into a toroidal aperture with an 80 mm diameter, 1.65 m curvature radius, and 30° angular sector. The project is inserted in the framework of the EuroSIG collaboration among CNAO, CERN, INFN, and MedAustron. Within this collaboration, the main goal of SIG is to perform a feasibility study of winding and assembling cos-<inline-formula><tex-math notation="LaTeX">\theta</tex-math></inline-formula> coils with a small curvature radius. In addition, a parallel program at CERN is dedicated to the study of the indirect cooling problem through the construction of a straight thermal demonstrator magnet sharing the SIG cross-section. The basic idea behind these programs is to check whether the vast experience of the community on superconducting accelerator magnets design can lead to a breakthrough in the gantry magnets domain. This article shows the main elements of the conceptual design of the SIG magnet and reports on the first winding trial performed at the LASA laboratory, in Milan, with a copper dummy cable. Moreover, possible solutions for the winding, curing, and impregnation of highly curved cos<inline-formula><tex-math notation="LaTeX">\theta</tex-math></inline-formula> coils are discussed.
The ion dose deposition in tissues is characterized by a favorable depth dose profile (i.e. Bragg peak) and a small lateral spread. In order to keep these benefits of ions in cancer treatments, a ...very high accuracy is required on the dose deposition (±3%). For given target stoichiometry and geometry, the largest uncertainty on the physical dose deposition is due to the ion nuclear fragmentation. We have performed an experiment at GANIL with a 95
MeV/u
12C beam on thick tissue equivalent PMMA targets (thicknesses: 5, 10, 15, 20 and 25
mm). The main goals of this experiment are to provide experimental fragmentation data for benchmarking the physical models used for treatment planning. Production rates, energy and angular distributions of charged fragments have been measured. The purpose of this paper is to present the results of this experiment.
A typical proton CT (pCT) detector comprises a tracking system, used to measure the proton position before and after the imaged object, and an energy/range detector to measure the residual proton ...range after crossing the object. The Bergen pCT collaboration was established to design and build a prototype pCT scanner with a high granularity digital tracking calorimeter used as both tracking and energy/range detector. In this work the conceptual design and the layout of the mechanical and electronics implementation, along with Monte Carlo simulations of the new pCT system are reported. The digital tracking calorimeter is a multilayer structure with a lateral aperture of 27 cm × 16.6 cm, made of 41 detector/absorber sandwich layers (calorimeter), with aluminum (3.5 mm) used both as absorber and carrier, and two additional layers used as tracking system (rear trackers) positioned downstream of the imaged object; no tracking upstream the object is included. The rear tracker’s structure only differs from the calorimeter layers for the carrier made of ∼200 μm carbon fleece and carbon paper (carbon-epoxy sandwich), to minimize scattering. Each sensitive layer consists of 108 ALICE pixel detector (ALPIDE) chip sensors (developed for ALICE, CERN) bonded on a polyimide flex and subsequently bonded to a larger flexible printed circuit board. Beam tests tailored to the pCT operation have been performed using high-energetic (50–220 MeV/u) proton and ion beams at the Heidelberg Ion-Beam Therapy Center (HIT) in Germany. These tests proved the ALPIDE response independent of occupancy and proportional to the particle energy deposition, making the distinction of different ion tracks possible. The read-out electronics is able to handle enough data to acquire a single 2D image in few seconds making the system fast enough to be used in a clinical environment. For the reconstructed images in the modeled Monte Carlo simulation, the water equivalent path length error is lower than 2 mm, and the relative stopping power accuracy is better than 0.4%. Thanks to its ability to detect different types of radiation and its specific design, the pCT scanner can be employed for additional online applications during the treatment, such as in-situ proton range verification.
Fluence, depth absorbed dose and linear energy transfer (LET) distributions of proton and carbon ion beams have been investigated using the Monte Carlo code Geant4 (GEometry ANd Tracking). An open ...source application was developed with the aim to simulate two typical transport beam lines, one used for ocular therapy and cell irradiations with protons and the other for cell irradiations with carbon ions. This tool allows evaluation of the primary and total dose averaged LET and predict their spatial distribution in voxelized or sliced geometries. In order to reproduce the LET distributions in a realistic way, and also the secondary particles' contributions due to nuclear interactions were considered in the computations. Pristine and spread-out Bragg peaks were taken into account both for proton and carbon ion beams, with the maximum energy of 62 MeV/n. Depth dose distributions were compared with experimental data, showing good agreement. Primary and total LET distributions were analysed in order to study the influence of contributions of secondary particles in regions at different depths. A non-negligible influence of high-LET components was found in the entrance channel for proton beams, determining the total dose averaged LET by the factor 3 higher than the primary one. A completely different situation was obtained for carbon ions. In this case, secondary particles mainly contributed in the tail that is after the peak. The results showed how the weight of light and heavy secondary ions can considerably influence the computation of LET depth distributions. This has an important role in the interpretation of results coming from radiobiological experiments and, therefore, in hadron treatment planning procedures.
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