The lowest possible energy of proton scanning beam in cyclotron proton therapy facilities is typically between 60 and 100 MeV. Treatment of superficial lesions requires a pre-absorber to deliver ...doses to shallower volumes. In most of the cases a range shifter (RS) is used, but as an alternative solution, a patient-specific 3D printed proton beam compensator (BC) can be applied. A BC enables further reduction of the air gap and consequently reduction of beam scattering. Such pre-absorbers are additional sources of secondary radiation. The aim of this work was the comparison of RS and BC with respect to out-of-field doses for a simulated treatment of superficial paediatric brain tumours. EURADOS WG9 performed comparative measurements of scattered radiation in the Proteus C-235 IBA facility (Cyclotron Centre Bronowice at the Institute of Nuclear Physics, CCB IFJ PAN, Kraków, Poland) using two anthropomorphic phantoms-5 and 10 yr old-for a superficial target in the brain. Both active detectors located inside the therapy room, and passive detectors placed inside the phantoms were used. Measurements were supplemented by Monte Carlo simulation of the radiation transport. For the applied 3D printed pre-absorbers, out-of-field doses from both secondary photons and neutrons were lower than for RS. Measurements with active environmental dosimeters at five positions inside the therapy room indicated that the RS/BC ratio of the out-of-field dose was also higher than one, with a maximum of 1.7. Photon dose inside phantoms leads to higher out-of-field doses for RS than BC to almost all organs with the highest RS/BC ratio 12.5 and 13.2 for breasts for 5 and 10 yr old phantoms, respectively. For organs closest to the isocentre such as the thyroid, neutron doses were lower for BC than RS due to neutrons moderation in the target volume, but for more distant organs like bladder-conversely-lower doses for RS than BC were observed. The use of 3D printed BC as the pre-absorber placed in the near vicinity of patient in the treatment of superficial tumours does not result in the increase of secondary radiation compared to the treatment with RS, placed far from the patient.
Proton therapy is a cancer treatment technique currently in growth since it offers advantages with respect to conventional X-ray and <inline-formula> <tex-math notation="LaTeX">\gamma ...</tex-math></inline-formula>-ray radiotherapy. In particular, better control of the dose deposition allowing to reach higher conformity in the treatments causing less secondary effects. However, in order to take full advantage of its potential, improvements in treatment planning and dose verification are required. A new prototype of proton computed tomography scanner is proposed to design more accurate and precise treatment plans for proton therapy. Our prototype is formed by double-sided silicon strip detectors and scintillators of LaBr 3 (Ce) with high energy resolution and fast response. Here, the results obtained from an experiment performed using a 100-MeV proton beam are presented. Proton radiographs of polymethyl methacrylate (PMMA) samples of 50-mm thickness with spatial patterns in aluminum were taken. Their properties were studied, including reproduction of the dimensions, spatial resolution, and sensitivity to different materials. Structures of up to 2 mm are well resolved and the sensitivity of the system was enough to distinguish the thicknesses of 10 mm of aluminum or PMMA. The spatial resolution of the images was 0.3 line pairs per mm (MTF-10%). This constitutes the first step to validate the device as a proton radiography scanner.
The response of a large-area two-dimensional (2D) thermoluminescence (TL) dosimetry system with 20 × 20 cm2 TL LiF:Mg,Cu,P foils, developed at the Institute of Nuclear Physics PAN was studied for ...doses of therapeutic proton beams with energies of 80 MeV, 150 MeV and 225 MeV. The one-hit detector model fitted to measured dose response yielded characteristic doses of 227 Gy, 209 Gy and 203 Gy respectively. The system was applied to investigate geometrical parameters of spots produced by proton pencil beams at the Bronowice Cyclotron Centre IFJ PAN. Mean spot sizes measured with TL foils were compared with mean spot sizes calculated for Gafchromic® films. It was shown that the 2D TL system was capable to measure the spot size up to peak doses of 20 Gy without additional correction for dose response. For measurements of the spot size using Gafchromic® EBT3 films an additional calibration must be applied to correct for the non-linear response for doses exceeding 1 Gy.
•Three proton energies were considered: 80, 150 and 225 MeV.•Characteristic dose of 227 Gy, 209 Gy and 203 Gy was calculated.•The linear dose response was found up to 20 Gy.•Spot sizes of pencil beam were measured with 2D TL dosimetry system.•The results were compared with Gafchromic EBT3 calculation.
Purpose:
To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors.
Methods:
Working Group 9 of the European Radiation ...Dosimetry Group (EURADOS WG9—Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended‐range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H∗(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs—tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem‐counters (WENDI‐II, LB 6411, RadEye™ NL, a regular and an extended‐range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low‐lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH‐40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm3) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm2 field size.
Results:
Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out‐of‐field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H∗(10) value of ∼51 μSv Gy−1; this was measured at 1.15 m along the beam axis. H∗(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy−1 at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy−1). Finally, the agreement on H∗(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem‐counters (LB 6411, RadEye™ NL, NM2‐458) underestimated the H∗(10) by up to a factor of 4, Hawk TEPCs and the WENDI‐II range‐extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient.
Conclusions:
Extended‐range BSS, TEPCs, and the WENDI‐II enable accurate measurements of stray neutrons while other rem‐counters are not appropriate considering the high‐energy range of neutrons involved in proton therapy.
The European Radiation Dosimetry Group (EURADOS) is a network of organizations and scientists promoting research and development in the dosimetry of ionizing radiation, contributing to harmonization ...in dosimetry practice across Europe, and offering education and training in areas relevant for dosimetry. As a registered non-profit association under German law, EURADOS is currently running eight active working groups (WGs): WG2 on “Harmonization of Individual Monitoring”, WG3 on “Environmental Dosimetry”, WG6 on “Computational Dosimetry”, WG7 on “Internal Dosimetry”, WG9 on “Dosimetry in Radiotherapy”, WG10 on “Retrospective Dosimetry”, WG11 on “Dosimetry in High-Energy Radiation Fields”, and WG12 on “Dosimetry in Medical Imaging”. This paper presents recent scientific results obtained within these working groups, and additionally highlights the role of EURADOS as an organization which contributes to the development of a systematic strategy of radiation protection research in Europe.
A new method of experimental verification of radial dose distribution models using solid state thermoluminescent (TL) detectors LiF:Mg,Cu,P has been recently proposed. In this work the method was ...applied to verify the spatial distribution of energy deposition within a single 131Xe ion track. Detectors were irradiated at the Department of Physics of the University of Jyväskylä, Finland. The obtained results have been compared with theoretical data, calculated according to the Zhang et al., Cucinotta et al. and Geiss et al. radial dose distribution (RDD) models. At the lowest dose range the Zhang et al. RDD model exhibited the best agreement as compared to experimental data. In the intermediate dose range, up to 104 Gy, the best agreement was found for the RDD model of Cucinotta et al. The probability of occurrence of doses higher than 104 Gy within a single 131Xe ion track was found to be lower than predicted by all the studied RDD models. This may be a result of diffusion of the charge, which is then captured by TL-related trapping sites, at the distances up to dozens of nanometers from the ionization site.
•Innovative method of experimental verification of RDD models has been proposed.•The method was tested for 9.3 MeV/n 131Xe ions and three different RDD models.•Up to 104 Gy the analyzed models present good agreement with experimental data.•Probability of occurrence of doses >104 Gy within particle track is relatively low.•Newly proposed method gives results consistent with experimental data within 15%.
Abstract Purpose To measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil ...beam scanning (PBS) technique. Method Measurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100–220 MeV), field sizes ((2 × 2)–(20 × 20) cm2 ) and modulation widths (0–15 cm). Results For pristine proton peak irradiations, large variations of neutron H∗ (10)/ D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H∗ (10)/ D for pristine proton pencil beams varied between 0.04 μSv Gy−1 at beam energy 100 MeV and a (2 × 2) cm2 field at 2.25 m distance and 90° angle with respect to the beam axis, and 72.3 μSv Gy−1 at beam energy 200 MeV and a (20 × 20) cm2 field at 1 m distance along the beam axis. Conclusions The obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters.
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