Peripheral organ equivalent dose estimation procedure in proton therapy

The aim of this work is to present a reproducible methodology for the evaluation of total equivalent doses in organs during proton therapy facilities. The methodology is based on measuring the dose equivalent in representative locations inside an anthropomorphic phantom where photon and neutron dosimeters were inserted. The Monte Carlo simulation was needed for obtaining neutron energy distribution inside the phantom. The methodology was implemented for a head irradiation case in the passive proton beam of iThemba Labs (South Africa). Thermoluminescent dosimeter (TLD)-600 and TLD-700 pairs were used as dosimeters inside the phantom and GEANT code for simulations. In addition, Bonner sphere spectrometry was performed inside the treatment room to obtain the neutron spectra, some relevant neutron dosimetric quantities per treatment Gy, and a percentual distribution of neutron fluence and ambient dose equivalent in four energy groups, at two locations. The neutron spectrum at one of those locations was also simulated so that a reasonable agreement between simulation and measurement allowed a validation of the simulation. Results showed that the total out-of-field dose equivalent inside the phantom ranged from 1.4 to 0.28 mSv/Gy, mainly due to the neutron contribution and with a small contribution from photons, 10% on average. The order of magnitude of the equivalent dose in organs was similar, displaying a slow reduction in values as the organ is farther from the target volume. These values were in agreement with those found by other authors in other passive beam facilities under similar irradiation and measurement conditions

Assembly, apparatus, system and method (PRaVDA strip detector)

Some embodiments of the present invention provide a 2D position-sensitive detector assembly comprising at least three substantially planar detector portions arranged in overlapping relationship as viewed normal to a plane of the detector portions, each detector portion comprising an array of substantially parallel, linear detector elements, the detector elements of respective detector portions being mutually non-parallel, the detector elements each being configured to generate one or more electrical signals in response to interaction of a particle of radiation therewith

Assembly, apparatus, system and method (PRaVDA range telescope)

Some embodiments of the present invention provide apparatus for detecting particles of radiation comprising: a plurality of solid state semiconductor detector devices provided at spaced apart locations along a beam axis, the detector devices each being configured to generate an electrical signal indicative of passage of a particle through or absorption of a particle by the device; and at least one absorber portion configured to absorb at least a portion of an energy of a particle, wherein one said at least one absorber portion is provided in a particle path between at least one pair of adjacent detector devices, the apparatus being configured to provide an output signal indicative of the energy of a particle, the output signal provided being dependent on the electrical signals indicative of passage of a particle through or absorption of a particle by the devices

PRaVDA: The First Solid-State System for Proton Computed Tomography

Proton CT is widely recognised as a beneficial alternative to con- ventional X-ray CT for treatment planning in proton beam radiotherapy. A novel proton CT imaging system, based entirely on solid-state detec- tor technology, is presented. Compared to conventional scintillator-based calorimeters, positional sensitive detectors allow for multiple protons to be tracked per read out cycle, leading to a potential reduction in proton CT scan time. Design and characterisation of its components are discussed. An early proton CT image obtained with a fully solid-state imaging sys- tem is shown and accuracy (as defined in Section IV) in Relative Stopping Power to water (RSP) quantified. A solid-state imaging system for proton CT, based on silicon strip detectors, has been developed by the PRaVDA collaboration. The sys- tem comprises a tracking system that infers individual proton trajecto- ries through an imaging phantom, and a Range Telescope (RT) which records the corresponding residual energy (range) for each proton. A back-projection-then-filtering algorithm is used for CT reconstruction of an experimentally acquired proton CT scan. An initial experimental result for proton CT imaging with a fully solid-state system is shown for an imaging phantom, namely a 75 mm diameter PMMA sphere containing tissue substitute inserts,imaged with a passively-scattered 125 MeV beam. Accuracy in RSP is measured to be ≤1.6% for all the inserts shown. A fully solid-state imaging system for proton CT has been shown capable of imaging a phantom with protons and successfully improving RSP accuracy. These promising results, together with system the capabil- ity to cope with high proton fluences (2×108 protons/s), suggests that this research platform could improve current standards in treatment planning for proton beam radiotherapy

Peripheral Organ Equivalent Dose Estimation Procedure in Proton Therapy

The aim of this work is to present a reproducible methodology for the evaluation of total equivalent doses in organs during proton therapy facilities. The methodology is based on measuring the dose equivalent in representative locations inside an anthropomorphic phantom where photon and neutron dosimeters were inserted. The Monte Carlo simulation was needed for obtaining neutron energy distribution inside the phantom. The methodology was implemented for a head irradiation case in the passive proton beam of iThemba Labs (South Africa). Thermoluminescent dosimeter (TLD)-600 and TLD-700 pairs were used as dosimeters inside the phantom and GEANT code for simulations. In addition, Bonner sphere spectrometry was performed inside the treatment room to obtain the neutron spectra, some relevant neutron dosimetric quantities per treatment Gy, and a percentual distribution of neutron fluence and ambient dose equivalent in four energy groups, at two locations. The neutron spectrum at one of those locations was also simulated so that a reasonable agreement between simulation and measurement allowed a validation of the simulation. Results showed that the total out-of-field dose equivalent inside the phantom ranged from 1.4 to 0.28 mSv/Gy, mainly due to the neutron contribution and with a small contribution from photons, 10% on average. The order of magnitude of the equivalent dose in organs was similar, displaying a slow reduction in values as the organ is farther from the target volume. These values were in agreement with those found by other authors in other passive beam facilities under similar irradiation and measurement conditions

The Impact of Dose Rate on DNA Double-Strand Break Formation and Repair in Human Lymphocytes Exposed to Fast Neutron Irradiation

The lack of information on how biological systems respond to low-dose and low dose-rate exposures makes it difficult to accurately assess the carcinogenic risks. This is of critical importance to space radiation, which remains a serious concern for long-term manned space exploration. In this study, the γ-H2AX foci assay was used to follow DNA double-strand break (DSB) induction and repair following exposure to neutron irradiation, which is produced as secondary radiation in the space environment. Human lymphocytes were exposed to high dose-rate (HDR: 0.400 Gy/min) and low dose-rate (LDR: 0.015 Gy/min) p(66)/Be(40) neutrons. DNA DSB induction was investigated 30 min post exposure to neutron doses ranging from 0.125 to 2 Gy. Repair kinetics was studied at different time points after a 1 Gy neutron dose. Our results indicated that γ-H2AX foci formation was 40% higher at HDR exposure compared to LDR exposure. The maximum γ-H2AX foci levels decreased gradually to 1.65 ± 0.64 foci/cell (LDR) and 1.29 ± 0.45 (HDR) at 24 h postirradiation, remaining significantly higher than background levels. This illustrates a significant effect of dose rate on neutron-induced DNA damage. While no significant difference was observed in residual DNA damage after 24 h, the DSB repair half-life of LDR exposure was slower than that of HDR exposure. The results give a first indication that the dose rate should be taken into account for cancer risk estimations related to neutrons

Peripheral organ equivalent dose estimation procedure in proton therapy

The aim of this work is to present a reproducible methodology for the evaluation of total equivalent doses in organs during proton therapy facilities. The methodology is based on measuring the dose equivalent in representative locations inside an anthropomorphic phantom where photon and neutron dosimeters were inserted. The Monte Carlo simulation was needed for obtaining neutron energy distribution inside the phantom. The methodology was implemented for a head irradiation case in the passive proton beam of iThemba Labs (South Africa). Thermoluminescent dosimeter (TLD)-600 and TLD-700 pairs were used as dosimeters inside the phantom and GEANT code for simulations. In addition, Bonner sphere spectrometry was performed inside the treatment room to obtain the neutron spectra, some relevant neutron dosimetric quantities per treatment Gy, and a percentual distribution of neutron fluence and ambient dose equivalent in four energy groups, at two locations. The neutron spectrum at one of those locations was also simulated so that a reasonable agreement between simulation and measurement allowed a validation of the simulation. Results showed that the total out-of-field dose equivalent inside the phantom ranged from 1.4 to 0.28 mSv/Gy, mainly due to the neutron contribution and with a small contribution from photons, 10% on average. The order of magnitude of the equivalent dose in organs was similar, displaying a slow reduction in values as the organ is farther from the target volume. These values were in agreement with those found by other authors in other passive beam facilities under similar irradiation and measurement conditions

Monte Carlo simulations for imaging in proton therapy

Proton therapy is rapidly gaining importance in the field of radiotherapy, because of its potential to deliver the planned dose over a small depth range and sparing dose to healthy tissue, when compared to conventional radiotherapy. Proton therapy, however, makes the need of new imaging modalities for treatment planning, based on direct measurements of tissue stopping power and eliminating the need to convert tissue density – as measured in conventional X-ray Computed Tomography) – to stopping power, upon which treatment planning is based [1] . The expected benefits of proton CT (pCT) for treatment planning in Proton Radiotherapy are producing great interest worldwide to develop instruments for clinical-quality pCT. The PRaVDA (Proton Radiotherapy Verifications and Dosimetry Applications) consortium has developed a novel purely solid state system and associated image reconstruction for pCT [2,3] . Custom detectors for the PRaVDA instrument include Silicon Strip Detectors (SSD) and Monolithic Active Pixel Sensors (MAPS). To assist design decisions, detector development and development of image reconstruction algorithms, comprehensive Geant4-based Monte Carlo simulations were developed, comprising realistic beam-line sources for two proton sources where the PRaVDA instrument has been tested (MC40 cyclotron at the University of Birmingham and iThemba LABS cyclotron), full device geometry and realistic readout for both SSDs and MAPSs. The full paper will focus on simulations of MAPS for imaging in proton therapy. The full read-out chains of a MAPS – including charge diffusion, collection, sharing and digitalization, has been simulated through the development of ad hoc classes integrated in the standard Geant4 toolkit. An experimental validation of the model (at two different proton sources) will be provided and the contribution of these simulations to assess imaging capabilities of MAPS, in the context of proton therapy, will be highlighted

DNA damage response of haematopoietic stem and progenitor cells to high-LET neutron irradiation

The radiosensitivity of haematopoietic stem and progenitor cells (HSPCs) to neutron radiation remains largely underexplored, notwithstanding their potential role as target cells for radiation-induced leukemogenesis. New insights are required for radiation protection purposes, particularly for aviation, space missions, nuclear accidents and even particle therapy. In this study, HSPCs (CD34(+)CD38(+) cells) were isolated from umbilical cord blood and irradiated with Co-60 gamma-rays (photons) and high energy p(66)/Be(40) neutrons. At 2 h post-irradiation, a significantly higher number of 1.28 +/- 0.12 gamma-H2AX foci/cell was observed after 0.5 Gy neutrons compared to 0.84 +/- 0.14 foci/cell for photons, but this decreased to similar levels for both radiation qualities after 18 h. However, a significant difference in late apoptosis was observed with Annexin-V+/PI+ assay between photon and neutron irradiation at 18 h, 43.17 +/- 6.10% versus 55.55 +/- 4.87%, respectively. A significant increase in MN frequency was observed after both 0.5 and 1 Gy neutron irradiation compared to photons illustrating higher levels of neutron-induced cytogenetic damage, while there was no difference in the nuclear division index between both radiation qualities. The results point towards a higher induction of DNA damage after neutron irradiation in HSPCs followed by error-prone DNA repair, which contributes to genomic instability and a higher risk of leukemogenesis