Particle tracking, recognition and LET evaluation of out-of-field proton therapy delivered to a phantom with implants.

OBJECTIVE: This study aims to assess the composition of scattered particles generated in proton therapy for tumors situated proximal to titanium dental implants. The investigation involves decomposing the mixed field and recording Linear Energy Transfer (LET) spectra to quantify the influence of metallic dental inserts located behind the tumor. Approach: A therapeutic conformal proton beam was used to deliver the treatment plan to an anthropomorphic head phantom with two types of implants inserted in the target volume (made of titanium and plastic, respectively). The scattered radiation resulted during the irradiation was detected by a hybrid semiconductor pixel detector MiniPIX Timepix3 that was placed distal to the Spread-out Bragg peak. Visualization and field decomposition of stray radiation were generated using algorithms trained in particle recognition based on artificial intelligence convolution neural networks (AI CNN). Spectral sensitive aspects of the scattered radiation were collected using two angular positions of the detector relative to the beam direction: 0° and 60°. Results: Using AI CNN, 3 classes of particles were identified: protons, electrons & photons, and ions & fast neutrons. Placing a Titanium implant in the beam's path resulted in predominantly electrons and photons, contributing 52.2%, whereas for plastic implants, the contribution was 65.4%. Scattered protons comprised 45.5% and 31.9% with and without metal inserts, respectively. The LET spectra was derived for each group of particles identified, with values ranging from 0.01 to 7.5 keV·µm-1 for Titanium implants/plastic implants. The low-LET component was primarily composed of electrons and photons, while the high-LET component corresponded to protons and ions. Significance: This method, complemented by directional maps, holds potential for evaluating and validating treatment plans involving stray radiation near organs at risk, offering precise discrimination of the mixt field, enhancing in this way the LET calculation. .

Cytogenetic and Biochemical Responses of Wheat Seeds to Proton Irradiation at the Bragg Peak.

The present study aimed to evaluate the morphological, cytogenetic and biochemical changes in wheat seedlings as affected by seed exposure to a proton beam at the Bragg peak. The average energy of the proton beam was of 171 MeV at the entrance into the irradiator room while at the point of sample irradiation the beam energy was of 150 MeV, with the average value of the Linear Energy Transfer of 0.539 keV/µm and the dose rate of 0.55 Gy/min, the radiation doses being of the order of tens of Gy. Cytogenetic investigation has revealed the remarkable diminution of the mitotic index as linear dose-response curve as well as the spectacular linear increase of the aberration index. Analyzing some biometric parameters, it was found that neither dry matter nor water content of wheat seedlings was influenced by proton beam exposure. Studying the biochemical parameters related to the antioxidant defense system, we found that the irradiation caused the slight increasing tendency of peroxidase activity as well as the decreasing trend in the activity of superoxidedismutase in the seedlings grown from the irradiated seeds. The level of malonedialdehyde (MDA) and total polyphenols showed an increasing tendency in all seedling variants corresponding to irradiated seeds, compared to the control. We conclude that the irradiation clearly induced dose-response curves at the level of cytogenetic parameters together with relatively slight variation tendency of some biochemical parameters related to the antioxidant defense system while imperceptible changes could be noticed in the biometric parameters.

Ionized Radiation-Mediated Retinoid Oxidation in the Retina and Retinal Pigment Epithelium of the Murine Eye.

The present study evaluated the effects of proton and gamma-ray ionizing radiation on the mouse eye. The aim of this work was to analyze radiation-mediated retinoid oxidation in the retina and retinal pigment epithelium (RPE). The findings from this analysis can be used to develop a noninvasive method for rapid assessment of the effects of ionizing radiation. Comparative fluorescence and chromatographic analyses of retinoids before and after irradiations were performed. The fluorescent properties of chloroform extracts from irradiated mouse retina and RPE exhibited an increase in fluorescence intensity in the short-wave region of the spectrum (λ < 550 nm). This change is due to increased retinal and RPE retinoid oxidation and degradation products after radiation exposure. Comparative analyses of radiation effects demonstrated that the effect of proton exposure on the retina and RPE was higher than that of gamma-ray exposure. The present study revealed a new approach to assessing the level of radiation exposure in ocular tissues.

Inter-chromosomal variation in aberration frequencies in human lymphocytes exposed to charged particles of LET between 0.5 and 55 keV/µm.

PURPOSE: To investigate the distribution of chromosomal aberrations in chromosomes 2, 8 and 14 induced by charged particles, using the fluorescence in situ hybridisation (FISH) technique. METHODS: Irradiation of peripheral blood from six healthy volunteers (four male and two female) was performed at the accelerators of the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). Whole blood samples were irradiated with 2 and 3 Gy of protons (170 MeV/nucleon (n), linear energy transfer (LET) ≈ 0.5 keV/µm), 3.5 Gy of (12)C ions (480 MeV/n, LET = 10.6 keV/µm), 3 Gy of (12)C ions 500 MeV/n, LET = 12 keV/µm), 4 Gy of (7)Li ions (30 MeV/n, LET ≈ 20 keV/µm) and 3 Gy of (11)B ions (32 MeV/n, LET ≈ 55 keV/µm). Chromosomal aberrations were analysed in metaphase and prematurely condensed chromosomes (PCC) induced in G(2)-cells using calyculin A. Chromosomes 2, 8 and 14 were painted in different colours and aberrations scored with the help of an image-analysis system. RESULTS: Chromosome 2 was generally less sensitive than expected on the basis of its DNA content. A higher than expected frequency of exchanges was found in chromosomes 8 and 14. On average, the dicentric frequency in chromosome 2 was higher than the translocation frequency, whereas variable dicentric to translocation ratios were observed in chromosomes 8 and 14. When aberrations in all painted chromosomes were summed up the ratio was close to 1. The frequency of complex aberrations correlated with LET. CONCLUSION: In lymphocytes of donors studied in this work chromosome 2 appears to be consistently less sensitive to protons and heavy ions than chromosomes 8 and 14. Complex aberrations appear to be a potential marker of radiation quality.

The comparison of doses measured by radiochromic films and semiconductor detector in a 175MeV proton beam.

We wanted to verify the response of radiochromic films in a 175MeV clinical proton beam used at the Joint Institute for Nuclear Research in Dubna against doses measured using semiconductor detectors and compare the results with published data from other centres. Radiochromic films (RCFs) MD-55 and a Vidar VXR-16 scanner were used. The films were irradiated in an unmodulated proton beam and with a beam modulated with a bolus and a ridge filter. Obtained dose distributions were compared with dose distributions measured with a Si-semiconductor detector. For the unmodulated beam the difference between the RCF and the semiconductor detector was 12% in the Bragg peak top. For the modulated beam the difference inside the spread-out Bragg peak region was 4%. Observed deviations between doses measured with RCF and Si-detector outside the Bragg peak were caused by the inhomogeneity of radiochromic emulsion. In the Bragg peak region the RCF doses were lower than those measured by semiconductors. The results were in agreement with published data from other proton therapy centres.

Doses and LET spectra in the beam of 12C with energy 500 MeV amu-1.

This paper describes the results of experimental studies performed at the Joint Institute for Nuclear Research (JINR) in a (12)C ion beam with the primary nominal energy 500 MeV amu(-1). Data measured by means of a diamond detector and a spectrometer of linear energy transfer (LET) based on chemically etched track detectors are presented, analysed and discussed. LET spectra are also calculated by program SRIM.

mFISH analysis reveals complexity of chromosome aberrations in individuals occupationally exposed to internal plutonium: a pilot study to assess the relevance of complex aberrations as biomarkers of exposure to high-LET alpha particles.

We recently demonstrated that a significant proportion of apparently stable insertions induced after exposure to a mean of one alpha particle/cell, detected using three-color FISH, were part of larger unstable complexes when visualized by 24-color FISH. Interestingly, regardless of the long-term persistence capability of the cell, the complexity of each alpha-particle-induced complex appeared to be specific to the nuclear traversal of a single alpha particle. To assess whether aberrations of a similar complexity are observed in vivo and also to examine the usefulness of detecting such aberrations as a biomarker of chronic exposure to alpha particles, we have carried out a limited pilot study of Russian workers with large body burdens of alpha-particle-emitting plutonium. We found unstable cells containing non-transmissible complex aberrations in all of the plutonium-exposed subjects analyzed by mFISH. In addition, all of the complexes seen were consistent with those previously observed in vitro. Non-transmissible complex aberrations were more common than transmissible-type complexes, consistent with ongoing/chronic exposure, and insertions were dominant features of both types of complex. Accordingly, this preliminary study supports the proposal that aberration complexity and non-transmissibility are the major cytogenetic features of alpha-particle exposure that could potentially be exploited as a specific indicator of chronic exposures to high-LET alpha particles.