Dosimetric comparison of ZAP-X, Gamma Knife, and CyberKnife stereotactic radiosurgery for single brain metastasis.

PURPOSE: To evaluate the dosimetric characteristics of ZAP-X stereotactic radiosurgery (SRS) for single brain metastasis by comparing with two mature SRS platforms. METHODS: Thirteen patients with single brain metastasis treated with CyberKnife (CK) G4 were selected retrospectively. The prescription dose for the planning target volume (PTV) was 18-24 Gy for 1-3 fractions. The PTV volume ranged from 0.44 to 11.52 cc.Treatment plans of thirteen patients were replanned using the ZAP-X plan system and the Gamma Knife (GK) ICON plan system with the same prescription dose and organs at risk (OARs) constraints. The prescription dose of PTV was normalized to 70% for both ZAP-X and CK, while it was 50% for GK. The dosimetric parameters of three groups included the plan characteristics (CI, GI, GSI, beams, MUs, treatment time), PTV (D2, D95, D98, Dmin, Dmean, Coverage), brain tissue (volume of 100%-10% prescription dose irradiation V100%-V10%, Dmean) and other OARs (Dmax, Dmean),all of these were compared and evaluated. All data were read and analyzed with MIM Maestro. One-way ANOVA or a multisample Friedman rank sum test was performed, where p < 0.05 indicated significant differences. RESULTS: The CI of GK was significantly lower than that of ZAP-X and CK. Regarding the mean value, ZAP-X had a lower GI and higher GSI, but there was no significant difference among the three groups. The MUs of ZAP-X were significantly lower than those of CK, and the mean value of the treatment time of ZAP-X was significantly shorter than that of CK. For PTV, the D95, D98, and target coverage of CK were higher, while the mean of Dmin of GK was significantly lower than that of CK and ZAP-X. For brain tissue, ZAP-X showed a smaller volume from V100% to V20%; the statistical results of V60% and V50% showed a difference between ZAP-X and GK, while the V40% and V30% showed a significant difference between ZAP-X and the other two groups; V10% and Dmean indicated that GK was better. Excluding the Dmax of the brainstem, right optic nerve and optic chiasm, the mean value of all other OARs was less than 1 Gy. For the brainstem, GK and ZAP-X had better protection, especially at the maximum dose. CONCLUSION: For the SRS treating single brain metastasis, all three treatment devices, ZAP-X system, CyberKnife G4 system, and GammaKnife system, could meet clinical treatment requirements. The newly platform ZAP-X could provide a high-quality plan equivalent to or even better than CyberKnife and Gamma Knife, with ZAP-X presenting a certain dose advantage, especially with a more conformal dose distribution and better protection for brain tissue. As the ZAP-X systems get continuous improvements and upgrades, they may become a new SRS platform for the treatment of brain metastasis.

Insights into the dosimetric and geometric characteristics of stereotactic radiosurgery for multiple brain metastases: A systematic review.

BACKGROUND: GammaKnife (GK) and CyberKnife (CK) have been the mainstay stereotactic radiosurgery (SRS) solution for multiple brain metastases (MBM) for several years. Recent technological advancement has seen an increase in single-isocentre C-arm linac-based SRS. This systematic review focuses on dosimetric and geometric insights into contemporary MBM SRS and thereby establish if linac-based SRS has matured to match the mainstay SRS delivery systems. METHODS: The PubMed, Web of Science and Scopus databases were interrogated which yielded 891 relevant articles that narrowed to 20 articles after removing duplicates and applying the inclusion and exclusion criteria. Primary studies which reported the use of SRS for treatment of MBM SRS and reported the technical aspects including dosimetry were included. The review was limited to English language publications from January 2015 to August 2023. Only full-length papers were included in the final analysis. Opinion papers, commentary pieces, letters to the editor, abstracts, conference proceedings and editorials were excluded. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. The reporting of conformity indices (CI) and gradient indices, V12Gy, monitor units and the impact of translational and rotational shifts were extracted and analysed. RESULTS: The single-isocentre technique for MBM dominated recent SRS studies and the most studied delivery platforms were Varian. The C-arm linac-based SRS plan quality and normal brain tissue sparing was comparable to GK and CK and in some cases better. The most used nominal beam energy was 6FFF, and optimised couch and collimator angles could reduce mean normal brain dose by 11.3%. Reduction in volume of the healthy brain receiving a certain dose was dependent on the number and size of the metastases and the relative geometric location. GK and CK required 4.5-8.4 times treatment time compared with linac-based SRS. Rotational shifts caused larger changes in CI in C-arm linac-based single-isocentre SRS. CONCLUSION: C-arm linac-based SRS produced comparable MBM plan quality and the delivery is notably shorter compared to GK and CK SRS.

Multiwell-based G0-PCC assay for radiation biodosimetry.

In major radiological events, rapid assays to detect ionizing radiation exposure are crucial for effective medical interventions. The purpose of these assays is twofold: to categorize affected individuals into groups for initial treatments, and to provide definitive dose estimates for continued care and epidemiology. However, existing high-throughput cytogenetic biodosimetry assays take about 3 days to yield results, which delays critical interventions. We have developed a multiwell-based variant of the chemical-induced G0-phase Premature Chromosome Condensation Assay that delivers same-day results. Our findings revealed that using a concentration of phosphatase inhibitor lower than recommended significantly increases the yield of cells with highly condensed chromosomes. These chromosomes exhibited increased fragmentation in a dose-dependent manner, enabling to quantify radiation damage using a custom Deep Learning algorithm. This algorithm demonstrated reasonable performance in categorizing doses into distinct treatment groups (84% and 80% accuracy for three and four iso-treatment dose bins, respectively) and showed reliability in determining the actual doses received (correlation coefficient of 0.879). This method is amendable to full automation and has the potential to address the need for same-day, high-throughput cytogenetic test for both dose categorization and dose reconstruction in large-scale radiation emergencies.

Biomarker dosimetry of acute low level of thermal neutrons and radiation adaptive response effect on rats.

In this paper, we demonstrated the biological effects of acute low-dose neutrons on the whole body of rats and investigated the impact of that level of neutron dose to induce an in vivo radio-adaptive response. To understand the radio-adaptive response, the examined animals were exposed to acute neutron radiation doses of 5 and 10 mSv, followed by a 50 mSv challenge dose after 14 days. After irradiation, all groups receiving single and double doses were kept in cages for one day before sampling. The electron paramagnetic resonance (EPR) method was used to estimate the radiation-induced radicals in the blood, and some hematological parameters and lipid peroxidation (MDA) were determined. A comet assay was performed beside some of the antioxidant enzymes [catalase enzyme (CAT), superoxide dismutase (SOD), and glutathione (GSH)]. Seven groups of adult male rats were classified according to their dose of neutron exposure. Measurements of all studied markers are taken one week after harvesting, except for hematological markers, within 2 h. The results indicated lower production of antioxidant enzymes (CAT by 1.18-5.83%, SOD by 1.47-17.8%, and GSH by 11.3-82.1%). Additionally, there was an increase in red cell distribution width (RDW) (from 4.61 to 25.19%) and in comet assay parameters such as Tail Length, (from 6.16 to 10.81 µm), Tail Moment, (from 1.17 to 2.46 µm), and percentage of DNA in tail length (DNA%) (from 9.58 to 17.32%) in all groups exposed to acute doses of radiation ranging from 5 to 50 mSv, respectively. This emphasizes the ascending harmful effect with the increased acute thermal neutron doses. The values of the introduced factor of radio adaptive response for all markers under study reveal that the lower priming dose promotes a higher adaptation response and vice versa. Ultimately, the results indicate significant variations in DNA%, SOD enzyme levels, EPR intensity, total Hb concentration, and RDWs, suggesting their potential use as biomarkers for acute thermal neutron dosimetry. Further research is necessary to validate these measurements as biodosimetry for radiation exposure, including investigations involving the response impact of RAR with varied challenge doses and post-irradiation behavior.

A dosimetric comparison of brachytherapy sources for endometrial cancer: an electronic brachytherapy and an iridium-192 source with multichannel cylinders and a three-dimensional technique.

BACKGROUND AND PURPOSE: Ir192 vaginal brachytherapy (IBT) is commonly used for patients with postoperative endometrial cancer (EC). We devised a novel multichannel vaginal applicator that could be equipped with an electronic brachytherapy (EBT) device. We aimed to explore the differences in physical parameters between the EBT and IBT. MATERIALS AND METHODS: This retrospective study included 20 EC patients who received adjuvant IBT from March 1, 2023, to May 1, 2023. Multichannel vaginal cylinders were used, and three-dimensional plans were generated. We designed an electronic multichannel vaginal applicator model and simulated a three-dimensional EBT plan. In order to ensure comparability, D90 of the CTV for the EBT plan was normalized to be equivalent to that of the IBT plan for the same patient. RESULTS: Twenty EBT plans were compared with 20 IBT plans. Results showed, the mean D90 value of clinical target volume (CTV) was 536.1 cGy for both treatment plans. For the mean dose of CTV, the EBT was significantly greater (738.3 vs. 684.3 cGy, p = 0.000). There was no significant difference in CTV coverage between the EBT and IBT plans. For high-dose areas (V200% and V150%), the EBTs were significantly greater. There were no significant differences in the maximum doses to the vaginal mucosa between the EBT and IBT, whether at the apex or in the middle segment. For the bladder and rectum, both the low-dose area and high-dose area were significantly lower in the EBT plans. For the conformity index, there was no significant difference between the EBT and IBT plans. For the dose homogeneity index, the EBT value was lower. CONCLUSION: In conclusion, under the premise of a three-dimensional brachytherapy plan, for patients receiving multichannel vaginal applicator brachytherapy, compared with IBT, EBT could reduce the dose to the surrounding organs at risk while maintaining the dose in the target area.

Combined biological effects of CBCT and therapeutic X-ray dose on chromosomal aberrations of lymphocytes.

BACKGROUND AND PURPOSE: Cone beam computed tomography (CBCT) is routinely used in radiotherapy to localize target volume. The aim of our study was to determine the biological effects of CBCT dose compared to subsequent therapeutic dose by using in vitro chromosome dosimetry. MATERIALS AND METHODS: Peripheral blood samples from five healthy volunteers were irradiated in two phantoms (water filled in-house made cylindrical, and Pure Image CTDI phantoms) with 6 MV FFF X-ray photons, the dose rate was 800 MU/min and the absorbed doses ranged from 0.5 to 8 Gy. Irradiation was performed with a 6 MV linear accelerator (LINAC) to generate a dose-response calibration curve. In the first part of the investigation, 1-5 CBCT imaging was used, in the second, only 2 Gy doses were delivered with a LINAC, and then, in the third part, a combination of CBCT and 2 Gy irradiation was performed mimicking online adapted radiotherapy treatment. Metaphases were prepared from lymphocyte cultures, using standard cytogenetic techniques, and chromosomal aberrations were evaluated. Estimate doses were calculated from chromosome aberrations using dose-response curves. RESULTS: Samples exposed to X-ray from CBCT imaging prior to treatment exhibited higher chromosomal aberrations and Estimate dose than the 2 Gy therapeutic (real) dose, and the magnitude of the increase depended on the number of CBCTs: 1-5 CBCT corresponded to 0.04-0.92 Gy, 1 CBCT + 2 Gy to 2.32 Gy, and 5 CBCTs + 2 Gy to 3.5 Gy. CONCLUSION: The estimated dose based on chromosomal aberrations is 24.8% higher than the physical dose, for the combination of 3 CBCTs and the therapeutic 2 Gy dose, which should be taken into account when calculating the total therapeutic dose that could increase the risk of a second cancer. The clinical implications of the combined radiation effect may require further investigation.

Superficial Dosimetry Study of the Frequency of Bolus Using in Volumetric Modulated Arc Therapy after Modified Radical Mastectomy.

OBJECTIVE: To investigate the effect of various frequencies of bolus use on the superficial dose of volumetric modulated arc therapy after modified radical mastectomy for breast cancer. METHODS: Based on the computed tomography images of a female anthropomorphic breast phantom, a 0.5 cm silicone-based 3D-printed bolus was created. Nine points evenly distributed on the breast skin were selected for assessing the skin dose, and a volume of subcutaneous lymphatic drainage of the breast (noted as ROI2-3) was delineated for assessing the chest wall dose. The treatment plans with and without bolus (plan_wb and plan_nb) were separately designed using the prescription of 50 Gy in 25 fractions following the standard dose constraints of the adjacent organ at risk. To characterize the accuracy of treatment planning system (TPS) dose calculations, the doses of the nine points were measured five times by thermoluminescence dosimeters (TLDs) and then were compared with the TPS calculated dose. RESULTS: Compared with Plan_nb (144.46 ± 10.32 cGy), the breast skin dose for plan_wb (208.75 ± 4.55 cGy) was significantly increased (t = -18.56, P < 0.001). The deviation of skin dose was smaller for Plan_wb, and the uniformity was significantly improved. The calculated value of TPS was in good agreement with the measured value of TLD, and the maximum deviation was within 5%. Skin and ROI2-3 doses were significantly increased with increasing frequencies of bolus applications. The mean dose of the breast skin and ROI2-3 for 15 and 23 times bolus applications were 45.33 Gy, 50.88 Gy and 50.36 Gy, 52.39 Gy, respectively. CONCLUSION: 3D printing bolus can improve the radiation dose and the accuracy of the planned dose. Setting Plan_wb to 15 times for T1-3N+ breast cancer patients and 23 times for T4N+ breast cancer patients can meet the clinical need. Quantitative analysis of the bolus application frequency for different tumor stages can provide a reference for clinical practice.

BAX and DDB2 as biomarkers for acute radiation exposure in the human blood ex vivo and non-human primate models.

There are currently no available FDA-cleared biodosimetry tools for rapid and accurate assessment of absorbed radiation dose following a radiation/nuclear incident. Previously we developed a protein biomarker-based FAST-DOSE bioassay system for biodosimetry. The aim of this study was to integrate an ELISA platform with two high-performing FAST-DOSE biomarkers, BAX and DDB2, and to construct machine learning models that employ a multiparametric biomarker strategy for enhancing the accuracy of exposure classification and radiation dose prediction. The bioassay showed 97.92% and 96% accuracy in classifying samples in human and non-human primate (NHP) blood samples exposed ex vivo to 0-5 Gy X-rays, respectively up to 48 h after exposure, and an adequate correlation between reconstructed and actual dose in the human samples (R2 = 0.79, RMSE = 0.80 Gy, and MAE = 0.63 Gy) and NHP (R2 = 0.80, RMSE = 0.78 Gy, and MAE = 0.61 Gy). Biomarker measurements in vivo from four NHPs exposed to a single 2.5 Gy total body dose showed a persistent upregulation in blood samples collected on days 2 and 5 after irradiation. The data indicates that using a combined approach of targeted proteins can increase bioassay sensitivity and provide a more accurate dose prediction.

Evaluation of monthly variations in electrometer calibration coefficients using a charge generator for radiation therapy.

Electrometers are important devices that are part of the standard dosimetry system. Therefore, we evaluated the variation of electrometer calibration coefficients (kelec) over 1 year in this study. We investigated two types of electrometers: a rate mode and an integrate mode. Each electrometer was connected to a charge generator, a constant charge was applied, and kelec was determined by measuring the current. The current measurements were repeated once a month. For electrometers with multiple ranges, measurements were taken at low and medium ranges. Almost all kelec measurements agreed within 0.2% of the initial measurements. However, the low range of the electrometer with an integrate mode showed seasonal variation, with a variation greater than 0.2%. This study shows that electrometers may exhibit errors that cannot be detected through annual inspections. The importance of quality assurance using a charge generator at one's own institution was demonstrated.

Investigation of a novel 2.5 MV sintered diamond target beam for intracranial linac-based stereotactic treatments.

Purpose. This work investigates the small-field dosimetric characteristics of a 2.5 MV sintered diamond target beam and its feasibility for use in linac-based intracranial stereotactic treatments. Due to the increased proportion of low energy photons in the low-Z beam, it was hypothesized that this novel beam would provide sharper dose fall-off compared to the 6 MV beam owing to the reduced energy, and therefore range, of secondary electrons.Methods. Stereotactic treatments of ocular melanoma and trigeminal neuralgia were simulated for 2.5 MV low-Z and 6 MV beams using Monte Carlo to calculate dose in a voxelized anatomical phantom. Two collimation methods were investigated, including a 5 × 3 mm2HDMLC field and a 4 mm cone to demonstrate isolated and combined effects of geometric and radiological contributions to the penumbral width.Results. The measured 2.5 MV low-Z dosimetric profiles demonstrated reduced penumbra by 0.5 mm in both the inline and crossline directions across all depths for both collimation methods, compared to 6 MV. In both treatment cases, the 2.5 MV low-Z beam collimated with the 4 mm cone produced the sharpest dose fall off in profiles captured through isocenter. This improved fall-off resulted in a 59% decrease to the maximum brainstem dose in the trigeminal neuralgia case for the 2.5 MV low-Z MLC collimated beam compared to 6 MV. Reductions to the maximum and mean doses to ipsilateral and contralateral OARs in the ocular melanoma case were observed for the 2.5 MV low-Z beam compared to 6 MV with both collimation methods.Conclusions. While the low dose rate of this novel beam prohibits immediate clinical translation, the results of this study support the further development of this prototype beam to decrease toxicity in intracranial SRS treatments.

Investigation of Ionization Chamber Characteristics for Ultrahigh-dose-rate Scanned Carbon-ion Beams.

BACKGROUND/AIM: There are only a few studies on dosimetry with ultrahigh-dose-rate (uHDR) scanned carbon-ion beams. This study investigated the characteristics of four types of ionization chambers for the uHDR beam. MATERIALS AND METHODS: We employed a newly developed large-plane parallel chamber to monitor a 208.3-MeV/u uHDR scanned carbon-ion beam with a 110-Gy/s average dose rate. The ionization chambers used were the Advanced Markus chamber (AMC), PinPoint 3D chamber (PPC), Farmer chamber (FC), and large-plane parallel chamber (StingRay). The AMC and StingRay surfaces and the PPC and FC geometric centers were aligned to the radiation isocenter using treatment room lasers. Using the voltage range stated in the instruction manuals, we obtained the saturation curves of the chambers. From these curves, we obtained the ion recombination correction factors using the two-voltage and three-voltage linear methods. The dose linearity was evaluated using five measurement points, and the chamber repeatability was verified by conducting repeated measurements for different dose values. RESULTS: Although all chambers, except for AMC, reached saturation when specified voltages were applied, they exhibited excellent linearity for different dose values. The ion recombination correction factors of the AMC obtained using the aforementioned linear methods were nearly 1. Additionally, all chambers exhibited excellent repeatability. Although the standard deviation of the PPC for the lowest dose was ~1.5%, those of all the other chambers were <1.0%. CONCLUSION: All ionization chambers can be used for measuring the relative dose, and absolute dose can be conveniently measured using the AMC with an uHDR carbon-ion scanned beam.

The Impact of Dose Calibration Point Differences Between the Treatment Plan and Patient-specific Quality Assurance in Passive Scattering Proton Beam Therapy.

BACKGROUND/AIM: Passive scattering proton beam therapy (PSPT) is performed by taking actual measurements of all pre-designated fields in a treatment plan followed by appropriate adjustments to the prescribed dose. For this reason, it is necessary to ensure precision management of the measurements (patient-specific calibration) in the administration of a planned dose. Therefore, this study investigated the impact on dose distribution in treatment planning when the patient calibration point differs from the normalized point in a treatment plan. PATIENTS AND METHODS: A total of 16 cases were selected, where the patient calibration point and normalized point did not match, and the normalized point used in the treatment plan was changed to the patient calibration point using a treatment planning system (VQA ver. 2.01, HITACHI). At this point, the displacement of the relative dose at the isocenter was estimated as an error owing to the difference compared to the patient calibration point. RESULTS: Overall, the error was within the range of ±1.5%, with the exception of orbit cases. Calibrated points also tended to be lower than the normalized points in the treatment plan. In terms of treatment sites, a greater deviation was observed for head cases. Cases with a large deviation in sites other than the head were attributed to poor flatness within the radiation field owing to a narrower opening of the patient collimator. CONCLUSION: Dose measurement errors in PSPT due to differing calibration points were generally within ±1.5%, with higher deviations observed in head treatments because of complex structures and narrow collimator openings. A γ analysis for significant deviations showed a 98.7% passing rate, suggesting limited overall impact. It is important to select stable calibration points in dosimetry to ensure high precision in dose administration, particularly in complex treatment areas.

3D small-scale dosimetry and tumor control of 225Ac radiopharmaceuticals for prostate cancer.

Radiopharmaceutical therapy using α -emitting 225 Ac is an emerging treatment for patients with advanced metastatic cancers. Measurement of the spatial dose distribution in organs and tumors is needed to inform treatment dose prescription and reduce off-target toxicity, at not only organ but also sub-organ scales. Digital autoradiography with α -sensitive detection devices can measure radioactivity distributions at 20-40 µ m resolution, but anatomical characterization is typically limited to 2D. We collected digital autoradiographs across whole tissues to generate 3D dose volumes and used them to evaluate the simultaneous tumor control and regional kidney dosimetry of a novel therapeutic radiopharmaceutical for prostate cancer, [225Ac]Ac-Macropa-PEG4-YS5, in mice. 22Rv1 xenograft-bearing mice treated with 18.5 kBq of [225Ac]Ac-Macropa-PEG4-YS5 were sacrificed at 24 h and 168 h post-injection for quantitative α -particle digital autoradiography and hematoxylin and eosin staining. Gamma-ray spectroscopy of biodistribution data was used to determine temporal dynamics and 213 Bi redistribution. Tumor control probability and sub-kidney dosimetry were assessed. Heterogeneous 225 Ac spatial distribution was observed in both tumors and kidneys. Tumor control was maintained despite heterogeneity if cold spots coincided with necrotic regions. 225 Ac dose-rate was highest in the cortex and renal vasculature. Extrapolation of tumor control suggested that kidney absorbed dose could be reduced by 41% while maintaining 90% TCP. The 3D dosimetry methods described allow for whole tumor and organ dose measurements following 225 Ac radiopharmaceutical therapy, which correlate to tumor control and toxicity outcomes.

Impact of contrast agents on organ dosimetry in pediatric diagnostic fluoroscopy: the voiding cystourethrogram.

Objective.International Commission on Radiological Protection (ICRP) Task Group 113 is developing reference values of organ and effective dose coefficients (DCs) for radiography, fluoroscopy, and computed tomography imaging exams. In support of these efforts, our focus is on pediatric diagnostic fluoroscopy. Contrast agents used during clinical examinations are an important consideration of the work undertaken by the Task Group. This work demonstrates the importance of including organ contrast volume concentrations for the calculation of reference organ DCs in the voiding cystourethrogram (VCUG).Approach.The ICRP newborn and 15 year female reference phantoms were utilized within the Particle and Heavy Ion Transport code system for the calculation of organ DCs. A pediatric radiologist with over 30 years of clinical experience defined the imaging fields for a VCUG examination consistent with clinical practice. Of these, four imaging fields were selected for investigation. The transport simulations modeled an iodinated contrast solution similar to Bracco Group's 18% weight per volume, cystografin diatrizoate meglumine and typical bladder content was supplemented to make up the remainder volume. Iodinated contrast volumes of 0%, 25%, 50%, 75%, and 100% concentration by volume were modeled and associated DCs for in-field organs were computed.Main results.Organ DCs were calculated for the urinary bladder wall, colon wall, ovaries, and uterus for both female phantoms under irradiation geometries representative of a VCUG examination. Some organ DCs increased with iodine volume in the bladder and other organ DCs decreased as the iodine contrast volume completely filled the bladder (100%).Significance.The study results demonstrate for the newborn phantom percent differences in organ DCs varied between 0%-10% for the organs of interest, while they varied between 0%-22% in the 15 year phantom suggesting the importance of including contrast media in Monte Carlo radiation transport simulations of the VCUG examination.

A finite volume approach to dosimetric calculations in diffusing alpha-emitters radiation therapy.

Objective.In diffusing alpha-emitters radiation therapy ('Alpha DaRT'), the diffusion-leakage (DL) model is used to determine the spatial distributions of the emitters and the corresponding alpha dose, critical for a successful treatment. This work first introduces a finite volume (FV) approach to develop numerical schemes to simulate the DL model in one, two and three dimensions then presents how variations over realistic ranges of the DL model parameters related to desorption, diffusion and leakage processes affect the alpha dose distribution and the position of the clinically significant alpha particle10Gy isodose. This work also presents the effects of three modeling approximations: two source geometry approximations (solid cylinder instead of hollow, pixelized cross section instead of circular), and one dosimetric approximation (single-source dose superposition instead of multiple-sources direct dose calculation).Approach.The introduced FV approach was used to obtain spatial distributions of the emitters, from which the corresponding alpha dose distributions were calculated under the assumption of a local deposition of the alpha particles' energies. Variation ranges of the DL model parameters were based on previously published data. For each modeling approximation studied, the error and relative error on the alpha dose distribution were calculated and the displacement of the10Gy isodose was evaluated.Main results.Over realistic ranges, the desorption probabilities, diffusion lengths, and leakage probabilities affect the position of the alpha particle10Gy isodose by∼0.1mm,∼1.5mm and∼0.5mm, respectively. The three modeling approximations studied have a negligible effect on the alpha particle10Gy isodose position, with displacements⩽0.01mm.Significance.This work quantitatively evaluates the relative importance of different parameters and approximations in Alpha-DaRT alpha dose calculations based on their impact not only on the dose variation at a given distance from the source but also on the displacement of clinically significant isodoses.

Evaluation of TOPAS MC tool performance in optical photon transport and radioluminescence-based dosimetry.

Radiation therapy plays a pivotal role in modern cancer treatment, demanding precise and accurate dose delivery to tumor sites while minimizing harm to surrounding healthy tissues. Monte Carlo simulations have emerged as indispensable tools for achieving this precision, offering detailed insights into radiation transport and interaction at the subatomic level. As the use of scintillation and luminescence dosimetry becomes increasingly prevalent in radiation therapy, there arises a need for validated Monte Carlo tools tailored to optical photon transport applications. In this paper, an evaluation process of the TOPAS (TOol for PArticle Simulation) Monte Carlo tool for Cerenkov light generation, optical photon transport and radioluminescence based dosimetry is presented. Three distinct sources of validation data are utilized: one from a published set of experimental results and two others from simulations performed with the Geant4 code. The methodology employed for evaluation includes the selection of benchmark experiments, making use of opt3 and opt4 Geant4 physics models and simulation setup, with observed slight discrepancies within the calculation uncertainties. Additionally, the complexities and challenges associated with modeling optical photons generation through luminescence or Cerenkov radiation and their transport are discussed. The results of our evaluation suggests that TOPAS can be used to reliably predict Cerenkov generation, luminescence phenomenon and the behavior of optical photons in common dosimetry scenarios.

A novel predictor for dosimetry data of lung and the radiation pneumonitis incidence prior to SBRT in lung cancer patients.

Normal tissue complication probability (NTCP) models for radiation pneumonitis (RP) in lung cancer patients with stereotactic body radiation therapy (SBRT), which based on dosimetric data from treatment planning, are limited to patients who have already received radiation therapy (RT). This study aims to identify a novel predictive factor for lung dose distribution and RP probability before devising actionable SBRT plans for lung cancer patients. A comprehensive correlation analysis was performed on the clinical and dose parameters of lung cancer patients who underwent SBRT. Linear regression models were utilized to analyze the dosimetric data of lungs. The performance of the regression models was evaluated using mean squared error (MSE) and the coefficient of determination (R2). Correlational analysis revealed that most clinical data exhibited weak correlations with dosimetric data. However, nearly all dosimetric variables showed "strong" or "very strong" correlations with each other, particularly concerning the mean dose of the ipsilateral lung (MI) and the other dosimetric parameters. Further study verified that the lung tumor ratio (LTR) was a significant predictor for MI, which could predict the incidence of RP. As a result, LTR can predict the probability of RP without the need to design an elaborate treatment plan. This study, as the first to offer a comprehensive correlation analysis of dose parameters, explored the specific relationships among them. Significantly, it identified LTR as a novel predictor for both dose parameters and the incidence of RP, without the need to design an elaborate treatment plan.

3D printed heterogeneous paediatric head and adult thorax phantoms for linear accelerator radiotherapy quality assurance: from fabrication to treatment delivery.

Objective. This study aims to design and fabricate a 3D printed heterogeneous paediatric head phantom and to customize a thorax phantom for radiotherapy dosimetry.Approach. This study designed, fabricated, and tested 3D printed radiotherapy phantoms that can simulate soft tissue, lung, brain, and bone. Various polymers were considered in designing the phantoms. Polylactic acid+, nylon, and plaster were used in simulating different tissue equivalence. Dimensional accuracy, and CT number were investigated. The phantoms were subjected to a complete radiotherapy clinical workflow. Several treatment plans were delivered in both the head and the thorax phantom from a simple single 6 MV beam, parallel opposed beams, and five-field intensity modulated radiotherapy (IMRT) beams. Dose measurements using an ionization chamber and radiochromic films were compared with the calculated doses of the Varian Eclipse treatment planning system (TPS).Main results. The fabricated heterogeneous phantoms represent paediatric human head and adult thorax based on its radiation attenuation and anatomy. The measured CT number ranges are within -786.23 ± 10.55, 0.98 ± 3.86, 129.51 ± 12.83, and 651.14 ± 47.76 HU for lung, water/brain, soft tissue, and bone, respectively. It has a good radiological imaging visual similarity relative to a real human head and thorax depicting soft tissue, lung, bone, and brain. The accumulated dose readings for both conformal radiotherapy and IMRT match with the TPS calculated dose within ±2% and ±4% for head and thorax phantom, respectively. The mean pass rate for all the plans delivered are above 90% for gamma analysis criterion of 3%/3 mm.Significance and conclusion. The fabricated heterogeneous paediatric head and thorax phantoms are useful in Linac end-to-end radiotherapy quality assurance based on its CT image and measured radiation dose. The manufacturing and dosimetry workflow of this study can be utilized by other institutions for dosimetry and trainings.

X-ray spectrometry for calculating conversion coefficients from air kerma to operational quantities in radiation protection.

This study explores the conversion coefficients from air kerma to operational quantities for radiation protection, using x-ray spectrometry for the narrow-beam qualities below 300 keV as defined by ISO 4037-1. By employing custom spectral correction algorithms combined with modern cadmium telluride (CdTe) semiconductor detectors, we effectively corrected spectral distortions caused by detection processes, ensuring more reliable measurements. These measurements are crucial for meeting radiation protection standards. The study also analyses the sources of uncertainty associated with the determination of conversion coefficients, thereby providing improved accuracy and reproducibility in photon dosimetry.