Assessment of lymph node area coverage with total marrow irradiation and implementation of total marrow and lymphoid irradiation using automated deep learning-based segmentation.

BACKGROUND: Total marrow irradiation (TMI) and total marrow and lymphoid irradiation (TMLI) have the advantages. However, delineating target lesions according to TMI and TMLI plans is labor-intensive and time-consuming. In addition, although the delineation of target lesions between TMI and TMLI differs, the clinical distinction is not clear, and the lymph node (LN) area coverage during TMI remains uncertain. Accordingly, this study calculates the LN area coverage according to the TMI plan. Further, a deep learning-based model for delineating LN areas is trained and evaluated. METHODS: Whole-body regional LN areas were manually contoured in patients treated according to a TMI plan. The dose coverage of the delineated LN areas in the TMI plan was estimated. To train the deep learning model for automatic segmentation, additional whole-body computed tomography data were obtained from other patients. The patients and data were divided into training/validation and test groups and models were developed using the "nnU-NET" framework. The trained models were evaluated using Dice similarity coefficient (DSC), precision, recall, and Hausdorff distance 95 (HD95). The time required to contour and trim predicted results manually using the deep learning model was measured and compared. RESULTS: The dose coverage for LN areas by TMI plan had V100% (the percentage of volume receiving 100% of the prescribed dose), V95%, and V90% median values of 46.0%, 62.1%, and 73.5%, respectively. The lowest V100% values were identified in the inguinal (14.7%), external iliac (21.8%), and para-aortic (42.8%) LNs. The median values of DSC, precision, recall, and HD95 of the trained model were 0.79, 0.83, 0.76, and 2.63, respectively. The time for manual contouring and simply modified predicted contouring were statistically significantly different. CONCLUSIONS: The dose coverage in the inguinal, external iliac, and para-aortic LN areas was suboptimal when treatment is administered according to the TMI plan. This research demonstrates that the automatic delineation of LN areas using deep learning can facilitate the implementation of TMLI.

SPECT/CT Image-Derived Absorbed Dose to Red Marrow Correlates with Hematologic Toxicity in Patients Treated with [177Lu]Lu-DOTATATE.

Hematologic toxicity, although often transient, is the most common limiting adverse effect during somatostatin peptide receptor radionuclide therapy. This study investigated the association between Monte Carlo-derived absorbed dose to the red marrow (RM) and hematologic toxicity in patients being treated for their neuroendocrine tumors. Methods: Twenty patients each receiving 4 treatment cycles of [177Lu]Lu-DOTATATE were included. Multiple-time-point 177Lu SPECT/CT imaging-based RM dosimetry was performed using an artificial intelligence-driven workflow to segment vertebral spongiosa within the field of view (FOV). This workflow was coupled with an in-house macroscale/microscale Monte Carlo code that incorporates a spongiosa microstructure model. Absorbed dose estimates to RM in lumbar and thoracic vertebrae within the FOV, considered as representations of the whole-body RM absorbed dose, were correlated with hematologic toxicity markers at about 8 wk after each cycle and at 3- and 6-mo follow-up after completion of all cycles. Results: The median of absorbed dose to RM in lumbar and thoracic vertebrae within the FOV (D median,vertebrae) ranged from 0.019 to 0.11 Gy/GBq. The median of cumulative absorbed dose across all 4 cycles was 1.3 Gy (range, 0.6-2.5 Gy). Hematologic toxicity was generally mild, with no grade 2 or higher toxicity for platelets, neutrophils, or hemoglobin. However, there was a decline in blood counts over time, with a fractional value relative to baseline at 6 mo of 74%, 97%, 57%, and 97%, for platelets, neutrophils, lymphocytes, and hemoglobin, respectively. Statistically significant correlations were found between a subset of hematologic toxicity markers and RM absorbed doses, both during treatment and at 3- and 6-mo follow-up. This included a correlation between the platelet count relative to baseline at 6-mo follow up: D median,vertebrae (r = -0.64, P = 0.015), D median,lumbar (r = -0.72, P = 0.0038), D median,thoracic (r = -0.58, P = 0.029), and D average,vertebrae (r = -0.66, P = 0.010), where D median,lumbar and D median,thoracic are median absorbed dose to the RM in the lumbar and thoracic vertebrae, respectively, within the FOV and D average,vertebrae is the mass-weighted average absorbed dose of all vertebrae. Conclusion: This study found a significant correlation between image-derived absorbed dose to the RM and hematologic toxicity, including a relative reduction of platelets at 6-mo follow up. These findings indicate that absorbed dose to the RM can potentially be used to understand and manage hematologic toxicity in peptide receptor radionuclide therapy.

Assessment of DNA damage in somatic and germ cells of animals living with increased radiation background and their offspring.

PURPOSE: The aim of this work is to assess DNA damage in the somatic and germ cells in root voles living for a long time under conditions of an increased radiation background and to examine the of manifestation of long-term consequences in their offspring. MATERIALS AND METHODS: Using the DNA comet assay (neutral version), we assessed the proportion of cells with DNA damage in the cells of the thyroid, bone marrow and testicular in root voles (Microtus oeconomus Pall.) that lived under conditions of increased radiation background (exposure dose rate - 0.50-20 µSv/h; Komi Republic, Russia) and in their offspring (F1-F3) that were reproduced in a vivarium with a normal radiation background. RESULTS: In animals caught in a radioactively contaminated area, the level of DNA fragmentation in the thyroid gland, bone marrow and testicular remained within the range of values of control animals. The studies that we continued on the offspring of irradiated root voles that were developing in the vivarium under normal radiation background allowed us to identify an increase in the level of DNA DSBs in the thyroid gland in the F1 generation, in the bone marrow and testicular cells in the F2 generation. The modifying effect of urethane showed a similarity in the response of somatic cells in voles that lived for a long time in a radioactively contaminated area and in their offspring that developed with a normal radiation background. The effect of urethane was more conspicuous in thyroid cells that, than in bone marrow cells. CONCLUSION: The data obtained on voles from the experimental site indicate adaptation to habitat conditions in a radioactively polluted environment. The provocative effect of urethane made it possible to reveal different response of organs with different proliferative activity. Long-term habitation of voles under conditions of an increased radiation background led to genome instability in their offspring.

Stochastic parametric skeletal dosimetry model for humans: General approach and application to active marrow exposure from bone-seeking beta-particle emitters.

The objective of this study is to develop a skeleton model for assessing active marrow dose from bone-seeking beta-emitting radionuclides. This article explains the modeling methodology which accounts for individual variability of the macro- and microstructure of bone tissue. Bone sites with active hematopoiesis are assessed by dividing them into small segments described by simple geometric shapes. Spongiosa, which fills the segments, is modeled as an isotropic three-dimensional grid (framework) of rod-like trabeculae that "run through" the bone marrow. Randomized multiple framework deformations are simulated by changing the positions of the grid nodes and the thickness of the rods. Model grid parameters are selected in accordance with the parameters of spongiosa microstructures taken from the published papers. Stochastic modeling of radiation transport in heterogeneous media simulating the distribution of bone tissue and marrow in each of the segments is performed by Monte Carlo methods. Model output for the human femur at different ages is provided as an example. The uncertainty of dosimetric characteristics associated with individual variability of bone structure was evaluated. An advantage of this methodology for the calculation of doses absorbed in the marrow from bone-seeking radionuclides is that it does not require additional studies of autopsy material. The biokinetic model results will be used in the future to calculate individual doses to members of a cohort exposed to 89,90Sr from liquid radioactive waste discharged to the Techa River by the Mayak Production Association in 1949-1956. Further study of these unique cohorts provides an opportunity to gain more in-depth knowledge about the effects of chronic radiation on the hematopoietic system. In addition, the proposed model can be used to assess the doses to active marrow under any other scenarios of 90Sr and 89Sr intake to humans.

Modeling bystander effects that cause growth delay of breast cancer xenografts in bone marrow of mice treated with radium-223.

RATIONALE: The role of radiation-induced bystander effects in cancer therapy with alpha-particle emitting radiopharmaceuticals remains unclear. With renewed interest in using alpha-particle emitters to sterilize disseminated tumor cells, micrometastases, and tumors, a better understanding of the direct effects of alpha particles and the contribution of the bystander responses they induce is needed to refine dosimetric models that help predict clinical benefit. Accordingly, this work models and quantifies the relative importance of direct effects (DE) and bystander effects (BE) in the growth delay of human breast cancer xenografts observed previously in the tibiae of mice treated with 223RaCl2. METHODS: A computational model of MDA-MB-231 and MCF-7 human breast cancer xenografts in the tibial bone marrow of mice administered 223RaCl2 was created. A Monte Carlo radiation transport simulation was performed to assess individual cell absorbed doses. The responses of the breast cancer cells to direct alpha particle irradiation and gamma irradiation were needed as input data for the model and were determined experimentally using a colony-forming assay and compared to the responses of preosteoblast MC3T3-E1 and osteocyte-like MLO-Y4 bone cells. Using these data, a scheme was devised to simulate the dynamic proliferation of the tumors in vivo, including DE and BE propagated from the irradiated cells. The parameters of the scheme were estimated semi-empirically to fit experimental tumor growth. RESULTS: A robust BE component, in addition to a much smaller DE component, was required to simulate the in vivo tumor proliferation. We also found that the relative biological effectiveness (RBE) for cell killing by alpha particle radiation was greater for the bone cells than the tumor cells. CONCLUSION: This modeling study demonstrates that DE of radiation alone cannot explain experimental observations of 223RaCl2-induced growth delay of human breast cancer xenografts. Furthermore, while the mechanisms underlying BE remain unclear, the addition of a BE component to the model is necessary to provide an accurate prediction of the growth delay. More complex models are needed to further comprehend the extent and complexity of 223RaCl2-induced BE.

Tables for effective dose assessment from diagnostic radiology (period 1946-1995) in epidemiologic studies.

Diagnostic radiology is a leading cause of man-made radiation exposure to the population. It is an important factor in many epidemiological studies as variable of interest or as potential confounder. The effective dose as a risk related quantity is the most often stated patient dose. Nevertheless, there exists no comprehensive quantification model for retrospective analysis for this quantity. This paper gives a catalog of effective dose values for common and rare examinations and demonstrates how to modify the dose values to adapt them to different calendar years using a quantification concept already used for retrospective analysis of the red bone marrow dose. It covers the time period of 1946 to 1995 and allows considering technical development and different practical standards over time. For an individual dose assessment, if the dose area product is known, factors are given for most examinations to convert the dose area product into the effective dose. Additionally factors are stated for converting the effective dose into the red bone marrow dose or vice versa.

Effect of microdistribution of alpha and beta-emitters in targeted radionuclide therapies on delivered absorbed dose in a GATE model of bone marrow.

Acute hematologic toxicity is a frequent adverse effect of beta-emitter targeted radionuclide therapies (TRTs). Alpha emitters have the potential of delivering high linear energy transfer (LET) radiation to the tumor attributed to its shorter range. Antibody-based TRTs have increased blood-pool half-lives, and therefore increased marrow toxicity, which is a particular concern with alpha emitters. Accurate 3D absorbed dose calculations focusing on the interface region of blood vessels and bone can elucidate energy deposition patterns. Firstly, a cylindrical geometry model with a central blood vessel embedded in the trabecular tissue was modeled. Monte Carlo simulations in GATE were performed considering beta (177Lu, 90Y) and alpha emitters (211At, 225Ac) as sources restricted to the blood pool. Subsequently, the radioactive sources were added in the trabecular bone compartment in order to model bone marrow metastases infiltration (BMMI). Radial profiles, dose-volume histograms and voxel relative differences were used to evaluate the absorbed dose results. We demonstrated that alpha emitters have a higher localized energy deposition compared to beta emitters. In the cylindrical geometry model, when the sources are confined to the blood pool, the dose to the trabecular bone is greater for beta emitting radionuclides, as alpha emitters deposit the majority of their energy within 70 µm of the vessel wall. In the BMMI model, alpha emitters have a lower dose to untargeted trabecular bone. Our results suggest that when alpha emitters are restricted to the blood pool, as when labeled to antibodies, hematologic toxicities may be lower than expected due to differences in the microdistribution of delivered absorbed dose.

Dose-Dependent Growth Delay of Breast Cancer Xenografts in the Bone Marrow of Mice Treated with 223Ra: The Role of Bystander Effects and Their Potential for Therapy.

The role of radiation-induced bystander effects in radiation therapy remains unclear. With renewed interest in therapy with α-particle emitters, and their potential for sterilizing disseminated tumor cells (DTCs), it is critical to determine the contribution of bystander effects to the overall response so they can be leveraged for maximum clinical benefit. Methods: Female Foxn1nu athymic nude mice were administered 0, 50, or 600 kBq/kg 223RaCl2 to create bystander conditions. At 24 hours after administration, MDA-MB-231 or MCF-7 human breast cancer cells expressing luciferase were injected into the tibial marrow compartment. Tumor burden was tracked weekly via bioluminescence. Results: The MDA-MB-231 xenografts were observed to have a 10-day growth delay in the 600 kBq/kg treatment group only. In contrast, MCF-7 cells had 7- and 65-day growth delays in the 50 and 600 kBq/kg groups, respectively. Histologic imaging of the tibial marrow compartment, α-camera imaging, and Monte Carlo dosimetry modeling revealed DTCs both within and beyond the range of the α-particles emitted from 223Ra in bone for both MCF-7 and MDA-MB-231 cells. Conclusion: Taken together, these results support the participation of 223Ra-induced antiproliferative/cytotoxic bystander effects in delayed growth of DTC xenografts. They indicate that the delay depends on the injected activity and therefore is dose-dependent. They suggest using 223RaCl2 as an adjuvant treatment for select patients at early stages of breast cancer.

Trabecula: A Random Generator of Computational Phantoms for Bone Marrow Dosimetry.

This study was motivated by the efforts to evaluate radiation risk for leukemia incidence in the Techa River cohort, where the main bone marrow dose contributors were Sr (bone-seeking beta emitters). Energy deposition in bone marrow targets was evaluated by simulating radiation particle transport using computational phantoms. The present paper describes the computer program Trabecula implementing an algorithm for parametric generation of computational phantoms, which serve as the basis for calculating bone marrow doses. Trabecula is a user-friendly tool that automatically converts analytical models into voxelized representations that are directly compatible as input to Monte Carlo N Particle code.

Evaluation and improvement the safety of total marrow irradiation with helical tomotherapy using repeat failure mode and effects analysis.

BACKGROUND & PURPOSE: Helical tomotherapy has been applied to total marrow irradiation (HT-TMI). Our objective was to apply failure mode and effects analysis (FMEA) two times separated by 1 year to evaluate and improve the safety of HT-TMI. MATERIALS AND METHODS: A multidisciplinary team was created. FMEA consists of 4 main steps: (1) Creation of a process map; (2) Identification of all potential failure mode (FM) in the process; (3) Evaluation of the occurrence (O), detectability (D) and severity of impact (S) of each FM according to a scoring criteria (1-10), with the subsequent calculation of the risk priority number (RPN=O*D*S) and (4) Identification of the feasible and effective quality control (QC) methods for the highest risks. A second FMEA was performed for the high-risk FMs based on the same risk analysis team in 1 year later. RESULTS: A total of 39 subprocesses and 122 FMs were derived. First time RPN ranged from 3 to 264.3. Twenty-five FMs were defined as being high-risk, with the top 5 FMs (first RPN/ second RPN): (1) treatment couch movement failure (264.3/102.8); (2) section plan dose junction error in delivery (236.7/110.4); (3) setup check by megavoltage computed tomography (MVCT) failure (216.8/94.6); (4) patient immobilization error (212.5/90.2) and (5) treatment interruption (204.8/134.2). A total of 20 staff members participated in the study. The second RPN value of the top 5 high-risk FMs were all decreased. CONCLUSION: QC interventions were implemented based on the FMEA results. HT-TMI specific treatment couch tests; the arms immobilization methods and strategy of section plan dose junction in delivery were proved to be effective in the improvement of the safety.

Validation of GATE for bone and bone marrow with calculation specific absorbed fraction for photons.

PURPOSE: GATE/GEANT is a Monte Carlo code dedicated to nuclear medicine that allows calculation of the dose to organs (bone and bone marrow) of voxel phantoms. On the other hand, Medical Internal Radiation Dose (MIRD) is a well-developed system for estimation of the dose to human organs. In this study, results obtained from GATE/GEANT using leg of Snyder phantom is compared to published MIRD data. MATERIALS AND METHODS: For this, the mathematical leg of Snyder phantom was discretized and converted to a digital phantom of 100 × 100 × 200 voxels. The activity was considered uniformly distributed within bone and bone marrow. The GATE/GEANT Monte Carlo code was used to calculate the dose to the bone and bone marrow of the leg phantom from mono-energetic photons of 10, 15, 20, 30, 50, 100, 200, 500, and 1000 keV. The dose was converted into a specific absorbed fraction (SAF) and the results were compared to the corresponding published MIRD data. RESULTS: On average, there was a good correlation between the two series of data for self-absorption (r 2 = 0.99) and for cross-irradiation (r 2 = 0.99). However, the GATE/GEANT data were on average 1.01 ± 0.79% higher than the corresponding MIRD data for self-absorption. As for cross-irradiation, the GATE/GEANT data were on average 8.11 ± 7.95% higher than the MIRD data. CONCLUSION: In this study, the SAF values derived from GATE/GEANT and the corresponding MIRD published data were compared. On average, the SAF values derived with GATE/GEANT showed an acceptable correlation and agreement with the MIRD data for the photon energies of 50-1000 keV. For photons of 10-30 keV, there was an only poor agreement between the GATE/GEANT results and MIRD data.

Early assessment of dosimetric and biological differences of total marrow irradiation versus total body irradiation in rodents.

PURPOSE: To develop a murine total marrow irradiation (TMI) model in comparison with the total body irradiation (TBI) model. MATERIALS AND METHODS: Myeloablative TMI and TBI were administered in mice using a custom jig, and the dosimetric differences between TBI and TMI were evaluated. The early effects of TBI/TMI on bone marrow (BM) and organs were evaluated using histology, FDG-PET, and cytokine production. TMI and TBI with and without cyclophosphamide (Cy) were evaluated for donor cell engraftment and tissue damage early after allogeneic hematopoietic cell transplantation (HCT). Stromal derived factor-1 (SDF-1) expression was evaluated. RESULTS: TMI resulted in similar dose exposure to bone and 50% reduction in dose to bystander organs. BM histology was similar between the groups. In the non-HCT model, TMI mice had significantly less acute intestinal and lung injury compared to TBI. In the HCT model, recipients of TMI had significantly less acute intestinal injury and spleen GVHD, but increased early donor cell engraftment and BM:organ SDF-1 ratio compared to TBI recipients. CONCLUSIONS: The expected BM damage was similar in both models, but the damage to other normal tissues was reduced by TMI. However, BM engraftment was improved in the TMI group compared to TBI, which may be due to enhanced production of SDF-1 in BM relative to other organs after TMI.

Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation.

The current feasibility of protecting emergency responders through bone marrow selective shielding is highlighted in the recent OECD/NEA report on severe accident management. Until recently, there was no effective personal protection from externally penetrating gamma radiation. In Chernobyl, first-responders wore makeshift lead sheeting, whereas in Fukushima protective equipment from gamma radiation was not available. Older protective solutions that use thin layers of shielding over large body surfaces are ineffective for energetic gamma radiation. Acute exposures may result in Acute Radiation Syndrome where the survival-limiting factor up to 10 Gy uniform, homogeneous exposure is irreversible bone marrow damage. Protracted, lower exposures may result in malignancies of which bone marrow is especially susceptible, being compounded by leukemia's short latency time. This highlights the importance of shielding bone marrow for preventing both deterministic and stochastic effects. Due to the extraordinary regenerative potential of hematopoietic stem cells, to effectively prevent the deterministic effects of bone marrow exposure, it is sufficient to protect only a small fraction of this tissue. This biological principle allows for a new class of equipment providing unprecedented attenuation of radiation to select marrow-rich regions, deferring the hematopoietic sub-syndrome of Acute Radiation Syndrome to much higher doses. As approximately half of the body's active bone marrow resides within the pelvis region, shielding this area holds great promise for preventing the deterministic effects of bone marrow exposure and concomitantly reducing stochastic effects. The efficacy of a device that selectively shields this region and other radiosensitive organs in the abdominal area is shown here.

Internal dosimetry for radioembolization therapy with Yttrium-90 microspheres.

The absorbed doses in the liver and adjacent viscera in Yttrium-90 radioembolization therapy for metastatic liver lesions are not well-documented. We sought for a clinically practical way to determine the dosimetry of this advent treatment. Six different female XCAT BMIs and seven different male XCAT BMIs were generated. Using Monte Carlo GATE code simulation, the total of 100MBq 90 Y was deposited uniformly in the source organ, liver. Self-irradiation and absorbed doses in lung, kidney and bone marrow were calculated. The mean energy of Yittrium-90 (i.e., 0.937 MeV) was used. The S-values and equivalent doses in target organs were estimated. The dose absorbed in the liver was between 84 and 53 Gy and below the target of 80 to 150 Gy. The absorbed dose in the bone marrow, lungs, and kidneys are very low and below 0.1 , 0.4, and 0.5 Gy respectively. Our study indicates that larger activities than the conventional dose of 3 GBq may be both required and safe. Further confirmations in clinical settings are needed.

Intravoxel incoherent motion MRI assessment of chemoradiation-induced pelvic bone marrow changes in cervical cancer and correlation with hematological toxicity.

PURPOSE: To investigate bone marrow changes after chemoradiation (CRT) using intravoxel incoherent motion magnetic resonance imaging (IVIM-MRI) and correlate imaging changes with hematological toxicity (HT) in patients with locally advanced cervical cancer. MATERIALS AND METHODS: Thirty-nine patients with newly diagnosed cervical cancer were prospectively recruited for two sequential 3.0T IVIM-MRI studies: before treatment (MRI-1) and 3-4 weeks after standardized CRT (MRI-2). The irradiated pelvic bone marrow was outlined as the regions of interest to derive the true diffusion coefficient (D) and perfusion fraction (f) based on a biexponential model. The apparent coefficient diffusion (ADC) was derived using the monoexponential model. Changes in these parameters between MRI-1 and MRI-2 were calculated as ΔD, Δf, and ΔADC. HT was defined accordingly to NCI-CTCAE (v. 4.03) of grade 3 and above. Statistical analysis was performed using Mann-Whitney U-test. RESULTS: The median age of patients was 54 years old (range 27-83 years old); 14 patients suffered from HT. Early bone marrow changes (3-4 weeks) of ΔD showed a significant difference between HT and non-HT groups (6.4 ± 19.7% vs. -6.4 ± 19.4%, respectively, P = 0.041). However, no significant changes were noted in Δf (3.7 ± 13.3% vs. 1.5 ± 12.5% respectively, P = 0. 592) and ΔADC (5.5 ± 26.3% vs. -3.3 ± 27.0% respectively, P = 0.303) between the HT and non-HT groups. Δf increased insignificantly for both groups. CONCLUSION: ΔD was the only significant parameter to differentiate early cellular environment changes in bone marrow after CRT, suggestive that ΔD was more sensitive than Δf and ΔADC to reflect the underlying microenvironment injury. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1491-1498.

Internal dose to active marrow and endosteum from radioactive iodine.

This study analyses the active marrow and endosteum dose differences between the new International Commission on Radiological Protection (ICRP) male and female reference computational phantoms and the stylised phantom for two thyroid agents. The active marrow and endosteum doses from (131)I and (123)I were calculated for 0-55 % maximum thyroid uptakes using the MCNP-4C Monte Carlo code. The biokinetic models were taken from ICRP Publication 53. To evaluate the absorbed doses to red marrow and endosteum, the deposited energy was determined for the 19 spongiosa regions and 6 medullary cavities and was mass weighted using the mass fractions available in ICRP Publication 116. The results were then compared with the published values given in ICRP Publication 53. The poor anatomic realism of the stylised phantom used in ICRP Publication 53 leads to important dose differences between the ICRP voxel phantoms and the stylised phantom. The influence of the use of different bone material was also investigated. Underestimations of ∼60% were observed for active marrow doses of the stylised phantom compared with reference voxel phantoms. The results highlight the importance of the accuracy of the shape and inter-organ distances of the anthropomorphic model used.

Oblique lateral radiographs and bitewings; estimation of organ doses in head and neck region with Monte Carlo calculations.

OBJECTIVES: When bitewing radiographs are not possible (e.g. patients with special needs), oblique lateral radiographs may offer an alternative. The aims of this study were to assess the impact of horizontal projection angulation, focus-to-skin distance, exposure time and age of the patient on the equivalent radiation dose of several organs in the head and neck region by means of personal computer X-ray Monte Carlo (PCXMC) calculations and to assess the dose obtained from conventional bitewing radiographs. METHODS: PCXMC v. 2.0 software (STUK(®), Helsinki, Finland) was used to estimate the equivalent radiation doses and the total effective dose. Three exposure times, five age categories, two focus-to-skin distances and eight horizontal geometric angulations were assumed. The organs involved were the thyroid gland, oesophagus, salivary glands, bone marrow, oral mucosa, skull, cervical spine and skin. A similar calculation was also performed for bitewings taken with a rectangular collimator. Results and conclusion Bitewings taken with rectangular collimation decrease the radiation burden of the patient to 50%, compared with circular collimation. In the oblique lateral radiographs, focus-to-skin distance, patient's age and beam collimation had a significant impact on the equivalent doses measured in this study. Exposure time had a significant impact on the equivalent doses of the salivary glands, oral mucosa, skull and skin. Horizontal angulations had a significant impact on the equivalent doses of the thyroid gland, bone marrow, oral mucosa, skull and cervical spine. The total effective radiation dose was significantly influenced by all parameters investigated in this study.

Investigation of effect of variations in bone fraction and red marrow cellularity on bone marrow dosimetry in radio-immunotherapy.

A method is described for computing patient-specific absorbed dose rates to active marrow which accounts for spatial variation in bone volume fraction and marrow cellularity. A module has been added to the 3D Monte Carlo dosimetry program DPM to treat energy deposition in the components of bone spongiosa distinctly. Homogeneous voxels in regions containing bone spongiosa (as defined on CT images) are assumed to be comprised only of bone, active (red) marrow and inactive (yellow) marrow. Cellularities are determined from biopsy, and bone volume fractions are computed from cellularities and CT-derived voxel densities. Electrons are assumed to deposit energy locally in the three constituent components in proportions determined by electron energy absorption fractions which depend on energy, cellularity, and bone volume fraction, and which are either taken from the literature or are derived from Monte Carlo simulations using EGS5. Separate algorithms are used to model primary ß particles and secondary electrons generated after photon interactions. Treating energy deposition distinctly in bone spongiosa constituents leads to marrow dosimetry results which differ from homogeneous spongiosa dosimetry by up to 20%. Dose rates in active marrow regions with cellularities of 20, 50, and 80% can vary by up to 20%, and can differ by up to 10% as a function of bone volume fraction. Dose to bone marrow exhibits a strong dependence on marrow cellularity and a potentially significant dependence on bone volume fraction.

Monte Carlo simulation of age-dependent radiation dose from alpha- and beta-emitting radionuclides to critical trabecular bone and bone marrow targets.

Alpha (α) particles and low-energy beta (ß) particles present minimal risk for external exposure. While these particles can induce leukemia and bone cancer due to internal exposure, they can also be beneficial for targeted radiation therapies. In this paper, a trabecular bone model is presented to investigate the radiation dose from bone- and marrow-seeking α and ß emitters to different critical compartments (targets) of trabecular bone for different age groups. Two main issues are addressed with Monte Carlo simulations. The first is the absorption fractions (AFs) from bone and marrow to critical targets within the bone for different age groups. The other issue is the application of (223)Ra for the radiotherapy treatment of bone metastases. Both a static model and a simulated bone remodeling process are established for trabecular bone. The results show significantly lower AFs from radionuclide sources in the bone volume to the peripheral marrow and the haematopoietic marrow for adults than for newborns and children. The AFs from sources on the bone surface and in the bone marrow to peripheral marrow and haematopoietic marrow also varies for adults and children depending on the energy of the particles. Regarding the use of (223)Ra as a radionuclide for the radiotherapy of bone metastases, the simulations show a significantly higher dose from (223)Ra and its progeny in forming bone to the target compartment of bone metastases than that from two other more commonly used ß-emitting radiopharmaceuticals, (153)Sm and (89)Sr. There is also a slightly lower dose from (223)Ra in forming bone to haematopoietic marrow than that from (153)Sm and (89)Sr. These results indicate a higher therapy efficiency and lower marrow toxicity from (223)Ra and its progeny. In conclusion, age-related changes in bone dimension and cellularity seem to significantly affect the internal dose from α and ß emitters in the bone and marrow to critical targets, and (223)Ra may be a more efficient radiopharmaceutical for the treatment of bone metastases than (153)Sm and (89)Sr, if the diffusion of (219)Rn to the bone marrow is insignificant.

Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations.

OBJECTIVES: The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerized tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations. STUDY DESIGN: Organ dose measurements were performed using 20 MOSFET dosimeters that were embedded in the 8 most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations. RESULTS: The effective dose measurements using MOSFET dosimeters yielded, using 0.5-cm steps, a value of 153 µSv and the PCXMC simulations resulted in a value of 136 µSv. CONCLUSIONS: The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial affect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region.