Neutron shielding for a new projected proton therapy facility: A Geant4 simulation study

In this work, we used the Monte Carlo-based Geant4 simulation toolkit to calculate the ambient dose equivalents due to the secondary neutron field produced in a new projected proton therapy facility. In particular the facility geometry was modeled in Geant4 based on the CAD design. Proton beams were originated with an energy of 250 MeV in the gantry rooms with different angles with respect to the patient; a fixed 250 MeV proton beam was also modeled. The ambient dose equivalent was calculated in several locations of interest inside and outside the facility, for different scenarios. The simulation results were compared qualitatively to previous work on an existing facility bearing some similarities with the design under study, showing that the ambient dose equivalent ranges obtained are reasonable. The ambient dose equivalents, calculated by means of the Geant4 simulation, were compared to the Australian regulatory limits and showed that the new facility will not pose health risks for the public or staff, with a maximum equivalent dose rate equal to 7.9 mSv/y in the control rooms and maze exit areas and 1.3·10⁻¹ mSv/y close to the walls, outside the facility, under very conservative assumptions. This work represents the first neutron shielding verification analysis of a new projected proton therapy facility and, as such, it may serve as a new source of comparison and validation for the international community, besides confirming the viability of the project from a radioprotection point of view.     

Feasibility study on the use of 230 MeV proton cyclotron in proton therapy centers as a spallation neutron source for BNCT

AimThe feasibility of using 230 MeV proton cyclotrons in proton therapy centers as a spallation neutron source for Boron Neutron Capture Therapy (BNCT) was investigated.BackgroundBNCT is based on the neutron irradiation of a ¹⁰B-containing compound located selectively in tumor cells. Among various types of neutron generators, the spallation neutron source is a unique way to generate high-energy and high-flux neutrons.Materials and MethodsNeutron beam was generated by a proton accelerator via spallation reactions and then the produced neutron beam was shaped to be appropriate for BNCT. The proposed Beam Shaping Assembly (BSA) consists of different moderators, a reflector, a collimator, as well as thermal and gamma filters. In addition, the simulated Snyder head phantom was utilized to evaluate the dose distribution in tumor and normal tissue due to the irradiation by the designed beam. MCNPX2.6 Monte Carlo code was used to optimize BSA as well as evaluate dose evaluation.ResultsA BSA was designed. With the BSA configuration and a beam current of 104 nA, epithermal neutron flux of 3.94 × 10⁶ [n/cm²] can be achieved, which is very low. Provided that we use the beam current of 5.75 μA, epithermal neutron flux of 2.18 × 10⁸ [n/cm²] can be obtained and the maximum dose of 38.2 Gy-eq can be delivered to tumor tissue at 1.4 cm from the phantom surface.ConclusionsResults for 230 MeV protons show that with proposed BSA, proton beam current about 5.75 μA is required for this purpose.     

A 13C(d,n)-based epithermal neutron source for Boron Neutron Capture Therapy

PurposeBoron Neutron Capture Therapy (BNCT) requires neutron sources suitable for in-hospital siting. Low-energy particle accelerators working in conjunction with a neutron producing reaction are the most appropriate choice for this purpose. One of the possible nuclear reactions is ¹³C(d,n)¹⁴N. The aim of this work is to evaluate the therapeutic capabilities of the neutron beam produced by this reaction, through a 30 mA beam of deuterons of 1.45 MeV.MethodsA Beam Shaping Assembly design was computationally optimized. Depth dose profiles in a Snyder head phantom were simulated with the MCNP code for a number of BSA configurations. In order to optimize the treatment capabilities, the BSA configuration was determined as the one that allows maximizing both the tumor dose and the penetration depth while keeping doses to healthy tissues under the tolerance limits.ResultsSignificant doses to tumor tissues were achieved up to ∼6 cm in depth. Peak doses up to 57 Gy-Eq can be delivered in a fractionated scheme of 2 irradiations of approximately 1 h each. In a single 1 h irradiation, lower but still acceptable doses to tumor are also feasible.ConclusionsTreatment capabilities obtained here are comparable to those achieved with other accelerator-based neutron sources, making of the ¹³C(d,n)¹⁴N reaction a realistic option for producing therapeutic neutron beams through a low-energy particle accelerator.     

Calculation of dose components in head phantom for boron neutron capture therapy.

Application of neutrons to cancer treatment has been a subject of considerable clinical and research interest since the discovery of the neutron by Chadwick in 1932 (3). Boron neutron capture therapy (BNCT) is a technique of radiation oncology which is used in treating brain cancer (glioblastoma multiform) or melanoma and that consists of preferentially loading a compound containing 10B into the tumor location, followed by the irradiation of the patient with a beam of neutron. Dose distribution for BNCT is mainly based on Monte Carlo simulations. In this work, the absorbed dose spatial distribution resultant from an idealized neutron beam incident upon ahead phantom is investigated using the Monte Carlo N-particles code, MCNP 4B. The phantom model used is based on the geometry of a circular cylinder on which sits an elliptical cylinder capped by half an ellipsoid representing the neck and head, both filled with tissue-equivalent material. The neutron flux and the contribution of individual absorbed dose components, as a function of depths and of radial distance from the beam axis (dose profiles) in phantom model, is presented and discussed. For the studied beam the maximum thermal neutron flux is at a depth of 2 cm and the maximum gamma dose at a depth of 4 cm.     

Organ doses from a proton gantry-mounted cone-beam computed tomography system characterized with MCNP6 and GATE

PurposeTo determine organ doses from a proton gantry-mounted cone-beam computed tomography (CBCT) system using two Monte Carlo codes and to study the influence on organ doses from different acquisition modes and repeated imaging.MethodsThe CBCT system was characterized with MCNP6 and GATE using measurements of depth doses in water and spatial profiles in air. The beam models were validated against absolute dose measurements and used to simulate organ doses from CBCT imaging with head, thorax and pelvis protocols. Anterior and posterior 190° scans were simulated and the resulting organ doses per mAs were compared to those from 360° scans. The influence on organ doses from repeated imaging with different imaging schedules was also investigated.ResultsThe agreement between MCNP6, GATE and measurements with regard to depth doses and beam profiles was within 4% for all protocols and the corresponding average agreement in absolute dose validation was 4%. Absorbed doses for in-field organs from 360° scans ranged between 6 and 8 mGy, 15–17 mGy and 24–54 mGy for the head, thorax and pelvis protocols, respectively. Cumulative organ doses from repeated CBCT imaging ranged between 0.04 and 0.32 Gy for weekly imaging and 0.2–1.6 Gy for daily imaging. The anterior scans resulted in an average increase in dose per mAs of 24% to the organs of interest relative to the 360° scan, while the posterior scan showed a 37% decrease.ConclusionsA proton gantry-mounted CBCT system was accurately characterized with MCNP6 and GATE. Organ doses varied greatly depending on acquisition mode, favoring posterior scans.     

Simultaneous production of mixed electron–photon beam in a medical LINAC: A feasibility study

PurposeThe electron or photon beams might be used for treatment of tumors. Each beam has its own advantage and disadvantages. Combo beam can increase the advantages. No investigation has been performed for producing simultaneous mixed electron and photon beam. In current study a device has been added to the Medical Linac to produce a mixed photon–electron beam.MethodsFirstly a Varian 2300CD head was simulated by MCNP Monte Carlo Code. Two sets of perforated lead sheets with 1 and 2 mm thickness and 0.2, 0.3, and 0.5 cm punches then placed at the top of the applicator holder tray. This layer produces bremsstrahlung x-ray upon impinging fraction electrons on it. The remaining fraction of electrons passes through the holes. The simulation was performed for 10 × 10, 6 × 6, and 4 × 4 cm² field size.ResultsFor 10 × 10 cm² field size, among the punched targets, the largest penumbra difference between the depth of 1 and 7 cm was 72%. This difference for photon and electron beams were 31% and 325% respectively. A maximum of 39% photon percentage was produced by 2 mm target with 0.2 cm holes diameter layer. The minimum surface dose value was 4% lesser than pure electron beam. For small fields, unlike the pure electron beam, the PDD, penumbra, and flatness variations were negligible.ConclusionsThe advantages of mixing the electron and photon beam is reduction of pure electron's penumbra dependency with the depth, especially for small fields, also decreasing of dramatic changes of PDD curve with irradiation field size.     

In vitro studies of DNA damage and repair mechanisms induced by BNCT in a poorly differentiated thyroid carcinoma cell line

Boron neutron capture therapy (BNCT) for aggressive tumors is based on nuclear reaction [¹⁰B (n, α) ⁷Li]. Previously, we demonstrated that BNCT could be applied for the treatment of undifferentiated thyroid carcinoma. The aim of the present study was to describe the DNA damage pattern and the repair pathways that are activated by BNCT in thyroid cells. We analyzed γH2AX foci and the expression of Ku70, Rad51 and Rad54, main effector enzymes of non-homologous end joining (NHEJ) and homologous recombination repair (HRR) pathways, respectively, in thyroid follicular carcinoma cells. The studied groups were: (1) C [no irradiation], (2) gamma [⁶⁰Co source], (3) N [neutron beam alone], (4) BNCT [neutron beam plus 10 µg ¹⁰B/ml of boronphenylalanine (¹⁰BPA)]. The total absorbed dose was always 3 Gy. The results showed that the number of nuclear γH2AX foci was higher in the gamma group than in the N and BNCT groups (30 min–24 h) (p?<?0.001). However, the focus size was significantly larger in BNCT compared to other groups (p?<?0.01). The analysis of repair enzymes showed a significant increase in Rad51 and Rad54 mRNA at 4 and 6 h, respectively; in both N and BNCT groups and the expression of Ku70 did not show significant differences between groups. These findings are consistent with an activation of HRR mechanism in thyroid cells. A melanoma cell line showed different DNA damage pattern and activation of both repair pathways. These results will allow us to evaluate different blocking points, to potentiate the damage induced by BNCT.     

Detection of γH2AX foci in mouse normal brain and brain tumor after boron neutron capture therapy

Aim

In this study, we investigated γH2AX foci as markers of DSBs in normal brain and brain tumor tissue in mouse after BNCT.

Background

Boron neutron capture therapy (BNCT) is a particle radiation therapy in combination of thermal neutron irradiation and boron compound that specifically accumulates in the tumor. ¹⁰B captures neutrons and produces an alpha (⁴He) particle and a recoiled lithium nucleus (⁷Li). These particles have the characteristics of extremely high linear energy transfer (LET) radiation and therefore have marked biological effects. High LET radiation causes severe DNA damage, DNA DSBs. As the high LET radiation induces complex DNA double strand breaks (DSBs), large proportions of DSBs are considered to remain unrepaired in comparison with exposure to sparsely ionizing radiation.

Materials and methods

We analyzed the number of γH2AX foci by immunohistochemistry 30 min or 24 h after neutron irradiation.

Results

In both normal brain and brain tumor, γH2AX foci induced by ¹⁰B(n,α)⁷Li reaction remained 24 h after neutron beam irradiation. In contrast, γH2AX foci produced by γ-ray irradiation at contaminated dose in BNCT disappeared 24 h after irradiation in these tissues.

Conclusion

DSBs produced by ¹⁰B(n,α)⁷Li reaction are supposed to be too complex to repair for cells in normal brain and brain tumor tissue within 24 h. These DSBs would be more difficult to repair than those by γ-ray. Excellent anti-tumor effect of BNCT may result from these unrepaired DSBs induced by ¹⁰B(n,α)⁷Li reaction.     

New horizons for therapy based on the boron neutron capture reaction

Boron neutron capture therapy (BNCT) is currently undergoing clinical trials in the USA, Japan and The Netherlands with patients afflicted with deadly brain cancer (glioblastoma multiforme) or melanoma. This therapy relies on a binary process in which the capture of a slow neutron by a ¹⁰B nucleus leads to an energetic nuclear fission reaction, with the formation of ⁷Li³⁺ and ⁴He²⁺ and accompanied by about 2.4 MeV of energy. The fleeting ⁷Li³⁺ and ⁴He²⁺ travel a distance of only about the diameter of one cell, and they are deadly to any cell in which they have been produced. Research in progress is concerned with the development of advanced boron agents and neutron sources, other than nuclear reactors, for the treatment of a variety of cancer types using novel ¹⁰B delivery methods. Non-malignant diseases such as rheumatoid arthritis offer additional opportunities for BNCT. The entire BNCT area awaits commercialization.     

Performance of silicon microdosimetry detectors in boron neutron capture therapy

Reverse-biased silicon p-n junction arrays using Silicon-On-Insulator technology have been proposed as microdosimeters. The performance of such detectors in boron neutron capture therapy (BNCT) is discussed. This work provides the first reported measurements using boron-coated silicon diode arrays as microdosimeters in BNCT. Results are in good agreement with measurements with gas proportional counters. Various boron-coating options are investigated along with device orientation effects. Finally, a 235U coating is tested to simulate the behavior of the device in a heavy-ion therapy beam.     

Boron neutron capture therapy (BNCT) for the treatment of spontaneous nasal planum squamous cell carcinoma in felines

Recently, Boron neutron capture therapy (BNCT) was successfully applied to treat experimental squamous cell carcinomas (SCC) of the hamster cheek pouch mucosa, with no damage to normal tissue. It was also shown that treating spontaneous nasal planum SCC in terminal feline patients with low dose BNCT is safe and feasible. In an extension of this work, the present study aimed at evaluation of the response of tumor and dose-limiting normal tissues to potentially therapeutic BNCT doses. Biodistribution studies with ¹⁰B-boronophenylalanine (BPA enriched in ¹⁰B) as a ¹⁰B carrier were performed on three felines that showed advanced nasal planum SCC without any standard therapeutic option. Following the biodistribution studies, BNCT mediated by ¹⁰BPA was done using the thermalized epithermal neutron beam at the RA-6 Nuclear Reactor. Follow-up included clinical evaluation, assessment of macroscopic tumor and normal tissue response and biopsies for histopathological analysis. The treated animals did not show any apparent radiation-induced toxicity. All three animals exhibited partial tumor control and an improvement in clinical condition. Enhanced therapeutic efficacy was associated with a high ¹⁰B content of the tumor and a small tumor size. BNCT is therefore believed to be potentially effective in the treatment of spontaneous SCC. However, improvement in targeting ¹⁰B into all tumor cells and delivering a sufficient dose at a greater depth are still required for the treatment of deep-seated, large tumors. Future studies are needed to evaluate the potential efficacy of the dual mode cellular (e.g. BPA-BNCT) and vascular (e.g. GB-10-BNCT) targeting protocol in a preclinical scenario, employing combinations of ¹⁰B compounds with different properties and complementary uptake mechanisms.     

Influence of beam incidence and irradiation parameters on stray neutron doses to healthy organs of pediatric patients treated for an intracranial tumor with passive scattering proton therapy

PurposeIn scattering proton therapy, the beam incidence, i.e. the patient’s orientation with respect to the beam axis, can significantly influence stray neutron doses although it is almost not documented in the literature.MethodsMCNPX calculations were carried out to estimate stray neutron doses to 25 healthy organs of a 10-year-old female phantom treated for an intracranial tumor. Two beam incidences were considered in this article, namely a superior (SUP) field and a right lateral (RLAT) field. For both fields, a parametric study was performed varying proton beam energy, modulation width, collimator aperture and thickness, compensator thickness and air gap size.ResultsUsing a standard beam line configuration for a craniopharyngioma treatment, neutron absorbed doses per therapeutic dose of 63 μGy Gy⁻¹ and 149 μGy Gy⁻¹ were found at the heart for the SUP and the RLAT fields, respectively. This dose discrepancy was explained by the different patient’s orientations leading to changes in the distance between organs and the final collimator where external neutrons are mainly produced. Moreover, investigations on neutron spectral fluence at the heart showed that the number of neutrons was 2.5 times higher for the RLAT field compared against the SUP field. Finally, the influence of some irradiation parameters on neutron doses was found to be different according to the beam incidence.ConclusionBeam incidence was thus found to induce large variations in stray neutron doses, proving that this parameter could be optimized to enhance the radiation protection of the patient.     

RBEs of Thermal Neutron Capture Therapy and 10B(n,α)7 Li Reaction on Melanoma-Bearing Hamsters

Using Greene's melanoma transplanted into Syrian (golden) hamsters, we determined the relative biological effectiveness (RBE) of thermal neutron capture therapy (TNCT) using ¹⁰B-paraboronophenylalanine (¹⁰B-BPA) in comparison with a 9-MeV electron beam. We also obtained the RBE of the ¹⁰B(n,α)⁷Li reaction by calculation based on summed dose data from TNCT. Throughout this study, the Kyoto University Research Reactor was used as the source for thermal neutrons; the reactor was specially altered to attain a low contamination level both for gamma-rays and fast neutrons. ¹⁰B-BPA was administered 8 hours before thermal neutron irradiation to the hamsters with melanoma. The tumor was then irradiated at 5 MW for 90 minutes. The absorbed dose from this TNCT was calculated by the method of Fairchild and Goodman (Phys. Med. Biol. 1966; 2:15–30). The RBEs of the TNCT and the ¹⁰B(n,α)⁷Li reaction obtained by the tumor growth delay time (TGDT) method were 2.22 and 2.51, respectively, at 10.5 days of TGDT. These RBE values varied with TGDT and the absorbed dose. The RBE value of TNCT had a peak at 7.0 days of TGDT; that of the ¹⁰B(n,α)⁷Li reaction was higher at a low absorbed dose level and lower at a high absorbed dose level.     

Geant4-DNA simulation of the pre-chemical stage of water radiolysis and its impact on initial radiochemical yields

This paper demonstrates the impact of the pre-chemical stage, especially the dissociation scheme and the associated probabilities, on water radiolysis simulation using the Geant4-DNA Monte Carlo track structure simulation toolkit. The models and parameters provided by TRACs have been collected and implemented into Geant4-DNA. In order to evaluate their influence on water radiolysis simulation, the radiochemical yields (G-values) are evaluated as a function of time and LET using the “chem6” Geant4-DNA example, and they are compared with published experimental and calculated data. The new pre-chemical models lead to a better agreement with literature data than the default pre-chemical models of Geant4-DNA, especially for OH radicals and H₂O₂. The revised chemistry constructor “G4EmDNAChemistry_option3” is available in Geant4-DNA version 10.7.     

Detailed dosimetry calculation for in-vitro experiments and its impact on clinical BNCT

PurposeBoron Neutron Capture Therapy (BNCT) is a form of hadrontherapy based on the selective damage caused by the products of neutron capture in ¹⁰B to tumour cells. BNCT dosimetry strongly depends on the parameters of the dose calculation models derived from radiobiological experiments. This works aims at determining an adequate dosimetry for in-vitro experiments involving irradiation of monolayer-cultured cells with photons and BNCT and assessing its impact on clinical settings.M&MDose calculations for rat osteosarcoma UMR-106 and human metastatic melanoma Mel-J cell survival experiments were performed using MCNP, transporting uncharged particles for KERMA determinations, and secondary particles (electrons, protons, ¹⁴C, ⁴He and ⁷Li) to compute absorbed dose in cultures. Dose-survival curves were modified according to the dose correction factors determined from computational studies. New radiobiological parameters of the photon isoeffective dose models for osteosarcoma and metastatic melanoma tumours were obtained. Dosimetry implications considering cutaneous melanoma patients treated in Argentina with BNCT were assessed and discussed.ResultsKERMA values for the monolayer-cultured cells overestimate absorbed doses of radiation components of interest in BNCT. Detailed dose calculations for the osteosarcoma irradiation increased the relative biological effectiveness factor RBE_1% of the neutron component in more than 30%. The analysis based on melanoma cases reveals that the use of survival curves based on KERMA leads to an underestimation of the tumour doses delivered to patients.ConclusionsConsidering detailed dose calculation for in-vitro experiments significantly impact on the prediction of the tumor control in patients. Therefore, proposed methods are clinically relevant.     

Radiotherapy dose enhancement using BNCT in conventional LINACs high-energy treatment: Simulation and experiment

Aim

To employ the thermal neutron background that affects the patient during a traditional high-energy radiotherapy treatment for BNCT (Boron Neutron Capture Therapy) in order to enhance radiotherapy effectiveness.

Background

Conventional high-energy (15–25 MV) linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons in the gantry with a mean energy of about 1 MeV due to (γ, n) reaction. This neutron flux, isotropically distributed, is considered as an unavoidable undesired dose during the treatment. Considering the moderating effect of human body, a thermal neutron fluence is localized in the tumour area: this neutron background could be employed for BNCT by previously administering ¹⁰B-Phenyl-Alanine (¹⁰BPA) to the patient.

Materials and methods

Monte Carlo simulations (MCNP4B-GN code) were performed to estimate the total amount of neutrons outside and inside human body during a traditional X-ray radiotherapy treatment.Moreover, a simplified tissue equivalent anthropomorphic phantom was used together with bubble detectors for thermal and fast neutron to evaluate the moderation effect of human body.

Results

Simulation and experimental results confirm the thermal neutron background during radiotherapy of 1.55E07 cm⁻² Gy⁻¹.The BNCT equivalent dose delivered at 4 cm depth in phantom is 1.5 mGy-eq/Gy, that is about 3 Gy-eq (4% of X-rays dose) for a 70 Gy IMRT treatment.

Conclusions

The thermal neutron component during a traditional high-energy radiotherapy treatment could produce a localized BNCT effect, with a localized therapeutic dose enhancement, corresponding to 4% or more of photon dose, following tumour characteristics. This BNCT additional dose could thus improve radiotherapy, acting as a localized radio-sensitizer.     

Thermal and resonance neutrons generated by various electron and X-ray therapeutic beams from medical linacs installed in polish oncological centers

BackgroundHigh-energy photon and electron therapeutic beams generated in medical linear accelerators can cause the electronuclear and photonuclear reactions in which neutrons with a broad energy spectrum are produced. A low-energy component of this neutron radiation induces simple capture reactions from which various radioisotopes originate and in which the radioactivity of a linac head and various objects in the treatment room appear.AimThe aim of this paper is to present the results of the thermal/resonance neutron fluence measurements during therapeutic beam emission and exemplary spectra of gamma radiation emitted by medical linac components activated in neutron reactions for four X-ray beams and for four electron beams generated by various manufacturers’ accelerators installed in typical concrete bunkers in Polish oncological centers.Materials and methodsThe measurements of neutron fluence were performed with the use of the induced activity method, whereas the spectra of gamma radiation from decays of the resulting radioisotopes were measured by means of a portable high-purity germanium detector set for field spectroscopy.ResultsThe fluence of thermal neutrons as well as resonance neutrons connected with the emission of a 20 MV X-ray beam is ～10⁶ neutrons/cm² per 1 Gy of a dose in water at a reference depth. It is about one order of magnitude greater than that for the 15 MV X-ray beams and about two orders of magnitude greater than for the 18–22 MeV electron beams regardless of the type of an accelerator.ConclusionThe thermal as well as resonance neutron fluence depends strongly on the type and the nominal potential of a therapeutic beam. It is greater for X-ray beams than for electrons. The accelerator accessories and other large objects should not be stored in a treatment room during high-energy therapeutic beam emission to avoid their activation caused by thermal and resonance neutrons. Half-lives of the radioisotopes originating from the simple capture reaction (n,γ) (from minutes to hours) are long enough to accumulate radioactivity of components of the accelerator head. The radiation emitted by induced radioisotopes causes the additional doses to staff operating the accelerators.     

Optimization of Boron and Neutron Delivery for Neutron Capture Therapy

A number of groups in the United States have received funding that will permit evaluation of the clinical efficacy of the neutron capture therapy (NCT) procedure. Various reactors are being modified to allow the construction of an epithermal neutron beam. At the Brookhaven Medical Research Reactor (BMRR), the patient irradiation facility is being modified to produce an optimized epithermal neutron beam. An 80-cm-thick Al-D₂O mixture (184 g/cm², 25% D₂O by volume) is being installed in the shutter assembly. One-dimensional calculations indicate that this configuration should provide an epithermal neutron flux density of ～1 × 10⁹ n/cm²/sec at 3 MW and a concomitant fast neutron dose rate of ～2 × 10^?11 rad per epithermal neutron (assuming a homogeneous Al-D₂O mixture). The actual geometry will be an inhomogeneous array of D₂O and Al layers producing parameters somewhat less favorable than those listed above; experimental verification is in progress. Significant gains have recently been made in selectively targeting B to melanoma with various melanaffinic compounds, including p-boronophenylalanine, and with boronated porphyrins that may be applicable to a variety of tumors. Neutron capture radiographs have been obtained with the above compounds, and efforts have been made to quantitate boron uptake in growing and quiescent or necrotic regions of tumor via double-labeling techniques obtained with tritiated thymidine. A correlation between therapeutic efficacy and the ability to deliver boron to viable areas of tumor has been observed.     

Effective dose in percutaneous transhepatic biliary drainage examination using PCXMC2.0 and MCNP5 Monte Carlo codes

ObjectivesTo estimate the organ equivalent doses and the effective doses (E) in patient undergoing percutaneous transhepatic biliary drainage (PTBD) examinations, using the MCNP5 and PCXMC2 Monte Carlo-based codes.MethodsThe purpose of this study is to estimate the organ doses to patients undergoing PTBD examinations by clinical measurements and Monte Carlo simulation. Dose area products (DAP) values were assessed during examination of 43 patients undergoing PTBD examination separated into groups based on the gender and the dimensions and location of the beam.ResultsMonte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 and PCXMC2 codes in order to estimate equivalent organ doses. Regarding the PTBD examination the organ receiving the maximum radiation dose was the lumbar spine. The mean calculated H_T for the lumbar spine using the MCNP5 and PCXMC2 methods respectively, was 117.25 mSv and 131.7 mSv, in males. The corresponding doses were 139.45 mSv and 157.1 mSv respectively in females. The H_T values for organs receiving considerable amounts of radiation during PTBD examinations were varied between 0.16% and 73.2% for the male group and between 1.10% and 77.6% for the female group. E in females and males using MCNP5 and PCXMC2.0 was 5.88 mSv and 6.77 mSv, and 4.93 mSv and 5.60 mSv.ConclusionThe doses remain high compared to other invasive operations in interventional radiology. There is a reasonable good coincidence between the MCNP5 and PCXMC2.0 calculation for most of the organs.     

The effects of boron neutron capture irradiation on oral mucosa: evaluation using a rat tongue model.

The ventral surface of the tongue of male Fisher 344 rats was used to evaluate the response of oral mucosa to boron neutron capture irradiation. Three hours after i.p. injection of 700 mg/kg of the boron delivery agent p-boronophenylalanine (BPA), the boron concentrations in blood and tongue mucosal epithelium were approximately 21 and 23 microgram (10)B/g, respectively. The doses required to produce a 50% incidence of ulceration with X rays, the Brookhaven Medical Research Reactor thermal neutron beam alone, or the thermal neutron beam in the presence of BPA were 13.4 +/- 0.2, 4. 2 +/- 0.1, and 3.0 +/- 0.1 Gy, respectively. Ulceration of the tongue was evident by 6 to 7 days after irradiation, irrespective of the irradiation modality; healing was related to dose and was relatively rapid (相似文献