Monte Carlo study of SPECT in boron neutron capture therapy for a heterogeneous human phantom

Background: Boron neutron capture therapy [BNCT] is a binary radiotherapy combining biochemical targeting with neutron irradiation. However, monitoring the boron distribution is a fundamental problem in BNCT. Prompt gamma rays emitted by boron capture reaction can be used to address the issue

Materials and Methods: The general-purpose Monte Carlo toolkits Geant4 and MCNP were used for the simulations. A cubic phantom with soft tissue was used to study the prompt gamma emission during BNCT. The Chinese hybrid phantom with arbitrary tumors was constructed and used to acquire the 0.478 MeV prompt gamma rays in BNCT. Tomographic images were reconstructed with the maximum likelihood expectation maximization [MLEM] algorithm

Results: Comparison between MCNP and Geant4 showed a similar gamma rays emission rate in soft tissue. Up to 30 gamma ray peaks were found in the simulation, and 0.478 MeV prompt gamma ray from boron was clearly observed. The single brain tumor with variable diameter from 1 cm to 4 cm in the heterogeneous anthropomorphic phantom was each time found to be recognizable in the reconstructed image. Furthermore, in a patient with four tumors, the variable distance between the source and the tumors leads to a neutron attenuation thus resulting in an inhomogeneous number of prompt gammas

Conclusion: The SPECT system for a heterogeneous phantom in BNCT was simulated with Geant4. The results show that BNCT-SPECT is valid for the reconstruction of the boron capture interaction position for a heterogeneous patient

Impacts of multiple-field irradiation and boron concentration on the treatment of boron neutron capture therapy for non-small cell lung cancer

Background: Boron neutron capture therapy [BNCT] is a radiotherapy that combines biological targeting and high linear energy transfer. A potential therapeutic approach for non-small cell lung cancer [NSCLC] is considered. However, dose in lung tumor is not homogeneous, and it will reduce the effect of BNCT treatment. In order to improve the dose distribution of BNCT, the multi-field irradiation strategy and its effects need to be explored

Materials and Methods: Common NSCLC model was defined in Chinese hybrid reference phantom and the boron concentration in skin and tumor varied from 6 to 18 ppm and from 30 to 65 ppm, respectively. Monte Carlo method for dose distribution calculation was used. Accelerator-based neutron source called [Neuboron source] was used and multi-field source irradiation plans were designed to optimize the dose distribution

Results: Under one-field irradiation, it was not feasible to perform BNCT, because the skin dose is unlikely to meet its dose limit. Under two- and three-field irradiation, the uniformity of tumor dose was improved and the maximum dose to organs at risk [OARs] decreased. If boron concentration in skin was between 6-18 ppm, BNCT was feasible with the boron concentration in tumor reaching about 57-60 ppm for two-field irradiation and 41-45 ppm for three-field irradiation, respectively

Conclusion: The multi-field irradiation plan could improve the dose distribution and the feasibility of BNCT for NSCLC. Theoretical distributions of Boron-10 were obtained to meet the treatable requirement of BNCT, which could provide a reference for NSCLC using BNCT in future multiple-field irradiation

Seroprevalence and risk factors for Toxoplasma gondii in sheep and goats in Jinzhou, Northeastern China

In the present study, serum samples from 402 sheep and 216 goats were collected from 5 counties in Jinzhou from August to October 2012 and antibodies to Toxoplasma gondii were detected by modified agglutination test (MAT). Overall, 104 (16.8%) had antibodies to T. gondii with antibody titres of 1:25 to 1:800. Seropositive samples were distributed in all the 5 counties and seroprevalences of T. gondii varied significantly with flock size, age and rearing system, but not with breed, gender and farm location. The seroprevalences in small farms (18.3%, 95/518, 95% confidence interval [CI], 15.0-21.7%) were statistically higher than that in large farms (9%, 9/100, 95% CI, 3.4-14.6%) (P < 0.05), older animals were statistically higher than that in younger animals (P < 0.01). The prevalence in extensively and semiintensively raised samples was statistically higher than that in intensively raised animals (P < 0.01). Small flock size and extensive rearing system are the potential risk factors for the prevalence of Toxoplasma infection in sheep and goats in Jinzhou. This is the first report of T. gondii infection in sheep and goats in Jinzhou, northeastern China, and of an association of seropositivity to T. gondii and the risk factors.

CVH-based computational female pelvic phantom for radiation dosimetry simulation

Accurate voxel phantom is needed for dosimetric simulation in radiation therapy for malignant tumors in female pelvic region. However, most of the existing voxel phantoms are constructed on the basis of Caucasian or non-Chinese population. A computational framework for constructing female pelvic voxel phantom for radiation dosimetry was performed based on Chinese Visible Human [CVH] datasets. First, several organs within pelvic region were segmented from CVH datasets. Then, polygonization and voxelization were performed based on the segmented organs and a 3D computational phantom is built in the form of a set of voxel arrays. The generated phantom can be converted and loaded into treatment planning system for radiation dosimetry calculation. From the observed dosimetric results of those organs and structures, we can evaluate their absorbed dose and implement some simulation studies. A voxel female pelvic phantom was developed from CVH datasets. It can be utilized for dosimetry evaluation and planning simulation, which would be very helpful to improve the clinical performance and reduce the radiation toxicity on organ at risk [OAR]