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.
 

Background: The aim of present study was to analyze the effectiveness of electron filters in the Telecobalt radiotherapy treatment by simulation technique.  Materials and Methods: The BEAMnrc Monte Carlo code was used to simulate the electron filters of thickness of 0.5 gm/cm² below the trimmer bar for 35 × 35 cm² field size in Theratron Equinox-80 telecobalt unit. The electron filters were made of an aluminum, copper, nickel, tin, PMMA, and lead with single or composite materials. The radiation beams at treatment distance were analyzed by generating profiles for photon and electron along the X-axis of radiation field.  Results: The electron energy fluence for unfiltered beam was 0.32% of the photon energy. The photon energy fluence intensity reduction due to filter was 3.7%. The filters with low atomic number have shown poor electron contamination removal efficiency. The tin, copper and nickel were found effective filters, removing nearly 38% of contaminant electron energy. The lead filter is equally effective as tin, however the high energy electrons emitted from filter due to “photo peaks” adds significant dose at 3.0 to 4.0 mm depth. Conclusion: The tin filter dominates over to other filters on the subject of surface dose reduction and depth of dose maximum (d_max). It reduces the surface dose by 9.6% and 13.9 % of unfiltered beam for 15 × 15 and 20 × 20 cm² field sizes respectively.

Background: Dose modulation is a key factor in practical proton therapy. This study investigates the dose modulation methodology of irregular radiation field (IRF)-based proton therapy using forward radiation treatment planning and conformal dose layer stacking (CDLS) methods. Materials and Methods: The geometric configuration of a virtual multi-leaf system was constructed to generate IRFs during Monte Carlo simulations. Two patient geometries—lymphatic metastasis and brain tumors—were configured to investigate the dosimetric feasibility and applications of IRF-based proton therapy in ideal patient anatomies. The investigated tumors were divided into slices perpendicular to proton beam axis. Segments were designed to be conformal to the profiles of these tumor slices. Conformal dose layers were produced by modulating the proton intensities and energies of the predesigned segments. Then, these dose layers were stacked throughout the tumors to obtain sufficient and conformal tumor doses. Results: From the proposed IRF-based proton therapy, tumors with 4-7 cm extents along the depth direction could be treated with fewer than 10 segments. The lymphatic metastasis and brain tumors were sufficiently covered by 95% dose lines, while appropriate distal and proximal dose conformities were achieved. The maximum tumor doses did not exceed 110%. Conclusions: Theoretically, the proposed IRF-based proton therapy using forward planning and CDLS methods is feasible from the viewpoint of dosimetry. This study can serve as a foundation for future investigations of potential proton therapy methods based on fast conformal dose layer stacking using radiation fields with irregular shapes.

This is a case report on stereotaxic (Stereotactic Body Radiotherapy-SBRT) for lung cancer located in the left lower lobe (Segment 6, S6). There have been no reports on marked displacement of the peripheral lung cancer during radiotherapy. A pulmonary nodule was discovered on computed tomography (CT) conducted for a persistent cough in an 87-year-old male. According to diagnostic imaging, this nodule was clearly delineated and had an irregular margin. The image diagnosis was T1N0M0, stage I primary lung cancer located in the left lower lobe and no pathological type was identified. The patient was treated with SBRT using a Linear accelerator (LINAC) at a total dose of 48 Gray (Gy) in 4 fractions. On performing cone beam CT (CBCT) at the third fraction, the tumor position had moved caudally by about 3 centimeters (cm). For this reason, we canceled further treatment and the case was re-planned. Four days after discontinuing treatment, 4-dimensional CT (4DCT) images were obtained before initiation of the remaining fractions of SBRT. Therefore, the patient completed 4 fractions of SBRT and the tumor location was confirmed before beam delivery. The tumor location differed based on the patient’s position (i.e., standing versus lying in a supine position), and we considered that it moved due to adhesion to the pleura when the patient was standing. If reproducibility of the tumor position cannot be guaranteed, the patient should undergo to CT re-simulation. Oncologists should re-evaluate the movement of the tumor on respiration and adjust the margins accordingly.

Background: The present study aims to investigate and characterize radiation dosimetric phantom that is made from Rhizophora spp. particleboards using SPC/NaOH/IA-PAE adhesive. Materials and Methods: Modification of soy protein concentrate (SPC) bonded Rhizophora spp. particleboard phantoms were carried out using sodium hydroxide (NaOH) with different amount of bio-based cross-linking agent (IA-PAE) with three different categories of particle size. The radiation attenuation parameters were evaluated with photons energies between 16.59 and 25.26 keV derived from X-ray fluorescence. SPC-based plug phantoms were scanned together with the CT density phantom 062M at 80, 120, and 135 kVp, and 250 mAs. Results: The physical and mechanical properties were found to be improved, while the dimensional stability was decreased through the addition of 15 wt% IA-PAE with decreasing particle size. The lowest HVL and MFP, and the highest μ_m with their corresponding values of Z_eƒƒ  (p-values of 0.054, 0.055, 0.060, and 0.075), and the relatively low X² values are the characteristics of samples labeled as A₁₅, B₁₅, C₁₀, and C₁₅. Sample C₁₅ gave the closest values of CT number, ED, and DDPs to water for all tested tube voltages. Conclusion: The results point to the possibility of employing C₁₅ as a promising TEPM.