Monte Carlo simulation of linac irradiation with dynamic wedges.

This study aims to simulate the dose distributions of LINAC with dynamic wedges (DWs) under various field sizes and wedge angles by the BEAMnrc code with DYNJAWS component module. These were compared with those calculated by the treatment planning system (TPS) and the measured data. All percentage depth doses (PDDs) were found to be in good agreement between TPS, Monte Carlo (MC) and measurements made in open fields and fields with DWs. For dose profiles, compared with the MC and the measurements, TPS gives reliable results for large field sizes (>10 × 10 cm(2)) but results in significant errors in small field sizes (5 × 5 cm(2)). The entrance surface doses calculated by TPS were found to be significantly overestimated. For depths deeper than 0.5 cm, TPS yields PDDs in agreement with MC simulations.

A comparison of physical and dosimetric properties of lung substitute materials.

PURPOSE: The need for an accurate estimate of absorbed doses within and around irradiated thorax tissues necessitates the use of carefully selected materials from which phantoms are constructed. A lung substitute is more difficult to establish mostly due to its low physical density. Although many researchers have used cork as a lung substitute, very little research data address cork's characteristics to determine which type of cork is optimal as a substitute for lung tissue. METHODS: Natural cork, composition cork, rubber cork, ATOM, RANDO, and a reference lung material (ICRU-44 lung tissue) were investigated to establish comparisons of physical properties. Following the determination of the respective physical properties, the dose distributions from 6 MV photon beams in water/lung substitute/water phantoms were assessed using the Monte Carlo method. Physical and electron densities affecting the dose distributions through lung tissues in different field size conditions were investigated. RESULTS: The physical properties (physical density, electronic density, and effective atomic number) of the composition cork are the most similar to those of the ICRU-44 lung, and the CT number of the composition cork is very similar to that of humans aged 30-60. PDD of the composition cork and the RANDO phantom are the most comparable to that of ICRU-44 lung in 1 × 1 cm(2) field size due to the combined properties of physical density (PD) and electron density per gram (EDG) of the studied lung materials. PD and EDG affect the lung dose primarily in small field size. The effects of PD are minimal in large fields, having a more rapid lateral electron equilibrium. EDG dominates PDD pattern in lung material when large fields are applied. Combined effects of PD and EDG are nonlinear for all field sizes. CONCLUSIONS: The composition cork is the preferred lung substitute based on physical and dosimetric properties.

Dosimetric evaluation of nanotargeted (188)Re-liposome with the MIRDOSE3 and OLINDA/EXM programs.

OBJECTIVE: The OLINDA/EXM computer code was created as a replacement for the widely used MIRDOSE3 code for radiation dosimetry in nuclear medicine. A dosimetric analysis with these codes was performed to evaluate nanoliposomes as carriers of radionuclides ((188)Re-liposomes) in colon carcinoma-bearing mice. METHODS: Pharmacokinetic data for (188)Re-N, N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine ((188)Re-BMEDA) and (188)Re-liposome were obtained for estimation of absorbed doses in normal organs. Radiation dose estimates for normal tissues were calculated using the MIRDOSE3 and OLINDA/EXM programs for a colon carcinoma solid tumor mouse model. RESULTS: Mean absorbed doses derived from(188)Re-BMEDA and (188)Re-liposome in normal tissues were generally similar as calculated by MIRDOSE3 and OLINDA/EXM programs. One notable exception to this was red marrow, wherein MIRDOSE3 resulted in higher absorbed doses than OLINDA/EXM (1.53- and 1.60-fold for (188)Re-BMEDA and (188)Re-liposome, respectively). CONCLUSIONS: MIRDOSE3 and OLINDA have very similar residence times and organ doses. Bone marrow doses were estimated by designating cortical bone rather than bone marrow as a source organ. The bone marrow doses calculated by MIRDOSE3 are higher than those by OLINDA. If the bone marrow is designated as a source organ, the doses estimated by MIRDOSE3 and OLINDA programs will be very similar.