Assessment of combined modality therapy for non-small-cell lung carcinoma: A simulation study concerning concurrent chemo-brachytherapy.

Although surgery is the treatment of choice for early-stage non-small-cell lung carcinoma, almost two-thirds of patients do not have acceptable pulmonary function for extensive surgeries. The alternative approach for this large group of patients is sublobar resection along with low-dose-rate (LDR) brachytherapy (BT). However, patients with resected lungs have a high risk of recurrence and are often treated with platinum-based (Pt-based) chemotherapy (CT). In this study, we aimed to evaluate the absorbed doses of lung and other thoracic organs, considering concurrent chemo-BT with LDR sources in two modalities: conventional vs. unconventional Pt-based CT. We used the MCNPX code for simulations and to obtain the lung absorbed dose, dose enhancement factor (DEF), and Pt threshold concentration for the abovementioned modalities. Our results indicate that DEF correlates directly with Pt concentration at prescription point and is inversely correlated with depth. Dose enhancement for conventional CT concurrent with BT is <2%, while it is >2% in case of unconventional Pt-based CT wherein the Pt concentration exceeds 0.2 mg/g lung tissue. Also, the absorbed dose of healthy thoracic organs decreased by 2-11% in the latter approach. In conclusion, the concurrent chemo-BT in the lung environment could enhance the therapeutic doses merely by using unconventional CT methods, while lung Pt accumulation exceeds 0.2 mg/g.

Lead-free transparent shields for diagnostic X-rays: Monte Carlo simulation and measurements.

In recent years, the preference for using lead-free radiation protection shields has increased because of concerns regarding lead poisoning and leakage. In medical and research laboratories, glass shields are preferred because of their transparency. In this study, various glass shields were examined and compared based on the international standards. One commercially available lead-based shield, four recently studied shields, and three new lead-free shields were considered, and their shielding factors were calculated. We presented three glasses based on borate, phosphate, and silicate compounds, which were named Ir1, Ir2, and Ir3, respectively. Based on the International Electrotechnical Commission standard (IEC 61331), the air-kerma ratios (attenuation ratios) and lead equivalent values were derived using Monte Carlo N-Particle eXtended (MCNPX) calculations, and mass attenuation coefficients and effective atomic numbers (Zeff) of all the shields were obtained from XCOM database, in the diagnostic X-ray energy range of 40-120 keV. In addition, some measurements were performed for the reference (lead-based) glass to validate the simulations. The above-mentioned factors for silicate-bismuth-based (Ir3) and borosilicate-barium-based (Tu) glasses were found to be higher than the others and comparable to those of commercially available lead-based glass. In conclusion, Ir3 and Tu glasses were found to be the preferred lead-free transparent shields in the diagnostic X-ray energy range.

Quantitative determination of tumor platinum concentration of patients with advanced Breast, lung, prostate, or colorectal cancers undergone platinum-based chemotherapy.

CONTEXT: Previous studies have reported direct relationship between tumor reduction and its platinum concentration following platinum-based (Pt-based) chemotherapy. However, quantitative data of tumor platinum concentration have not yet been reported for the most common cancers. AIMS: Determination of tumor platinum concentration of breast, lung, prostate, and colorectal cancers after Pt-based chemotherapy; and evaluation of the influence of chemo drug type, chemotherapy regimen, and time lapse from last chemotherapy on tumor platinum concentration. MATERIALS AND METHODS: Tumor samples of patients with advanced breast, lung, prostate, and colorectal cancers undergone Pt-based chemotherapy were collected from pathology collection of various hospitals. The platinum concentration of each sample was measured by inductively coupled plasma optical emission spectrometry. The data were categorized by drug type, time lapse from last chemotherapy, and regimen type to evaluate their effects on platinum concentration. STATISTICAL ANALYSIS: ANOVA, Mann-Whitney U and Kruskal-Wallis tests were used. RESULTS: Tumor platinum concentrations of breast, lung, prostate, and colorectal cancers were all obtained in the range of 1-10 µg/g tumor tissue. Large values of P (>0.05) indicate no significant differences between various chemo drug, regimen, and time groups. CONCLUSIONS: In general, the platinum concentration was higher in prostate and lower in lung tumors. The type of Pt-based chemo drug, time lapse from the last chemotherapy, and concurrency of other antineoplastic agents administered with Pt-based chemo drugs had no significant effect on tumor platinum concentration.

Mathematical formulation of 125I seed dosimetry parameters and heterogeneity correction in lung permanent implant brachytherapy.

OBJECTIVES: Precise determination of dose distribution around low-energy brachytherapy sources as well as considering tissue heterogeneity is crucial for optimized treatment planning. This study is aimed at determination and mathematically formulation of American Association of Physicists in Medicine Task Group No. 43 (AAPM TG-43) dosimetry parameters of 125I seed (model 6711) and calculation of dose difference caused by neglecting lung heterogeneity in permanent implant brachytherapy. MATERIALS AND METHODS: Using MCNPX 2.6.0 code, 125I seed (model 6711) was simulated in a cubic water environment, and its dosimetry parameters mentioned in AAPM TG-43 protocol were obtained. After benchmarking of parameters and comparison with prior studies, mathematical equations were fitted to the data, and a specific set of 125I seeds was simulated on a plane in simulated lung and water environments. Appropriate photon histories were considered to achieve data with maximum accuracy (max error 1%). In the end, isodose curves, profiles, depth dose, and dose difference between lung and water environments were obtained. RESULTS: For 125I seed (model 6711), radial dose function and anisotropy functions were obtained precisely with R2 > 0.99, all in good agreement with previous studies and protocol. In addition, percentage dose difference between inhomogeneous lung and homogenous water environments in a 5 cm distance was calculated and presented as D (r) function with R2 > 0.99. CONCLUSIONS: Considering practical difficulties in dose calculations, 125I seed dosimetry parameters and lung heterogeneity corrections can be obtained precisely by MCNPX. Equations presented in this study are recommended to be considered in future studies based on lung permanent implantation.