Obtaining a new empirical (n,2n) cross section formula using Flerov and Talyzin non-elastic cross sections at 14-15 MeV.

The knowledge of (n,2n) cross sections is required in shielding and breeding calculations. It's also important, in nuclear reactor applications, for neutron dosimetry research. In nuclear reaction mechanism, (n,2n) reaction channel is the dominant reaction for medium and heavy mass nuclei at 14 MeV energy range. The empirical and semi-empirical (n,2n) reaction cross sections have been investigated by many authors, but theoretical calculations have not been adequate because of the character of the nuclear structure is not exactly known. In this work, a new empirical formula has been proposed to calculate the (n,2n) reaction cross sections at 14-15 MeV neutron incident energy. In the calculations different fitting method have been used to obtain cross-section formula for target nuclei in the range 14 ≤ A ≤ 241 mass number. The (n,2n) experimental cross sections have been taken from EXFOR nuclear data library. In this new formula, the Flerov and Talyzin expression for the inelastic cross section σne was used to fit the experimental (n,2n) cross sections. It has been observed that the obtained formulas give quite coherent results with the experimental data.

Simple parametrization of (n,d) cross sections using Flerov and Talyzin's formula.

This article aims at providing new cross section data from empirical formulas for the (n,d) reactions of which experimental measurements at 14-15 MeV energy are not available or limited. If the experimental data for a nuclear reaction at a given energy are scarce, theoretical calculations and also developing empirical formulas have a critical importance. Here, we propose a new empirical formula of (n,d) reactions for analysis of the relationship between the experimental data and the parameters of empirical formula. The present formula was obtained by using the non-elastic Flerov and Talyzin expression to calculate (n,d) cross sections at 14-15 MeV. Due to the good overall agreement with the measured cross sections, our empirical formula with polynomial fitting model including asymmetry parameter can be useful in planning new experiments of (n,d) reactions for energies around 14 MeV.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer.

PURPOSE: The aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo-Helical (TH)/Tomo-Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC). METHODS: Twenty-five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed-rank test was used to analyze the difference in dosimetric parameters. p-Value < 0.05 was considered statistically significant. RESULTS: TH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001). CONCLUSION: Concurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.

Dosimetric evaluation of phantoms including metal objects with high atomic number for use in intensity modulated radiation therapy.

The dosimetric effect of artefacts caused by metal hip prostheses in computed tomography imaging is most commonly encountered in the planning of prostate cancer treatment. In this study, a phantom, containing a metal with high atomic number, was prepared for intensity-modulated radiotherapy (IMRT) treatment plans to be used in quality assurance (QA) procedures. Two sets of image files, one without metal artefact correction (ORG) and another with MAR correction (MAR+), were sent to the treatment planning system. In this study, 12 IMRT treatment plans with different fields and segment numbers were calculated. The normal tissue complication probability (NTCP) values of imaginary organs at risk (OARs), such as the rectum and bladder, were investigated, as was the difference in dose maps for ORG and MAR+ derived by calculating gamma passing rates (GPRs). The MatriXX was used for the gamma evaluation of patient-specific IMRT QA measurements. The gamma evaluation was repeated, based on the measurements using an EBT3 gafchromic film, for the plan showing the lowest GPR. The mean relative difference in NTCP values between the two sets of image files was found to be 2.5, 2.1 and 1.4 for the rectum; and 5.33, 6.80 and 9.82 for the bladder, for the investigated 5-, 7- and 9-field beam arrangements, respectively. The relative differences and the standard deviations in GPRs for the standard and metal-containing phantoms were calculated for the MAR+ and ORG sets. The maximum difference found was 7.69% ± 0.88 for the 9-field beam arrangement calculated without metal artefact correction. In the IMRT QA procedures for prostate patients with hip prostheses, the application of a metal-containing phantom that is both easy and inexpensive to prepare, is considered to be a useful method for examining any dose changes involved in introducing a hip prosthesis. Therefore, it is recommended for use in clinics that do not have MAR correction algorithms.