ABSTRACT
Aim of Study: The report of the task group number 43(TG-43) of AAPM has been known as the most common method to obtain the dose distribution around brachytherapy sources. The error caused by independent obtaining and rounding and combinational error caused by algebraic operations of each TG-43 dosimetry parameters increase the total error in the calculation of the dose distribution around the brachytherapy sources. The aim of the present study is to present and evaluate a matrix-based approach for simplifying and reducing calculation errors. Materials and Methods: In this study, the simulation method with MCNPX code was used to obtain the dose distribution. Four sources were simulated, and the dose matrix around these sources was obtained. Finally, the dose distribution obtained from the matrix-based method was compared with the dose distribution obtained from the method of TG-43 report. Results: There is little difference between the values obtained from the two methods in some points. Absolute mean differences between the values obtained by these two methods were 1.4% for the 60Co, 3.52% for the 137Cs, 2.67% for the 192Ir, and 2.42% for the 103Pd sources. The advantage of the matrix-based method is its simple computing process and less computation time. Conclusion: Considering that the comparison of brachytherapy sources is not raised in calculations of treatment planning systems and also considering the more uncertainty in the calculation of the dose distribution in TG-43 method, it is recommended that dose distribution obtained from matrix-based method be used as input for treatment planning systems.
ABSTRACT
Objective:To investigate the number of metastasized lymph node groups (Ng) and the prognosis of gastric cancer pa-tients. Methods:Data from 1 009 patients receiving radical gastrectomy in the Cancer Center and with more than 15 lymph nodes re-trieved between January 2000 and September 2010 were included in the study. Lymph nodes were grouped by using the definition of the Japanese Research Society for Gastric Cancer (13th Japanese edition). Log-rank test and Cox regression analysis were used to ex-plore the relationship between the Ng and overall survival. Results:The metastasized lymph nodes were divided into 5 groups:1 group without lymph node metastasis (Ng0), 1 group with lymph node metastasis (Ng1), 2 groups with lymph node metastasis (Ng2), 3 to 5 groups with lymph node metastasis (Ng3), and more than 6 groups with lymph node metastasis (Ng4). The 3-year survival rates were 91.6%, 84.7%, 72.0%, 59.6%, and 43.0% for Ng0, Ng1, Ng2, Ng3, and Ng4, respectively. The 5-year survival rates were 89.9%, 82.4%, 66.9%, 54.6%, and 38.3%for Ng0, Ng1, Ng2, Ng3, and Ng4, respectively. These 3-and 5-year overall survival rates differed significantly among the groups (P<0.05). Gastric cancer patients with high Ng have low 3-year overall survival rates. Ng is an indepen-dent prognostic factor of gastric cancer. Conclusion:The concept of Ng can be a good supplement to existing UICC N staging.