Lymph nodes are anatomically always located at the same distance from the blood vessels regardless of the type of cancer. It has been shown that 99% of the lymph nodes in the pelvis are found within a seven millimeter diameter around the blood vessels, and this is due to the fact that those have the same angiogenic origin as the abdominal blood vessels [9]. Since such studies on abdominal blood vessels do not exist, it seems very useful and important to investigate the Lnfluence of the size of the lymph nodes CTV margin on the dose received by organs at risk, and to evaluate the safety of the use of conformal radiotherapy for gastric cancer. Нe aim of this study was to determine the dosimetrically optimal CTV margin of the lymph nodes so that the selected margin covers all the lymph nodes, and that the doses to organs at risk are as low as possible. НLs was done by determining and comparing the Lnfluence of the radiation dose to liver and kidneys for the target volumes that included the lymph nodes CTVs of 5 mm, 7 mm and 10 mm, in gastric cancer patients treated with 3DCRT.