Background and Aim: The incidence of internal lymph node (IMN) involvement was 4- 65% in breast cancer patients. Despite studies indicating the positive effects of IMNRT on the oncological results, most of the clinicians avoided IMNRT because of the toxicity related to the increased dose of organs at risk (OAR). We aimed to compare the dosimetric results of RT plans with and without IMN containing planning target volumes (PTVs) using helical tomotherapy (HT) in obese patients. Materials and Methods: The PMRT data of 23 obese patients were evaluated retrospectively / dosimetrically. Two PTVs with and without IMN were defined and two separate plans were made with HT. Dose received by IMN and OAR were compared. Results: The untargeted IMN V₄₀ were calculated between 0% to 99%. When the plans are evaluated in terms of critical organs, the inclusion of the IMN into the target volume, the most significant adverse effect was observed in heart doses in the left chest wall (CW) irradiation. The significant increases in cardiac V₅ (%62.6 vs %48.6 p=0.007), V₁₀ (%38.2 vs %23.2 p=0.011), V₂₀ (%14.15 vs %9.06 p=0.045) and maximum heart dose (48.04 vs 43.2 p=0.043) were observed in the left-side CW irradiations that involving the IMN. In CW irradiation on the right side with IMN, only a significant increase in mean heart dose (5.44 vs 4.52 p=0.036) was observed. Lung V₅ doses were increased by inclusion with IMN in both sides. There was no difference in the contralateral breast doses in both plans for both sides. Conclusions: If the IMN is not targeted, some of the patients are getting appropriate doses in obese patients.