en Medical Physics Medical Physics تحقيق بديع Original Research <div style="text-align: justify;">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.</div> Internal Mammary Nodal Area, Breast Cancer, Intensity-modulated radiation therapy. 191 200 http://ijrr.com/browse.php?a_code=A-10-2055-3&slc_lang=en&sid=1 I.P. Aral ipekpt@hotmail.com 7900319475328460015723 7900319475328460015723 Yes Nevşehir Hospital, Department of Radiation Oncology, Nevsehir, Turkey S.A. Arslan 7900319475328460015724 7900319475328460015724 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey A.F. Yurekli 7900319475328460015725 7900319475328460015725 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey G.A. Inan 7900319475328460015726 7900319475328460015726 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey S. Tekin 7900319475328460015727 7900319475328460015727 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey H. Bozdemir 7900319475328460015728 7900319475328460015728 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey S. Sunel 7900319475328460015729 7900319475328460015729 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey H. Karabuga 7900319475328460015730 7900319475328460015730 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey S. Acıkgoz 7900319475328460015731 7900319475328460015731 No Ankara Ataturk Education and Training Hospital, Department of Radiation Oncology, Ankara, Turkey