en Medical Physics Medical Physics تحقيق بديع Original Research <div style="text-align: justify;">Background: The current study aimed to compare the tumor control probability (TCP) and normal tissue complication probability (NTCP) of three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) for left-sided breast cancer using radiobiological models. Methods: This study was conducted on 30 patients with left-sided breast cancer, who&nbsp;were planned for 3D-CRT and 6-9 fields IMRT treatments using the PROWESS treatment planning system.&nbsp;&nbsp;The planning target volume (PTV) dose of 50 Gy was administered for the 3D-CRT and IMRT plans, respectively.&nbsp;&nbsp;The Niemierko&rsquo;s equivalent uniform dose (EUD) model was utilized for the estimation of tumor control probability (TCP) and normal tissue complication probability (NTCP).&nbsp;Results: According to the results, the mean TCP values for 3D-CRT, 6-fields IMRT, and 9-fields IMRT plans were 99.07 &plusmn;0.07, 99.24 &plusmn;0.05 and 99.28 &plusmn;0.04, respectively, showing no statistically significant difference. The NTCPs of the&nbsp;lung and heart were considerably lower in the IMRT plans, compared to those in the 3D-CRT plans.</div> Conclusions: From the radiobiological point of view, our results indicated that 3D-CRT produces a lower NTCP for ipsilateral lung. In contrast, for TCP calculations, there was a higher gain with IMRT plans compared to 3D-CRT plans. Radiobiological evaluation, left-sided breast cancer, three dimensional conformal and intensity-modulated radiation therapy. 315 322 http://ijrr.com/browse.php?a_code=A-10-2055-16&slc_lang=en&sid=1 A. Shanei 7900319475328460015820 7900319475328460015820 No Faculty Member of Medical Physics Department, Isfahan University of Medical Sciences, Isfahan, Iran A. Amouheidari 7900319475328460015821 7900319475328460015821 No Radiation Oncologist, Isfahan Milad Hospital, Isfahan, Iran I. Abedi i.abedi@med.mui.ac.ir 7900319475328460015822 7900319475328460015822 Yes Faculty Member of Medical Physics Department, Isfahan University of Medical Sciences, Isfahan, Iran A. Kazemzadeh 7900319475328460015823 7900319475328460015823 No Medical Physics, Kashan University of Medical Sciences, Kashan, Iran A. Jaafari 7900319475328460015824 7900319475328460015824 No Medical Physics, Isfahan University of Medical Sciences, Isfahan, Iran