en Radiation Biology Radiation Biology تحقيق بديع Original Research <span style="font-weight: bold">Background:</span> We have validated the monitor unit calculations from a commercially available treatment planning system (TPS) for three intensity modulated radiotherapy (IMRT) planning techniques for tangential breast irradiation by using ionization chamber measurements. <span style="font-weight: bold">Materials and Methods:</span> Treatment plans were generated for forty-two breast patients by a forward planned field in field technique, electronic tissue compensation (ETC), and an inverse planned sliding window technique. We also performed a reproducibility of delivery and dose linearity analysis for each technique. The treatments were delivered to a phantom using a Varian CL21EX linear accelerator. A 2571 0.6 cm³ Farmer type ionization chamber and Farmer 2570/1 electrometer from NE Technology was used to measure output of the linear accelerator and the dose at predefined point in the verification plan. <span style="font-weight: bold">Results:</span> The agreement between the measured and calculated dose was -0.87% ± 0.54% for field in field technique, -0.74% ± 0.23% for electronic tissue compensators, and -1.26% ± 0.48% for the inverse planning technique and. In terms of reproducibility the mean deviation was -1.10% ± 0.44% for the field in field technique, -0.38% ± 0.42% for electronic tissue compensators, -1.04% ± 0.42% for inverse planning technique. Dose linearity experiments showed no significant variations for clinical situations but a breakdown was observed in relative dose for very low monitor units. <span style="font-weight: bold">Conclusion:</span> We have found that the monitor unit calculations for all three planning techniques are correct to the order of 1%, and that the plans can be delivered in a reproducible and accurate manner. <span style="font-weight: bold">Iran. J. Radiat. Res., 2011 9(3): 145-150 </span> IMRT QA, dose delivery system, dose calculation accuracy, electronic tissue compensators, reproducibility, dose linearity 145 150 http://ijrr.com/browse.php?a_code=A-10-1-395&slc_lang=en&sid=1 M.N. Anjum muhammad.anjum@mail.mcgill.ca 790031947532846002382 790031947532846002382 Yes W. Parker 790031947532846002383 790031947532846002383 No I. Aldahlawi 790031947532846002384 790031947532846002384 No R. Ruo 790031947532846002385 790031947532846002385 No M. Afzal 790031947532846002386 790031947532846002386 No