evaluation of treatment planning system monitor unit calculations for three intensity modulated radiotherapy delivery techniques

background: 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. materials and methods: 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. results: 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. conclusion: 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. iran. j. radiat. res., 2011 9(3): 145-150