Stereotactic IMRT for prostate cancer: Dosimetric impact of multileaf collimator leaf width in the treatment of prostate cancer with IMRT

The focus of this work is the dosimetric impact of multileaf collimator (MLC) leaf width on the treatment of prostate cancer with intensity‐modulated radiation therapy (IMRT). Ten patients with prostate cancer were planned for IMRT delivery using two different MLC leaf widths—4 mm and 10 mm— representing the Radionics micro‐multileaf collimator (mMLC) and Siemens MLC, respectively. Treatment planning was performed on the XKnifeRT2 treatment‐planning system (Radionics, Burlington, MA). All beams and optimization parameters were identical for the mMLC and MLC plans. All the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose. The differences in dose distribution between the two different plans were assessed by dose–volume histogram (DVH) analysis of the target and critical organs. We specifically compared the volume of rectum receiving 40 Gy [Formula: see text] , 50 Gy [Formula: see text] , 60 Gy [Formula: see text] , the dose received by 17% and 35% of rectum ([Formula: see text] and [Formula: see text]), and the maximum dose to 1 cm(3) of the rectum for a prescription dose of 74 Gy. For the urinary bladder, the dose received by 25% of bladder [Formula: see text] , [Formula: see text] , and the maximum dose to 1 cm(3) of the organ were recorded. For PTV we compared the maximum dose to the “hottest” 1 cm(3) [Formula: see text] and the dose to 99% of the PTV [Formula: see text]. The dose inhomogeneity in the target, defined as the ratio of the difference in [Formula: see text] and [Formula: see text] to the prescribed dose, was also compared between the two plans. In all cases studied, significant reductions in the volume of rectum receiving doses less than 65 Gy were seen using the mMLC. The average decrease in the volume of the rectum receiving 40 Gy, 50 Gy, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with [Formula: see text] for [Formula: see text] and [Formula: see text] and [Formula: see text] for [Formula: see text]. The mean dose reductions for [Formula: see text] and [Formula: see text] for the rectum using the mMLC were 20.4% [Formula: see text] and 18.3% [Formula: see text] , respectively. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 29%. In the high‐dose range, there was no significant difference in the dose deposited in the “hottest” 1 cm(3) of the rectum between the two plans for all cases [Formula: see text]. In conclusion, the use of the mMLC for IMRT of the prostate resulted in significant improvement in the DVH parameters of the prostate and critical organs, which may improve the therapeutic ratio. PACS number: 87.53.Tf