Purpose: This study compares the quality of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans optimized for an Elekta Agility(TM) (Elekta, Stockholm, Sweden) multileaf collimator (MLC; leaf width 5 mm) and an Elekta MLCi2 (leaf width 10 mm) for complex target volumes (anal, AC; head and neck, H&N and prostate cancer, PC).
Patients and methods: For plan comparisons, 15 patients who had been treated with IMRT or VMAT using the MLCi2 were selected. For each patient, a retrospective treatment plan using the MLCi2 for the technique not applied was created, as were treatment plans for both techniques using the Agility(TM) MLC. Dose-volume histograms (DHVs) for planning target volumes (PTVs) and organs at risk (OARs) were compared. Further parameters relating to dose conformity, dose homogeneity and mean dose (Dmean) to the PTV, compliance with the intended OAR dose criteria and overall dose to normal tissue were analyzed. Verification measurements were performed and optimization and treatment times were compared.
Results: Compared to the MLCi2 plans, the Agility(TM) IMRT and VMAT plans show better or equivalent results in terms of PTV dose conformity and homogeneity. Compliance with the intended OAR dose criteria does not differ according to technique or MLC type. Slight differences are shown for dose distributions in OARs and normal tissue. Verification measurements show that all plans fulfill the acceptance criteria of a minimum of 95 % matched dose points for the 3 %/3 mm γ criterion. Optimization times for the VMAT plans increase compared to the IMRT plans, whereas treatment times decrease.
Conclusion: With the MLCi2, treatment of complex target volumes with VMAT was only possible with compromises in terms of target coverage. Using the Agility(TM) MLC, even complex target volumes can be treated with VMAT without compromising target coverage or resulting in higher exposure of OARs or normal tissue.