Purpose: To systematically evaluate step‐and‐shoot Intensity‐Modulated‐Radiation‐Therapy (IMRT) plans generated by Direct‐Machine‐Parameter‐Optimization (DMPO) and by Two‐Step‐Approach (TSA) using identical optimization parameters in Pinnacle 3 treatment planning system. Method and Materials: Using Pinnacle 3 version7.6c, TSA plans of total eight patients with Head‐and‐Neck, Prostate and Lung cancers were generated using identical optimization parameters from clinical plans used DMPO. The dose of planned‐target‐volume (PTV) in TSA plan was scaled to closely match at prescribed dose volume in the DMPO plan. Three PTV dosimetric indices: dose‐coverage, dose‐conformity and dose‐inhomogeneity, were generated for each plan. Dosimetric comparisons were performed for organ‐at‐risk (OAR) with both “maximum‐dose‐objectives” and “dose‐volume‐based‐objectives”. Final dose recalculation using EGS4‐based in‐house Monte‐Carlo program for each plan was performed and corresponding dosimetric data were obtained. Film‐based IMRT QA was performed for three patients. Results: On average, total monitor‐units (MUs) are about 25% higher of TSA than DMPO. The averaged segment‐numbers and PTV dosimetric indices are almost identical between plans from DMPO and TSA. The maximum‐dose (defined at 0.1cc) of Head‐and‐Neck and Lung OARs with “maximum‐dose‐objectives” of TSA are, on average, ∼2.5Gy and ∼0.9Gy lower than those of DMPO, respectively. The averaged dose difference in prostate OARs with “maximum‐dose‐objectives” is small. For OARs with “dose‐volume‐based‐objectives”, there is little difference between TSA and DMPO for all sites. The Monte‐Carlo dose recalculations showed similar trends. The agreement between Pinnacle3 calculations and film measurements is 99% for all fields using 3%–3mm criteria. Conclusion: Dosimetric comparisons between DMPO and TSA IMRT plans demonstrated that using identical optimization parameters, DMPO plans have less total MUs and similar averaged segment‐number as well as almost identical PTV dosimetric index values as TSA plans. For Head‐and‐Neck and lung plans, TSA has noticeable better sparing of OARs with “maximum‐dose‐based‐objectives”, which is confirmed by Monte‐Carlo recalculations. Film QA demonstrated both TSA and DMPO plans are very accurate.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging