Purpose: To report on the clinical implementation of the VOLOTMoptimization algorithm for SRS/SBRT treatments and its dosimetric comparison with the previous Sequential Optimization (SO) algorithm.
Materials and methods: Forty patients treated for brain, spine, prostate and lung tumors, and planned with the SO algorithm were re-planned with VOLOTM. Comparison involved target coverage, conformity, gradient and homogeneity indexes (CN, GI and HI) and specifc indicators of dose to OARs. Plans were also compared in terms of number of nodes, beams, MU and delivery time. All dose distributions designed with VOLOTM were validated via ionisation chamber measurements.
Results: The following statistically signifcant dosimetric differences were observed. VOLOTM was superior in terms of target coverage for prostate (99% vs 96%) and spine (92% vs 81%), GI for brain (4.41 vs 4.76), CN for brain (0.77 vs 0.72), and for brain and urethra dose sparing. SO gave better results for GI for prostate (3.67 vs 4.05) and maximum dose to brain stem. VOLOTM showed a steeper peripheral dose fall-off for brain and lung cases; SO was superior for prostate and spine cases. Overall, the number of nodes, beams and MU were reduced with VOLOTM up to 36%, 14% and 31%, respectively. The average reduction of delivery time was 20% (ranging from 8% for brain to 30% for prostate). The mean 1D dose measurement deviation from calculation was –0.2% (range –1.3–1.7%). 2D dose measurements returned a mean distance-to-agreement of 0.8±0.8 mm and a mean dose difference of 0.6±1.0%.
Conclusions: VOLOTM optimization algorithm provided clinically acceptable dose distributions, most of the time better than SO. The treatment time was signifcantly reduced up to 30%. The peripheral dose fall-off increased for large collimator sizes. The verifcation measurements proved its clinical implementation.