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Biological-Based Optimization and VMAT Is Unnecessary for Stereotactic Body Radiation Therapy

D Mihailidis*(1), M Harmon(1), L Whaley(1), P Raja(1), G. Kagadis(2), (1)Charleston Radiation Therapy Cons, Charleston, WV, (2)University of Patras, Greece

SU-E-T-463 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
This study shows that there is no clear dosimetric benefit of biological-based optimization for either fixed-beam IMRT or VMAT. Other than shorter delivery times, even VMAT does not offer additional advantage to fixed-beam IMRT.

Methods:
A small number of patients for lung, pancreas, spine and brain CA were planned with fixed-beam IMRT, optimized with (gEUD) and without (DV) biological objectives and, also planned for VMAT with and without gEUD, for comparison. For the lung and brain cases, a non-coplanar 7-11 beam arrangement was used for fixed-beam IMRT and a coplanar 'hybrid' arc simulated VMAT with beams set every 5° spacing. For the other treatment sites, all beams were coplanar. For each case, the fixed-beam IMRT and VMAT plans were optimized with the same objectives. It is important to note that, only 2 segments/beam were allowed for each plan, in order to create small fluence modulation, appropriate for small target volumes during SBRT.

Results:
For all plans we noticed that there were minor or no dosimetric differences between fixed-beam IMRT and VMAT, whether DV or gEUD objectives were used or whether fixed-beam IMRT or VMAT is used. Keeping the level of beam modulation as-low-as possible, for small SBRT targets, one can show that VMAT with or without gEUD optimization does not offer any dosimetric advantage against fixed-beam IMRT with multiple non-coplanar beams. This is against the expectation that gEUD-optimization can result superior plans than DV-optimization. The difference is that, for small target volumes like those encountered in SBRT, the complexity of the fluence is not as high as in large field intensity modulated cases.

Conclusions:
The fact that VMAT with or without gEUD can produce as good plans as fixed-IMRT does not make VMAT a preferred treatment modality, other than the fact that requires reduced treatment time.

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