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SU-E-T-593: VMAT Vs. IMRT for Treatment of Neoplasms of the Brain: Dosimetric Quality and Delivery.

PURPOSE
A retrospective study was performed to determine any dosimetric or delivery benefits for treatment planning with intensity-modulated radiotherapy (IMRT) versus volumetric-modulated arc therapy (VMAT) for the treatment of brain neoplasms.


METHODS
Eighteen patients treated with modulated brain radiotherapy treatments were included in this study (primary treatment volumes of 15.3 to 374.9 cc). IMRT and VMAT plans were generated for each patient using the same criteria for prescription coverage and normal tissue sparing. IMRT optimizations ranged from five to seven fields and VMAT from two to four arcs. Plans were generated with Varian Eclipse treatment planning system utilizing AAA-8615 dose calculation algorithm.


RESULTS
VMAT optimizations provided limited dosimetric advantages versus IMRT. VMAT provided superior treatment volume coverage (volumes receiving 95%, 100% of prescription dose (V95%, V100%)) over IMRT, but differences were not statistically significant (paired t-test p > 0.05). Relative maximum dose values, conformity and homogeneity indices also exhibited no statistical differences. IMRT plans resulted in similar mean brain minus treatment volume (Brain- TV) dose (mean = 1460.1 vs. 1506.3 cGy; p = 0.056). The volume of Brain- TV receiving 40Gy was lower for VMAT than IMRT (average = 38.96 vs. 44.97 cc; p = 0.050). Maximum skin dose was lower for VMAT (mean = 4568.8 vs. 5063.3cGy; p = 0.006), as well as skin V20Gy (6.56% vs 7.69%; p = 0.027) and V40Gy (0.56% vs. 0.35%; p = 0.017). VMAT plans required fewer fields along with fewer MU than IMRT (mean = 388.2 vs. 721.1 MU, respectively), allowing for approximately 20% faster delivery times.


CONCLUSIONS
VMAT treatments significantly reduced treatment time due to reduced MU and fewer fields. Certain skin and Brain-TV high dose spread parameters were superior for VMAT as compared to IMRT plans. All other dosimetric parameters tested were statistically equivalent for VMAT and IMRT techniques.