A comparison of volumetric modulated arc therapy and conventional intensity-modulated radiotherapy for frontal and temporal high-grade gliomas.
OBJECTIVE
Volumetric modulated arc therapy (VMAT), the predecessor to Varian's RapidArc, is a novel extension of intensity-modulated radiotherapy (IMRT) wherein the dose is delivered in a single gantry rotation while the multileaf collimator leaves are in motion. Leaf positions and the weights of field samples along the arc are directly optimized, and a variable dose rate is used. This planning study compared seven-field coplanar IMRT (cIMRT) with VMAT for high-grade gliomas that had planning target volumes (PTVs) overlapping organs at risk (OARs).


METHODS
10 previously treated patients were replanned to 60 Gy in 30 fractions with cIMRT and VMAT using the following planning objectives: 98% of PTV covered by 95% isodose without violating OAR and hotspot dose constraints. Mean OAR doses were maximally decreased without reducing PTV coverage or violating hotspot constraints. We compared dose-volume histogram data, monitor units, and treatment times.


RESULTS
There was equivalent PTV coverage, homogeneity, and conformality. VMAT significantly reduced maximum and mean retinal, lens, and contralateral optic nerve doses compared with IMRT (p < 0.05). Brainstem, chiasm, and ipsilateral optic nerve doses were similar. For 2-Gy fractions, mean monitor units were as follows: cIMRT = 789 +/- 112 and VMAT = 363 +/- 45 (relative reduction 54%, p = 0.002), and mean treatment times (min) were as follows: cIMRT = 5.1 +/- 0.4 and VMAT = 1.8 +/- 0.1 (relative reduction 65%, p = 0.002).


CONCLUSIONS
Compared with cIMRT, VMAT achieved equal or better PTV coverage and OAR sparing while using fewer monitor units and less time to treat high-grade gliomas.
Shaffer
Richard
R
Department of Radiation Oncology, BC Cancer Agency, Vancouver, British Columbia V5Z 4E6, Canada.
Nichol
Alan M
AM
Vollans
Emily
E
Fong
Ming
M
Nakano
Sandy
S
Moiseenko
Vitali
V
Schmuland
Moira
M
Ma
Roy
R
McKenzie
Michael
M
Otto
Karl
K
D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D001933:Brain Stem / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D005260:Female; D005910:Glioma / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D007908:Lens, Crystalline / Q000528:radiation effects; D008297:Male; D009900:Optic Nerve / Q000528:radiation effects; D011832:Radiation Injuries / Q000517:prevention & control*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012160:Retina / Q000528:radiation effects; D047368:Tumor Burden