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Published on: February 6, 2019
Volumetric modulated Arc therapy and conventional intensity-modulated radiotherapy for simultaneous maximal
R Shaffer1, W J Morris, V Moiseenko
1British Columbia Cancer Agency, 600 West 10th Avenue, Vancouver, British Columbia, Canada. rickyshaffer@yahoo.co.uk
Aims:
Volumetric modulated arc therapy (VMAT) is a novel extension of intensity-modulated radiotherapy (IMRT) where an optimised three-dimensional dose distribution may be delivered in a single gantry rotation. This optimisation algorithm is the predecessor to Varian's RapidArc. The aim of this study was to compare the ability of conventional static nine-field IMRT (cIMRT) and VMAT to boost as much of the clinical target volume (CTV) as possible to 88.8Gy without exceeding organ at risk (OAR) dose-volume constraints.
Materials And Methods:
Optimal cIMRT and VMAT radiotherapy plans were produced for 10 patients with localised prostate cancer using common planning objectives: (1) Treat >or=98% of the planning target volume (PTV) to >or=95% of the prescription dose (74Gy in 37 fractions); (2) keep OAR doses within predefined limits; (3) treat as much of prostate CTV (minus urethra) as possible to >or=120% of prescription dose (=88.8Gy); (4) keep within maximum dose limits in and out of target volumes; (5) conformality index (volume of 95% isodose/volume of PTV)
Results:
VMAT and cIMRT boosted an average of 68.8 and 63.5% of the CTV to >or=120% of the prescription dose (P=0.002). All dose constraints were kept within predefined limits. VMAT and cIMRT required an average of 949 and 1819 monitor units and 3.7 and 9.6min, respectively, to deliver a single radiation fraction.
Conclusions:
VMAT is able to boost more of the CTV to >or=120% than cIMRT without contravening OAR dose constraints, and uses 48% fewer monitor units. Treatment times were 61% less than with cIMRT.
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