Comparison of IMRT with Planar RapidArc in Diffuse Cerebral Meningiomatosis

Spratt, Daniel E.; Phillips, John G.; Díaz, Roberto; Crass, J.; Kirby, Wyndee; Stinson, S.F.; Cmelak, Anthony J.

doi:10.1016/j.ijrobp.2009.07.1520

Cited by 1 publication

(1 citation statement)

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“…5 and 6) have been implemented clinically, investigators have steadily reported plan and dosimetric comparisons for several tumor sites as compared to other modalities. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In addition to dynamic leaf motion as in dynamic-MLC IMRT, RapidArc TM (Varian Medical Systems, Palo Alto, CA) utilizes gantry rotation as well as variations in gantry speed and dose rate. Many studies have advocated that the inherent complexities of this technique require similar, but additional, commissioning and quality assurance than that of conventional IMRT.…”

Section: Introductionmentioning

confidence: 99%

Is RapidArc more susceptible to delivery uncertainties than dynamic IMRT?

Betzel

Niu

et al. 2012

Medical Physics

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Purpose: Rotational IMRT has been adopted by many clinics for its promise to deliver treatments in a shorter amount of time than other conventional IMRT techniques. In this paper, the authors investigate whether RapidArc is more susceptible to delivery uncertainties than dynamic IMRT using fixed fields. Methods: Dosimetric effects of delivery uncertainties in dose rate, gantry angle, and MLC leaf positions were evaluated by incorporating these uncertainties into RapidArc and sliding window IMRT (SW IMRT) treatment plans for five head-and-neck and five prostate cases. Dose distributions and dose-volume histograms of original and modified plans were recalculated and compared using Gamma analysis and dose indices of planned treatment volumes (PTV) and organs at risk (OAR). Results of Gamma analyses using passing criteria ranging from 1%-1 mm up to 5%-3 mm were reported. Results: Systematic shifts in MLC leaf bank positions of SW-IMRT cases resulted in 2-4 times higher average percent differences than RapidArc cases. Uniformly distributed random variations of 2 mm for active MLC leaves had a negligible effect on all dose distributions. Sliding window cases were much more sensitive to systematic shifts in gantry angle. Dose rate variations during RapidArc must be much larger than typical machine tolerances to affect dose distributions significantly; dynamic IMRT is inherently not susceptible to such variations. Conclusions: RapidArc deliveries were found to be more tolerant to variations in gantry position and MLC leaf position than SW IMRT. This may be attributed to the fact that the average segmental field size or MLC leaf opening is much larger for RapidArc. Clinically acceptable treatments may be delivered successfully using RapidArc despite large fluctuations in dose rate and gantry position.

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