Increasing dose gradient and uniformity in small fields using modulation: Theory and prototypes for cone-based stereotactic radiosurgery

Abstract

Using modulation with features on a submillimeter distance scale, it is possible to increase the dose gradient and/or uniformity in small fields.

Design of a modulated orthovoltage stereotactic radiosurgery system

“…Previous work has shown the potential for using orthovoltage energies for SRS and SBRT treatment platforms, [8][9][10][11][12] as well as for using modulation as a means to manipulate dose distributions. 7 This work has described the mathematical optimization techniques as well as the Monte Carlo simulations used to design collimator and filter assemblies in a modulated orthovoltage stereotactic radiosurgery system prototype. Simulation results indicate that modulated beam profiles attain decreased flatness and penumbra statistics compared to unmodulated beams.…”

“…For small fields such as those in this work as well as in previously published literature, a portion of the penumbra is included in the flatness calculation. Previously published work examining using optimization to approach rectangular functions included example beam profiles for visual analysis, but did not include quantitative data. Penumbra and flatness were calculated in this work to allow for a more quantifiable assessment; however, as previously stated, the modulated beams are not “flat” in the sense of a conventional linear accelerator large flattening filtered beam.…”

“…The methods described in this work could be followed to optimize such a system. The same methodology could be used for a range of beam energies; however, for megavoltage linear accelerators, a simpler calculus‐based optimization approach may be used as described by Bender based on data fit to a differentiable, analytical expression . Even small benefits in terms of dose distribution improvement may be useful for extreme treatment cases of human subjects or for small animal irradiators.…”

Technical Note: Dose gradients and prescription isodose in orthovoltage stereotactic radiosurgery

“…[16][17][18][19][20] Previous work in the megavoltage energy range has examined the trade-off between prescription isodose and dose gradient index in a 6 MV Linac SRS delivery. 21 This work proposes to examine such a trade-off in orthovoltage SRS.…”

A method to improve dose gradient for robotic radiosurgery

“…Similarly, Wagner et al (5) proposed a mixed score index averaging a conformity score and a gradient score for ranking rival stereotactic radiosurgery plans. Although recent univariate and multivariate analysis has not shown the significance of GI as a predictive parameter for complication in brain metastases treatment 6 , 7 , 8 based on GKS patient studies, it is generally believed a fast dose falloff is critical for stereotactic radiosurgery/radiotherapy in most cases 9 , 10 , 11 …”