Advances in Radiation Oncology (May 2020)

Intracranial Stereotactic Radiation Therapy With a Jawless Ring Gantry Linear Accelerator Equipped With New Dual Layer Multileaf Collimator

  • Nels C. Knutson, PhD,
  • William R. Kennedy, MD,
  • Francisco J. Reynoso, PhD,
  • Jiayuan Peng, MS,
  • Lauren E. Henke, MD,
  • Eric Laugeman, MS,
  • Michael Watts, MS,
  • Jessica Hillard, MS,
  • Ana Heermann, AS,
  • Geoffrey D. Hugo, PhD,
  • Sasa Mutic, PhD,
  • Bin Cai, PhD

Journal volume & issue
Vol. 5, no. 3
pp. 482 – 489

Abstract

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Purpose: To test the feasibility of a simplified, robust, workflow for intracranial stereotactic radiation therapy (SRT) using a ring gantry linear accelerator (RGLA) equipped with a dual-layer stacked, staggered, and interdigitating multileaf collimator. Materials and Methods: Twenty recent clinical SRT cases treated using a radiosurgery c-arm linear accelerator were anonymized. From these data sets, a new planning workflow was developed and used to replan these cases, which then were compared to their clinical counterparts. Population-based dose-volume histograms were analyzed for target coverage and sparing of healthy brain. All plans underwent plan review and quality assurance and were delivered on an end-to-end verification phantom using image guidance to simulate treatment. Results: The RGLA plans were able to meet departmental standards for target coverage and organ-at-risk sparing and showed plan quality similar to the clinical plans. RGLA plans showed increases in the 50% isodose in the axial plane but decreases in the sagittal and coronal planes. There were no statistically significant differences in the homogeneity index or number of monitor units between the 2 systems. There were statistically significant increases in conformity and gradient indices, with median values of 1.09 versus 1.11 and 2.82 versus 3.13, respectively, for the c-arm versus RGLA plans. These differences were not believed to be clinically significant because they met clinical goals. The population-based dose-volume histograms showed target coverage and organ-at-risk sparing similar to that of the clinical plans. All plans were able to meet the departmental quality assurance requirements and were delivered under image guidance on an end-to-end phantom with measurements agreeing within 3% of the expected value. RGLA plans showed a median reduction in delivery time of ≈50%. Conclusions: This work describes a simplified and efficient workflow that could reduce treatment times and expand access to SRT to centers using an RGLA.