On the reduction of aperture complexity in kidney SABR

Abstract

Background: Stereotactic ablative body radiotherapy (SABR) of primary kidney cancers is confounded by motion. There is a risk of interplay effect if the dose is delivered using volumetric modulated arc therapy (VMAT) and flattening filter-free (FFF) dose rates due to target and linac motion. This study aims to provide an efficient way to generate plans with minimal aperture complexity. Methods: In this retrospective study, 62 patients who received kidney SABR were reviewed. For each patient, two plans were created using internal target volume based motion management, on the average intensity projection of a four-dimensional CT. In the first plan, optimization was performed using a knowledge-based planning model based on delivered clinical plans in our institution. In the second plan, the optimization was repeated, with a maximum monitor unit (MU) objective applied in the optimization. Dose-volume, conformity, and complexity metric (with the field edge metric and the modulation complexity score) were compared between the two plans. Results are shown in terms of median (first quartilethird quartile). Results: Similar dosimetry was obtained with and without the utilization of an objective on the MU. However, complexity was reduced by using the objective on the MUs (modulation complexity score = 0.55 (0.50-0.61) / 0.33 (0.29-0.36), Pvalue < 10 −10 , with/without the MU objective). Reduction of complexity was driven by a larger aperture area (area aperture variability = 0.68 (0.64-0.73) / 0.42 (0.37-0.45), P-value < 10 −10 , with/without the MU objective). Using the objective on the MUs resulted in a more spherical dose distribution (sphericity 50% isodose = 0.73 (0.69-0.75) / 0.64 (0.60-0.68), P-value < 10 −8 , with/without the MU objective) reducing dose to organs at risk given respiratory motion. Conclusions: Aperture complexity is reduced in kidney SABR by using an objective on the MU delivery with VMAT and FFF dose rate.

Efficacious patient‐specific QA for Vertebra SBRT using a high‐resolution detector array SRS MapCHECK: AAPM TG‐218 analysis

“…The following complexity metrics were computed for all treatment plans: Modulation Complexity Score (MCS), Edge Metric (EM), Monitor units per Grey (MU/cGy), and Average Leaf Pair Opening (ALPO) 11 , 12 MCS measures the variability in shape of MLC segments, while EM uses MLC y‐leaf side length normalized by aperture area. MU/cGy is the number of monitor units required to deliver one Gray of dose, and ALPO is a measure of how closed the MLC‐defined field is.…”

Development of an automated treatment planning approach for lattice radiation therapy

“…The MCS is a number defined between 0 and 1, with decreasing MCS indicating increasing complexity. The MCS was calculated by using an in‐house method developed previously by our group 20 . AI measures the deviation of the open aperture from a circular shape, with a value of 1 representing a perfectly circular shape, and deviations from this shape increasing with AI.…”

“…The MCS was calculated by using an in-house method developed previously by our group. 20 AI measures the deviation of the open aperture from a circular shape, with a value of 1 representing a perfectly circular shape, and deviations from this shape increasing with AI. The MU/cGy ratio was recorded as a surrogate for the treatment time.…”