Use of dose-area product to assess plan quality in robotic radiosurgery

Markus Eichner; Alexandra Hellerbach; Mauritius Hoevels; Klaus Luyken; Michael Judge; Daniel Rueß; Maximilian Ruge; Martin Kocher; Stefan Hunsche; Harald Treuer

doi:10.1016/j.zemedi.2023.01.001

Use of dose-area product to assess plan quality in robotic radiosurgery

Z Med Phys. 2023 Jan 28:S0939-3889(23)00001-6. doi: 10.1016/j.zemedi.2023.01.001. Online ahead of print.

Authors

Affiliations

¹ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: markus.eichner@uk-koeln.de.
² Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: alexandra.hellerbach@uk-koeln.de.
³ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: mauritius.hoevels@uk-koeln.de.
⁴ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: klaus.luyken@uk-koeln.de.
⁵ Department of Radiation Oncology, Cyberknife and Radiation Therapy, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: michael.judge@uk-koeln.de.
⁶ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: daniel.ruess@uk-koeln.de.
⁷ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: maximilian.ruge@uk-koeln.de.
⁸ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: martin.kocher@uk-koeln.de.
⁹ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: stefan.hunsche@uk-koeln.de.
¹⁰ Department of Stereotaxy and Functional Neurosurgery, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany. Electronic address: h.treuer@uni-koeln.de.

PMID: 36717311
DOI: 10.1016/j.zemedi.2023.01.001

Abstract

Purpose: In robotic stereotactic radiosurgery (SRS), optimal selection of collimators from a set of fixed cones must be determined manually by trial and error. A unique and uniformly scaled metric to characterize plan quality could help identify Pareto-efficient treatment plans.

Methods: The concept of dose-area product (DAP) was used to define a measure (DAP_ratio) of the targeting efficiency of a set of beams by relating the integral DAP of the beams to the mean dose achieved in the target volume. In a retrospective study of five clinical cases of brain metastases with representative target volumes (range: 0.5-5.68 ml) and 121 treatment plans with all possible collimator choices, the DAP_ratio was determined along with other plan metrics (conformity index CI, gradient index R50%, treatment time, total number of monitor units TotalMU, radiotoxicity index f12, and energy efficiency index η50%), and the respective Spearman's rank correlation coefficients were calculated. The ability of DAP_ratio to determine Pareto efficiency for collimator selection at DAP_ratio < 1 and DAP_ratio < 0.9 was tested using scatter plots.

Results: The DAP_ratio for all plans was on average 0.95 ± 0.13 (range: 0.61-1.31). Only the variance of the DAP_ratio was strongly dependent on the number of collimators. For each target, there was a strong or very strong correlation of DAP_ratio with all other metrics of plan quality. Only for R50% and η50% was there a moderate correlation with DAP_ratio for the plans of all targets combined, as R50% and η50% strongly depended on target size. Optimal treatment plans with CI, R50%, f12, and η50% close to 1 were clearly associated with DAP_ratio < 1, and plans with DAP_ratio < 0.9 were even superior, but at the cost of longer treatment times and higher total monitor units.

Conclusions: The newly defined DAP_ratio has been demonstrated to be a metric that characterizes the target efficiency of a set of beams in robotic SRS in one single and uniformly scaled number. A DAP_ratio < 1 indicates Pareto efficiency. The trade-off between plan quality on the one hand and short treatment time or low total monitor units on the other hand is also represented by DAP_ratio.

Keywords: Dose-area product; Non-isocentric irradiation; Pareto efficiency; Plan quality; Stereotactic radiosurgery; Treatment plan optimization.