Robustness Analysis for External Beam Radiation Therapy Treatment Plans: Describing Uncertainty Scenarios and Reporting Their Dosimetric Consequences

Abstract

Purpose: With external beam radiation therapy, uncertainties in treatment planning and delivery can result in an undesirable dose distribution delivered to the patient that can compromise the benefit of treatment. Techniques including geometric margins and probabilistic optimization have been used effectively to mitigate the effects of uncertainties. However, their broad application is inconsistent and can compromise the conclusions derived from cross-technique and cross-modality comparisons. Methods and Materials: Conventional methods to deal with treatment planning and delivery uncertainties are described, and robustness analysis is presented as a framework that is applicable across treatment techniques and modalities. Results: This report identifies elements that are imperative to include when conducting a robustness analysis and describing uncertainties and their dosimetric effects.NotedEarn CME credit by taking a brief online assessment at https://academy.astro.org.Conclusion: The robustness analysis approach described here is presented to promote reliable plan evaluation and dose reporting, particularly during clinical trials conducted across institutions and treatment modalities.

Dose distribution of intensity-modulated proton therapy with and without a multi-leaf collimator for the treatment of maxillary sinus cancer: a comparative effectiveness study

“…The value of 3 mm was the margin of uncertainty for patients with head and neck tumors, allowing for machine variability. The value of 3.5% was the range of uncertainty resulting from uncertainties in the range calculation, the acquisition of CT number, and the CT number-stopping power conversion table [13, 16].…”

Acknowledge uncertainties

“…[2][3][4][5] When the dosimetric objective is mean dose or a relative dose-volume metric, the variation in contouring can introduce significant uncertainty. As described in Yock et al, 1 the dosimetric impact has been demonstrated to be as much as 5% for clinically relevant uncertainties. In our institution's contour review, we observed a mean heart volume of 600 cc with a standard deviation of 300 cc My point is that if we as clinical physicists do not explore such sources of uncertainty and clearly explain them to our physician colleagues, we are doing our physician colleagues (and by extension their patients) a disservice by not understanding how these factors interrelate to impact the patient's care.…”

“…When the dosimetric objective is mean dose or a relative dose–volume metric, the variation in contouring can introduce significant uncertainty. As described in Yock et al, 1 the dosimetric impact has been demonstrated to be as much as 5% for clinically relevant uncertainties. In our institution's contour review, we observed a mean heart volume of 600 cc with a standard deviation of 300 cc due to differences among planners in the extent of superior pericardium contoured — yet the main dosimetric objective for non‐SBRT plans is mean dose.…”

“…We have access to exquisite image data, sophisticated image registration algorithms, automated tissue segmentation models, and powerful dose calculation algorithms. Consequently, we risk falling prey to “false accuracy” 1 . In its most benign form, this results in reduced efficiency as the planner expends time and effort to achieve a very small shift in a particular dosimetric parameter in order to be “under tolerance.” In a less benign form, this can result in suboptimal target coverage or suboptimal normal‐tissue dose.…”

The impact of proton LET/RBE modeling and robustness analysis on base-of-skull and pediatric craniopharyngioma proton plans relative to VMAT

“…The 'robustness' of proton plans to physical and biological uncertainties is a topic receiving substantial attention, as summarized in recent reviews [11,12]. Within commercial proton treatment planning systems (TPSs), physical uncertainties (both geometrical isocenter shifts and uncertainties in Hounsfield Unit (HU) to proton stopping power ratio (SPR) conversion) can not only be analyzed (in terms of dosimetric effect) but also used to drive plan treatment optimizations [12].…”