Abstract
We apply the concept of equivalent uniform dose (EUD) to our data set of model distributions and intensity modulated radiotherapy (IMRT) treatment plans as a method for analyzing large dose inhomogeneities within the tumor volume. For large dose nonuniformities, we find that the linear‐quadratic based EUD model is sensitive to the linear‐quadratic model parameters, α and β, making it necessary to consider EUD as a function of these parameters. This complicates the analysis for inhomogeneous dose distributions. EUD provides a biological estimate that requires interpretation and cannot be used as a single parameter for judging an inhomogeneous plan. We present heuristic examples to demonstrate the dose volume effect associated with EUD and the correlation to statistical parameters used for describing dose distributions. From these examples and patient plans, we discuss the risk of incorrectly applying EUD to IMRT patient plans.PACS number(s): 87.53.Tf
Highlights
There is a significant number of radiation therapy departments that are actively implementing and using intensity modulated radiotherapyIMRT
The resultant dose distribution and extent of tumor dose nonuniformity depends on the dose optimization algorithm, treatment delivery device, planning method, and the geometric relation between the critical structures and target
Optimization algorithms differ in the degree of tumor dose nonuniformity they induce, which is partially determined by the scoring scheme or criteria used to select the radiation beams.[1]
Summary
There is a significant number of radiation therapy departments that are actively implementing and using intensity modulated radiotherapyIMRT. Optimization algorithms differ in the degree of tumor dose nonuniformity they induce, which is partially determined by the scoring scheme or criteria used to select the radiation beams.[1] Some optimization systems, like the PeacockPlanNOMOS Corporation, Sewickly, PA, minimize the sum of the squared tumor dose residuals which allows for zero dose to a small part of the target volume and can produce a large dose nonuniformity.[2] For conditions where a critical structure lies adjacent to the tumor, a substantial dose inhomogeneity may exist, depending on the penalty associated with the structure To exacerbate this condition, treatment delivery devices like the Peacock intensity modulated multileaf collimatorMIMiCinduce dose inhomogeneity due to the field matching problem within the tumor.[3] Field junctioning within the tumor may produce regions of reduced dose with respect to the surrounding target volume, and in these instances, the matchline is usually associated with the minimum dose to the target. This presents problems for planning evaluation since the bulk of experience is with fairly uniform dose distributions, where typically, plans contain large fields with small dose deficits that occur at or near the periphery of the target volume
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