Obstacles and Advances in Intensity-Modulated Radiation Therapy Treatment Planning

Abstract

In this paper, the current state of intensity-modulated radiation therapy (IMRT) treatment planning systems is reviewed, including some inefficiencies along with useful workarounds and potential advances. Common obstacles in IMRT treatment planning are discussed, including problems due to the lack of scatter tails in optimization dose calculations, unexpected hot spots appearing in uncontoured regions, and uncontrolled tradeoffs inherent in conventional systems. Workarounds that can be applied in current systems are reviewed, including the incorporation of an 'anchor zone' around the target volume (including a margin of separation), which typically induces adequate dose falloff around the target, and the use of pseudostructures to reduce conflicts among objective functions. We propose changing the planning problem statement so that different dosimetric or outcome goals are prioritized as part of the prescription ('prioritized prescription optimization'). Higher-priority goals are turned into constraints for iterations that consider lower-priority goals. This would control tradeoffs between dosimetric objectives. A plan review tool is proposed that specifically summarizes distances from a structure to hot or cold doses ('dose-distance plots'). An algorithm for including scatter in the optimization process is also discussed. Lastly, brief comments are made about the ongoing effort to use outcome models to rank or optimize treatment plans.

A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma

“…One issue of such planning process is termed the “weight paradox” by Deasy, whereby the optimal choices for the relative weights of different PTV and OAR optimization criteria are not known and may take many iterations of trial and error to determine. [30] Choosing criteria that are too constraining for the OAR can compromise the target coverage, or vice versa. [30] In the optimizing of a FF-VMAT plan using parameters derived from a FFF-VMAT plan in our study, there's always a possibility that the resulting FF-VMAT plan was suboptimal.…”

“…[30] Choosing criteria that are too constraining for the OAR can compromise the target coverage, or vice versa. [30] In the optimizing of a FF-VMAT plan using parameters derived from a FFF-VMAT plan in our study, there's always a possibility that the resulting FF-VMAT plan was suboptimal. Our way to avoid this problem was tried to make the optimization parameters as general as possible in the optimization process.…”

Comparing planning time, delivery time and plan quality for IMRT, RapidArc and tomotherapy

“…One issue is termed the "weight paradox" by Deasy, whereby the optimal choices for the relative weights of different PTV and OAR optimization criteria are not known and may take many iterations of trial and error to determine. (32) Choosing DVH criteria that are too constraining on the OAR compromises the PTV coverage, or vice versa, and may end up producing a plan that the user does not desire. (32) These dosimetric obstacles have been addressed by two different approaches including multi-criteria optimization (33)(34)(35) and Pareto optimization, (36,37) and when implemented in commercial treatment planning systems may be able to provide improved results.…”

A multicriteria framework with voxel‐dependent parameters for radiotherapy treatment plan optimization

“…There exist several methods to handle this complicated procedure, such as fine-tuning optimization parameters in a trial-and-error fashion or by some heuristic approaches, 1, 2 precomputing a well discrete representative of Pareto surface and navigating among them, [3][4][5][6][7][8][9][10][11][12][13][14][15] and prioritizing the evaluation criteria to avoid sacrificing those goals of more importance while improving those less important ones. [16][17][18][19][20][21][22] Among them, fine-tuning optimization parameters is arguably the most common paradigm.…”