Julianne Marie Pollard PhD, Presenter: Speaker, Sun Nuclear Corporation Travel support, Sun Nuclear Corporation

1) Be able to identify the different terminology used to describe margins in radiation therapy. 2) Understand how different types of uncertainty contribute to the appropriate treatment margin. 3) Demonstrate an understanding of the many ways that can be used to define margins to account for treatment uncertainties. 4) Have the rationale to determine which approach could/should be used to apply to their own patients.

Presentation: Incorporating IGRT uncertainties into treatment margins (theory) During treatment planning a safety margin is added to the clinical target volume to ensure that the planned dose is actually delivered to the target dose. This margin may be calculated by correctly combining the contributions to the overall treatment uncertainty from numerous individual uncertainties, both systematic and random. Once the uncertainties have been categorized, there are many ways in which they can be combined to give the actual treatment margin, and this must be done in a considered way. In this presentation we will describe how different uncertainties should be combined. The details of this vary, depending on the margin recipe used. We will describe published margin recipes, including the impact of different assumptions made in each recipe. For example, what percentage of the patient population will receive what percentage of the prescribed dose? Dosimetric and biological approaches to treatment margins will be described. Presentation: Incorporating IGRT uncertainties into treatment margins (practice) ; ;One advantage of IGRT is the potential for reducing margins. Clinical margins are typically determined in one of 3 ways: : (1) Use same margins as before (pre-IGRT), (2) Reduce margins based on ‘supposed’ improvement in accuracy/precision, perhaps based on published data, or (3) Evaluate institutions own uncertainties, and establish appropriate margins. The first two are probably the most common. However, each of these approaches has its own pitfalls: (1) does not take full advantage of our new technologies, (2) is fraught with potential error, including the fact that many published works do not adequately assess uncertainties, and (3) can be difficult, and not all physicists have the background knowledge to do this. In this presentation we will describe some practical approaches to using margin formulae and other methods used to determine safe clinical margin

Pollard, J, Terminology to Describe Uncertainties and Methodologies for Evaluating Uncertainties in IGRT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/12020056.html