Imaging Changes during Therapy: Does it Matter?

Abstract

Recent developments in 3D X-ray imaging have made available new tools for imaging patients in the treatment room. Several researchers in the radiation oncology community are recognizing that these imaging tools not only help to achieve better patient positioning, but also provide a wealth of information relative to the various changes that occur during the course of treatment. This article discusses some of the changes that are observed and what can be done to assess their importance. Two types of changes that can be observed with in-room 3D imaging are considered: positioning changes and anatomical changes. Examples of such changes are given for head and neck and prostate patients. The different magnitudes of these changes are discussed first. Because the biological effect of radiation on anatomical structures is determined by dose, the importance of these changes is then considered through their dosimetric consequences. Early findings show that not all anatomical structures receive the dose that was intended during treatment planning. Because the convolution of positioning and anatomical changes is difficult to predict, the consequences of these changes is better evaluated on a case-by-case basis as a first step towards adaptive radiation therapy.