Emilie Soisson PhD, Presenter: Nothing to Disclose

Imaging has a growing role in radiation therapy as a method to guide patient positioning and allow for reduced treatment margins and unnecessary irradiation of normal tissue. A wide variety of in-room imaging systems are now available to detect and correct initial setup errors due to patient positioning and organ motion. Although effective in many cases, there are several sources of patient setup uncertainty associated with the use of in-room imaging systems themselves.

This work systematically details potential sources of residual patient setup uncertainty that result from the use of on-board or in-room imaging to localize targets in radiation therapy. Uncertainty is introduced in the calibration of the imaging system, pre-treatment image quality, reference image quality, use of surrogates, automatic and manual fusion techniques, and imaging frequency.

The effectiveness of image guided treatment strategies are both technique and site specific. There are many sources of uncertainty introduced with image guided strategies however, many of these uncertainties can be mitigated by clearly understanding both the imaging technology being used and the clinical situation. Although most imaging systems used in radiotherapy produce images of inferior quality to diagnostic images, techniques and clinical procedures can be optimized to ensure visualization of certain anatomical features required to ensure accurate patient setup. Many sources of uncertainty can be corrected with increased training and site-specific protocols.

In cases where the use of image guidance is limited due to the availability of clinical resources, it important to understand the magnitude of residual uncertainties that result from correcting patient setup on the basis of pre-treatment imaging. Image guidance should be allocated to patient that are most likely to benefit from its use and physics involvement in departmental imaging procedures can be essential in this optimization. In addition, image guided protocols should be routinely evaluated to determine their effectiveness.

The aim of this work is to provide educational material to medical physicists to allow for a better understanding of the uncertainty associated with routine image guidance in radiation therapy.

Soisson, E, Uncertainty Associated with the Use of Image Guidance to Mitigate Inter-Fraction Setup Errors from Patient Positioning and Organ Motion in Radiation Therapy.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015970.html