JACR: Is CT dose reduction optimal for RT planning?

In complying with CT dose reduction programs, radiologists should be aware that reduced-dose CT techniques may not be appropriate for all patients, particularly for radiotherapy planning CT scans, according to an article published in the February issue of the Journal of the American College of Radiology.

That’s not to say dose reduction initiatives such as the Image Gently campaign from the Alliance for Radiation Safety in Pediatric Imaging aren’t successful, according to authors James M. Hevezi, PhD, of Austin CyberKnife Center in Austin, Texas, and Mahadevappa Mahesh, PhD, of Johns Hopkins University in Baltimore. Numerous organizations have adjusted their CT protocols to set dose at levels to provide only the necessary image quality for a given exam.

“Most of the protocols call for lower doses compared with the technique in use previously to scan patients, again on the basis of obtaining sufficient image quality to allow a diagnosis to be made,” wrote the authors. “With increased media attention to CT protocol errors and misadministrations using high-dose CT techniques and the increased frequency of physicians' ordering CT studies to obtain diagnoses, there has been a plethora of articles suggesting CT dose reduction strategies in the recent literature.”

Hevezi and Mahesh called for a mindfulness of the medical course of the patient and an understanding that CT dose reduction strategies may not apply to all patients. There may be no benefit from reduced dose strategies for radiotherapy planning CT scans, for example, as the CT planning dose is only a fraction of the total dose the patient will receive during disease treatment.

The authors suggested that radiology and radiation oncology department staff should consult with the attending radiation oncologist to set scan protocols to ensure sufficient CT image quality for the planning procedure.

“This may require an actual increase in CT scan technique from that used for reduced-dose diagnostic techniques. This is especially important when using CT imaging for planning whose image sets will be fused with those from other imaging modalities, such as MRI or PET/CT, to allow the radiation oncologist to accurately contour the tumor targets that will be the subject of the radiotherapy procedure,” wrote Hevezi and Mahesh.

CT scans to follow the progress of treatment should be thought of in a similar fashion, they wrote, because while “it is important to be mindful of overutilization of these follow-up scans, the incremental radiation dose from these tests is small in comparison with the larger doses that have been delivered by the course of radiotherapy.”