Stephen B. Chiang MD, Presenter: Nothing to Disclose

Bin Sing Teh MD, Abstract Co-Author: Nothing to Disclose

E. Brian Butler MD, Abstract Co-Author: Nothing to Disclose

Arnold C. Dela Paulino MD, Abstract Co-Author: Nothing to Disclose

To evaluate the use of FDG-PET/CT in tumor response after SBRT.

14 patients with 22 tumors were treated with SBRT, using the Brainlab Novalis Stereotactic system (kV-Xray for image-guidance).  13 tumors were in the lung/mediastinum/hilum, four in the liver, two in the adrenal glands, and one each in the renal fossa, cervical spine, and pelvis.  The tumors included both primary and metastatic lesions.  FDG-PET/CT was performed before and after SBRT.  Target delineation of gross tumor volume (GTV) with the aid of PET/CT was determined by joint efforts of a radiation oncologist and a nuclear medicine specialist.  For SBRT, there is no clinical target volume (CTV).  SBRT dose fraction regimens included:  5Gy x 5, 6Gy x 5, 10Gy x 4, 10Gy x 5, 12 Gy x 4, and 12 Gy x 5.  Changes in maximal standardized uptake value (SUVmax) were used for the evaluation of tumor response.  Complete response (CR) is defined as complete resolution of SUVmax to background; partial resonse-more than 25% reduction in SUVmax; progression-more than 25% increase in SUVmax; and stable disease (SD) described others.

Out of 22 tumors, 16 (73%) achieved CR and three tumors achieved PR and SD, respectively.  There was no local progression after SBRT.  CR was observed as early as day 23 post SBRT.  Radiation changes of normal tissues on PET/CT were seen only at a later time interval of 2-5 months post SBRT.

Our initial experience suggests that incorporation of PET/CT in target delineation for SBRT treatment produced adequate tumor coverage as there was no local progression.  PET/CT is an ideal imaging tool for the assessment of tumor response after SBRT and adds to the traditional imaging modalities (CT, MRI) for assessing tumor response.  SBRT is also an effective treatment approach as significant numbers of CR were seen.  Heterogeneity and different patterns of metabolic responders and non-responders may reflect intrinsic tumor characteristics and may be useful to modify treatment approaches.  It is also important to note the time interval between tumor response and radiation changes on PET/CT after SBRT.  Prospective trial involving a more homogenous population of patients is planned.

FDG-PET/CT aids in SBRT planning and follow up.

Chiang, S, Teh, B, Butler, E, Paulino, A, Initial Experience with FDG-PET/CT in Evaluating Stereotactic Body Radiation Therapy (SBRT) Treatment Response.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015996.html