The impact of PET/CT in radiotherapy treatment planning

Objectives Growing literature evidence proves the importance of the use of PET/CT in radiation oncology. We report our first results on PET/CT based radiotherapy treatment planning (RTP).

Methods More than 300 patients have been referred to PET/CT between 2006 and 2008 from our Department. In 53 patients PET/CT was intended to use directly in contouring for RTP. Tumor localizations: head and neck 19, lung 12, lymphoma 7, gynecologic 3, intestinal recurrence 3, sarcoma 2. Pinnacle planning software was used for fusion and planning. Changes in treatment strategy, target region selection and delineation of gross tumor volume (GTV) based on CT and PET/CT dataset has been evaluated. Effects of patient positioning during PET/CT on RTP and geometrical parameters of treatment delivery have been analyzed.

Results Radiotherapy was omitted in 3/53 patients due to the distant metastases revealed by PET, and in 4 cases where the lesion did not show any FDG uptake. In most of the cases of lung (n=8) and head and neck (n=12) cancer patients, target volume or doses to different lymph node regions has been changed. In lymphomas, residual bone involvement (n=2) could be delineated only on PET/CT. Comparing all CT- and PET/CT-based change in GTVs >20% could be observed in 27/46 patients (58.69%). Positioning during PET/CT is a key-question. In 70% of patients scanning on conventional CT tabletop caused difficulties in fusion, geographical error and change in GTV > 20% (n=16).

Conclusions The use of PET/CT in RTP affected treatment strategy, target definition and delineation in more then half of the patients. Integration of PET/CT in RT requires applications of careful quality assurance methods.