18 F‐ FDG PET / CT for planning external beam radiotherapy alters therapy in 11% of 581 patients

Summary Background 18 F‐ FDG PET / CT ( FDG PET / CT ) used in radiotherapy planning for extra‐cerebral malignancy may reveal metastases to distant sites that may affect the choice of therapy. Aim To investigate the role of FDG PET / CT on treatment strategy changes induced by the use of PET / CT as part of the radiotherapy planning. ‘A major change of treatment strategy’ was defined as either including more lesions in the gross tumour volume ( GTV ) distant from the primary tumour or a change in treatment modalities. Methods The study includes 581 consecutive patients who underwent an FDG PET / CT scan for radiotherapy planning in our institution in the year 2008. All PET / CT scans were performed with the patient in treatment position with the use of immobilization devices according to the intended radiotherapy treatment. All scans were evaluated by a nuclear medicine physician together with a radiologist to delineate PET ‐positive GTV ( GTV ‐ PET ). Results For 63 of the patients (11%), the PET / CT simulation scans resulted in a major change in treatment strategy because of the additional diagnostic information. Changes were most frequently observed in patients with lung cancer (20%) or upper gastrointestinal cancer (12%). In 65% of the patients for whom the PET / CT simulation scan revealed unexpected dissemination, radiotherapy was given – changed ( n  = 38) or unchanged ( n  = 13) according to the findings on the FDG PET / CT . Conclusion Unexpected dissemination on the FDG PET / CT scanning performed for radiotherapy planning caused a change in treatment strategy in 11% of 581 patients.