Variations in target volume definition and dose to normal tissue using anatomic versus biological imaging (18F-FDG-PET) in the treatment of bone metastases: results from a 3-arm randomized phase II trial

IntroductionTo report the impact on target volume delineation and dose to normal tissue using anatomic versus biological imaging (F-18-FDG-PET) for bone metastases. MethodsPatients with uncomplicated painful bone metastases were randomized (1:1:1) and blinded to receive either 8Gy in a single fraction with conventionally planned radiotherapy (ConvRT-8Gy) or 8Gy in a single fraction with dose-painting-by-numbers (DPBN) dose range between 6 and 10Gy) (DPBN-8Gy) or 16Gy in a single fraction with DPBN (dose range between 14 and 18Gy) (DPBN-16Gy). The primary endpoint was overall pain response at 1month. Volumes of the gross tumour volume (GTV) - both biological (GTV(PET)) and anatomical (GTV(CT)) -, planning target volume (PTV), dose to thenormal tissue and maximum standardized-uptake values (SUVMAX) were analysed (secondary endpoint). ResultsSixty-three percent of the GTV(CT) volume did not show F-18-FDG-uptake. On average, 20% of the GTV(PET) volume was outside GTV(CT). The volume of normal tissue receiving 4Gy, 6Gy and 8Gy was at least 3x, 6x and 13x smaller in DPBN-8Gy compared to ConvRT-8Gy and DPBN-16Gy (P<0.05). ConclusionPositron emitting tomography-information potentially changes the target volume for bone metastases. DPBN between 6 and 10Gy significantly decreases dose to the normal tissue compared to conventional radiotherapy.