Use of FDG-PET to guide dose prescription heterogeneity in stereotactic body radiation therapy for lung cancers with volumetric modulated arc therapy: a feasibility study

The aim of this study was to assess if FDG-PET could guide dose prescription heterogeneity and decrease arbitrary location of hotspots in SBRT. For three patients with stage I lung cancer, a CT-simulation and a FDG-PET were registered to define respectively the PTV_CT and the biological target volume (BTV). Two plans involving volumetric modulated arc therapy (VMAT) and simultaneous integrated boost (SIB) were calculated. The first plan delivered 4 × 12 Gy within the PTV_CT and the second plan, with SIB, 4 × 12 Gy and 13.8 Gy (115% of the prescribed dose) within the PTV_CT and the BTV respectively. The Dmax-PTV_CT had to be inferior to 60 Gy (125% of the prescribed dose). Plans were evaluated through the D95%, D99% and Dmax-PTV_CT, the D2 cm, the R50% and R100% and the dice similarity coefficient (DSC) between the isodose 115% and BTV. DSC allows verifying the location of the 115% isodose (ideal value = 1). The mean PTV_CT and BTV were 36.7 (±12.5) and 6.5 (±2.2) cm³ respectively. Both plans led to similar target coverage, same doses to the OARs and equivalent fall-off of the dose outside the PTV_CT. On the other hand, the location of hotspots, evaluated through the DSC, was improved for the SIB plans with a mean DSC of 0.31 and 0.45 for the first and the second plans respectively. Use of PET to decrease arbitrary location of hotspots is feasible with VMAT and SIB for lung cancer