SU-E-J-168: 4D-PET for Target Volume Delineation in Respiratory-Gated Radiation Therapy

Medical Physics
C CavedonM Ferdeghini

Abstract

To find an optimized workflow for the use of respiratory-gated PET (4D-PET) in target volume delineation of tumors subject to respiratory-gated radiation therapy. 15 patients with lung (11) and pancreas (4) tumors who had FDG-PET-CT for target delineation prior to EBRT were studied. Patients were selected among the group that showed respiratory-induced tumor motion 〉5mm. 4D-PET was performed by means of a Philips Gemini BigBore scanner, using the Varian RPM gating system. An identical system was available at the linac for treatment. The breathing cycle was equally divided in 4 phases, according to a previous study. Since planning was made on a single CT-phase, no ITV was explicitly built from the set of phases. The BTV was identified with SUV=2.2 threshold and the PTV was obtained expanding the BTV by 8mm(S-I), 5mm(A-P) and 3mm(L-R) to account for residual motion and setup errors. The most advantageous CT-phase for treatment planning was then identified by simulating plans on each phase and analyzing the resulting DVHs of OARs (lung, trachea, oesophagus, spinal cord, left ventricle). The observed maximum range of motion was 5.5mm(L-R), 12.3mm(A-P) and 19.2mm(S-I). The standard deviation of the BTV volume in the 4 phases ranged ...Continue Reading

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