n.142 – 18F-FDG PET/CT AND OSIRIX TO CALCULATE VOLUME IN HYPERTHERMIC ISOLATED LIMB PERFUSION: A VALIDATION STUDY.



Abstract

BACKGROUND-AIM
Patients, with metastases from melanoma confined to one limb, can be candidates for Hyperthermic Isolated Limb Perfusion (HILP). This technique combines the effect of hyperthermia and cytostatic drugs and offers two advantages compared to systemic treatment: low systemic toxicity and high concentration of drug in the tumor. To apply HILP, however, the volume of the affected limb should be calculated mainly using the water replacement method. The CT portion of 18F-FDG PET/CT, frequently requested in melanoma to exclude metastases, could be used as an alternate method to calculate volume. Aim of the study was to validate volume calculation based on PET/CT and open source software Osirix and compare results with validated methods.
METHODS
Twentyfour patients (12 male; 12 female) candidated for HILP and referred to PET/CT were included. During PET/CT a small metallic marker was positioned on the limb and used as a reference point.
In each case volume has been calculated using: a) the water replacement method; b) Osirix 5.7.1 and CT; c) Oncentra MasterPlan 4.3 (validated for volume calculation in radiotheraphy) and CT. In the two latter methods a segmentation of the CT was also applied to separate limb in three sub-volumes: bone, fat and water. Lower and upper threshold used in segmentation were the same for both software.
RESULTS
The whole limb volume (and also the bone and fat volumes but not the water volume) obtained with Oncentra was nearly identical to the volume calculated using Osirix (% difference 1.07±0.12). Both methods demonstrated mild differences as compared to the traditionally used water replacement method probably because of low reproducibility of this method. Two patients have been excluded from HILP because of distant metastases on PET/CT
CONCLUSION
18F-FDG PET/CT confirmed to be a useful tool for staging patients with melanoma candidated to HILP. The CT portion of the PET/CT, reliably, could be used to calculate whole limb volume, bone volume and fat volume using the open source software Osirix that we proved to offer nearly identical results as the validated Oncentra Masterplan. Water/edema segmentation shoud be used with caution because of significant differences between methods.

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