Imaging and dosimetric errors in 4D PET/CT-guided radiotherapy from patient-specific respiratory patterns: a dynamic motion phantom end-to-end study.

Effective positron emission tomography / computed tomography (PET/CT) guidance in radiotherapy of lung cancer requires estimation and mitigation of errors due to respiratory motion. An end-to-end workflow was developed to measure patient-specific motion-induced uncertainties in imaging, treatment planning, and radiation delivery with respiratory motion phantoms and dosimeters. A custom torso phantom with inserts mimicking normal lung tissue and lung lesion was filled with [(18)F]FDG. The lung lesion insert was driven by six different patient-specific respiratory patterns or kept stationary. PET/CT images were acquired under motionless ground truth, tidal breathing motion-averaged (3D), and respiratory phase-correlated (4D) conditions. Target volumes were estimated by standardized uptake value (SUV) thresholds that accurately defined the ground-truth lesion volume. Non-uniform dose-painting plans using volumetrically modulated arc therapy were optimized for fixed normal lung and spinal cord objectives and variable PET-based target objectives. Resulting plans were delivered to a cylindrical diode array at rest, in motion on a platform driven by the same respiratory patterns (3D), or motion-compensated by a robotic couch with an infrared camera tracking system (4D). Errors were estimated relative to the static ground truth condition for mean target-to-background (T/Bmean) ratios, target volumes, planned equivalent uniform target doses, and 2%-2 mm gamma delivery passing rates. Relative to motionless ground truth conditions, PET/CT imaging errors were on the order of 10-20%, treatment planning errors were 5-10%, and treatment delivery errors were 5-30% without motion compensation. Errors from residual motion following compensation methods were reduced to 5-10% in PET/CT imaging, <5% in treatment planning, and <2% in treatment delivery. We have demonstrated that estimation of respiratory motion uncertainty and its propagation from PET/CT imaging to RT planning, and RT delivery under a dose painting paradigm is feasible within an integrated respiratory motion phantom workflow. For a limited set of cases, the magnitude of errors was comparable during PET/CT imaging and treatment delivery without motion compensation. Errors were moderately mitigated during PET/CT imaging and significantly mitigated during RT delivery with motion compensation. This dynamic motion phantom end-to-end workflow provides a method for quality assurance of 4D PET/CT-guided radiotherapy, including evaluation of respiratory motion compensation methods during imaging and treatment delivery.

MR-driven metal artifact reduction in PET/CT.

Among the proposed system architectures capable of delivering positron emission tomography/magnetic resonance (PET/MR) datasets, tri-modality systems open an interesting field in which the synergies between these modalities can be exploited to address some of the problems encountered in standalone systems. In this paper we present a feasibility study of the correction of dental streak artifacts in computed tomography (CT)-based attenuation correction images using complementary MR data. The frequency and severity of metal artifacts in oncology patients was studied by inspecting the CT scans of 152 patients examined at our hospital. A prospective correction algorithm using CT and MR information to automatically locate and edit the region affected by metal artifacts was developed and tested retrospectively on data from 15 oncology patients referred for a PET/CT scan. In datasets without malignancies, the activity in Waldeyer's ring was used to measure the maximum uptake variation when the proposed correction was applied. The measured bias ranged from 10% to 30%. In datasets with malignancies on the slices affected by artifacts, the correction led to lesion uptake variations of 6.1% for a lesion 3 cm away from the implant, 1.5% for a lesion 7 cm away and <1% for a lesion 8 cm away.

Hemoglobin F in myelodysplastic syndrome.

Reactivation of fetal hemoglobin synthesis in adulthood can be seen in hematological disorders affecting the erythropoietic system. The objective of the present study was to evaluate the incidence and prognostic significance of increased hemoglobin F in patients with myelodysplastic syndrome. Hemoglobin F concentrations and Ggamma/Ggamma + A gamma-globin chain ratios were determined in 26 patients with primary myelodysplastic syndrome. Median age of the patients was 65 years; all FAB subtypes were included. Increased hemoglobin F concentration of up to 20% of total hemoglobin (normal: below 2%) was seen in 16 patients; ten patients had normal values. There was a significant relation between hemoglobin F concentration and the course of disease, e.g., 12 of the 16 patients with elevated hemoglobin F survived at least 1 year after the examination, in contrast to only three of the ten patients with normal hemoglobin F (p < 0.025). All of six patients with hemoglobin F above 5% survived at least 1 year. There was no significant difference in the hemoglobin F concentration between patients with and without cytogenetic anomalies. The Ggamma/Ggamma + A gamma-globin chain ratio was slightly elevated in all patients, with a weak correlation to the degree of hemoglobin F elevation. The values were not of additional prognostic significance. The data of the present study suggest that the hemoglobin F concentration may be a prognostic parameter in myelodysplastic syndrome; increased hemoglobin F concentration may indicate a better prognosis.