ABSTRACT
Dose characteristics of a stereotactic radiotherapy unit based on a standard Varian Clinac 4/100 4 MV linear accelerator, in-house-built Lipowitz collimators and the SMART stereotactic radiotherapy treatment planning software have been determined. Beam collimation is constituted from the standard collimators of the linear accelerator and a tertiary collimation consisting of a replaceable divergent Lipowitz collimator. Four collimators with isocentre diameters of 15, 25, 35 and 45 mm, respectively, were constructed. Beam characteristics were measured in air, acrylic or water with ionization chamber, photon diode, electron diode, diamond detector and film. Monte Carlo simulation was also applied. The radiation leakage under the collimators was less than 1% at 50 mm depth in water. Specific beam characteristics for each collimator were imported to SMART and dose planning with five non-coplanar converging 140 degrees arcs separated by 36 degrees angles was performed for treatment of a RANDO phantom. Dose verification was made with TLD and radiochromic film. The in-house-built collimators were found to be suitable for stereotactic radiotherapy and patient treatments with this system are in progress.
Subject(s)
Particle Accelerators/instrumentation , Radiosurgery/instrumentation , Radiotherapy Planning, Computer-Assisted , Biophysical Phenomena , Biophysics , Brain Diseases/radiotherapy , Humans , Monte Carlo Method , Particle Accelerators/statistics & numerical data , Phantoms, Imaging , Radiosurgery/statistics & numerical data , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/statistics & numerical data , Radiotherapy, High-Energy , Scattering, Radiation , Software , Technology, RadiologicABSTRACT
Glucose metabolism has been shown to be increased in neoplastic tissue. It has been suggested that high activity of glucose metabolism is associated with a high grade of malignancy of human cancer. We studied in vivo glucose metabolism in 22 patients with untreated non-Hodgkin's lymphoma with fluorine-18-fluorodeoxyglucose (FDG) and positron emission tomography (PET). FDG uptake in lymphoma deposits was measured blinded to clinical data, and compared with histologic classification and proliferative activity. Tracer uptake was measured by using two indices of FDG accumulation: the standardized uptake value (SUV) and the regional metabolic rate (rMR) for the tracer. The median SUV of the lymphomas was 8.5 (range, 3.5 to 31.0), and the median rMR 22.7 mumol/100 g/min (range, 9.0 to 124.3 mumol/100 g/min). A high FDG uptake in tumors was associated with high histologic degree of malignancy as defined by the Working Formulation (P = .005 for the SUV, and P = .04 for the rMR) or by the Kiel classification (P = .003 for the SUV, and P = .02 for the rMR). A high FDG accumulation was also associated with a high S-phase fraction (r = .786 for the SUV, P = .0002; and r = .774 for the rMR, P = .02). We conclude that in untreated non-Hodgkin's lymphomas high FDG uptake is associated with high histologic grade of malignancy and a high proliferation rate. This minimally invasive method may find application in assessing lymphoma lesions in patients who are poor candidates for surgery, and it may provide further information in cases where the grade of aggressiveness of lymphoma is not settled based on clinical or histologic data.
