Accuracy of a photogrammetry-based patient positioning and monitoring system for radiation therapy.

A photogrammetry system designed to reduce simulator-to-treatment and treatment-to-treatment patient positioning errors has been developed. Two complete systems have been installed in our department: one in the simulator room and one in a treatment room. Each system consists of three charge-coupled device (CCD) cameras; a ring of infrared LEDs around the lens of each camera; and several small, circular, retroreflective markers that are applied to the patient. The markers reflect infrared light directly back to the cameras, producing a binary image of oval hot spots when the image is thresholded. The three-dimensional position of each marker is calculated by conventional photogrammetry methods. At simulation, marker positions are measured, then transferred to the treatment room system. The system may be used to actively position patients, and to passively monitor a patient's position and motion during treatment. Studies have focused on measuring the system's temporal stability, precision, and accuracy; on optimal positioning of markers and cameras; and on assessing the system's capability to reduce the positioning error. The repeatability of measuring a marker's position is <0.1 mm in each orthogonal direction. The accuracy is approximately 0.5 mm over a 40 X 40 X 40 cm3 field of view. The system drift over four hours is approximately +/-0.2 mm. The photogrammetry system has been used to actively position a lead BB, embedded within a head phantom, at the isocenter; repeatability was +/-0.3 mm, as determined radiographically. The system has also been used to passively monitor the positioning of several head and neck patients that were set up by a therapist; setup errors of up to 10 mm in each orthogonal direction were measured, as well as the motion of the patient during treatment.

An equation to QA check the total treatment time for single-catheter HDR brachytherapy.

PURPOSE: To develop a simple equation that can be used to quickly QA check the total treatment time needed for straight or moderately bending, single-catheter implants from the treatment length and dose-prescription depth. A method to quickly check the total treatment time is useful for high dose rate (HDR) treatments, but may be most useful for intravascular patients that are catheterized while planning the treatment. METHODS AND MATERIALS: Nucletron-Oldelft treatment planning software was used to plan treatments with treatment lengths from 50 to 200 mm, and dose-prescription depths from 2 to 14 mm. For each plan, dose points were defined at a fixed depth away from the catheter. Doses were calculated, normalized, and optimized using the dose points. From these plans, a single equation was developed for the total treatment time as a function of treatment length and dose-prescription depth. RESULTS: Total treatment time increases linearly with treatment length and supra-linearly with dose-prescription depth. A difference of 3% or more between the treatment time determined by the QA check equation and by the treatment planning software will alert the clinician and physicist to check for potential errors in dose prescription, prescription depth, source activity, treatment length, or inadvertent modifications to physics parameters used in the treatment planning software. CONCLUSION: The simple equation that is developed can be used to quickly and accurately QA check the total treatment time needed for straight or moderately bending, single-catheter implants.

Head phantoms for neutron capture therapy.

A water-filled head phantom that is designed for use in boron neutron capture therapy is described. The shape of this ellipsoidal phantom, based on the Synder head model, and its composition are designed to simulate the neutron slowing down properties of the human skull and brain. Small ion chambers or activation foils can be placed in many locations within the phantom volume. This permits accurate three-dimensional mapping of all relevant dose components and use of these dose contours for beam development as well as for benchmarking of computer-based patient treatment codes.

Mixed field dosimetry of epithermal neutron beams for boron neutron capture therapy at the MITR-II research reactor.

During the past several years, there has been growing interest in Boron Neutron Capture Therapy (BNCT) using epithermal neutron beams. The dosimetry of these beams is challenging. The incident beam is comprised mostly of epithermal neutrons, but there is some contamination from photons and fast neutrons. Within the patient, the neutron spectrum changes rapidly as the incident epithermal neutrons scatter and thermalize, and a photon field is generated from neutron capture in hydrogen. In this paper, a method to determine the doses from thermal and fast neutrons, photons, and the B-10(n, alpha)Li-7 reaction is presented. The photon and fast neutron doses are measured with ionization chambers, in realistic phantoms, using the dual chamber technique. The thermal neutron flux is measured with gold foils using the cadmium difference technique, the thermal neutron and B-10 doses are determined by the kerma factor method. Representative results are presented for a unilateral irradiation of the head. Sources of error in the method as applied to BNCT dosimetry, and the uncertainties in the calculated doses are discussed.

Radionuclide selection and model absorbed dose calculations for radiolabeled tumor associated antibodies.

An absorbed dose calculation comparison has been computed for radiolabeled tumor associated antibodies distributed over a standard geometry and tumor location. Half-life data, maximum specific activities, and relative organ doses of nine radionuclides, Cu-67, Br-77, Br-82, Y-90, Tc-99m, In-111, I-131, Re-186, and At-211, have been compiled in which the radionuclides were assumed to be coupled with antibody. These nuclides were chosen on the basis of physical characteristics that warranted their inclusion as either imaging or therapy radiolabels. Radionuclide biodistribution data based on current available estimates for antibody uptake and clearance in humans has been adopted. Re-186 and Y-90 have been determined to be among the best therapy radiolabels since they possess sufficiently long half lives necessary for tumor localization, little or no gamma radiation, intermediate beta energy, stable daughter products, and have a reasonable chance to form a stable chelate with an antibody system.