Cell secretion - finally sees the light.
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Animals↗
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L L Anderson
Publications and source records attributed to L L Anderson.
Spacing nomograph for interstitial implants of 125I seeds.
Permanent implants of 125I seeds at Memorial Sloan-Kettering Cancer Center are performed by the method of "dimension averaging" to determine the total activity to be implanted; that is, the activity (in mCi) is taken to be five times the average dimension (in cm) of the target region. A nomograph has recently been developed to permit a rapid calculation of the seed spacing required for a uniform distribution of the number of seeds specified by dimension averaging. The number of seeds is also given by the nomograph. The spacing calculation performed with the nomograph, since it involves the two-thirds power of average dimension and the one-third power of seed strength, is well beyond the reach of mental arithmetic. Elongation and shape corrections are included. The nomograph spacing result is valid for an equipartition of measured volume among seeds but must be increased by an easily determined factor if peripheral seeds are considered to define the surface of the target region.
Iodine Radioisotopes↗
A "natural" volume-dose histogram for brachytherapy.
The most useful formulation of the volume-dose histogram for brachytherapy is one which suppresses inverse square law effects while preserving proportionality between volume and the area under the curve. These objectives are met by plotting the distribution of volume per unit-3/2 power of dose rate versus the-3/2 power of dose rate; such a distribution is constant for a single point source. Adding sources results in the formation of a peak, which provides a graphical indication of dose rate uniformity. Evaluation of other peak parameters such as width, position, and contained volume, in relation to treatment dose rate, permits a quantitative and clinically relevant volume-dose assessment of interstitial implants.
Brachytherapy↗
Dose rate determination for 125I seeds.
Dose rates in water have been determined for the two types of 125I seed currently used in brachytherapy. The need for such determinations became evident when water/air ratios measured with a silicon diode were found to be lower than expected. Extensive measurements using lithium fluoride thermoluminescent dosimeters (TLD's) have been performed in a solid water phantom, at distances from 0.1 to 10 cm from the seed center and at angular increments of 10 degrees, 15 degrees, or 30 degrees within a plane through the seed axis. Dose calibration of the TLD's was accomplished by irradiation in air with 125I seeds of the same type and of strengths traceable to a calibration at the National Institute of Standards and Technology (NIST). Relative calibration of TLD's was monitored by irradiation, in an oven-type x-ray machine, of control dosimeters simultaneously and all dosimeters intercurrently with the 125I irradiations. Values obtained for the dose rate constant, i.e., dose rate per unit air-kerma strength at 1 cm on the transverse axis, were 0.853 and 0.932 cGy h-1 U-1 (1.08 and 1.18 cGy h-1 mCi-1) for the 6711 and 6702 seeds, respectively. Measured data were supplemented with Monte Carlo-calculated relative dose rate data generated using the MORSE code. These calculations used 100 energy groups from 10 to 35.4 keV and involved energy collection bins ranging from 0.025 to 1.2 cm on an edge. Normalized at 1 cm, transverse axis calculated data are not significantly different from measured data (ours or cited literature) at distances either less than 2.5 or greater than 8 cm. Normalized at different distances along the transverse axis, our off-axis calculated and measured distributions agree closely at all angles but differ from literature measured distributions at small (less than or equal to 1 cm) distances and, for small angles, increasingly at larger distances (greater than or equal to 5 cm).
Brachytherapy↗
Thermoluminescent dosimetry for 103Pd seeds (model 200) in solid water phantom.
Dose measurements using LiF thermoluminescent dosimeters (TLD) have been performed for single 103Pd seeds (model 200) at the center of a solid water phantom. TLD cubes 1 mm on an edge were used for measurements from 1 mm to 1 cm at 1-mm intervals. The cubes were centered along transverse and longitudinal axes and along radial lines from seed center at 10 degrees increments. TLD chips of dimension 3.1 X 3.1 X 0.89 mm were used at distances of 2, 2.5, 3, and 4 cm at 15 degrees angular intervals. Data are presented as the product of distance squared and dose rate per unit source strength, plotted versus distance and angle. At 1 cm from seed center along the transverse axis this product was found to be 0.88 cGy cm2 mCi-1h-1. A dose-rate table in polar coordinates has been formulated for use with multiseed dose distribution calculations. Comparison with data of Meigooni et al. [Endocuriether./Hyperthermia Oncol. 6, 107-117 (1990)] shows general agreement for distances of 2 cm or greater. A comparison of our transverse axis data with Russell's calculated values (Theragenics Internal Report, 4 November 1984) for an ideal point source of 103Pd shows very good agreement except at distances less than 0.5 cm, where differences are attributable to the extended source effect in the actual seed.
Brachytherapy↗
Diode dosimetry of models 6711 and 6712 125I seeds in a water phantom.
Two-dimensional relative dose distributions have been measured around 125I brachytherapy seeds. The two seed models studied, models 6711 and 6712, were manufactured by the 3M Company. Silicon detectors immersed in water phantoms were used to measure the dose. A computerized data acquisition system that controlled the radial position of the diode and the angular rotation of the seed, as well as a manually controlled system were used to collect and store the data. Our results show that the two seed models have relative dose distributions which are quite similar; however, the absolute dose distributions are sufficiently different to warrant separate look-up tables for the two seed models. Additionally, our results are compared with dose distribution data previously obtained for the model 6711 seed.
Brachytherapy↗
A versatile method for planning stereotactic brain implants.
Our approach to planning stereotactic 125I brachytherapy of brain tumors has involved least-squares optimization of individual seed positions within the target contour, followed by repeated combining of seeds from nearest-neighbor catheters in order to achieve an acceptably low number of catheters and an acceptable-separation of entry points. In one option, the catheters diverge from an extra-cranial point that can be close to the skull if all catheters are to be placed through a small craniectomy to treat a larger-diameter target. In another option, catheters converge toward a point beyond the target, to facilitate perpendicularity at the skull surface if a separate opening is to be drilled for each catheter. In either case, the fact that seed orientations are known, permits including anisotropy in dose calculations. Trial seed locations are constrained to a target region defined on a 1-mm mesh, both in the initial optimization of single-seed catheters and in subsequent combinations followed by tune-up optimizations. In the optimization process, sum-of-squares contributions are weighted more heavily when the dose rate is lower than the target dose rate; the weighting imbalance falls short of keeping all target points above the target dose rate and requires targeting on a dose rate about 25% higher than the desired minimum dose rate.
Biophysical Phenomena↗
Dosimetry for 125I seed (model 6711) in eye plaques.
The effect of eye plaque materials (gold backing and silastic seed-carrier insert) on the dose distribution around a single 125I seed has been measured, using cubic lithium fluoride thermoluminescent dosimeters (TLDs) 1 mm on an edge, in a solid water eye phantom embedded in a solid water head phantom. With an 125I seed (model 6711) positioned in the center slot of the silastic insert for a 20-mm plaque of the design used in the collaborative ocular melanoma study (COMS), dose was measured at 2-mm intervals along the plaque central axis (the seed's transverse axis) and at various off-axis points, both with and without the COMS gold backing placed over the insert. Monte Carlo calculations (MORSE code) were performed, as well, for these configurations and closely the same geometry but assuming a large natural water phantom. Additional Monte Carlo calculations treated the case, both for 20- and 12-mm gold plaques, where the silastic insert is replaced by natural water. Relative to previous measurements taken in homogeneous medium of the same material (without the eye plaque), the dose reduction found by both Monte Carlo and TLD methods was greater at points farther from the seed along the central axis and, for a given central-axis depth, at larger off-axis distances. Removal of the gold backing from the plaque did not make measurable difference in the dose reduction results (10% at 1 cm).
Brachytherapy↗
A simple remote system for the high-level radioiodination of monoclonal antibodies.
We have developed a system for the remote control radiolabeling of monoclonal antibodies (MoAb). The system is simple, inexpensive to assemble, and completely disposable. Reagents are pneumatically manipulated into vials containing Iodogen and an anion exchange resin, wherein iodination and separation of bound from free iodine occur, respectively, and sterilized (by filter) into a final vial. Radiolabeling yields of 38.9 +/- 5.5% were consistently produced with 99.3 +/- 0.2% of the isotope bound to the antibody. These results were not significantly different from those obtained in manual iodinations. However, the radiation dose to the hands of the laboratory worker in the remote mode was reduced at least ninefold. The system is presently being introduced for 300 to 400 mCi 131I iodinations of the anti-ovarian cancer MoAb OC 125 in a Phase I radioimmunotherapy trial.
Antibodies, Monoclonal↗