Richard G. Lane

FRACTION SIZE, DOSE AND TIME DEPENDENCE OF X RAY INDUCED LATE RENAL INJURY

Histologic quantitation of renal radiation injury based on an intact mouse model correlates well with loss of renal mass, as measured by the ratio of right to left renal weight, radiation dose, and time after irradiation. Use of the radiation dose at which 50% of animals show renal tubular changes of a specified grade (ED50), allows comparison of 1, 5 and 15 fraction exposures. The X-ray dose necessary to effect significant injury (Grade 3 change) by six months after irradiation (ED50) was 11.6, 25.7, and 44.0 Gy for single, 5, and 15 fractions, respectively. Isoeffect plots of total radiation dose as a function of fraction number are linear on logarithmic coordinates, indicating that this relationship followed a power function. When plotted as inverse total dose versus dose per fraction, the six month post-irradiation data were linear, but the 12 month data were not. Lack of linearity is not in agreement with the multi-fraction isoeffect linear quadratic model.

Static pion beam treatment planning of deep seated tumors using computerized tomographic scans

Abstract Static negative pion beam treatment of deep seated tumors is in progress at LAMPF. The influence of the physical principles of pions on treatment planning, e.g., an enhanced peak dose, multiple scattering, variations of beam quality, pin beam emittance, and a fixed vertical beam, are discussed. Computerized tomographic (CT) scan data have proven invaluable in providing quantitative information on inhomogeneities within the anatomy. The methods of designing collimation and compensating bolus for tailoring the pion beam to individual patient ports are described. An interim method, using dosimetry measurements in a water phantom and CT scan data to construct patient isodose distribution is outlined. Typical treatment plans for patients with abdominal and head and neck cancers are presented. The method of X-ray simulation in verifying localization of CT-defined tumor volumes is demonstrated for the head and neck.

Dosimetry of pion therapy beams.

Cellular, animal, and human radiobiology studies are in progress at the Los Alamos Meson Physics Facility as part of a joint University of New Mexico and Los Alamos Scientific Laboratory pion therapy project. To support these activities, dosimetry has been performed on many different pion beam configurations. The effect of both static and dynamic momentum spreaders and of collimators on beam profiles, depth-dose distributions, and peak-to-plateau ratios have been studied. The absorbed dose is obtained by the application of Bragg-Gray cavity theory to ionization chamber measurements. Calculations have been made for the effective W values and average mass-stopping-power ratios needed for the Bragg-Gray equation. Kerma corrections are applied to transform the dose from the chamber wall to dose in muscle.

The effect of geometric errors in the reconstruction of iridium-192 seed implants.

In the treatment of tumors using interstitial implants of radioactive seeds, the accuracy of computed dose distributions depends upon the accuracy with which the three-dimensional source geometries are reconstructed from radiographs of the implants. The effect of geometric reconstruction errors in iridium-192 seed implants were studied, using tumor dose as the measure. Tumor dose was defined as the average dose around the periphery of the treatment volume. Three ideal mathematical implants and five actual patient implants were used. The implants were distorted by randomly moving a specified number of seeds a specified distance. Tumor doses were directly calculated for the ideal implants. For the actual implants, isodose distributions were plotted and were read by a radiotherapist. For both types of implants, percentage errors in the tumor doses were calculated for the distorted reconstructions relative to the correct reconstructions. It was found that the tumor dose was accurate to within 5% if all the seeds were reconstructed to within 0.5 cm of their actual positions. Furthermore, up to 5% of the seeds could be mismatched between films, or otherwise incorrectly reconstructed, with position errors as large as 20 cm, and not change the tumor dose by more than 5%.

Treatment planning for negative pi-meson radiation therapy: UNM-LASL experience

Abstract Human radiobiological studies using negative pi-mesons have recently been conducted at the Los Alamos Meson Physics Facility; metastatic tumor nodules in the skin and superficial tumors have been treated. Large tumors of the head and neck, cervix and rectum will be treated later this year to evaluate mucosal reactions. The dosimetry and treatment planning for these clinical studies is presented. Comparisons of measurements and calculations of the effect of inhomogeneities on pion dose distributions are shown. The pion treatment code, PIPLAN, and the Oak Ridge National Laboratory Monte Carlo code have been compared and an example of their respective dose distribution calculations is given.

Measurement of the effect of inhomogeneities and compensating bolus in clinical pion beams.

Measurement of the effects of Telfon and air inhomogeneities on the ionization distributions of clinical negative-pion beams have been made at the Los Alamos Meson Physics Facility. Inhomogeneity location and pion-beam energy vary the effect of multiple coulomb scattering on the dose distribution lying in the penumbra of the inhomogeneity. CH2 bolus adequately corrects for the effects of these inhomogeneities. Bolus misalignment less than 0.5 cm does not seem critical because of large multiple coulomb scattering of the pion beam. However, this and secondary particles emitted from pion stars prevent the pion beam from being precisely shaped with sharp edges, as demonstrated by measurements under a patient bolus.

Radiation Exposure During Fluoroscopically Controlled Percutaneous Lithotripsy

Radiation measurements in the vicinity of a standard urologic table modified for fluoroscopic-guided lithotripsy demonstrate radiation levels as high as 3000 mrem per hour at the edge of the table. Excessive radiation exposure to the physician, exceeding the annual maximum permissible dose to the eyes and thyroid, can be expected after only 10 cases. Suggested radiation protection measures include the use of finger, wrist and neck radiation monitors, eye and thyroid shields and improved shielding of both collimator and patient scatter radiation.

Accuracy of a two-sensor sonic digitizer.

Digitizing devices are typically used in radiotherapy computer treatment planning for entering patient anatomy, the locations of internal radioactive source, and the outlines of irregularly shaped external beams. The errors encountered in the use of a large-area two-sensor sonic digitizer for computer input have been studied. Conversion of data from triangular to Cartesian coordinates makes the precision of the digitizer nonuniform over the sensitive area. The response of each senor has been measured and found to be a nonlinear function of distance. The assumption of linearity in computing the triangular distances from the sensor readings produces errors in the computed distances of up to 0.8%. An alternative method of computing the distances using a fitted cubic function reduces the errors to less than 0.1%. For a test pattern, the maximum position error was reduced from 0.5 to 0.1 cm.

An automated dosimetry data-acquisition and analysis system at the LAMPF pion therapy facility.

An automated data-acquisition and analysis system has been developed for dosimetry measurements on the pion therapy beam at the Clinton P. Anderson Meson Physics Facility Biomedical Channel in Los Alamos using a PDP-11/45 computer and CAMAC interface. Initialization, test, and monitor programs allow the user to set the physical limits of scanner travel, test the data lines, calibrate the analog signals for the scanner position, and monitor the analog versus digital values of the scanner position during operation. Data-acquisition programs scan beams in one, two, and three dimensions. Many options are available to the user in selecting the scan parameters and in changing some of these parameters during scanning. Data-analysis programs provide reproduction of stored data, comparison of linear scans, beam profiles along any line of a planar or volume scan, and isodose distributions from any planar scan or from any planar scan or from any plane of a volume scan. Other programs summarize stored data files and search for specific data according to the users instruments.

COMPUTATION OF DOSE DISTRIBUTIONS FOR RADIOACTIVE SEED IMPLANTS

An interactive treatment planning program for the computation of dose distributions for 125I and 192Ir seed implants of up to 300 sources is described. The seed coordinates are entered using either the keyboard or a sonic digitizer from either orthogonal or stereo films. The program produces a dose matrix which can be displayed and plotted directly or combined with the putput of other treatment planning programs to provide composite plans for treatments using multiple modalities. Seeds of different activities can be combined within a single plan. The program uses two-letter mnemonics for specifying the available options, among which are commands for choosing standard antero-posterior, lateral, and transverse plans.