In vivo isocenter dose in two hip prosthesis patients.

Hip prostheses may cause irradiation dose inhomogeneities in conventional four-field target volumes to the pelvis. Two patients, with bilateral and unilateral prostheses, were subjected to thermoluminescent dosimetry measurements in the prostatic urethra during 24 MV photon portal exposures. The results suggested a 13% decrease in absorbed dose only for conventional four-field beam geometry with bilateral prostheses, as compared to oblique four-field beam geometry or unilateral prosthesis. This supports the suggestion that beam technique modifications may be warranted for patients with hip prostheses.

Backscatter radiation at bone-titanium interface from high-energy X and gamma rays.

Occasionally head and neck cancer patients treated with high-energy X rays and gamma rays have titanium metal dental implants in their maxillae or mandibles. The resulting effect of the bone-metal interface on the radiation dose is of interest. Ionization measurements for 60Co gamma rays and 6 MV and 25 MV X rays were made. A thin-window parallel-plate chamber was used to determine the magnitude of the dose enhancement that was due to the backscattered electrons from titanium. The results showed that for 60Co there is a 15% increase in dose to solid bone at the entrance side of the titanium. For higher energy X rays, the increase in dose was about the same or slightly lower than for 60Co. Monte Carlo calculations substantiated the measurements. This increase in dose fell off rapidly and became negligible at 1-2 mm from the interface. This backscattered dose should be taken into account when planning radiation therapy treatment for patients with dental implants.

Effect of vitamin A on lung tumorigenesis in irradiated and unirradiated strain A mice.

The effect of vitamin A (retinyl acetate) on lung tumor development in strain A mice exposed to radiation was assessed. Four groups of 75 mice were utilized. Two groups were fed a low vitamin A diet (less than 100 IU/100 g diet) and the other 2 were fed a high vitamin A diet (800 IU/100 g diet). After 2 weeks one group maintained on the high vitamin A diet and one group maintained on the low vitamin A diet were given an acute dose of 500 rad of gamma radiation to the thoracic region. Circulating levels of plasma vitamin A in all 4 groups of mice were monitored. A difference in circulating vitamin A in the mice maintained on high and low vitamin A diet became evident by 20 weeks and continued for the duration of the experiment. Mice were killed 18, 26 and 40 weeks post-irradiation, their lungs were removed and the number of surface adenomas were counted. There was a significant increase in the number of mice bearing lung tumors and the mean number of lung tumors per mouse in the irradiated group maintained on the high vitamin A diet at 40 weeks post-irradiation as compared to the irradiated group maintained on a low vitamin A diet. Under the conditions of this experiment the development of pulmonary adenomas in irradiated strain A mice appears to relate directly to circulating levels of vitamin A.

Lung tumorigenic response of strain A mice exposed to hypoxic cell sensitizers alone and in combination with gamma-radiation.

The influence of metronidazole, misonidazole, and desmethylmisonidazole on the induction of lung adenomas in the strain A mouse was examined. Two dose levels of the hypoxic cell sensitizers, 0.2 and 0.6 mg/g, were used either alone or in combination with 900 rads of gamma-radiation in a fractionated dose schedule of twice a week for 3 weeks. In the groups of mice which received hypoxic cell sensitizers only, the prevalence and the mean number of lung tumors per mouse were somewhat increased (p less than 0.10) in the group receiving the higher dose (0.6 mg/g) of misonidazole but was not significantly different from results for the control animals in the other two sensitizer groups. The combination of hypoxic cell sensitizer and radiation did not show any significant enhancement of lung tumor response when compared with the group which received radiation only. The dose of radiation used in this study significantly enhanced lung tumor formation in mice when compared with that in the control group. Thus, under the experimental exposure conditions used in this investigation, which were somewhat similar to the exposure conditions occurring in clinical treatment, each of the hypoxic cell sensitizers tested failed to sensitize significantly the mice to the carcinogenic effects of gamma-radiation.

Radiation dose and biological effects to mouse testis from sodium 32P-phosphate.

Radiation dose to mouse testis was estimated to be about 1.65 rad per microCi of intravenously injected 32P. This high dose to the organ was due to the incorporation of this isotope into the macromolecules of the testis. Up to 30% of the total testis activity was in DNA molecules. Biologic effects on mouse testis from 32P were determined by testis weight loss and the decrease in the number of sperm heads in the testis. Number of sperm heads reached a minimum of 1.3% of control 36 days after injection of 3.5 microCi/g body weight of 32P. Significant decreases in sperm head counts were observed after as little as 0.2 microCi/g body weight of 32P.

Radiation damage to mouse testis cells from [99mTc] pertechnetate.

The radiation dose and the biologic damage to mouse testis from intravenously administered [99mTc] pertechnetate were studied. The dose was measured for penetrating radiations from Tc-99m, using calibrated thermoluminescent dosimeters and calculations from the uptake of the nuclide in the testis, and was found to be 4.9 rada per mCi of Tc-99. The biologic damage was measured by the decrease in the number of sperm heads in the testis, counted both by hemacytometer and by Coulter counter. In preliminary experiments using external gamma radiation from Cs-137, the number of sperm heads reached a minimum 29 days after irradiation. Twenty-nine days after injection of 5.8 mCi of Tc-99m, which gives 28 rads to the testis, the number of sperm hads decreased to 70% of control. The biologic effect corresponds to that seen after 40 rads of gamma radiation from Cs-137. The damage to mouse testis cells from internally administered Tc-99m as measured in an in vivo system appears to be at least as significant as that from external gamma irradiation, if not more so.