We have investigated the interaction of the nitroimidazole radiosensitizer desmethylmisonidazole (Ro 05 9963) with interstitial radiation using a clonogenic cell assay as the endpoint. Removable I-125 sources were implanted at right angles to the outer surface of globular RIF-1 tumors grown in the flanks of C3H/He mice. Desmethylmisonidazole was administered by continuous intraperitoneal infusion at a rate of 2.7 mg/gm body weight /24 hr. Tumor and serum drug levels were measured by high performance liquid chromatography. Tumor drug levels of 40--100 mugm/gm tumor tissue were achieved consistently. No appreciable cytotoxicity was produced by desmethylmisonidazole alone, but a radiosensitization effect with a dose modifying factor of 1.6 was found.

Animals↗

PubMedDate not supplied

Characterization of the dose perturbation by stents as a function of X-ray beam energy.

PURPOSE: External beam irradiation of coronary arteries has been shown to be detrimental in an animal model for the prevention of neointimal hyperplasia in the presence of stents when orthovoltage x-ray beams are used. The present study investigated the effect of beam energy on the dose distribution in the wall of the artery in the presence of stents. MATERIALS AND METHODS: We used 250-kVp x-rays and 6-MV x-rays to irradiate a stent placed in a homogeneous phantom. Radiochromic film densitometry and Monte Carlo calculations were used to measure and to simulate the dose distribution in the proximity of the stent. RESULT: External beam irradiation not only failed to prevent neointimal hyperplasia, but actually accentuated the neointimal response to a prompt mechanical injury in the artery. The photoelectric effect, which dominates low-energy x-ray interactions, produces recoil electrons in the stent, which enhance the dose surrounding the intima. The photoelectrons generated in nickel and iron have an extremely short range in normal tissue, approximately 0.1 mm. Initial estimates of orthovoltage x-ray interactions with the stent indicate a dose enhancement in the orthovoltage range by a factor of 2-6 due to the rise in the photoelectric cross section in this energy range depending on the elemental composition of the stent. Film densitometry verifies this dose enhancement. The Monte Carlo calculation yields a dose enhancement and the dose fall-off with distance from the stent when irradiated with orthovoltage x-rays. Conversely when the tissue and stent are irradiated with megavoltage x-rays, the dose enhancement in this region is a factor of 1.15 in close proximity to the stent and 1.0 at distances greater than 0.1 mm. The 6-MV photon interactions in tissue and Ni/Ti are predominantly through Compton scattering. The Compton effect is dependent on the electron density in the medium, in contrast to the atomic number, which is more relevant for photoelectric absorption. The dose estimates for megavoltage x-rays adjacent to the stent are complicated by the lack of charged particle equilibrium. CONCLUSIONS: There is a limited but definite increase in the dose delivery to the arterial wall when stents are irradiated with orthovoltage x-ray energies. This increase may explain the negative response in other studies. The presence of the stent does perturb the character and magnitude of the dose in the normal arterial wall as a function of beam quality.

Alloys↗

PubMedDate not supplied

Relationship between integrated sucking pressures and first bottle-feeding scores in premature infants.

Reasons for delays in initiating premature infant bottle-feeding and the complications associated with various methods of providing nutrition to premature infants are discussed. A quantitative, correlational study was undertaken to assess premature infants' readiness to bottle-feed. Thirty premature infants, weighing 1,230 to 2,020 g were studied to determine the relationship between integrated sucking pressures and bottle-feeding scores. Sucking pressures were measured with research nipples and an electronic suckometer. Feeding ability was measured using a complex research scale and a simpler clinical scale. Feeding scales correlated significantly (r = 0.79, p less than 0.001) while sucking pressures and feeding scores did not correlate significantly. Study limitations may have been responsible for the lack of a significant correlation between sucking pressures and feeding scores. Further research is needed to establish simple, quantitative safety parameters for beginning oral feedings for premature infants.

Gestational Age↗

PubMedDate not supplied

Comparison of fast neutron beams for radiotherapy produced by 17.3-MeV deuterons incident on beryllium and deuterium targets.

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Beryllium↗

PubMedDate not supplied

Correction factors for neutron dose changes caused by inhomogeneities.

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Neutrons↗

PubMedDate not supplied

Dosimetric properties of neutrons from 21-MeV deuteron bombardment of a deuterium gas target.

Spectra, yields, average energies, and kerma rates in tissue of neutrons from 21-MeV deuteron bombardment of deuterium gas targets have been calculated for target thicknesses of 1, 3.5, and 5 MeV. A high pressure gas cell was constructed and was filled with 33 atm of D2 gas (equivalent to an energy loss of 3.5 MeV for 21-MeV deuterons); dose rate, dose buildup, and depth-dose properties of neutrons produced by the D(d,n) reaction were measured. Dosimetric properties of these neutrons are superior to those of neutrons from a thick Be target bombarded by a deuteron beam of the same energy.

Fast Neutrons↗

PubMedDate not supplied

A review of the discrepancy between the in-air and in-water calibration of cobalt-60 machines.

Causes for the discrepancy noted by Grant et al. between the in-water and in-air calibration of 60Co are discussed. Data are presented from measurements with a set of ionization chambers with thimbles of 0.5, 1.0, and 1.5 cm outside radii. These data include measurements of percentage depth dose, backscatter factors, and displacement factors. The results show that the discrepancy noted by Grant et al. is caused by a combination of small errors both in depth dose data and in the displacement factor incorporated into C lambda.

Air Ionization↗

PubMedDate not supplied

Response of LiF powder to 125I photons.

125I seeds are being used to treat a variety of diseases, including brain tumors. However, the uncertainty in the energy response of LiF for 125I photons relative to megavoltage radiation limits the accuracy of dosimetry with this material. An array of 12 40-mCi 125I seeds was used to irradiate LiF powder in throwaway capsules, and an ion chamber was used to measure the absorbed dose. A comparison of the response of these LiF dosimeters with the response of capsules given a similar dose of 60Co radiation has yielded values of 1.39 +/- 0.03 (dose to water) and 1.32 +/- 0.03 (dose to muscle) for the LiF response for 125I relative to that for 60Co. Details of the procedure and sources of uncertainty are discussed.

Brachytherapy↗

PubMedDate not supplied

The dosimetry of 125I seed eye plaques.

The ability of a brachytherapy treatment-planning computer program to calculate accurately the dose from 125I seeds at distances relevant to eye plaque therapy was investigated. Thermoluminescent dosimetry measurements were made in a plastic phantom at depths of 0.5, 0.97, and 1.5 cm, and results were corrected for finite dosimeter size and phantom effects. Doses were calculated at the same depths with an 125I seed linear source model that accounted for dose anisotropy. Measurements and calculations were found to agree within their mutual uncertainties. The presence of a gold plaque was found to reduce the dose at all measured depths by 8%.

Brachytherapy↗

PubMedDate not supplied

Dose parameters of 125I and 192Ir seed sources.

As mandated by an NCI brachytherapy contract, we measured dosimetric parameters for 192Ir seeds and two models of 125I seeds. Measurements were with LiF powder in a water-equivalent phantom. Data were corrected for background, sample mass, and finite detector volume. Selected parameters were also investigated through Monte Carlo calculations. Results are presented in terms of a dose parametrization that is described in detail, and are compared to published data. Our results agreed well with published data for relative quantities such as radial and angular dose dependence. Our measured value for the 192Ir dose factor was 4.55 cGy(H2O) cm2 mCi-1 h-1, also in good agreement with commonly used values. However, the measured dose factors for 125I seed models 6702 and 6711 were 1.18 and 1.06 cGy(H2O) cm2 mCi-1 h-1, values well below those in general use.

Brachytherapy↗

PubMedDate not supplied

Dose distribution of 125I sources in different tissues.

The low-energy photons of 125I deposit energy in tissues primarily by the photoelectric effect, which is strongly dependent on the atomic number Z. Thus dose distributions of 125I sources in media of different Z are not the same. LiF and CaF2 thermoluminescent dosimeters were used for relative dose distribution measurements in materials that are equivalent to muscle, breast, and bone. The experimental data are in good agreement with published results for muscle, and in reasonable agreement with Monte Carlo calculations for all the tissues tested. These measured data provide the basis for dose distribution calculations when 125I seeds are implanted in or near inhomogeneous tissues.

Bone and Bones↗