Johan Baarli

Lens Opacification in Mice Exposed to 14-MeV Neutrons

The induction of lens opacification in mice exposed to 14-MeV neutrons was evaluated by counting the number of opacities observed in the posterior region of the lens using a slit-lamp microscope. The incidence of cataract formation in the anterior region of the lens was also observed. Serial observations were carried out from 3 up to 25 months after irradiation. Male hybrid mice (C54B1 X C3H), 75 days old at the time of the exposure, have been used. A linear progression of opacities was observed with age at a rate depending on the dose. By comparison with 250-kVp X rays the RBE was found to increase, with decreasing dose, from 9 to 21. The incidence of opacification in the anterior region of the lens gives an RBE value of 8. Split-dose irradiations were carried out with an interval of 24 hr between doses. There was very little difference in the number of opacities observed after single or fractionated neutron doses of approximately the same total amount. In contrast, fractionation of the X-ray dose reduced the effectiveness of the irradiation.

Biological responses to various neutron energies from 1 to 600 mev. II. Lens opacification in mice.

Eye lens opacification in mice has been used to evaluate the RBE of neutrons of 1, 5, and 600 MeV. The experimental observations were based on counting the points of opacities appearing in the posterior region of the lens. RBE values have been calculated with reference to the equal effects observed after exposure to 250-kVp X rays. Data previously reported for 15- and 400-MeV neutrons have also been included. For all neutron energies, the RBE increases with decreasing dose. In addition, at very low doses the RBE appears to reach about the same value independently of the neutron energy used. In contrast, for higher dose values the RBE decreases with increasing neutron energy from about 24 for 1 MeV to about 6 for the 600-MeV neutrons.

Biological responses to various neutron energies from 1 to 600 mev. I. Testes weight loss in mice.

Testes weight loss in mice has been used as a test system to determine the relative biological efficiency (RBE) of neutrons ranging in energy from fission to a beam of 600 MeV nominal energy. The RBE values, calculated as equal effect dose ratios show a maximum at the neutron energy of 1 MeV. No significant dependence was found on the level of absorbed dose. Analyses of the dose-effect relations obtained suggest the existence of a radiation-insensitive component of the testes that accounts for 32.5% of the total weight. By considering only the radiosensitive component, the X-ray data show an exponential dose-effect relation. When the same correction is applied to the neutron data, dose-effect curves with an extrapolation number less than one are obtained for some neutron energies.

An Estimation of the RBE of Stopped Pions from Observations of Spermatogonia Survival in Mice

SummaryThe survival of spermatogonia of type B in mice after exposure to negative and positive pions is presented. It is found that the survival curve in the case of negative pions has an inverse shoulder and in the case of positive pions the best fit seems to be a straight line. The observed survival curves have been compared to provide information about the radiobiological significance of the negative pion nuclear interactions. Discussions of the results obtained show that one cannot exclude the possibility that the biological system used might behave as a mixed population in the case of negative pions as compared with x-rays.

Some measurements on the slowing down of pi mesons in tissue-equivalent material.

Measurements of the attenuation of positive and negative pion beams are described. An analysis is made of the results where it is estimated that the average energy locally deposited in a tissue-equivalent absorber by a strong interaction of a negative pion is 19·6±1·3 MeV. In the negative pion beam absorption peak it is shown that the absorbed dose from nuclear interactions amounts to about 45% of the total dose.

Dose fractionation effects with negative pions

Past studies of the biological effects of negative pions have largely been limited to determining RBE and OER values in the peak and entrance (plateau) region of the pion depthdose curve (Raju and Richman, 1972; Skarsgard, 1979). The results obtained have shown a higher RBE and a lower OER value in the peak compared with the entrance region. Another possible advantage of pions in their application to radiotherapy is the expected lower degree of biological recovery after irradiation in the peak compared with the entrance region. To investigate this effect experimentally, we have irradiated Vicia faba bean roots at SIN (Swiss Institute for Nuclear Research, Villigen) in the πE3 biomedical pion beam using various fractionation schemes. The beam had an average energy of 82MeV (momentum 172 MeV/c) with a spread of 13% (8%). The dose rate, as determined with an EGG tissue-equivalent ion chamber placed at the irradiation position in the water tank (Bianchi et al., 1978), varied during the irradiation between 260...

Radiological physics of pions.

Pions, and in particular negative pions, are of interest to radiology for at least three outstanding reasons: First, a beam of negative pions can produce in tissue depth and isodose distributions which, for treatment of deep-seated tumors, give a considerably better tumor-to-total-dose ratio than any other commonly used therapeutic radiation source (1). This improved ratio with pion irradiation is largely due to the short-ranged, heavily ionizing products resulting from nuclear pion interactions at the end of the pion track. Thus, second, an additional effectiveness of the dose delivered to the tumor relative to that delivered to healthy tissue is likely because of the oxygen effect observed with heavily ionizing radiation (2). Third, a pion beam seems at present to be the best choice in order to create a well-defined region in which nuclear reactions or nuclear stars give a substantial contribution to the radiation dose. Such conditions are essential for dosimetry and radio-biological research of strong nuclear interactions and thus for approaching a deeper understanding of the particular problems of high-energy dosimetry and radiobiology (3). In the following discussion, some experimental studies of the pion beam from the CERN 600-MeV Synchro-Cyclotron are reported. The results are limited to dosimetry and radiation quality measurements in a water phantom exposed to a 70-MeV pion beam; an attempt was also made to evaluate the average local energy deposition per stopped pion. The results are of a preliminary nature, and more extensive experimental investigations along the same lines are continuing.

RBE and OER values of negative pion beams from growth inhibition of Vicia Faba roots

SummaryTwo pion beams of different momentum width have been used to expose meristems of Vicia Faba roots under aerobic and hypoxic conditions. The measurements of the resulting 10 days growth inhibition after exposures at various locations on the pion beam axes have been made and RBE and OER values evaluated for 50% effects compared to60Co tiγ-rays. The results have been related to the fractional doses from star products defined by telescope measure ments of stopped pions along the same beams. It has been found that the RBE value increases with the fractional “star dose” up to a maximum after which the RBE decreases. The OER values, however, were found to decrease with increas ing “star dose” fraction rather rapidly after which it was found to be independent of the “star dose” contribution.

Observations on Late Effects in Mice Exposed to 400 MeV Neutrons

Life-long observations on mortality and pathology at death were carried out on groups of mice irradiated with 250 kV X-rays or exposed to a 400 MeV neutron beam, both directly and after attenuation corresponding to the maximum dose build-up region, at comparable dose-rates. Doses up to 84 rad of 400 MeV neutrons and up to 200 rad of X-rays showed no effect on the longevity of the animals, which suggest an upper limit to the r.b.e. for life-shortening of approximately 2-5. Similar conclusions were drawn from the data on all types of leukemias. For all other neoplasms, the age-specific death-rate showed a similar shortening of the latency times for groups of mice irradiated with 0-84 rad of 400 MeV direct neutrons and 0-400 rad of X-rays, also suggesting an upper limit to the r.b.e. slightly higher than that previously indicated for life-shortening. No definite effect was observed after exposure to the attenuated neutron beam at the doses used in these experiments.

The biological effect of very high energy hadrons.

The meristems of Vicia faba bean roots were irradiated at different depths in water in a 250 GeV/c positive hadron beam from the CERN Super Proton Synchrotron (SPS). The growth during the 10 days following irradiation was determined and compared with results obtained from 60Co gamma-ray exposures. The data indicate a Relative Biological Efficiency (r.b.e.) near to one, independent of the contribution of secondaries to the dose. However, some anomalies in the radiation response of the irradiated beans were noted.