Preirradiation Growth Research Articles

Pretreatment Growth Rate Predicts Radiation Response in Vestibular Schwannomas

Vestibular schwannomas (VS) are often followed without initial therapeutic intervention because many tumors do not grow and radiation therapy is associated with potential adverse effects. In an effort to determine whether maximizing initial surveillance predicts for later treatment response, the predictive value of preirradiation growth rate of VS on response to radiation therapy was assessed. Sixty-four patients with 65 VS were treated with single-fraction stereotactic radiation surgery or fractionated stereotactic radiation therapy. Pre- and postirradiation linear expansion rates were estimated using volumetric measurements on sequential magnetic resonance images (MRIs). In addition, postirradiation tumor volume change was classified as demonstrating shrinkage (ratio of volume on last follow-up MRI to MRI immediately preceding irradiation <80%), stability (ratio 80%-120%), or expansion (ratio >120%). The median pre- and postirradiation follow-up was 20.0 and 27.5 months, respectively. Seven tumors from neurofibromatosis type 2 (NF2) patients were excluded from statistical analyses. In the 58 non-NF2 patients, there was a trend of correlation between pre- and postirradiation volume change rates (slope on linear regression, 0.29; P=.06). Tumors demonstrating postirradiation expansion had a median preirradiation growth rate of 89%/year, and those without postirradiation expansion had a median preirradiation growth rate of 41%/year (P=.02). As the preirradiation growth rate increased, the probability of postirradiation expansion also increased. Overall, 24.1% of tumors were stable, 53.4% experienced shrinkage, and 22.5% experienced expansion. Predictors of no postirradiation tumor expansion included no prior surgery (P=.01) and slower tumor growth rate (P=.02). The control of tumors in NF2 patients was only 43%. Radiation therapy is an effective treatment for VS, but tumors that grow quickly preirradiation may be more likely to increase in size. Clinicians should take into account tumor growth rate when counseling patients about treatment options.

Predicting behavioral problems in craniopharyngioma survivors after conformal radiation therapy

Although radiation therapy is a primary treatment for craniopharyngioma, it can exacerbate existing problems related to the tumor and pre-irradiation management. Survival is often marked by neurologic deficits, panhypopituitarism, diabetes insipidus, cognitive deficiencies, and behavioral and social problems. The Achenbach Child Behavior Checklist (CBCL) was used to evaluate behavioral and social problems during the first 5 years of follow-up in 27 patients with craniopharyngioma treated with conformal radiation therapy. All group averages for the CBCL scales were within the age-typical range at pre-irradiation baseline. Extent of surgical resection was implicated in baseline differences for the internalizing, externalizing, behavior problem and social scores. Significant longitudinal changes were found in internalizing, externalizing, behavior problem and school scores that correlated with tumor and treatment-related factors. The most common variables implicated in post-irradiation behavioral and social problems were CSF shunting, presence of an Ommaya reservoir, diabetes insipidus, and low pre-irradiation growth hormone levels.

Involvement of RecB-mediated (but not RecF-mediated) repair of DNA double-strand breaks in the γ-radiation production of long deletions in Escherichia coli

Experiments were designed to determine the association between the repair of γ-radiation-induced DNA double-strand breaks (DSB) and the induction of 700–1000 bp long deletions (Lac − → Lac +), base substitutions ( leuB19 → Leu +), and frameshifts ( trpE9777 → Trp +) in Escherichia coli K-12. Over the range of 2.5–20 krad, deletions were induced with linear kinetics, as has been shown for the induction of DSB, while the induction kinetics of base substitutions and frameshifts were curvilinear. Like the repair of DSB, deletion induction showed an absolute requirement for an intact recB gene as well as a dependency on the type of preirradiation growth medium; these requirements were not seen for base substitutions or frameshifts. In addition, about 80% of the spontaneous deletions were absent in the recB21 strain. A recC1001 mutation, which confers a “hyper-Rec” phenotype, increased the rate of γ-radiation-induced deletions as well as the low-dose production of base substitutions and frameshifts. A recF143 mutation increased the yield of γ-radiation-induced deletions without increasing base substitutions or frameshifts. A mutS mutation markedly enhanced the γ-radiation induction of frameshifts, and had a slight effect on base substitutions, but did not affect the induction of deletions. Resistance to γ-irradiation and the capacity to repair DSB (albeit at about half the normal rate) were restored to the radiosensitive recB21 strain by the addition of the sbcB215 and sbcC201 mutations. However, the radioresistant recB sbcBC strain, which is recombination proficient via the RecF pathway, was still grossly deficient in the ability to produce deletions. A model for deletion induction as a by-product of the recB-dependent (Chi-dependent) repair of γ-radiation-induced DSB is discussed, as is the inability to detect deletions in cells that use only the recF-dependent (Chi-independent) mechanism to repair DSB.

External irradiation of growth hormone producing pituitary adenomas: Prolactin as a marker of hypothalamic and pituitary effects

Fifty-six patients with acromegaly were treated with external irradiation, 50 Gy, after unsuccessful pituitary surgery. A 50% reduction of pre-irradiation growth hormone levels was obtained in 51 56 patients. This level was reached after 26 ± 14 months in 33 patients with prolactin levels < 25 μg/l at diagnosis, after 21 ± 17 months in 18 patients with prolactin ≥ 25 μg/l, and after 20 ± 21 months in 12 patients with prolactin > 40 μg/l at diagnosis. A further 50% decrease of growth hormone levels was obtained in 40 51 patients 42 ± 22 months after radiotherapy, indicating that in clearly responsive patients, the growth hormone depression after radiotherapy follows a first order reaction. Four patients did not reach a 50% reduction of growth hormone levels 48–80 months after radiotherapy. During 10 years of follow-up, the growth hormone depression tended to be more pronounced in patients with mixed secretion of growth hormone and prolactin. The reduction of growth hormone levels was not correlated with the irradiated volume or the cumulative radiation effect. Within the first year, prolactin increased within the normal range in normoprolactinemic patients and remained so during follow-up. In hyperprolactinemic patients, prolactin decreased successively but to a lesser extent than growth hormone. Pituitary insufficiencies increased over time and three patients developed GH-insufficiency. Hypothalamic damage as indicated by prolactin changes was a regular phenomenon after radiotherapy.

Proliferation Kinetics of a Murine Fibrosarcoma during Fractionated Irradiation

Accelerated growth of tumor clonogens during the course of fractionated irradiation has been considered one of the major causes of radiation treatment failure. Alterations in clonogen growth rate could occur through three basic mechanisms: changes in cell-loss factor, changes in cell-cycle time, and recruitment of previously quiescent cells into the proliferative pool. This study was designed to assess changes in the cell-cycle time of clonogens of a murine fibrosarcoma during fractionated irradiation using an artificial pulmonary micrometastasis model. Lung colonies of various ages (4 h, 1 day, or 4 days) were exposed to single doses of irradiation ranging from 5-13 Gy; the fraction of surviving colonies was used to determine the preirradiation growth kinetics. The growth kinetics during fractionated irradiation was derived from colony-survival data of 4-day-old micrometastasis exposed to single doses or to 2, 5, 9, and 15 fractions separated by 4, 12, or 24-h intervals. The size of dose fractions used ranged from 1.7 to 14 Gy. The estimated clonogen doubling times before irradiation and during overall treatment periods of up to 14 days were 0.71 and 1.1 days, respectively. This significant (P less than 0.0001) increase in the doubling time was most likely a consequence of lengthening of the overall cell-cycle time of the clonogens by radiation-induced division delay. This observation suggests that accelerated growth, when it occurs in some tumors during fractionated treatment, is the result of a decreased cell-loss factor or recruitment of quiescent cells, but not a shortening of the cell-cycle time of the clonogens.

The sensitivity of an actinic reticuloid cell strain to near-ultraviolet radiation and its modification by trolox-C, a vitamin E analogue.

Near-UV radiation (365 nm)-induced lethality, as measured by colony-forming ability, showed an actinic reticuloid cell strain to be sensitive relative to normal human fibroblasts, when irradiated at 25 degrees C. This effect was not seen after far-UV (254 nm) irradiation. Trolox-C, a water-soluble analogue of vitamin E, incorporated in the pre-irradiation growth medium or in the post-irradiation plating medium, protected the actinic reticuloid cells to the extent that they were as resistant as normal cells. Plating medium containing Trolox-C did not provide differential protection against inactivation of the two cell strains by wavelengths in the far-UV region. The protection provided by Trolox-C, an analogue of the natural antioxidant vitamin E, suggests some free radical involvement in the aetiology of the disease.

Study of MFD-type repair in locus determining resistance of Escherichia coli to streptomycin

The yield of induced mutations to streptomycin resistance (Str) in E. coli, UV-irradiated and temporarily incubated in liquid medium not permitting protein synthesis, depends upon the conditions of preirradiation growth and preirradiation treatment of the bacteria, i.e. on their physiological state at the moment of irradiation. This fact is not readily reconciled with a model postulating mutation production in the structural genes of E. coli during excision repair. A preferred explanation is offered, based on the assumption that the efficiency of mutagenesis at the rpsL (strA) locus is determined by interference of antimutagenic (generalized excision repair and MFD) and promutagenic (mutation fixation of excision repair) events. The participation of macromolecular syntheses in Str mutation fixation is suggested.

Variation of the radiobiological oxygen constant, K, with the proliferative activity of the cells.

The value of K for mouse Ehrlich ascites cells depends on their phase of growth. Cells were grown either in vitro or in vivo but were irradiated and assayed in vitro. K was 1.7 times greater for cells in the exponential phase of growth than for those in plateau phase irrespective of the pre-irradiation growth conditions.

Modification by preirradiation growth conditions of the shoulder of the UV fluence-survival curve of Escherichia coli B/r WP2 thy trp and changes in mutagenic response toward tryptophan prototrophy

The distinct three-section UV fluence-mutation frequency response (MFR) curve demonstrated in Escherichia coli strain B/r WP2 thy trp and its uvrA derivative supports the SOS hypothesis and suggests that trp + revertants can arise either from isolated lesions (1DM) plus SOS induction of from two lesions in proximity (2DM). Preirradiation growth on arabinose instead of glucose converted the fluence—survival curve from highly shouldered to exponential but did not affect the three-section MFR curve. Prestarvation of the uvrA + strain for tryptophan, which drastically increases the expanse of the shoulder of the survival curve, greatly decreased both 1DM and 2DM. With the uvrA strain the increase in shoulder expanse after tryptophan prestarvation was accompanied by greatly increased 2DM but no change in 1DM. Preincubation with chloramphenicol induced an even greater increase in 2DM response than amino acid prestarvation. Nalidixic acid, which prevents DNA accumulation, eliminated the response.

The role of inducible gene rer of Escherichia coli K-12 in DNA repair and mutagenesis

Further characterization of a UV- and gamma-ray-sensitive mutant of Escherichia coli K-12 mutated in gene rer revealed that, as a result of this mutation: (1) neither bacterial capacity to excise thymine dimers from its DNA nor capacity to reactivate UV-irradiated phage λ (Hcr +) was affected; (2) sensitivity to EMS and MC was increased; (3) WR of phage λ was poor, whereas pre-irradiation growth of the mutant in MM only marginally restored WR; (4) the yield of UV-induced mutations was normal on MM, whereas on RM a decline below the spontaneous level was observed; and (5) induction of prophage by UV was not affected. The medium effect on UV sensitivity was largely post-irradiation. The rer recA double mutant was as UV senstive as recA alone, and the media-dependent UV sensitivity exhibited bu the rer strain disappeared in the double mutant. We provide further evidence to strengthen the earlier suggestion that rer might be involved in the control of replication of damaged DNA rather than participating directly in repair. It is further proposed that the rer + gene is inducible and has a role in post-replication repair.

Independence of the radiobiological oxygen constant, K, and the respiration rate of mammalian cells.

The radiosensitivity, and the radiobiological oxygen-constant K for mouse Ehrlich ascites cells depend on the pre-irradiation growth conditions. Measurements of the oxygen-consumption rate of cells grown by different methods have been made to ascertain whether the differences in radiobiological properties could be associated with different rates of respiration. Inhibition of respiration by sodium amytal had no significant effect on either the radiosensitivity or the estimate of K.

The use of gamma radiation for the elimination of Salmonella from frozen meat.

The use of a gamma radiation process for the elimination of Salmonella from frozen meat is considered with particular reference to the treatment of boned-out horsemeat and kangaroo meat imported into the UK and intended for use as pet meat.Examination of dose/survival curves produced for several serotypes of Salmonella in frozen meat shows that a radiation dose of 0.6 Mrad. will reduce a population by at least a factor of 10(5). The influence on the radiation resistance of salmonellas of such factors as preirradiation growth in the meat and temperature during irradiation have been examined and considered. It is also demonstrated with both preinoculated and naturally contaminated meat that postirradiation storage in the frozen state does not lead to the revival of irradiated salmonellas.The properties of Salmonella survivors deliberately produced in meat using conditions of irradiation designed to simulate a commercial process are studied after six recycling treatments through the process. There were no important changes in characteristics normally used for identification of Salmonella but radiation resistance was lowered. Survivors grown in situ in meat after irradiation showed an abnormally long lag phase, and removal of competitive microflora in meat by the radiation treatment can influence the growth of salmonellas.

The relative biological effect of 252Cf radiation on HeLa cells in culture.

CALIFORNIUM 252 undergoes spontaneous fission with a half-life of two and six-tenths years. The fission-spectrum neutrons are densely ionizing and therefore may be more efficient than x rays or gamma rays in eradicating malignant tumors, particularly those containing anoxic foci. The use of this nuclide for interstitial and intracavitary radiotherapy was suggested by Schlea and Stoddard (1), and sources have been fabricated for this purpose at the Savannah River Laboratory of the USAEC (2). Ten of the above sources, each originally about 4.5 µg, were obtained by us for the purpose of performing pretherapeutic radiobiological experiments. The determinations of relative effectiveness of 252Cf vis-à-vis conventional forms of protracted irradiation is necessary prior to clinical application. Materials And Methods HeLa S3 cells were cultured in Puck's N16 medium containing 10 per cent fetal calf serum, and 5,000 units of penicillin and 5,000 µg of streptomycin per 100 ml, Six-to seven-day-old stock cultures with confluent growth were used for preparation of clone cultures; the medium was discarded, cells washed once with isotonically buffered Versene 1: 5,000 and treated for five to ten minutes at 37°C with GIBCO EDTA-Trypsin solution (IX). The cell suspension was transferred to a 10 ml screw-cap centrifuge tube and centrifuged five minutes at 700 r.p.m.; the medium was carefully removed and cells resuspended in 2 ml of N 16 medium and cell count made in a counting chamber. If necessary, a further dilution of cells in medium was made and approximately 3,000 cells added to 2.7 ml of medium in Falcon plastic, 25 cc tissue culture flasks. The cultures were gassed with 5 per cent CO2-air mixture, shaken gently to distribute the cells, and placed on a level surface in a 37°C incubator. The preirradiation growth period was about seventeen hours in most instances. Ten needles containing ~4.5µg 252Cf each with a linear intensity of 2.25 µg/cm active length were arranged in a planar array to provide a homogeneous irradiation field over an area of 16 cm2 at a distance of 9.2 mm corresponding to the inner surface of the floor of the tissue culture flask. The dose rate at this distance was 16.1 rads/hr. initially and decreased slightly by completion of the experiments. A similar arrangement of radium needles (total of 40 mg) provided a dose rate of 31 rads/hr. to the floor of the tissue culture flask. Cells were also irradiated acutely with 250 kVp x rays (h.v.l, = 1.2 mm Cu, dose rate = 111 rads/min.). Results The survival curves for HeLa S3 cells irradiated with 252Cf at ~16 rads per hour, radium at 31 rads per hour, and acute 250-kVp x rays are illustrated in Figure 1.

Factors influencing the survival of bacteria after exposure to ionizing radiation

Results are reported from a series of studies on the effects of preirradiation growth in the presence of glucose or under anaerobic conditions on the radiation resistance of cells of E. coli B/r. The effect of pH of the growth media, desoxyribonucleic acid content, ribonucleic acid content, postirradiation plating effects, basic media, hydrogen peroxide anaerobic growth conditions, catalase or cytochrome activity, and other variables are discussed. It is concluded that growth in glucose favors the synthesis of a protective system or a recovery system. The system may be a single compound acting as a chemical protectfve agent or a more complex enzyme system that allows the cell to repair or bypass radiation-caused damage. In any case, the synthesis of the system involves only anaerobic steps in the dissimilation of glucose since ft can develop in anaerobically grown cells. (C.H.)