Skin reactions after different fractionation schedules giving the same cumulative radiation effect.

The CRE formula was used for calculation of biologically equivalent radiation doses with different fractionation schedules. The early radiation effects, skin erythema and pigmentation were measured with a reflectance spectrophotometer at wavelengths 578 and 660 nm. The course and maximum for both erythema and pigmentation agreed well with the two types of fractionation. The results seem to justify further use of this simple formula.     

Mathematical models for predicting G-duration tolerances

Mathematical models that predict fatigue-based G-duration tolerances for relaxed and straining subjects are developed and validated using published data. These models are based on regression analysis calculations using published G-duration tolerance data of relaxed subjects exposed to 3-5 G and subjects exposed to 6-9 G using an anti-G suit and performing the anti-G straining maneuver. These G-duration models are derived from published G-level tolerance models based on intravascular hydrostatic pressures and physiologic responses to maximum voluntary contractions (MVC%). Included in the validation of these models are the baroreceptor and muscle contraction cardiovascular reflexes that support arterial BP. A basic energy pool that supports a G-duration of 140 s for G exposures > 5 G is theorized. Because of the long duration of sustained G exposures in these models, the physiologic dynamics involved in predicting straining G-duration tolerances, are identified and validated using different time periods, i.e., Phases I and II. These models, based on sustained G exposures to a constant G level are also applicable to exposures of variable G levels known as simulated aerial combat maneuver (SACM) G-profile tolerances. G-duration tolerances > 9 G are predicted using these models for subjects using reclined-seat backs and positive pressure breathing.     

Mathematical models for predicting G-level tolerances

The mathematical models developed in this article predict the following human G-level tolerances: 1) rapid onset relaxed (ROR); 2) gradual onset relaxed (GOR); and, 3) straining-rapid onset. Included in the model are specific functions of: 1) anti-G suit; 2) positive pressure breathing (PBG); 3) baroreceptor reflex; 4) handgrip reflex; 5) anti-G straining maneuver (AGSM) increasing intrathoracic pressures (Pi); 6) leg elevation; and, 7) reclining seatback angles < or = 55 degrees. These functions are based on sound physiologic principles. Also discussed in the development of this model, but not included in the models, were: 1) isometric muscle contraction reflex; 2) Qigong (Q-G) maneuver; and, 3) straining GOR tolerances. The straining GOR tolerance profile was calculated to be a measure of G-duration tolerance and not G-level tolerance. A maximum P of 125 mm Hg from the AGSM was used in these models that could be augmented with PBG to 185 mm Hg. G-level tolerance predictions using this model were validated with published data.     

Radiosensitivity and effect of dose fractionation in cultured cells

Survival, division delay and repair of sublethal damage were studied as a function of the cellular age in cells of EUE line exposed to 31 MeV protons, (LET of 1.83 keV/micron in tissue). The findings are compared with data reported in the literature on various mammalian cell lines exposed to X and gamma rays, common behaviours are pointed out and the characteristics parameters quantified. Survival varies with cell age and reaches a maximum value at mid S and its minimum at late G1; the ratio between maximum and minimum ranges between 1.5 and 15 depending on the survival level. Division delay resulted to be equal to 6 and 12% of the generation time per Gy for mid G1 and mid-late S respectively. All the investigated lines are able to repair as much as 50% of the sublethal damage within one hour.     

Cell survival description of the cumulative radiation effect.

An equation is proposed to link the Cumulative Radiation Effect (CRE) scale of radiation damage with the fraction of basal cells surviving after irradiation of skin epithelium. The model assumes an expression for the basal cell survival curve which fits the various hit-target models over the range of doses found in clinical practice. The model is consistent with CRE in the dependence on total treatment dose and fractionation number. A 'first order' analysis using a Gompertzian re-growth of cells also yields reasonable agreement with the CRE equation in time dependence during treatment and during a gap. This model is suitable for acute skin reactions but not necessarily for late effects in connective tissue.     

A cumulative effect of physical training on bone strength in males

Weight-bearing, high-impact exercise, as opposed to nonimpact exercise, has been demonstrated to increase bone mineral density. This was traditionally demonstrated with dual energy X-ray absorptiometry. Our objective was to assess the differences in bone properties, using quantitative ultrasound (QUS, Sunlight Omnisense, Sunlight Medical, Ltd., Tel Aviv, Israel), in male athletes involved in a weight-bearing, impact sport (soccer, SC) or a nonimpact sport (swimming and water polo, AQ), compared with nonathletic control (C) males. A total of 266 boys and men, aged 8 - 23 years, were divided into children (11.1 +/- 1.0 years; 34 SC, 34 AQ, 25 C), adolescents (14.7 +/- 1.2 years; 32 SC, 31 AQ, 31 C), and young adults (19.8 +/- 1.1 years; 31 SC, 24 AQ, 24 C) . Training experience varied between 1.5 years in the children to 15 years in the adults. Bone speed of sound (SOS) was measured bilaterally at the distal radius and the mid-tibia. Body fat was significantly lower in athletes compared with C. AQ were generally heavier and had a higher fat-free mass compared with SC and C, with no significant differences in height between groups. Radial SOS increased with age, but no differences were observed between activity groups or between the dominant (D) and nondominant (ND) arm. Tibial SOS also increased with age. In the children and adolescents, no differences were observed between activity groups. However, among adults, both SC and AQ had higher tibial SOS compared with C. These differences were mainly explained by differences in fat-free mass. Among young adults but not among children and adolescent males, both soccer and aquatic sports appear to be associated with higher bone SOS in the lower, but not the upper, extremities. Further studies are needed to assess possible sport-specific mechanisms which affect bone properties and to determine the minimal cumulative effect which is needed to influence bone properties.     

Mathematical optimization of gamma-ray-sensor thickness for best contrast of radiographic images

The emission of radiations in radiographic films or xerographic plates by the “uncollided flux” of penetrating γ-rays has been studied. Algorithms for the constrained optimization of the thickness of these films or plates to provide the best related image contrast are reported and analysed.     

Repopulation in mouse oral mucosa: changes in the effect of dose fractionation

PURPOSE: To define the fractionation effect, including the magnitude and kinetics of dose compensation, on days 3 and 8 after a single priming dose of 8 Gy. MATERIALS AND METHODS: Graded radiation doses were given to the snouts of C3H/Neu mice in 1 to 5 fractions within a time period of < or = 36 h, or in four fractions with intervals from 5 min to 4 h. Each protocol was terminated by a top-up dose of 2.5 Gy to a 3 x 3 mm2 test area in order to precipitate the subclinical damage induced by the snout treatment and to generate the full dose response. RESULTS: No significant increase in isoeffective dose by increasing fraction numbers or by increasing interfraction intervals could be detected at each time point after the priming treatment. This indicates that the effect of dose fractionation was entirely lost. CONCLUSIONS: The loss of fractionation effect may be interpreted as a substantial impairment of the processes underlying recovery from sublethal damage as a consequence of a repopulation-inducing priming dose given 3 days or 8 days in advance.     

Effect of fractionation on the immunosuppressive effect of total lymphatic irradiation (TLI)

The influence of single dose and fractionation on the immunosuppressive effect of a total lymphoid irradiation (TLI) was investigated by experimentation on animals and compared to literature. Lewis rats were irradiated with a constant temporal dose distribution. The weekly dose of 7,0 Gy was fractionated into 1 X 7,0 Gy, 2 X 3,5 Gy and 7 X 1,0 Gy, with rising total doses. The survival time of cutaneous allografts served as parameter for the immunosuppression; the toxicity of the treatment was related to the immunosuppressive effect. Immunosuppression as well as toxicity showed differences depending on fractionation. For both criteria, the fractionation of 2 X 3,5 Gy per week had better results. The validity of the Ellis formula for the immunosuppression induced by total lymphoid irradiation was restricted.