Effects of single doses of X-rays on renal function in the pig after the irradiation of both kidneys

Volume effects in radiobiology as applied to radiotherapy

PURPOSE

To explore the radiobiological evidence for a dependence of normal tissue complication probability on irradiated normal tissue volume.

MATERIALS AND METHODS

Data from experimental studies on the volume effect in different organs, using different criteria of structural or functional organ damage and in different animals, were evaluated to investigate the volume effects for structural radiation damage as opposed to functional radiation damage, and the importance of organ anatomy and dose distribution within the organ on the development of chronic radiation damage in the respective organ.

RESULTS

There is little or no volume effect for structural radiation damage, however, some very pronounced volume effects have been reported for functional damage. Volume, as such, is not the relevant criterion, since critical, radiosensitive structures are not homogeneously distributed within organs.

CONCLUSION

Volume effects in patients and experimental animals are more related to organ anatomy and organ physiology than to cellular radiobiology.

The volume effect in radiotherapy--its biological significance

Volume-related effects are an important consideration in clinical radiotherapy. The early rationale for the need to consider treatment volume has become clouded by the lack of clarity and a misinterpretation of some early clinical findings. In particular, there is a need to separate our understanding of biologically iso-effective radiation responses from the clinical concept of normal tissue tolerance, as they relate to changes in treatment volume. Animal data, including those for large animals, are reviewed. These animal studies indicate the need for caution in extrapolating retrospective clinical data to new treatment situations, since the conclusions reached may have been dictated by dogma and not by careful consideration of different factors that may have been involved. These include anatomical and physiological factors, and variations in the dose distribution pattern to a specific organ or tissue. These biological factors could limit the general applicability of simple approaches based on mathematical models to the volume effect relationship in radiotherapy.

Radiation response of the monkey kidney following contralateral nephrectomy

PURPOSE

The long-term functional and morphologic responses of the hypertrophied monkey kidney after unilateral nephrectomy to fractionated irradiation were assessed.

METHODS AND MATERIALS

The right kidney of 13 adult female rhesus monkeys was removed. Twelve weeks after unilateral nephrectomy (UN) the remaining kidney received fractionated doses of gamma-rays ranging from 35.2 Gy/16 fractions (F) up to 44 Gy/20 F. Glomerular filtration rate, effective renal plasma flow, blood urea nitrogen, serum creatinine, and hematocrit values were measured up to 107 weeks postirradiation (PI). The monkeys were killed and the remaining kidneys were removed 107 weeks PI or earlier when end-stage renal failure was exhibited. Glomeruli were scored for the presence/absence of several pathologic features including increased intercapillary eosinophilic material (ICE), ectatic capillaries, and thrombi. The relative proportion of renal cortex occupied by glomeruli, interstitium, normal tubules or abnormal tubules was determined using a Chalkley point grid. These quantal dose response data were analyzed using a logistic regression model.

RESULTS

Irradiation of the remaining kidney in UN monkeys resulted in a dose-dependent reduction in renal function and anemia. Glomerular dysfunction preceded tubular dysfunction. Animals receiving 44 Gy all manifested progressive clinical renal failure. Conversely, those receiving < or = 39.6 Gy showed stable, albeit impaired, renal function for the duration of the observation period of 107 weeks. Morphologically, the incidence of ICE, ectatic glomerular capillaries, thrombi, and periglomerular fibrosis was significantly dose-related (p < 0.005). A significant (p < 0.001) dose-related increase in the relative proportion of renal cortex occupied by abnormal tubules was indicative of tubular injury. A highly significant (p < 0.001) dose-dependent increase in the proportion of abnormal to normal tubules was also seen.

CONCLUSION

The pathogenesis of radiation nephropathy is difficult to fully understand because of the complex and dynamic interactions among all components of the nephron that make discrimination between primary radiation effects and secondary pathophysiological consequences very difficult. Notwithstanding, the current experiment shows that the functional and morphological expressions of radiation injury in the kidney are dose dependent. Renal failure occurs when both the glomeruli and tubules are dysfunctional. In monkeys following UN, a total dose of 44 Gy to the remaining kidney damages all components of the nephron and causes renal failure in less than 45 weeks. With lower doses, changes to the glomeruli predominate and the animals survive. Kidney doses of up to 39.6 Gy/18 fractions of 2.2 Gy are compatible with survival for at least 2 years in primates.

Positron emission tomography in the study of acute radiation effects on renal blood flow in dogs

Renal blood flow measurements have been carried out by means of positron emission tomography (PET) to facilitate the detection of radiation-induced injuries. The advantages of the method employed in animal experiments are described.

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues in the pig. IV. Effects on renal function

The effects of fractionated doses of fast neutrons (42 MeVd----Be) on the radiation response of the pig kidney have been assessed and compared with those observed after X irradiation. Following X irradiation there was a marked increase in the total dose at which renal function was preserved with decreasing fraction size. The rate of this increase was dependent on the overall treatment time; for fractionated irradiation given over 18 or 39 days the exponents related to fraction number, N, were 0.36 +/- 0.03 and 0.48 +/- 0.003, respectively. In contrast, there was no significant change in the iso-effect dose for renal injury following fractionated irradiation with fast neutrons where there was also little effect of varying the overall treatment time. Analysing these data by means of the linear-quadratic (LQ) model, using both an Fe-plot and the Tucker test, gave alpha/beta ratios of 2.42 +/- 0.06 Gy and 2.99 +/- 0.16 Gy, respectively, for X-ray doses given in 18 days. For fractionated doses of X rays given in 39 days the alpha/beta ratios were 0.40 +/- 0.01 Gy and 0.47 +/- 0.02 Gy, respectively. The alpha/beta ratios for renal tissue following fast neutron irradiation obtained by the two methods were also similar, i.e. 15.00 +/- 0.60 Gy and 15.72 +/- 3.76 Gy, respectively. The pronounced fractionation effect seen with X irradiation, particularly for doses administered over 39 days as opposed to 18 days, coupled with the absence of any such effect with fast neutrons, resulted in a marked increase in relative biological effectiveness (RBE) with decreasing X-ray dose/fraction. The slopes of the resulting regression lines were -0.73 +/- 0.05 and -0.33 +/- 0.02, respectively. The lack of dose sparing associated with fractionation, or variation of the overall treatment time for fast neutron irradiation, suggests that doses administered to tumours adjacent to the kidney can be given as a few relatively large dose/fractions in a short overall treatment time without an increased risk of complications related to renal tissue. This may be of therapeutic advantage in the treatment of rapidly proliferating tumours where dose may be wasted using more conventional protracted fractionated irradiation schedules.

The effect of age and the proportion of renal tissue irradiated on the apparent radiosensitivity of the pig kidney

In 14-week-old (immature) and 45-week-old (mature) pigs either the right kidney (unilateral irradiation, UI) or both kidneys (bilateral irradiation, BI) were irradiated. The kidneys of immature pigs received single doses of 7.0-12.6 Gy of 250 kV X-rays; mature pigs received single doses of 7.8-14.0 Gy of 60Co gamma-rays. These were assumed to be approximately equivalent to the X-ray doses using a RBE of 0.9 gamma-rays/X-rays. The glomerular filtration rates (GFR) and effective renal plasma flows (ERPF), were determined for up to 24 weeks after irradiation. From these data dose-effect curves were obtained by determining, at each dose level, the percentage of irradiated kidneys which exhibited a greater than or equal to 50 per cent reduction in GFR and ERPF. 60Co gamma-ray doses were normalised to approximately equivalent X-ray doses. The dose-effect curves were fitted by probit analysis, and ED50 values (+/- SE) calculated for both GFR and ERPF. Similar conclusions could be drawn from the results obtained following the determination of both GFR and ERPF. However, the ED50 values obtained for ERPF were significantly lower than those for GFR (p less than 0.05). In 14-week-old animals the kidney of UI animals was significantly more radiosensitive than that of BI animals, i.e. the ED50 values, in terms of GFR, were 8.74 +/- 0.31 Gy and 10.97 +/- 0.23 Gy, respectively (p less than 0.001). In 45-week-old pigs the reverse was true; the ED50 values were 12.67 +/- 0.34 Gy and 8.78 +/- 0.15 Gy (p less than 0.001) for unilateral- or bilateral-irradiated animals, respectively. The kidney of BI mature animals appeared to be as radiosensitive as the UI immature pigs. Thus the renal response to radiation was markedly influenced by the age of the animals and by the proportion of the renal tissue irradiated.

Radiation nephropathy in mature pigs following the irradiation of both kidneys

Both kidneys in mature female Large White pigs, ca. 45 weeks old were irradiated with single doses of 7.8-14.0 Gy of 60Co gamma-rays. Radiation-induced changes in renal function were assessed on the basis of sequential individual measurements of kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) for up to 24 weeks after irradiation. At the same time intervals blood samples were taken to determine plasma renin levels and the haematological status of each animal. Two weeks after irradiation the ERPF and in particular the GFR was increased. This was followed by a pronounced, dose-dependent, decline in renal haemodynamics. Minimal functional levels were observed 8-12 weeks after irradiation. Function then somewhat recovered. There was a significant (r greater than or equal to 0.98; p less than 0.001) inverse relationship between the mean values of GFR and ERPF, determined at 4-24 weeks after irradiation, and the radiation dose. After a dose of 7.8 Gy the reduction in ERPF was greater than that for GFR. However, at higher doses both parameters were reduced to an equal extent. The resulting slope of the dose-effect curve for impaired renal function versus dose was significantly steeper for GFR than that for ERPF (p less than 0.001). There was a significant reduction (p less than 0.002) in the erythrocyte count, the haematocrit and haemoglobin levels within 6-8 weeks of irradiation; this anaemia was characterized as a normochromic normocytic anaemia. There were no marked changes in plasma renin levels as a result of renal irradiation. The pathogenesis of late radiation-induced damage to the kidney is discussed in the light of these findings.