FROM THE DEPARTMENTS OF PAEDIATRICS (DIRECTOR: B. LINDQUIST), RADIATION PHYSICS (DIRECTOR: K. LIDEN) AND ANATOMY (DIRECTOR: C.-H. HJORTSJO), UNIVERSITY HOSPITAL, S-221 85 LUND, SWEDEN.
BONE GROWTH IN THE RABBIT AFTER IRRADIATION A. S. ARONSON, MONICA GUSTAFSSON and G. SELVIK The stunting effect of high local radiation doses on the growing bone has been convincingly and repeatedly reported both in animals (PERTHES 1903, HINKEL 1942) and in man (for review, see RUBIN & CASARETT 1968, PROBERT & PARKER 1975). The effect of lower doses, below 1 Gy (100 rad), have not been evaluated, neither experimentally nor clinically. From extrapolation of the graded effects of higher doses, this low range has been considered safe and the minimum stunting dose has been estimated to be well above 1 Gy (rCRP No. 14, 1969, RAUSCH et coll. 1964). Small growth disturbances on a subclinical level, undetectable by conventional bone length measurements, still cannot be excluded and have in fact been discussed (Moss 1959, RUBIN & CASARETT 1968). The introduction of a new high-sensitive roentgen spectrophotogrammetric method for the determination of the bone length growth makes it possible to record otherwise undetectable small disturbances (ARONSON et coll. 1977). This report presents the effect of 0.1 Gy to the tibia of the rabbit as measured with the stereophotogrammetric method. Material and Method One litter of 8 rabbits was used during their 27th to 132nd day of life. They were kept institutionalized togetherwith their mother. Submitted for publication 3 March 1976. Acta Radiologica Diagnosis 17 (1976) Fasc. 6 November
838
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION GROWTH
839
RATE,
I'm/DAY 800
800
200
iII
40
r==n\
60
I
80
o
i.
a
... ... 1 ...... I 20
r .. l
40
I i ...... I 60 80
DAYS
a
b
800
o
Ii
a
...... j.to ... I
I " ...
40
20
i 60
1 ... 1
I
Growth rates after irradiation of the right calf (. - .) of rabbit 1 (a) (24 Gy on day 0) and of the group of rabbits 2-7 (b) (0.1 Gy on day 0) compared with the left non-irradiated calf (0 - 0). A dramatic fall ensued after the high dose but the low dose had no effect. c) Spontaneous variation in growth rates for the right and the left tibia of non-irradiated rabbit 8.
80
DAYS
c
The tibial bone growth was measured bilaterally with roentgen stereophotogrammetry (SELVIK 1974, ARONSON et coll. 1977). To increase the accuracy of these measurements, the legs had. been furnished with intraosseous markers. Tantalum balls 0.50 mm in diameter were deposited in the two epiphyseal ends of the left and right tibial bones (ARONSON et coll. 1974, ARONSON & JONSSON 1977). At each measuring instance, the rabbit was placed in a calibration cage, and the lower extremities were simultaneously exposed with two roentgen tubes. The double image of the set-up was recorded on a Kodak D7 fine grain film. The film was evaluated in an autograph (A8 Wild, Heerbrugg, Switzerland) and the spatial locations of bone markers in relation to markers in the test cage were computed, mathematical analysis being based on perspective transformation (HALLERT 1970, SELVIK 1974). The bone growth was computed from the increase in the distance between the intraosseous bone markers at repeated recordings. The methodologic error in a growth rate determination based on two length measurements was 30.5 V2!-tm =43!-tm (ARONSON et coll. 1977).
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
840
A. S. ARONSON, M. GUSTAFSSON AND G. SELVIK
Table Growth difference between the left and right rabbit tibia (L-R) after an unfractionated irradiation to the right leg at time o. Difference in 11m for the interval before (day - 2-0) and for the nine intervals after irradiation and also total difference for the full test period after irradiation (0-75.5 days). Individual values for all rabbits and mean values for the group of rabbits receiving 0.1 Gy (f0 rad) (2-7)
Absorbed Rabbit L-R in 11m for the time intervals day - 2 to 75.5 dose Gy No. - 2-0 0-7 7-9 9-14 14-17 17-42.4 42.5-45 45-72.5 72.5-75.5 0-75.5 - 6
24 0.1
2 3 4 5 6 7 2-7 M ±SEM
0
8
2583 1029 2681 1320
9201
766
5940
324
23845
3 56 12 -108 164 247 15 -56 34 43 84 -160
-1 -4 -40 -23 21 -20
-1 28 -193 -118 349 -329
45 39 -65 29 -50 29
18 377 165 31 85 -93
5 126 83 -13 15 -43
203 215 389 -198 653 -581
62* 23
-7 58
-11 9
-44 95
5 20
97 66
29 26
114 179
31
136
109
149
16
-226
7
262
- 8 78 -12 -255 28 38 -73 -64 156 66 -27 -49 - 3 20
-18 58
3
40
* almost significant, Student's t-test.
Irradiation. The right calf was irradiated with a 137CS therapy unit. The irradiation was given with a 100 mm long field through a standard applicator in close contact with the leg. The whole tibial bone was covered in all instances. The left leg was bent away from the radiation field and adequately shielded by lead. The absorbed dose in the growth zones of the right leg was 24 Gy for rabbit 1,0.1 Gy for rabbits 2 to 7 and 0 Gy for rabbit 8. Both legs received an additional 0.002 Gy to the epiphyseal cartilage for each stereophotogrammetric exposure. The rabbits were exposed to radiation at the age of 57 days. This is denoted as time O. Tantalum markers were inserted on day ~ 30, and stereophotogrammetric recordings were made immediately after radiation and at days - 2, 7, 9, 14, 17, 42.5, 45, 72.5 and 75.5. The radiation effects on growth were expressed as differences in growth between the left and the right leg (L-R) in [lm. The differences both for the whole test period of 75.5 days and for the eight intervals were computed. In the statistical analyses, the difference L-R was determined for each individual rabbit and for the group of rabbits 2 to 7. For the individual measurements, the L-R growth rate difference was considered significant if it was more than 129 [lm (three times methodologic error of 30.5 V2[lmjinterval). For the group of rabbits 2 to 7, a significant deviation of the mean value for the L-R difference was computed by t-test.
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION
841
Results The daily growth rates of the right (irradiated) and left (non-irradiated) legs from day - 2 of the investigation to day 75 (rabbit age 55 and 132 days, respectively) appear in the Figure. There was a dramatic fall in growth rate of the irradiated right leg of rabbit 1 after 24 Gy. In 7 to 9 days, the rate had fallen linearily to about 15 per cent of the original; within 42 days, the growth had completely ceased. A very slight rise was noted on day 72.5 to 75.5. On the other hand, 0.1 Gy given to the right tibia of rabbits 2 to 7 had no effect on growth when the left and right legs were compared for the whole 75.5 day test period (Table). The mean L-R difference was only 114 f-tm and the SEM 179 f-tm. When the test period was subdivided, the difference in one of the eight periods was almost significant. In day 7 to 9, the L-R difference was 62 ± 23 f-tm. For the nonirradiated rabbit 8, the growth difference between the two legs was 265 f-tm for the whole test period and between 3 and 226 f-tm during the eight intervals of the whole test period. The individual differences L-R were statistically significant (> 129 f-tm) for individual rabbits 2 to 7 in 10 of 54 intervals and for rabbit 8 in 3 of 9 intervals. Discussion Roentgen stereophotogrammetry has been introduced for bone growth measurements in diagnostic radiology (ARONSON et colI. 1975, ARONSON & SELVIK 1977). An objection to this method could be that the irradiation of the examined growth zone might disturb the growth process. Therefore, it seemed necessary to determine whether a low radiation dose could interfere with growth. A linear dose response relation for the increase of the minimum stunting dose with age was demonstrated by HINKEL (1942). The lowest stunting dose for newborn rats was about 400 R. This exposure corresponds to approximately 3.8 Gy in the epiphyseal cartilage (calculated according to ICRU No. 17, 1970) in the growth zone, except for a 20 to 30 f-tm zone of increased absorption next to the calcified bone (SPIERS 1969). Reports on the effect of doses below 4 Gy on the growth process are few and the results are not uniform. HINKEL found no growth retardation below 5 Gy, BAUNACH (1935) could register a slight growth stimulation at about 1.5 Gy, and BROOKS & HILLSTROM (1933) found no stimulation at about 0.25 Gy. Microscopic abnormalities were reported from about 2 Gy (BISGARD & HUNT 1936) and radiologic from about 3.25 Gy (HULTH & WESTERBORN 1960). BLACKBURN & WELLS (1963) found no change of 45Ca uptake after 0.95 and 2.4 Gy. The mitotic activity of the growth cartilage cells i rknown to be temporarily stopped by about 4.75 Gy but the effect of low doses is not known (BLACKBURN & WELLS). The highly sensitive stereophotogrammetric growth measurement method used in the present material has a methodologic error of 43 f-tm. The unilateral radiation dose of 0.1 Gy was chosen as a representative maximum dose to be used in diagnostic
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
842
A. S. ARONSON, M. GUSTAFSSON AND G. SELVIK
stereophotogrammetry. No difference was found after this dose, except for the period of day 7 to 9, when an almost significant difference in growth between irradiated and non-irradiated legs was observed. In view of the remaining eight periods, when the differences were not significant, this single almost significant difference is compatible with chance. It should also be noted that there was no radiation effect on the total growth during the 75.5 days after irradiation, as the difference in growth between the irradiated and the non-irradiated leg was not significant. The absence of effect agrees with calculations of cell survival according to KEMBER (1967). Thus no effect of 0.1 Gy was found but a dramatic fall in growth rate occurred after 24 Gy. In eight days, it was only about 15 per cent of the original rate before irradiation. After a period of complete arrest slight growth resumed, probably due to the appearance of recovery clones in the growth zone (KEMBER). It was thought that the rabbit receiving no unilateral irradiation would serve as an ideal control animal and would show equal growth rates for the two legs. But this was not so, which illustrates that, in the individual rabbit, growth rate normally may differ between the two legs with an alternate predominance for either leg. In a group of rabbits, however, equal growth may be expected (HANSSON 1967). As the results are based on differences between the left and right leg, an equal disturbance of the growth rate of both legs would not be detectable. Therefore the results were not influenced by any effect of the additional 0.002 Gy given to both legs at each of the 10 measuring instances. Acknowledgement The authors are greatly indebted to Docent Tord Olin for his generous support, including all facilities of the Laboratory of Experimental Radiology. Funds from the University of Lund, from Landstinget Milan, and from Stiftelsen Svensk Naringsforskning provided economic support.
SUMMARY The effect on bone growth of two locally given, different, unfractionated radiation doses (0.1 and 24 Gy) was tested in a rabbit litter aged 57 days. The effects on growth were registered with roentgen stereophotogrammetric length measurements for 75 days after irradiation. Growth of the right irradiated tibia was compared with the growth of the left non-irradiated tibia. After 7 to 9 days, 24 Gy had caused a linear fall in growth to about 15 per cent. After a period of complete cessation, a slight growth was registered. 0.1 Gy had no significant growth retarding effect.
ZUSAMMENFASSUNG Die Wirkung von zwei lokal gegebenen, unterschiedlichen nichtfraktionierten Strahlendosen (0,1 und 24 Gy) auf das Knochenwachstum wurde an 57 Tage alten Kaninchen untersucht. Die Wirkung auf das Wachstum wurde mittels rontgenstereophotogrammetrischen
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION
843
Langemessungen 75 Tage lang nach der Bestrahlung registriert. Das Wachstum der rechten bestrahlten Tibia wurde mit dem Wachstum der linken nichtbestrahlten Tibia verglichen. 24 Gy hatten nach 7 bis 9 Tagen einen linearen Abfall im Wachstum von etwa 15 Prozent hervorgerufen. Nach einer Periode vollstandiger Hemmung wurde ein leichter Zuwachs registriert. 0,1 Gy hatte keinen signifikanten Zuwachsherabsetzenden Effekt.
RESUME Les auteurs ont experimente sur une portee de lapins ages de 57 jours l'effet sur la croissance osseuse de 2 doses de radiations differentes, non fractionnees, administrees localement (0,1 et 24 Gy). Les effets sur la croissance ont ete enregistres par des mesures de longueur stereophotogrammetrique pendant 75 jours apres l'irradiation. La croissance du tibia droit irradie a ete comparee avec celle du tibia gauche non irradie, Au bout de 7 a 9 jours, la dose de 24 Gy avait causee un ralentissement lineaire de la croissance d'environ 15 pour-cent. Apres une periode d'arret complet de la croissance on a observe une legere croissance. La dose de 0,1 Gy n'avait pas d'effet retardateur significatif sur la croissance.
REFERENCES ARONSON A. S. and JONSSON N.: Tantalum markers for X-ray studies. Histological investigation. To be published in J. biomed. Res. (1977). - and SELVIK G.: X-ray stereophotogrammetric determination of endochondral growth. Clinical application in hypopituitarism. To be published in Pediatr. Res. (1977). - HANSSON L. I. and SELVIK G.: Daily longitudinal bone growth in the rabbit as determined with X-ray stereophotogrammetry. To be published in Acta radiol. Diagnosis (1977). - HOLST L. and SELVIK G.: An instrument for insertion of radiopaque bone markers. Radiology 113 (1974), 733. - FURST P., KUYLENSTIERNA B. and NYBERG G.: Essential amino acids in the treatment of advanced uremia. Twenty-two months' experience in a 5-year-old girl. Pediatrics 56 (1975), 538. BAUNACH A.: Uber den Einfluss von Dosis und Rhythmus auf den Grad der Wachstumsschadigung des Knochenwachstums bei Rontgenstrahlungen. Strahlentherapie 54 (1935), 52. BISGARD J. D. and HUNTH. B.: Influence of roentgen rays and radium on epiphyseal growth of long bones. Radiology 26 (1936), 56. BLACKBURN J. and WELLS A. B.: Radiation damage to growing bone: the effect of X-ray doses of 100 to 1000 r on mouse tibia and knee-joint. Brit. J. Radiol. 36 (1963), 505. BROOKS B. and HILLSTROM H. T.: Effect of roentgen rays on bone growth and bone regeneration. Amer. J. Surg. 14 (1933), 599. HALLERT B.: X-ray photogrammetry. 1st edition. Elsevier Publishing Co, Amsterdam 1970. HANSSON L. I.: Daily growth in length of diaphysis measured by oxytetracycline in rabbit normally and after medullary plugging. Acta orthop. scand. (1967) Suppl. No. 101. HINKEL C. L.: The effect of roentgen rays upon the growing long bones of albino rats. Amer. J. Roentgenol. 47 (1942), 439. HULTH A. and WESTERBORN 0.: Early changes of the growth zone in rabbit following roentgen irradiation. Acta orthop. scand. 30 (1960), 155. International Commission on Radiological Protection. ICRP Publication 14: Radiosensitivity and spatial distribution of dose, p, 16. Pergamon Press, Oxford 1969.
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International Commission on Radiation Units and Measurements. ICRU Report 17, Radiation Dosimetry: X-rays Generated at Potentials of 5 to 150 kV, p. 28. ICRU, Washington 1970. KEMBER N. F.: Cell survival and radiation damage in growth cartilage. Brit. J. Radiol. 40 (1967), 496. Moss W. T.: Therapeutic radiology. Mosby, St. Louis 1959. PERTHES G.: Uber den Einfluss der Rontgenstrahlen auf epitheliale Gewebe insbesondere auf Carcinom. Langenbecks Arch. klin. Chir. 51 (1903), 955. PROBERT J. C. and PARKER B. R.: The effects of radiation therapy on bone growth. Radiology 114 (1975), 155. RAUSCH L., KOCH W. und HAGEMANN G.: Klinische und dosimetrische Untersuchungen zur Frage der kritischen Dosis und typischer Strahlenschaden am Skelett bestrahlter AngiomPatienten. Deutscher Rontgenkongress 1963, Teil B: Strahlenbehandlung und Strahlenbiologie. Sonderband zur Strahlentherapie, p. 198. Urban Schwarzenberg, Miinchen, Berlin 1964. RUBIN P. and CASARETT G. W.: Clinical radiation pathology. Growing cartilage of bone. Vol. II, Chapter 14, p. 518. W. B. Saunders Co, Philadelphia 1968. SELVIK G.: A roentgen stereophotogrammetric method for the study of the kinematics of the skeletal system. Thesis, AV-Centralen, Lund 1974. SPIERS F. W.: Transition-zone dosimetry. In: Radiation dosimetry. Vol. 3, p. 809. Edited by F. M. Attix and E. Tochilin. Academic Press, New York, London 1969.
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION A. S. ARONSON, MONICA GUSTAFSSON and G. SELVIK The stunting effect of high local radiation doses on the growing bone has been convincingly and repeatedly reported both in animals (PERTHES 1903, HINKEL 1942) and in man (for review, see RUBIN & CASARETT 1968, PROBERT & PARKER 1975). The effect of lower doses, below 1 Gy (100 rad), have not been evaluated, neither experimentally nor clinically. From extrapolation of the graded effects of higher doses, this low range has been considered safe and the minimum stunting dose has been estimated to be well above 1 Gy (rCRP No. 14, 1969, RAUSCH et coll. 1964). Small growth disturbances on a subclinical level, undetectable by conventional bone length measurements, still cannot be excluded and have in fact been discussed (Moss 1959, RUBIN & CASARETT 1968). The introduction of a new high-sensitive roentgen spectrophotogrammetric method for the determination of the bone length growth makes it possible to record otherwise undetectable small disturbances (ARONSON et coll. 1977). This report presents the effect of 0.1 Gy to the tibia of the rabbit as measured with the stereophotogrammetric method. Material and Method One litter of 8 rabbits was used during their 27th to 132nd day of life. They were kept institutionalized togetherwith their mother. Submitted for publication 3 March 1976. Acta Radiologica Diagnosis 17 (1976) Fasc. 6 November
838
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION GROWTH
839
RATE,
I'm/DAY 800
800
200
iII
40
r==n\
60
I
80
o
i.
a
... ... 1 ...... I 20
r .. l
40
I i ...... I 60 80
DAYS
a
b
800
o
Ii
a
...... j.to ... I
I " ...
40
20
i 60
1 ... 1
I
Growth rates after irradiation of the right calf (. - .) of rabbit 1 (a) (24 Gy on day 0) and of the group of rabbits 2-7 (b) (0.1 Gy on day 0) compared with the left non-irradiated calf (0 - 0). A dramatic fall ensued after the high dose but the low dose had no effect. c) Spontaneous variation in growth rates for the right and the left tibia of non-irradiated rabbit 8.
80
DAYS
c
The tibial bone growth was measured bilaterally with roentgen stereophotogrammetry (SELVIK 1974, ARONSON et coll. 1977). To increase the accuracy of these measurements, the legs had. been furnished with intraosseous markers. Tantalum balls 0.50 mm in diameter were deposited in the two epiphyseal ends of the left and right tibial bones (ARONSON et coll. 1974, ARONSON & JONSSON 1977). At each measuring instance, the rabbit was placed in a calibration cage, and the lower extremities were simultaneously exposed with two roentgen tubes. The double image of the set-up was recorded on a Kodak D7 fine grain film. The film was evaluated in an autograph (A8 Wild, Heerbrugg, Switzerland) and the spatial locations of bone markers in relation to markers in the test cage were computed, mathematical analysis being based on perspective transformation (HALLERT 1970, SELVIK 1974). The bone growth was computed from the increase in the distance between the intraosseous bone markers at repeated recordings. The methodologic error in a growth rate determination based on two length measurements was 30.5 V2!-tm =43!-tm (ARONSON et coll. 1977).
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
840
A. S. ARONSON, M. GUSTAFSSON AND G. SELVIK
Table Growth difference between the left and right rabbit tibia (L-R) after an unfractionated irradiation to the right leg at time o. Difference in 11m for the interval before (day - 2-0) and for the nine intervals after irradiation and also total difference for the full test period after irradiation (0-75.5 days). Individual values for all rabbits and mean values for the group of rabbits receiving 0.1 Gy (f0 rad) (2-7)
Absorbed Rabbit L-R in 11m for the time intervals day - 2 to 75.5 dose Gy No. - 2-0 0-7 7-9 9-14 14-17 17-42.4 42.5-45 45-72.5 72.5-75.5 0-75.5 - 6
24 0.1
2 3 4 5 6 7 2-7 M ±SEM
0
8
2583 1029 2681 1320
9201
766
5940
324
23845
3 56 12 -108 164 247 15 -56 34 43 84 -160
-1 -4 -40 -23 21 -20
-1 28 -193 -118 349 -329
45 39 -65 29 -50 29
18 377 165 31 85 -93
5 126 83 -13 15 -43
203 215 389 -198 653 -581
62* 23
-7 58
-11 9
-44 95
5 20
97 66
29 26
114 179
31
136
109
149
16
-226
7
262
- 8 78 -12 -255 28 38 -73 -64 156 66 -27 -49 - 3 20
-18 58
3
40
* almost significant, Student's t-test.
Irradiation. The right calf was irradiated with a 137CS therapy unit. The irradiation was given with a 100 mm long field through a standard applicator in close contact with the leg. The whole tibial bone was covered in all instances. The left leg was bent away from the radiation field and adequately shielded by lead. The absorbed dose in the growth zones of the right leg was 24 Gy for rabbit 1,0.1 Gy for rabbits 2 to 7 and 0 Gy for rabbit 8. Both legs received an additional 0.002 Gy to the epiphyseal cartilage for each stereophotogrammetric exposure. The rabbits were exposed to radiation at the age of 57 days. This is denoted as time O. Tantalum markers were inserted on day ~ 30, and stereophotogrammetric recordings were made immediately after radiation and at days - 2, 7, 9, 14, 17, 42.5, 45, 72.5 and 75.5. The radiation effects on growth were expressed as differences in growth between the left and the right leg (L-R) in [lm. The differences both for the whole test period of 75.5 days and for the eight intervals were computed. In the statistical analyses, the difference L-R was determined for each individual rabbit and for the group of rabbits 2 to 7. For the individual measurements, the L-R growth rate difference was considered significant if it was more than 129 [lm (three times methodologic error of 30.5 V2[lmjinterval). For the group of rabbits 2 to 7, a significant deviation of the mean value for the L-R difference was computed by t-test.
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION
841
Results The daily growth rates of the right (irradiated) and left (non-irradiated) legs from day - 2 of the investigation to day 75 (rabbit age 55 and 132 days, respectively) appear in the Figure. There was a dramatic fall in growth rate of the irradiated right leg of rabbit 1 after 24 Gy. In 7 to 9 days, the rate had fallen linearily to about 15 per cent of the original; within 42 days, the growth had completely ceased. A very slight rise was noted on day 72.5 to 75.5. On the other hand, 0.1 Gy given to the right tibia of rabbits 2 to 7 had no effect on growth when the left and right legs were compared for the whole 75.5 day test period (Table). The mean L-R difference was only 114 f-tm and the SEM 179 f-tm. When the test period was subdivided, the difference in one of the eight periods was almost significant. In day 7 to 9, the L-R difference was 62 ± 23 f-tm. For the nonirradiated rabbit 8, the growth difference between the two legs was 265 f-tm for the whole test period and between 3 and 226 f-tm during the eight intervals of the whole test period. The individual differences L-R were statistically significant (> 129 f-tm) for individual rabbits 2 to 7 in 10 of 54 intervals and for rabbit 8 in 3 of 9 intervals. Discussion Roentgen stereophotogrammetry has been introduced for bone growth measurements in diagnostic radiology (ARONSON et colI. 1975, ARONSON & SELVIK 1977). An objection to this method could be that the irradiation of the examined growth zone might disturb the growth process. Therefore, it seemed necessary to determine whether a low radiation dose could interfere with growth. A linear dose response relation for the increase of the minimum stunting dose with age was demonstrated by HINKEL (1942). The lowest stunting dose for newborn rats was about 400 R. This exposure corresponds to approximately 3.8 Gy in the epiphyseal cartilage (calculated according to ICRU No. 17, 1970) in the growth zone, except for a 20 to 30 f-tm zone of increased absorption next to the calcified bone (SPIERS 1969). Reports on the effect of doses below 4 Gy on the growth process are few and the results are not uniform. HINKEL found no growth retardation below 5 Gy, BAUNACH (1935) could register a slight growth stimulation at about 1.5 Gy, and BROOKS & HILLSTROM (1933) found no stimulation at about 0.25 Gy. Microscopic abnormalities were reported from about 2 Gy (BISGARD & HUNT 1936) and radiologic from about 3.25 Gy (HULTH & WESTERBORN 1960). BLACKBURN & WELLS (1963) found no change of 45Ca uptake after 0.95 and 2.4 Gy. The mitotic activity of the growth cartilage cells i rknown to be temporarily stopped by about 4.75 Gy but the effect of low doses is not known (BLACKBURN & WELLS). The highly sensitive stereophotogrammetric growth measurement method used in the present material has a methodologic error of 43 f-tm. The unilateral radiation dose of 0.1 Gy was chosen as a representative maximum dose to be used in diagnostic
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
842
A. S. ARONSON, M. GUSTAFSSON AND G. SELVIK
stereophotogrammetry. No difference was found after this dose, except for the period of day 7 to 9, when an almost significant difference in growth between irradiated and non-irradiated legs was observed. In view of the remaining eight periods, when the differences were not significant, this single almost significant difference is compatible with chance. It should also be noted that there was no radiation effect on the total growth during the 75.5 days after irradiation, as the difference in growth between the irradiated and the non-irradiated leg was not significant. The absence of effect agrees with calculations of cell survival according to KEMBER (1967). Thus no effect of 0.1 Gy was found but a dramatic fall in growth rate occurred after 24 Gy. In eight days, it was only about 15 per cent of the original rate before irradiation. After a period of complete arrest slight growth resumed, probably due to the appearance of recovery clones in the growth zone (KEMBER). It was thought that the rabbit receiving no unilateral irradiation would serve as an ideal control animal and would show equal growth rates for the two legs. But this was not so, which illustrates that, in the individual rabbit, growth rate normally may differ between the two legs with an alternate predominance for either leg. In a group of rabbits, however, equal growth may be expected (HANSSON 1967). As the results are based on differences between the left and right leg, an equal disturbance of the growth rate of both legs would not be detectable. Therefore the results were not influenced by any effect of the additional 0.002 Gy given to both legs at each of the 10 measuring instances. Acknowledgement The authors are greatly indebted to Docent Tord Olin for his generous support, including all facilities of the Laboratory of Experimental Radiology. Funds from the University of Lund, from Landstinget Milan, and from Stiftelsen Svensk Naringsforskning provided economic support.
SUMMARY The effect on bone growth of two locally given, different, unfractionated radiation doses (0.1 and 24 Gy) was tested in a rabbit litter aged 57 days. The effects on growth were registered with roentgen stereophotogrammetric length measurements for 75 days after irradiation. Growth of the right irradiated tibia was compared with the growth of the left non-irradiated tibia. After 7 to 9 days, 24 Gy had caused a linear fall in growth to about 15 per cent. After a period of complete cessation, a slight growth was registered. 0.1 Gy had no significant growth retarding effect.
ZUSAMMENFASSUNG Die Wirkung von zwei lokal gegebenen, unterschiedlichen nichtfraktionierten Strahlendosen (0,1 und 24 Gy) auf das Knochenwachstum wurde an 57 Tage alten Kaninchen untersucht. Die Wirkung auf das Wachstum wurde mittels rontgenstereophotogrammetrischen
Downloaded from acr.sagepub.com at Karolinska Institutets Universitetsbibliotek on August 8, 2015
BONE GROWTH IN THE RABBIT AFTER IRRADIATION
843
Langemessungen 75 Tage lang nach der Bestrahlung registriert. Das Wachstum der rechten bestrahlten Tibia wurde mit dem Wachstum der linken nichtbestrahlten Tibia verglichen. 24 Gy hatten nach 7 bis 9 Tagen einen linearen Abfall im Wachstum von etwa 15 Prozent hervorgerufen. Nach einer Periode vollstandiger Hemmung wurde ein leichter Zuwachs registriert. 0,1 Gy hatte keinen signifikanten Zuwachsherabsetzenden Effekt.
RESUME Les auteurs ont experimente sur une portee de lapins ages de 57 jours l'effet sur la croissance osseuse de 2 doses de radiations differentes, non fractionnees, administrees localement (0,1 et 24 Gy). Les effets sur la croissance ont ete enregistres par des mesures de longueur stereophotogrammetrique pendant 75 jours apres l'irradiation. La croissance du tibia droit irradie a ete comparee avec celle du tibia gauche non irradie, Au bout de 7 a 9 jours, la dose de 24 Gy avait causee un ralentissement lineaire de la croissance d'environ 15 pour-cent. Apres une periode d'arret complet de la croissance on a observe une legere croissance. La dose de 0,1 Gy n'avait pas d'effet retardateur significatif sur la croissance.
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