Cytogenetics in radiotherapy [I]

    Since the first observation on the induction of chromosome aberrations in blood lymphocytes of patients received radiotherapy by I. M. Tough, K. E. Buckton, A. G. Baikie and W. M. Court Brown in 1960 (Tough et al., Lancet, ii:849-851, 1960), lymphocyte chromosome aberration analysis rapidly expanded in varying area of radiation cytogenetics of humans exposed to ionizing radiation. Chromosome aberration analysis provides not only a quantitative measure of the biological effects of radiation in humans (IAEA Technical Report 2011; ISCN 2016) but also an important information in establishing correct clinical management in radiotherapy and radiation accident.

[1] Lymphocyte lifetime: Determination by elimination rate of chromosome aberration in radiotherapy patients 

     In the early stage of study, the estimation of lymphocyte lifetime has been made by the use of chromosome aberrations of peripheral blood lymphocytes of patients received radiotherapy. The knowledge has has been an important parameter in biological dosimetry for low dose and low dose-rate radiation exposure and estimation of dose of the past exposure (retrospective biodosimetry). The followings are typical examples of such studies; one by Norman et al. (1965) in patients received radiotherapy for cervical cancer and another by Buckton et al. (1967) in patients received radiotherapy for ankylosing spondylitis. The lymphocyte mean lifetime has been estimated to m=530±64 days in Norman et al. (1965) and m=1,574 (50% CI; 891, 6,743) days in Buckton et al. (1967) (fitting to data for longer than 1400 days). The difference may come from the inclusion of rapid decline in post-therapy early stage by lymphocyte renewal in the former and significant contribution of long-lived memory cells (Bogen, 1993). Currently, a value of about 1,000 days is often applied. The followings are the revisit to the original data to encourage the reanalysis.

[A] Analysis in 25 patients treated with gamma-rays for cervical cancer. Threatment was carried out to give 6,000-8,000 rad to paracervical triangle over a period of 4-6 weeks. It was estimated that 5-10 % of body mass was in the direct irradiation field, and the rest of the body mass, except for circulating cells, received about 10 rad.
     Reference
     Norman, A., Sasaki, M. S., Ottoman, R. E. and Fingerfut, A. G. (1965): Lymphocyte lifetime in women. Science, 147:1007-1013.
     Norman, A., Sasaki, M. S., Ottoman, R. E. and Fingerfut, A. G. (1966): Elimination of chromosome aberrations from human lymphocytes. Blood, 27:706-714.
     Sasaki, M. S. and Norman, A. (1967): Selection against chromosome aberrations in human lymphocytes. Nature, 214:502-503.

[B] and [C] Analysis in 58 patients treated X-rays for ankylosing spondylitis. Irradiation was applied along the spinal strip field to give a total skin dose of 1,500, 2,000 or 2,500 rads in 10 fractions in 12 to 14 days.
     Reference
     Buckton, K. E., Jacobs, P. A., Court Brown, W. M. and Doll, R. (1962): A study of the chromosome damage persisting after X-ray therapy for ankylosing spondylitis. Lancet, ii:676-682.
     Court Brown, W. M., Buckton, K. E. and McLean, A. S. (1965): Quantitative studies of chromosome aberrations in man following acute and chronic exposure to X rays and gamma rays. Lancet, i:1239-1241.
     Buckton, K. E., Smith, P. G. and Court Brown, W. M. (1967): The estimation of lymphocyte lifespan from studies on males treated with X-rays for ankylosing spondylitis. In; Evans, H. J., Court Brown, W. M. and McLean, A. S., eds., Human Radiation Cytogenetics, Amsterdam, North Holland, pp.106-114.
     Buckton, K. E., Hamilton, G. E., Paton, L. and Langlands, A. O. (1978): Chromosome aberrations in irradiated ankylosing spondylitis patinets. In; Evans, H. J. and Lloyd, D. C., eds., Mutagen-induced Chromosome Damage in Man. Edinburgh University Press, pp.142-150.
     Buckton, K. E. (1983): Chromsome aberrations in patients treated with X-rays for ankylosing spondylitis. In; Ishihara, T. and Sasaki, M. S., eds., Radiation-induced Chromosome Damage in Man. Alan R. Liss, Inc., New York, pp.491-511.

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[A] Norman et al. 1966 (72-h culture) [B] Buckton et al. 1978 (40-50 hour culture) [C] Buckton et al. 1967 (40-50 hour culture)a
Post-RTa No. of No. of No. of No. of No. of Post-RTa No. of No. of No. of No. of No. of No. of Post-RTb No. of No. of No. of No. of No. of
(days) cells Dic+Ring Acentrics Cu-cellsb Cs-cellsc (yr) cells Dicentric Rings Acentrics Cu-cellsb Cs-cellsc (days) mean sampling cells Cu-cells X1Cu-cellsc Cs-cells
7 47 11 23 12 7 <0.08 1,375 446 57 230 517 135 0-10 1.2 12 555 201 168 54
13 100 17 29 16 11 0.08-0.5 930 263 39 169 305 103 11-20 16.4 10 457 160 143 46
15 324 54 93 53 30 0.5-1.5 1,097 168 13 116 206 113 21-50 29.9 11 530 195 167 57
25 140 57 79 35 13 1.5-2.5 350 46 6 24 60 49 51-100 68.5 8 380 130 103 40
33 78 21 41 18 8 2.5-3.5 393 24 3 15 28 34 101-200 146.3 9 450 139 100 53
45 49 7 19 9 6 3.5-4.5 990 38 8 30 54 89 201-400 299.6 11 577 142 111 66
64 160 20 40 16 20 4.5-5.5 1,812 83 4 46 96 164 401-800 592.0 10 575 73 56 58
103 44 6 10 4 4 5.5-6.5 1,336 44 10 23 53 170 801-1400 1,017.9 10 500 41 32 41
115 100 26 20 13 14 6.5-7.5 2,043 55 3 34 62 190 1401-1800 1,563.9 7 400 20 16 26
116 68 8 9 6 7 7.5-8.5 1,422 39 11 19 45 124 1801-1900 1,834.8 9 583 37 34 43
127 100 16 27 15 14 8.5-9.5 1,410 18 6 10 24 128 1901-2400 2,083.5 9 650 31 22 65
157 80 17 29 10 13 9.5-10.5 1,575 26 2 25 38 155 2401-2700 2,599.0 11 830 36 28 72
168 55 5 12 6 3 10.5-11.5 1,320 10 2 9 18 165 2701-3200 2,953.6 6 450 11 7 29
195 100 15 31 11 10 11.5-12.5 960 8 1 7 12 87 3201-3700 3,420.4 6 500 11 13 49
229 51 4 8 6 4 12.5-13.5 935 14 2 7 17 87 a) This table is derived from the data in Table [B].
330 50 3 7 4 5 13.5-14.5 991 10 1 14 19 142 b) time after the end of therapy (days).
413 200 15 12 7 13 14.5-15.5 1,350 4 1 5 9 115 c) X1Cu-cells: cells with at least one dissimilar fragment with or without dics or rings.
477 73 14 15 9 7 15.5-16.5 1,150 11 1 6 17 128
545 78 14 21 7 9 16.5-17.5 830 8 1 3 8 82
631 100 3 4 3 5 17.5-18.5 1,340 8 2 15 21 197
647 80 3 11 4 10 18.5-19.5 920 4 1 4 9 117
719 83 3 6 5 11 19.5-20.5 980 5 0 3 6 86
977 80 7 12 5 9 20.5-21.5 550 3 0 3 4 81
1,000 63 1 0 0 8 21.5-22.5 380 0 1 0 2 24
1,125 59 4 6 2 7 22.5-23.5 810 4 2 7 13 45
1,285 180 0 3 3 15 23.5-24.5 510 3 0 1 5 36
1,305 100 1 1 1 7 24.5-25.5 325 0 0 1 1 33
1,382 117 2 0 0 6 25.5-26.5 225 2 0 0 4 21
1,627 82 1 0 0 5 26.5-27.5 300 0 0 0 1 23
1,946 50 0 0 0 4 27.5-28.5 200 0 0 0 0 10
2,870 100 0 0 0 7 >29 260 5 0 1 5 18
2,909 51 1 0 0 3 a) Time after radiation therapy (years).
2,822 100 0 0 0 6 b) Cu-cells: cells with unstable aberrations (dicentrics, rings, acentric fragments).
3,622 46 0 0 0 4 c) Cs-cells: cells with stable-type rearrangements only.
3,704 100 1 0 0 8
4,920 160 1 0 0 5
a) Time after radiation therapy (days).
b) Cu-cells: cells with at least one acentric fragment.
c) Cs-cells: quasidiploid cells: cells with stable rearrangements only.
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Commentary: Curve fitting (red lines)
     The frequencies of cells, p(t), against time (t) after the end of radiotherapy were fitted to the following formula by iteratively re-weight maximum likelihood combined with bootstrap resampling.
                                                     p(t)+p(0)=a∙exp(-b∙t)+c∙exp(-d∙t),
where p(0) is spontaneous frequency, and a, b, c and d are parameters. Spontaneous frequency was p(0)=0 for Norman et al. (1966) and p(0)=0.011 for Buckton et al. (1967). In the right-hand terms, the first term represents a decline by lymphocyte recovery from radiation damage with a mean survival time of 1/b and the second term represents a decline due to lymphocyte turnover with mean lifetime of 1/d.

. Access to Norman et al 1965, 1966 Access to Buckton et al. 1978 Access to Buckton et al. 1967
Parameter [A] [B] [C]
Cu-cells Cs-cells Cu-cells X1Cu-cells
a (1.222±0.266)×10-1/day (9.659±0.525)×10-2/day (2.110±1.539)×10-1/year (2.193±0.127)×10-1/day
b (1.499±1.149)×10-2/day (1.292±0.844)×10-4/day (6.560±5.721)×10-1/year 3.063±0.334)×10-3/day
c (1.024±0.393)×10-1/day (2.402±0.463)×10-2/day (1.875±1.449)×10-1/year (8.853±1.110)×10-2/day
d (1.383±0.260)×10-3/day (4.992±2.328)×10-3/day (4.070±3.763)×10-1/year (6.274±0.992)×10-4/day
p(0) 0 0 0.011 0.011
mean lifetime, m=1/d 723 days 2.46 year (897 days) 1594 days