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CHAPTER 9

Converting T65DR Mean Kerma Values to Mean Internal Organ-Doses




          In this chapter, we shall obtain average internal organ-doses in the T65DR dosimetry. Chapter 8, Part 2, has already indicated that this step simply consists of multiplying the shielded kerma values by two types of factor:   The body transmission-factor and (for neutrons only) an RBE factor.

The Body Transmission-Factors :

          The body transmission-factors are provided in our Table 9-A, for obtaining whole-body internal organ-doses from mean kerma values.

          In reality, no individual can receive a uniform whole-body organ-dose from an external source of radiation, since a beam of radiation diminishes as it travels through the body. However, this problem of dosimetry is reduced in the A-Bomb Study because people were randomly oriented with respect to the bomb;   some received higher doses in the front, others in the back, and others in the side. Thus the approximation of a mean whole-body internal organ-dose may be better in this study than for some other types of studies involving whole-body irradiation by external sources.

The Shielded Neutron Kermas :

          In reporting the 1950-1982 follow-up, RERF did not show the gamma and neutron shielded kerma values separately -- only the total (TR-1-86, Pr86, Pr87a). This omission creates no problem, however, because the necessary shielded neutron values are provided in an earlier RERF follow-up, 1950-1974 (Bee78), and subsequent changes in the cohorts would cause only trivial changes. Of course the shielded GAMMA kermas can be obtained too, by subtraction of the neutrons from the total.

          Both the neutron and gamma shielded kerma values are provided in Table 9-B.

Internal Organ-Dose for RERF's Eight Dose-Groups :

          Table 9-C performs the conversion, from shielded kerma in rads, to mean internal organ-dose in rems (or cSv), for RERF's eight dose-groups. Table 9-C is based on the constant RBE value of 2 for neutrons, which is a reasonable value with the T65DR dosimetry (see Chapter 8, Part 5).

Reference Group -- 1 + 2 :

          Two important reasons exist for the common practice of combining Dose-Groups 1 and 2, and they were given already in Chapter 8, Part 4:   Realism about hidden doses from residual radioactivity, and achievement of a statistically more reliable control-group.

          In Table 9-C, the combination of Dose-Groups 1 and 2 (in the righthand column) produces a mean internal organ-dose of only 0.654 cSv or 654 millirems. In other words, we obtain a control-group or Reference Group with much greater stability than Dose-Group 1 alone, yet its members received only a very low internal organ-dose.

          Whenever analysts must subdivide the control-group by age-bands or sex, having the extra people and cancer-cases from both dose-groups is particularly important. Analysts who seek scientifically strong results would combine the two dose-groups, even if the uncertainty about doses (including the yield of the Hiroshima bomb) were absent. And the uncertainty will never be absent (Chapter 8, Part 4).

Internal Organ-Dose for RERF's 160 Subsets :

          As readers will see in Chapter 15, full analysis of cancer-risk requires separate mean organ-doses for each of RERF's 160 subsets of the database (see Master Table 26-A,B,C,D). Our method for obtaining these organ-doses is illustrated below for RBE = 2.

          The first step is tabulating the correlation between the mean total kerma-doses (neutron plus gamma) and the corresponding mean total organ-doses (neutron plus gamma). This is done for RBE = 2 in Table 9-D.

          Now, if we go to the Master Table 26-A, for Hiroshima males, we find that the average of 3.3 kerma rads (from Table 9-D, Col.C) shows up in Column F five times -- once for each of RERF's five age-bands. But in Table 26-A, Column G, we see how the average varies with each age-band. Let us consider the 42-year-old age-band ATB. It includes ages 35 through 49 years at the time of bombing (Table 4-B).

          For the 42-year-old age-band, we see the true kerma-dose is 3.5 rads instead of 3.3. In other words, it is (3.5 / 3.3) or 1.0606 times the overall average for Dose-Group 2. We obtain the corresponding organ-dose for Table 26-A, Column H, by saying:

          Since 3.3 kerma rads at Hiroshima correspond with 1.658 organ cSv (from Table 9-D), then (3.5 / 3.3) x (1.658 cSv), or 1.76 cSv, is the appropriate organ-dose for that subset of Hiroshima males (age 42 ATB).

          This is the method by which all 160 organ-doses for the T65DR dosimetry were obtained for Column H of the Master Table 26-A,B,C,D. Care was taken to use the Hiroshima pairs from Table 9-D for calculating the 80 HIROSHIMA subsets, and Nagasaki pairs for the 80 NAGASAKI subsets. Later, when we analyse RERF's five age-bands separately, we make special organ-dose adjustments for the small body-size of those who were age 0-9 years ATB (Chapter 31).
Table 9-A
Body Transmission-Factors,
to Obtain Internal Organ-Doses from Mean Shielded Kerma Values. 
=========================================================================================
|         Col.A       |      Col.B      |   Col.C    |     Col.D      |     Col.E       |
|       Dosimetry     |    Internal     |   Gamma    | Direct Neutron | Neutron-Capture |
|Row    and Source    |     Organ       | Absorption |   Absorption   |     Gamma       |
|====================================================================================== |
|    T65DR            |    Combined     |            |                |                 |
| 1   (Kerr79)        |  Cancer-Sites   |    0.50    |     0.22       |      0.07       |
|     (Beir80, p.197) |   Excl. Leuk.   |            |                |                 |
|====================================================================================== |
|    T65DR            |     Colon       |            |                |                 |
| 2   (Shi87, p.43)   | Large Intestine |    0.40    |     0.14       |      0.08       |
|====================================================================================== |
|    DS86             |     Colon       |            |                |                 |
| 3   (Shi87, p.43;   | Large Intestine |    0.74    |     0.19       |      0.41       |
|      see also p.14) |                 |            |                |                 |
=========================================================================================
These factors, for Hiroshima and Nagasaki persons combined, are used to obtain "whole-body" internal organ-doses (see text).
  1. For our T65DR analysis (Table 9-C), we use the factors in Row 1.
    For our DS86 analysis (Table 10-E), we use the factors in Row 3.
    In Row 3, the choice of large intestine (colon) is not arbitrary. RERF analysts report that the dose absorbed by this organ is the best approximation of internal dose absorbed by all the cancer-sites, excluding leukemia (TR-9-87, p.3, and TR-5-88, p.50). Preston and Pierce, and Shimizu and co-workers, all use colon-dose in their own DS86 estimates of Lifetime Fatal Cancer-Yields arising from whole-body exposure (combined cancer-sites).
  2. In Table 9-C, we use the transmission-factors from Row 1 instead of Row 2 for the T65DR dosimetry. Using Row 1 increases mean organ-dose (relative to using Row 2), without increasing the corresponding cancer-mortalities, so lower Cancer-Yields are the net effect of the choice.
  3. Column E provides the body transmission-factor for the n,gamma reaction, in which neutrons are captured in tissue, and gamma rays are emitted.
Table 9-B
Mean Shielded Kerma-Doses (T65DR) in Rads, with Neutron and Gamma Components,
by Separate Cities and by Cities Combined. 

=============================================================================================
|                            Col.A   Col.B   Col.C   Col.D   Col.E   Col.F   Col.G   Col.H  |
|                            Dose-   Dose-   Dose-   Dose-   Dose-   Dose-   Dose-   Dose-  |
|                            Group   Group   Group   Group   Group   Group   Group   Group  |
| Row                        1       2       3       4       5       6       7       8      |
|========================================================================================== |
|  1   HIROSHIMA Persons   27569   15931   10909    2783    1740     659     369     510    |
|                                                                                           |
|  2   Mean Dose (n)         0.0     0.8     4.3    13.4    30.3    56.8    92.1   144.1    |
|  3   Mean Dose (g)         0.0     2.5    17.8    56.9   108.7   186.7   254.3   380.3    |
|  4   Mean Dose (n+g)       0.0     3.3    22.1    70.3   139.0   243.5   346.4   524.4    |
|========================================================================================   |
|  5   NAGASAKI Persons     9604   12924    4034    1442    1388     722     270     377    |
|                                                                                           |
|  6   Mean Dose (n)         0.0     0.0     0.0     0.2     1.3     3.4     5.4    10.5    |
|  7   Mean Dose (g)         0.0     2.6    21.2    71.0   145.6   240.3   338.3   518.7    |
|  8   Mean Dose (n+g)       0.0     2.6    21.2    71.2   146.9   243.7   343.7   529.2    |
|========================================================================================   |
|BOTH CITIES Persons       37173   28855   14943    4225    3128    1381     639     887    |
|                                                                                           |
|  9  Kerma-Dose, calc.        0     3.0    21.9    70.6   142.5   243.6   345.3   526.4    |
| 10  Kerma-Dose from 26-E     0     3.0    21.8    70.6   142.5   243.6   345.2   526.4    |
=============================================================================================
    NOTES -----                                 (n) = NEUTRONS             (g) = GAMMA
  1. The entries in Rows 1 and 5 for Persons are "cases" from Tables 26-H and 26-I.
  2. The entries in Rows 4 and 8 for total Mean Dose, neutron and gamma components combined, come from "Meandose" in Tables 26-H and 26-I. Also they match the entries in Master File 26-A,B,C,D, Column F, for "Disk Kerma-Dose" as provided by RERF diskette R10ALL.
  3. The entries in Rows 2 and 6 for the mean neutron shielded kerma-dose come from Bee78. The gamma values in Rows 3 and 7 are obtained by subtraction of the neutron values from the totals (n+g).
  4. The entries in Row 9 are calculated from the entries in Rows 1, 4, 5, and 8 directly above them. The entries in Row 10, taken from Table 26-E, are provided as a check;   Rows 9 and 10 are the same, except for very small rounding-artifacts.
Table 9-C
Mean Organ-Doses (T65DR) in Centi-Sieverts, for Neutron RBE = 2,
by Separate Cities and by Cities Combined. 

==========================================================================================================
|                             Col.A   Col.B    Col.C   Col.D   Col.E   Col.F    Col.G   Col.H    Col.I   |
|      T65DR, RBE = 2         Dose-   Dose-    Dose-   Dose-   Dose-   Dose-    Dose-   Dose-    Ref.    |
|                             Group   Group    Group   Group   Group   Group    Group   Group    Group   |
| Row                           1       2        3       4       5       6         7      8     (1 + 2)  |
|======================================================================================================= |
|  1   HIROSHIMA Persons      27569   15931    10909    2783    1740      659      369      510   43500  |
|                                                                                                        |
|  2   Organ-Dose (n) RBE=2       0   0.352    1.892   5.896  13.332   24.992   40.524   63.404          |
|  3   Organ-Dose (n,gamma)       0   0.056    0.301   0.938   2.121    3.976    6.447   10.087          |
|  4   Organ-Dose (g)             0   1.250    8.900  28.450  54.350   93.350  127.150  190.150          |
|                                                                                                        |
|  5   Total Organ-Dose, cSv      0   1.658   11.093  35.284  69.803  122.318  174.121  263.641   0.607  |
|======================================================================================================= |
|  6   NAGASAKI Persons        9604   12924     4034    1442    1388      722      270      377   22528  |
|                                                                                                        |
|  7   Organ-Dose (n) RBE=2       0   0.000    0.000   0.088   0.572    1.496    2.376    4.620          |
|  8   Organ-Dose (n,gamma)       0   0.000    0.000   0.014   0.091    0.238    0.378    0.735          |
|  9   Organ-Dose (g)             0   1.300   10.600  35.500  72.800  120.150  169.150  259.350          |
|                                                                                                        |
| 10   Total Organ-Dose, cSv      0   1.300   10.600  35.602  73.463  121.884  171.904  264.705   0.746  |
|======================================================================================================= |
|      BOTH CITIES Persons    37173   28855    14943    4225    3128     1381      639      887   66028  |
|                                                                                                        |
| 11   Total Organ-Dose, cSv      0   1.498   10.960  35.393  71.427  122.091  173.184  264.093   0.654  |
| 12   Organ-Dose from Neut.      0   0.194    1.381   3.914   7.670   12.708   24.405   38.419   0.085  |
| 13   Organ-Dose from Gamma      0   1.303    9.579  31.479  63.757  109.383  148.779  225.674   0.570  |
| 14   Neutron cSv / Total cSv    0   0.130    0.126   0.111   0.107    0.104    0.141    0.145   0.130  |
==========================================================================================================
    NOTES FOR T65DR, neutron RBE = 2 -----           (n) = NEUTRONS         (g) = GAMMA
  1. Table 9-C corresponds with Table 9-B, except that all entries in Table 9-C are now whole-body internal organ-doses, not shielded kerma-doses
  2. The entries in Rows 2 and 7 for the neutron-component are the corresponding neutron entries in Table 9-B times 0.44 (which is two times the conversion factor of 0.22 from Table 9-A, Col.D). The extra factor of two is necessary because calculations are for neutron RBE = 2.
  3. The entries in Rows 3 and 8 are the entries for neutrons in Table 9-B times the conversion factor of 0.07 (from Table 9-A, Col.E). No RBE factor of 2 is used because, after the n,gamma reaction has occurred (see Table 9-A), the dose is delivered by GAMMA radiation.
  4. The entries in Rows 4 and 9 for the direct gamma component are the corresponding gamma entries in Table 9-B times the conversion factor of 0.50 (from Table 9-A, Col.C).
  5. The entries in Row 11, for mean organ-dose in the combined cities, are calculated for each column by the formula [(Row 1 times Row 5) + (Row 6 times Row 10)] / (Row 1 + Row 6).
      The entries in Row 12 are [(Row 1 times Row 2) + (Row 6 times Row 7)] / (Row 1 + Row 6).
      The entries in Row 13 are obtained by subtracting Row 12 from Row 11.
      The entries in Row 14 are, of course, Row 12 / Row 11.
    Ostensible errors in the third decimal place of Row 13 come from rounding after making a calculation with longer strings of digits.
  6. Table 4-A provides the most convenient way to compare the values in Row 11 for the T65DR dosimetry with the comparable values in the DS86 dosimetry.
Table 9-D
(T65DR Dosimetry) Correlation of Kerma-Doses with Organ-Doses, RBE = 2. 

=====================================================================================
|    Col.A      Col.B    Col.C   Col.D   |    Col.E    Col.F    Col.G   |     Col.H |
|                                                                                   |
|                         HIRO    HIRO   |              NAGA    NAGA    |      BOTH |
|               HIRO     KERMA   ORGAN   |     NAGA    KERMA    ORGAN   |    CITIES |
|               PERSONS (RADS)   (cSv)   |  PERSONS   (RADS)    (cSv)   |   PERSONS |
|================================================================================== |
|                                        |                              |           |
|  Dose-Grp 1    27569       0        0  |     9604        0        0   |     37173 |
|  Dose-Grp 2    15931     3.3    1.658  |    12924      2.6    1.300   |     28855 |
|  Dose-Grp 3    10909    22.1   11.093  |     4034     21.2   10.600   |     14943 |
|  Dose-Grp 4     2783    70.3   35.284  |     1442     71.2   35.602   |      4225 |
|  Dose-Grp 5     1740   139.0   69.803  |     1388    146.9   73.463   |      3128 |
|  Dose-Grp 6      659   243.5  122.318  |      722    243.7  121.884   |      1381 |
|  Dose-Grp 7      369   346.4  174.121  |      270    343.7  171.904   |       639 |
|  Dose-Grp 8      510   524.4  263.641  |      377    529.2  264.705   |       887 |
| SUM, Persons   60470                   |    30761                     |     91231 |
=====================================================================================
Columns C and F come from Table 9-B. Columns D and G come from Table 9-C.
Persons are included in this table just for reference.



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