Z . Mehrabankhoo et al .: Radioprotection 2024 , 59 ( 1 ), 19 – 25 21 Fig . 1 . Fluence to effective dose conversion coefficients for the different weight percentiles in a : AP , b : ROT irradiation geometries .
Table 2 . Relative difference between effective dose of 95 th percentile and VIPMAN phantom .
Relative Difference 1 |
Irradiation Geometry |
|
AP |
PA |
RLAT |
LLAT |
ISO |
ROT |
RD 5 % |
58 |
5.2 |
– |
– |
47.4 |
58 |
5 < RD 15 % |
42 |
47.4 |
– |
– |
47.4 |
42 |
15 < RD 25 % |
– |
47.4 |
– |
– |
5.2 |
– |
25 < RD 50 % |
– |
– |
100 |
100 |
– |
– |
1
RD ¼
Eðdesired percentileÞ�E ð 50 Þ 100 : Eð50Þ
effective dose values has been previously discussed in studies such as Endo et al . ( 2013 ) and Miri et al . ( 2012 ).
3 Results
The calculated fluence-to-absorbed and effective dose conversion coefficients are expressed in units of pGycm 2 and pSvcm 2 , respectively . The statistical error of the result is less than 1 %. The run time of programs depends on the irradiation geometries , the incident neutron energy , and the phantom weight percentile . To obtain these errors , about 2 10 7 particles were tracked ( especially for 10 �9 MeV ) for AP , PA , RLAT , and LLAT irradiation geometries , 410 7 particles for ISO , and 2 10 8 particles for ROT on the 50 th weight percentile phantom . As the weight percentile increases , the mean time-consuming also increases so that it reaches approximately tripled for the 95 th weight percentile .
Figures 1a and 1b display the effective dose for all weight percentiles in AP and ROT irradiation geometries , respectively . For AP geometry , the maximum relative differences ( RD ) between the 50 th and 95 th percentiles are about 18 %. These differences arrive to 28 %, 22 %, 24 %, 26 %, and 27 % for PA , RLAT , LLAT , ISO , and ROT irradiation geometries .
The 95 th percentile effective dose conversion coefficients for ORNL phantom were compared with those obtained from the VIPMAN for AP , PA , LLAT , RLAT , ISO , and ROT geometries . The relative difference between two data sets was calculated and tabulated in Table 2 . The first column of Table 2 shows the range of relative differences . The value in each cell is the percentage of cases within the specified relative difference in each row . For example , the first number in Table 2 means that 58 % of results between the 95 th percentile and VIPMAN differ by less than 5 % in AP geometry .
In addition to the neutron effective dose , the organ absorbed dose conversion coefficients were also studied for various tissues . Figures 2a and 2b show examples of comparisons between absorbed dose values of the 95 th percentile and VIPMAN for the AP adrenals and LLAT stomach , respectively . Figures 3a to 3d present the relative differences in absorbed doses of various organs between the 95 th percentile and corresponding data in the VIPMAN phantom . These organs include the spleen , liver , heart , lungs , and stomach in PA , RLAT , ROT , and ISO irradiation