Assessment of Cancer Risks Associated with Patient Organ Doses from Medical Diagnostic Computed Tomography in Bangladesh

Along with the high-quality image, the enormous observance of CT in medical di-agnosis delivers radiation doses to patients that are alarmingly higher than other modalities. Observance of entrance doses of patients undergoing selected diagnostic CT in Bangladesh, calculations of Effective Dose (ED) to analyze ED distribution and to determine the whole-body effect of exposure were carried out on Alderson Rando male human phantom maintaining IAEA TRS 457 protocols. Entrance doses of different organs were observed using IBA Kermax plus Tino DDP and pocket dosimeters. Corresponding specific ED (by conversion coefficient) and whole-body ED (by tissue weighting factor) were estimated from it. ED CC found in this study has a wide range from 0.30 to 395.00 µSv for Head, 12.75 to 1075.00 µSv for Chest, 7.35 to 2578.80 µSv for abdomen and 2.40 to 3320 µSv for Gonad. EDwhole was calculated and further used to estimate risk factor and incident per population. Cancer risks estimated by risk calculator were found higher for chest and abdomen CT respectively 2.59×10 -2 (1:3854) and 4.45×10 -2 (1:2246) at the age of 25 and due to having double exposure. The results were compared with established international reference dose levels and found below reference dose levels. Abbreviations: ED: Effective Dose; CT: Computed Tomography; NMPI: Nuclear Medical Physics Institute; SSDL: Secondary Standard Dosimetry Laboratory; IPEM: Institute of Physics and Engineering in Medicine Abstract The present work has been done for the assessment of radiation dose to patients and to optimize the dose in diagnostic CT. Some measurements were performed and comparisons of the measured data with established international reference dose levels were done for the entrance dose and estimated effective dose on Alderson Rando human phantom undergoing selected diagnostic CT. Experiments were held in the Nuclear Medical Physics Institute (NMPI), AERE, using different dose measuring equipment calibrated earlier in Secondary Standard Dosimetry Laboratory (SSDL), AERE, Savar, Dhaka, Bangladesh. Calculations and analyze of Effective Dose (ED) in CT examinations to determine fatal cancer risk from whole body effective dose using risk calculator are focused in this study.

The present work has been done for the assessment of radiation dose to patients and to optimize the dose in diagnostic CT. Some

Materials and Methods
Head, chest, abdomen and gonad CTs are the most frequently suggested CT scans in medical diagnosis. The main instrument used in the present study is ingenuity TF PET/CT, Philips of 128 slices located at NMPI, AERE. In lieu of actual patients Anderson Rando human phantom, which comprises ingredients similar to human tissue used to investigate the effect of radiation beams on human beings, has been used. Dosimetry protocols proposed by IAEA international code of practice TRS 457 and by the report no. 77, Institute of Physics and Engineering in Medicine (IPEM) were used to measure the quality control parameters [5,6] [8]. This dosimeter was placed on the selected target organ to do CT with and pocket dosimeters were placed on the other concerned organs to measure the scattered dose. All CT scans have been performed at 120 KV voltage keeping the scan length same for the selected organ and taking different time duration. Quality control tests such as CTDI (volume), mAs (mili ampere second), DLP (Dose Length Product) were also observed from the CT machine for different CT examinations. Entrance dose has been observed through direct measurement. Effective dose has been defined by the ICRP as the sum of the weighted equivalent doses to specified organs and provides a useful measure of radiation risk (ICRP, 1991) [9]. Conversion coefficients were used to relate entrance dose and ED (specific). ED from entrance dose was derived from the formula given below:

ED=(mSυ )=Entrance dose(mGy) ×CC Entrance dose (mSυ /mGy)
where, the symbol has their usual meaning. CC Entrance dose was used from the table presented in report of NRPB [10]. Tissue weighting factor represents the proportion of the stochastic risk resulting from tissue to the total risk, when the whole body is irradiated uniformly [11]. The radiation weighting factor is the value selected for a specified type and energy of the radiation. To find whole body effective dose the entrance dose was multiplied by radiation weighting factor first and then multiplied by tissue weighting factor. This whole-body ED is mandatory for assessment of cancer risk using risk calculator. The following is used in this study to estimate ED (whole body) [10].
, , Hiroshima and Nagasaki atomic bombings and from the populations exposed medically, occupationally and environmentally. Conversion coefficients were used to relate entrance dose and ED. It can be measured by computation rather than direct measurement.

Results and Discussion
Accumulated and adverse health when the whole body is irradiated uniformly can be assessed by whole body ED using tissue weighting factor. EDs by conversion coefficient are shown in Tables 2-4 whole body ED and associated cancer risks for different organs are displayed for both single scan and double scan.     (Table 4) and found within the safety limits (Table 5). It is difficult to compare the present data with reference data since almost each study has considered different phantom or irradiation conditions. To understand the impact of exposure deeply both male and female patients should be taken in consideration but in this research only male human phantom has been used.

Conclusion
The proper risk of malignancy from CT is a burning context of dispute [17]. Accurate carcinogenic risk from low doses of ionizing radiation involves uncertainty [14][15][16]. The current statistics show the gigantic growth of CT through the world and thus it will continue to contribute a significant portion of the collective dose delivered to the concerned people [14]. Bangladesh is a country of around 160 million people. The dose and associated cancer risks from CT has been scrutinized currently in the world and so as in Bangladesh [18][19]. The objectives of the present study are to minimize the health effects due to radiation and to minimize risk to the patient. ED per examination was found lower in Bangladesh than in other countries A quality assurance program for the CT would be emphasized based on the data acquired from present study to reduce the patient dose and fatal cancer risk. The data obtained in this study hopefully may add to the available information in national records for general use.