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What Does The CT Scan Reprot Indicate?

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Posted on Mon, 5 May 2014
Question: Dear Sir, My Son is 3.1 Yrs. And he went for plain helical head CT scan on 16 Slice Philips Scanner as he fallen from Bed CT scan carried out at 120 KV, 249 mAs CTDI is 38.08 mgy and DLP is 741 mgycm CT Scan report is normal Following are my questions 1.What will be the effective dose from this scan ( Whether conversion factor .005 is correct to calculate effective dose ) 2 What will be the absorbed dose for brain & RBM from this scan 3.Any Risk in future 4.What will be effective dose, absorbed dose for brain & RBM from one SKULL ‘X’ Ray 5. How much brain absorbed dose can cause brain cancer & Leukemeia 6. In how much brain absorbed dose the brain cells repairs without any error 7. How much CT scan is safe. Thanks XXXX
doctor
Answered by Dr. Vivek Chail (1 hour later)
Brief Answer: Please find detailed answer below Detailed Answer: Hi XXXX Thanks for writing in to us. I am glad to be answering your query once again. There are few clarifications to be made regarding CT effective dose constant which you have asked about. I have found out by reading literature on the topic that the constant differs with respect to the part scanned. Therefore for head CT scan the constant is 0.002, for CT scan neck it is 0.005 and for CT scan chest it is 0.017. Therefore if you refer to my earlier query, the effective dose mentioned was 12.597 for the whole body which is by taking 0.017 as constant and also the highest possible dose, this was keeping in mind that the patient is a child of 3 years in age and so allowing the maximum possible effective dose calculation. Further you had quoted ICRP 103 and that effective dose of 3.7 mSv by using constant 0.005 and I had mentioned it as acceptable. There is a problem when calculating doses for children because their size is small and the head is larger as compared to the rest of the body than in adults. Keeping in mind these differences, I had earlier mentioned the brain dose is 28 mGy and RBM dose is 9 mGy. The additional cancer risk is 0.03% more than before getting CT scan exposure. The effective dose from one skull X ray is 0.1 mSv. This is a significantly low value. In radiation dose exposure there is no fixed value of exposure that can cause any cancer or leukemia. It is only a relative risk. This is explained by the effects of radiation on different cells and individuals. There is stochastic and no stochastic effects of radiation which are dose dependent and non dose dependent. But beyond a certain level (say 3 CT scans) the relative risk rises significantly. There is no answer to in how much brain absorbed dose the brain cells repair without any error because of the non dose dependency as mentioned above. CT scan is a life saving investigation and to be always used with caution especially in children. If it is not an emergency then non radiation imaging modalities like MRI may be used. Falling down is an emergency situation and a CT scan was justified for your child. Hope your query is answered. Do write back if you have any doubts. Regards, Dr.Vivek
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
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Follow up: Dr. Vivek Chail (52 minutes later)
Dear Sir, Thank you for your guidance, I am very much worried about my son as many peoples told me that CT scan can cause brain cancer & Leukemia, since last three month I am in tension. 1. Which dose is used for risk calculation, Effective dose Or Absorbed dose ? 2. You mentioned that beyond a certain level (say 3 CT scans) the relative risk rises significantly, Is there any relative risk for one or two head ct scan. Thanks
doctor
Answered by Dr. Vivek Chail (4 hours later)
Brief Answer: Please find detailed answer below Detailed Answer: Hi XXXX Thanks for writing back with an update. I certainly understand your tension involving what other people are saying. I would like to share an article citing the scientific use of CT scan in children and its risk in causing childhood leukemia. Please read the reference article using the link http://www.ncbi.nlm.nih.gov/pmc/articles/PMC0000/ This clearly states that few tens of milligray RBM dose may increase the risk and can can be considered as 3 scans or more before the 15th birthday. Therefore there is very little risk for one or two CT scan head in children. The effective dose is used for risk calculation. Hope your query is answered. Do write back if you have any doubts. Regards, Dr.Vivek
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
doctor
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Follow up: Dr. Vivek Chail (13 hours later)
Dear Sir, Thanks for sharing the very useful article, following are my last questions. 1.How brain and RBM absorbed dose calculated, is there any formula please share. 2. Few tens of milligray means how much milligray ? Thanks
doctor
Answered by Dr. Vivek Chail (11 hours later)
Brief Answer: Please find detailed answer below Detailed Answer: Hi XXXX Thanks for writing back with an update. The brain and RBM absorbed dose is estimated from earlier research done in a large population for various age groups. As mentioned earlier the brain dose for a 3.0 years old male who gets brain CT scan done is 25.6 mGy and RBM is 8.5 mGy respectively. This is changing with the type of machine and with time. Please see table 4 in the article using following link. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC0000/ You may see that before 2001 the doses were higher than after 2001. Few tens of milligray means approximately more than 20 milligray. Hope your query is answered. Do write back if you have any doubts. Regards, Dr.Vivek
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
doctor
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Follow up: Dr. Vivek Chail (45 minutes later)
Dear Sir, Thank you very much for your updation as CTDI and DLP varies in CT scan, whether brain and RBM absorbed dose are dependent on CTDI and DLP or not. Thanks
doctor
Answered by Dr. Vivek Chail (8 hours later)
Brief Answer: Please find detailed answer below Detailed Answer: Hi XXXX Thanks for writing back with an update. The dose length product (DLP) is the CTDIvol multiplied by the scan length (slice thickness × number of slices) in centimeters. It should be noted that the DLP is independent of what is actually scanned. The brain dose and RBM are dependent on CTDI and DLP. These measurements are done with precision instruments and by using phantoms separately for adults and children. You may read more about the methods using the link http://www.birpublications.org/doi/pdf/10.1259/bjr/0000 Hope your query is answered. Do write back if you have any doubts. Regards, Dr.Vivek
Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar
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Dr. Vivek Chail

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What Does The CT Scan Reprot Indicate?

Brief Answer: Please find detailed answer below Detailed Answer: Hi XXXX Thanks for writing in to us. I am glad to be answering your query once again. There are few clarifications to be made regarding CT effective dose constant which you have asked about. I have found out by reading literature on the topic that the constant differs with respect to the part scanned. Therefore for head CT scan the constant is 0.002, for CT scan neck it is 0.005 and for CT scan chest it is 0.017. Therefore if you refer to my earlier query, the effective dose mentioned was 12.597 for the whole body which is by taking 0.017 as constant and also the highest possible dose, this was keeping in mind that the patient is a child of 3 years in age and so allowing the maximum possible effective dose calculation. Further you had quoted ICRP 103 and that effective dose of 3.7 mSv by using constant 0.005 and I had mentioned it as acceptable. There is a problem when calculating doses for children because their size is small and the head is larger as compared to the rest of the body than in adults. Keeping in mind these differences, I had earlier mentioned the brain dose is 28 mGy and RBM dose is 9 mGy. The additional cancer risk is 0.03% more than before getting CT scan exposure. The effective dose from one skull X ray is 0.1 mSv. This is a significantly low value. In radiation dose exposure there is no fixed value of exposure that can cause any cancer or leukemia. It is only a relative risk. This is explained by the effects of radiation on different cells and individuals. There is stochastic and no stochastic effects of radiation which are dose dependent and non dose dependent. But beyond a certain level (say 3 CT scans) the relative risk rises significantly. There is no answer to in how much brain absorbed dose the brain cells repair without any error because of the non dose dependency as mentioned above. CT scan is a life saving investigation and to be always used with caution especially in children. If it is not an emergency then non radiation imaging modalities like MRI may be used. Falling down is an emergency situation and a CT scan was justified for your child. Hope your query is answered. Do write back if you have any doubts. Regards, Dr.Vivek