• Any radiologists or other medical pros? How is actual tumor size determined?

    Asked by FreeBird on Saturday, October 20, 2012

    Any radiologists or other medical pros? How is actual tumor size determined?

    As a family caregiver, I read every radiology report. The CT scan reports include a vague description of the tumor, with a linear horizontal and vertical measurement, on what I assume is a visual plane. That seems to me like an insufficient way to determine or describe tumor size. Is there a standard way to determine tumor mass or volume, so that you are sure a tumor is growing or shrinking over time? And why is this measurement not included in radiology reports? Why would there be a descrepancy in what we are told vs. what the radiology reports appear to show as far as size?

    6 Answers from the Community

    6 answers
    • GregP_WN's Avatar

      I can't answer the technical side of that Freebird, But on the same order, my last lymph node that went rogue on me in my neck was scanned, CT. The report came back that the lymph node, while enlarged, displayed no characteristics that should cause concern.

      One biopsy later, I was in treatment again.

      Hope Dad is doing as well as he can be.

      Greg P

      over 8 years ago
    • Peroll's Avatar

      Freebird, this is actually san exelent question, one that I encountered several years ago when I had a couple of tumors in my lungs that at one point seemed to be growng dispite the chemo that had to tha tpoint held thne in check. As an engineer someting did not sit quite right wityh me so I asked a bunch of questions and determined exacly how accurate the sizing of tumors in radiology reports is.

      First it is important to understand how CT scans work. CT scans do not produce a continious picture throuhg your body but instead take pistures of slices about every 7 mm. Thus if we assume that a tumor is roughly spherical in shape it is possible for a CT scan to totall miss a tumor that is a little over 6 mm. When a tumor is seen it is difficult to determine the exacty size, evem more so when the tumor is small. It you have a tumor that shows up on only one slice as 6 mm it could be that they just got the edge of the tumor and it is somwhat larger or it could be that the hit the middle and it is 6mm in diameter. I am told that the resolution of a CT scan is about 5 to 6 mm, which mens anything smaller will not be locateable in the CT scan, it just fades into the background.

      No as to the method of measuring the size of the tumor on the CT scan immages, I am told by several sources that the radiologists hole a ruler up to the computer screen displaying the image and use that to measure the size of the tumor.

      So what does it say about the actual size of a tumor? Well if the tumor is small (less than 15 mm - about 0.6 inches) the resolution of the scan is probably about equal to the size of the tumor thus if it appears to grow by 1.5 timesw or even in some cases up to twict its original size it in fact may not have grown at all. On larger tumors the resolution as a percentage of the tumor size becomes smaller so it is easier to determine growth.

      So now to the bottom line how do we read the radilolgy report and get useful information out of it.? Every cancer has an average untreated growth rate, so you first need to know that . It is usually given in time for the tumior to double in size. For my cancer it is 12 weeks. Thus with active cancer I get scans every 12 weeks. If the radaoliogy report says teh tumor is 6 to 8 mm (the size of the tumors I had in my lungs) I would not be too alarmed if the tumors appeared to grow 1.5 times in size, but would continue treatment and see what the next scan showed. If a tumor is 1.8 cm in size and grows to 3.3 cm (what happened to the tumor now in my right adrenal gland) then it is time to think that the treatment is not working. Thus the important factor is knowing if the reported growth is within the resolution of the scan.

      As for being told one thing and the radiology report saying another back when the radilolgy report said my lung tumors were growing (from 6 to 9 mm) I had to see one of my regular oncologistsa partners for a check up. When she looked at the radiology report she exclaimed "they can't say that" and I immediatrly knew that I was right about the sizing. The problem is that not all dioctors are really well versed in scan resolution and not all of them are necessarily well spacially oriented so in some cases they do not question reports and other will. When you think you are not being tiold the correct information be sure to question it and ask for a clear explanation as to what is going on.

      Hope thta this helps and if you have any more questions on this please let me know.

      over 8 years ago
    • nobrand's Avatar

      Not a medical pro here, I just assumed they just measured it across the longest parts. It would be much better to know the volume of the tumor instead. I can think in cups and teaspoons much easier.

      I poked around the net and couldn't get an explanation, but it does seem that CT scans aren't always so precise:


      over 8 years ago
    • nancyjac's Avatar

      It is also important to remember that turmors are only vague representations of cancers. Some cancer cells are contained in tumors, some are not. Some cells in tumors are cancerous, others are not. So, in an of itself, even if the measurement of a tumor is entirely accurate, it is not measuring the size of the cancer, only the tumor that most or all of the tumor cells are in. So, to compound the complexity (and usefulness) of measuring tumors, is that they are only a respresentation of the scope of a cancer, and while it may not be the norm, it is certainly possible for a tumor to shrink but a cancer to grow and vice versa.

      over 8 years ago
    • FreeBird's Avatar

      Thanks for all the good input.

      over 8 years ago
    • FreeBird's Avatar

      After thinking it through, I think I understand how there can be a difference in what the numbers on a report show, and what they say. That is, that reason comes into play. Because of the infrequency of measurement (expensive scans), you end up with a less accurate picture of what's happening on change-over-time. So you must use reason and the big picture of all the data to create the big fuzzy picture of what's happening in between to fill in the blanks. You can see the tumor numbers go up on a chart at the same time they tell you the tumor has gotten smaller. It is just not smaller since the last time it was measured. Because you measure so infrequently, you have no clue what happens between the points without additional data.

      So let's say you started with a measurement of a 3 centimeter tumor. Months later, you have another CT scan, and they tell you--- Your tumor is 3.8 centimeters. Congratulations. It's shrinking. But you're staring at the radiology report and it's telling you the tumor has gotten bigger, by the measurement. Well let's say you are just getting started, or you get sick and there is a gap between measurement and the time of your next treatment. Based on previous data, and on their experience with tumor growth, they can assume a rate of growth that's going to continue at least until the next treatment. You have gone up from the lower number and down to the higher number.

      The doctor gave me the wrong number at one point, pointing to it in the exam room, and the other number I had didn't look right. It suddenly dawned on me that the other number could be correct for that reason. So it appears that chemotherapy with Gemzar was working for Dad at one point, during the first 3 chemo rounds. With this kind of reasoning, and plotting the additional baseline of zero back to his scan before this year it does appear that the tumor was shrinking after chemotherapy, then started to grow again--- even though every tumor measurement has gone higher.

      over 8 years ago

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