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We define treatment success or failure of radiofrequency ablation by change
in appearance and increased lesion volume visible in the follow-up CT scan.
Many radiology reports only state "appears to decreased in size" or
"multiple liver lesions remain stable". To determine RF treatment
success, the measurement of the diameters of treated lesions in the follow up
CT scans is indispensable.
Here is a description of how lesions are measured at the Cleveland Clinic.
We propose the same technique as a guideline for the tumor registry.
Each lesion is measured from all scheduled CTs with a technique similar to
ultrasound measurement. CT scans should be done with a slice thickness not greater
than 7 millimeter.
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First the image, where the lesions appear to be biggest, is defined. In this case, it appears to be the first lesion in the second row. |
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The lesion is identified according to the number given during RF ablation.
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With a caliper the greatest diameter (length) is measured |
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The distance is estimated on the reference scale. |
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The second diameter (width) is taken at a right angle to the first. |
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The distance is again estimated at the reference scale |
Diameters are measured in centimeters (cm) with one decimal point. The measured diameter should be entered in the lesion follow-up sheets. The volume of the lesion is calculated with the formula V= 4/3 ยน * x * y * (x+y)/2. By entering the x and y values in the registry, our database will calculate the volume and compare it with previous values, which determines the success/failure decision for each lesion.
Tips for tracking lesions:
(Re)identifying lesions on CT scans can be very tricky, especially if more than 10 tumors were treated, or if 2 or more lesions are close. The key is the detailed documentation during RF ablation in the operating room.
Sometimes even with these guidelines, a definite identification of lesions can remain unclear at the time of ablation. Examinaion of the postoperative CT scan with its clear distinction of ablated areas should answer this question. Any additional treated areas, which failed to appear as tumor in the preoperative CT scan, can be also identified at this time.
A good reference to determine the segment anatomy in CT scans is the article by G. D. Dodd III An American Guide to Couinausd's Numbering System, American Journal of Radiology, Vol. 161, September 1993, Pages 574-575
What about resolved lesions?
If an ablated lesion appears to be resolved (no evidence of necrotic or tumor tissue at the predicted site in a follow-up CT), the x and y values of diameter are entered as 0 (zero) and the follow-up of this lesion is finished.
What about coalesced lesions?
If two or more lesions are indistinguishable in follow-up CTs, their diameters are measured as a single lesion, and the calculated volume is then divided by the number of coalesced lesions.