4mm middle Lobe Nodule

Hi,  I had a CT scan for kidney that came back fine in Dec 2010.  They found a 2mm lung nodule right middel lobe.
The doctor sent me for a follow up scan in March and the 2mm was unchanged. 4 months later In August he sent for another CT scan, the 2mm is still unchaged but they found a 4mm that they said on the report was "more conspicuous".  I am very concerned that this could be cancer. I have no previous history of cancer in my family and I quit smoking over 20 years ago.  I am in great shape, work out eat right etc. and I am 50 year old femail.  
How can a 4mm nodule show up in 3 months in a CT scan and it wasn't there before.
The doctor wants me to get another scan in 3 months.,  I am also afraid I am over radiated from all the CT scans'
What are the chances this is cancer.

Help, very worried.

[Dr. Kokil Mathur]

Hi
Welcome to the MedHelp forum!
Usually most lung nodules that are not calcified are benign if they are less than 10 mm in size. Also, the possibility of nodules becoming cancerous increases with history of smoking/current smoking/previous history of cancer/family history of cancer. One can get multiple small non calcified lung nodules and they may all be benign.
If you are in otherwise great shape, then you will need annual follow-ups. Any change in size, density, appearance of nodules, calcification etc will need further follow up, and maybe closer follow-up.
However, since I cannot examine you, nor see the films first hand, it would be best to take a second opinion from another cancer specialist who can examine you.
Hope this helps. Take care!