Wilms and Lung nodules

Lung nodules .... what causes them in a 9 or 10 year old boy?

My son was diagnosed in March 2011 with Wilms tumor stage II. He had 2 nodules at time of diagnosis. 3 months into treatment he developed 9 more nodules. These eleven have remained stable for 11 months. In June 2012, 3 new nodules have developed making a total of 14 lung nodules ranging in size of 2 mm to 6 mm. Small, very small.

Has anyone else developed this many lung nodules during treatment? If so, what were they?

Next month my son has another lung scan to determine if these nodules have grown.

Scared......