Sometimes the thyroglobulin is not reliable. I do not know why you had a Thyrogen stimulated thyroglobulin without having had radioactive iodine. Typically when lymph nodes are involved we do give radioactive iodine. You would need to discuss the details of this with your endocrinologist.
You were probably given the higher dose due to the lymph node involvement. I would think that a negative stimulated thyroglobulin is likely a reassuring prognostic indicator in your case. I would not anticipate the need for more radioactive iodine in the future.
I did have radioactive iodine therapy but wondered why I would have 150 millicuries?