Hair started thinning during radiation

I had a sentinel node biopsy and lumpectomy followed by 30 radiation treatments for invasive ductal carcinoma of the right breast.  It was less than one centimeter, node negative, well-differentiated.  I had no chemotherapy.  My hair started to thin rather dramatically about halfway through my radiation treatments and it hasn't stopped.  They ended April 2nd.  I began taking 20mg. of tamoxifen daily on April 30th and I know that hair thinning is a possible side effect.  I'm concerned since I have probably lost about one-third of my hair.  Any thoughts on might what be going on?  I'm premenopausal (age 49).  Thanks so much!

[CCF-RN,MSN-rf]

Dear Wordly:  Radiation can cause hair loss - when its given to the head.  There must be another explanation.  Certainly, hormone changes such as menopause or tamoxifen can contribute to hair loss but the amount of hair loss you describe preceeded the tamoxifen and would not usually be that dramatic if your were beginning menopause.  Also, some medications, poor nutrition and some medical conditions can contribute to hair loss.  One thought, though, is to have your thyroid function tested.  Hypo or hyperthyroid is a common cause of hair loss.  The thyroid gland is located in your neck and although it is not usually in the radiation field, it is close.