mammograms and lympedema

(By the way, here in South Africa we spell it lymphoedema; in the US it is spelt lymphedema and I am spelling it like that in this posting so that it is picked up in internet searches.)

I was worried. Being high risk for lymphedema following my radiation for breast cancer (today at my appointment with the expert my arm was slightly up in two places above the elbow, but neither measurement more than it had been at some point in the past), I have been told for eg not to wear underwire bras and not to have my blood pressure taken on the affected arm etc.
So how was I going to have a mammogram, which I am scheduled to have in about two weeks' time?
It's fine, The Lymph Lady assured me. It is mainly the arm I need to concern myself about, although a major injury to my chest/breast/neck area could affect my arm. Unless one had lymphedema in the breast.
So a mammogram will be fine. Nothing to worry about. Mmmm.. wonder why no underwire bras though. Must ask.
And we chatted about sun block, cos I am concerned that I have gone to so much trouble to find non alkaline soaps and creams for the affected area - so that bacterial infections cannot thrive in the lymph-affected area, so how can I then slap on alkaline sunblock? Yet I have been told by both the radiation gals and The Lymph Lady to use sunblock.
She told me that it was not necessary to use sunblock on my arm unless I was going to be outside. That is, not for general in and out going about my business. (SA is hot and I use sunblock on my face and neck every single day, summer and winter.) But it sounds like I need to use it on my neck and upper chest area, the part that is still so damn itchy following radiation, as if it gets sunburnt, it will stay red forever. The pigment will change.