I had a lumpectomy early March followed by a re- excision to get clear margins 2 weeks later.My radiotherapy started mid April so sounds about right.
Radiotherapy in our cases is a mop up exercise for any stray cancer cells.For others it can be used to shrink the tumour.
Given you are LHS and on chest wall you’ll be taught how to lift the breast away from the heart at the mapping session. 16 rounds of radiotherapy is quite light so skin damage will be minimal if you cream up 3-4 times daily with a good emollient. I liked Calendula cream but many on here liked moo goo.You will be given instructions about this. A front opening bra will help the process. Amoena bras are great but I didn’t know about so bought 2 from Target - they do get grubby.
The worst thing about radiotherapy for me was finding a park .The mapping session takes around 45 mins and each round takes about 15 mins - mostly getting changed and redressed.
After it’s all finished expect a few days of engulfing tiredness so plan ahead for it with meals and your activities.
Finally heat and UV will activate the radiated breast even with a rashie.Probably best to stay out of the sun until things settle down - a few weeks.
PS I am a very fair red head and had same cycle as you - all went well and my skin held up fine.