Some excellent advice from Selkie and Tri already .... CattyB .. just be kind to yourself during the Rads treatment (and afterwards) as it may take 'more' out of you, than you think. It is important that your body 'repairs itself' without added stress, so it is very important not to over-exercise until the body is ready for it. Doing too much, too early can actually set you back 😕. So definitely, stay away from your rowing machine and the resistance bands for the time being! 😳
On top of your desire to exercise is the fact that you are under a bit of stress already, just getting to and from your daily Rads appointments. I was lucky to be able to stay in the locally provided 'lodge' that was attached to the hospital where I was having my Rads, which was an hour away from my home. If you are travelling daily to your Rads, you may be also covered by the State's 'Isolated Patient Travel Scheme' ... whereby accommodation and/or fuel costs may be partially refunded to you. Which State do you live in? Check it out on the link at the bottom! It sounds like you are 'almost' covered for accommodation and/or fuel reimbursement ... depending on which state you are in, as each one's 'distance requirements' are different! This form (below) is a few years old now but shows the assistance available to regional/rural/remote patients .... and may have been updated since 2019.
Saying this - Stretching and weigh bearing upper body exercises should be minimal until post Rads - and even then, start back slowly. Doing gentle exercises are fine - but don't try & push those 'reaching' exercises. In this case, it would be 'No Pain, No Brain', so maybe back off on the Yoga Stuff just now! Walking is just FINE, during your treatment. xx. Just wait & see how you 'go' during your treatment .....
There is Plenty of time to get back into it all AFTER your treatment has finished and you have worked out your 'rhythm' post treatment xx. You won't be losing that much fitness during the Rads .... as your underlying muscle structure will still be there, to 'fine tune' after your treatment has finished. Just 'freshen up' slowly as you feel up to it, after Rads.
Take care & all the best