The campaigner began radiotherapy on Monday.
Vicky Phelan has shared a health update with her followers and revealed she may "go quiet" on social media over the next couple of weeks.
The Cervical Cancer campaigner began a ten-session course of radiotherapy on Monday in order to alleviate the pain caused by a tumour on her spine.
She told fans that she may not be able to post regularly as she deals with the side effects of the treatment.
"Day one of radiotherapy down," Vicky wrote on Instagram.
https://www.instagram.com/p/CZ9sWFWs4lU/
"On my way home now after finishing Round 1 of a 10 session course of radiation to relieve pain in my spine.
"I can't promise to keep you all posted on social media over the coming two weeks on how I'm doing. If I go quiet, you will know that I am probably just about coping with side effects from treatment.
"If I feel up to it, I will post sporadically to keep you all updated."
She went on to thank all of her supporters.
"Thanks again to ALL of you for all the lovely messages of support that you are sending in to me. They really mean a lot."
Later, she responded to some comments, to explain more about her treatment, saying she is "hoping for relief from pain and a bit more mobility" as she is "really only moving from bed to chair to car seat at the minute".
It comes after Vicky revealed she
would no longer be able to join Charlie Bird on his Croagh Patrick climb in April for the
Climb with Charlie campaign.
While she had been looking forward to the event, she admitted she was "not in any shape or form to be able to climb anything".
However, she told the former RTE broadcaster that she would try her best to be there on the day, even if she can't take part.
In a heartfelt Tweet, she wrote: "Charlie, I will do EVERYTHING within my power to be at Croagh Patrick on April 2 to wave you and all my family and friends and our supporters off.
"THIS is my goal once treatment finishes at the beginning of March. Fingers, toes and everything crossed I will BE there with you."
