The "Charmed" actress, 45, shared a black and white Instagram photo of her standing beside the large machine she calls "Maggie."
"This is Maggie. I’ve seen Maggie five days a week for what seems like forever. We have a love hate relationship. I love her because she’s part of the life saving treatment I’m receiving," she wrote.
"It’s astounding how far we have come with technology. One day, Maggie will be retired and the cure will be found," the actress continued. "Things like immunotherapy are the future but for now.... it's me and Maggie."
She signed off with, "I’m seeing her twice tomorrow so that I can wrap this phase up faster. Goodnight sweet Maggie. See ya tomorrow. #cancerslayer."
Doherty also posted an Instagram video of her dancing with her trainer during a workout.
"Radiation is tiring. It builds up within you and sometimes one just struggles to keep their eyes open. You can see how tired I am here but I'm still moving!! she wrote.
"Radiation is frightening to me. Something about not being able to see the laser, see the treatment and having this machine moving around you just scares me. I'm sure I'll get used to it but right now.... I hate it," she wrote on Instagram at the time.