The 45-year-old actress - who was diagnosed with breast cancer in February 2015 - had her first radiotherapy session, and the former 'Charmed' star has admitted she hated it and was so scared about the treatment she was tempted to run away.
The star shared a picture of her leaning forward in the hospital chair with the patient's gown on to her Instagram on Monday (28.11.16), which she captioned: "First day of radiation treatment. I look like I'm about to make a run for it which is accurate. 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. #radiation #radiationmondaysucks #stillfightinglikeagirl (sic)."
And Shannen - who is currently married to her third husband Kurt Iswarienko - is nearly finished her chemotherapy, which she began in July.
Speaking previously about Shannen and her treatment, her doctor, Lawrence Prio, said: "Shannon is doing amazing. We have just a few more weeks of treatment, and then we'll be nearly finished with the chemotherapy."
Although the Tennessee-born star is ploughing through her medical treatments, the cancer stricken star has admitted she sometimes fears she won't survive the disease, although those negative "moments" soon pass.
Alongside a heartbreaking photograph of Shannen lying on her side on a hospital bed after a round of chemo-therapy, she wrote: "#fbf to a very short bit ago. Day after #chemoday isn't always so great. Sometimes one isn't able to dance, or eat or even to think about the next day. Sometimes it just feels like you aren't going to make it. That passes. Sometimes the next day or 2 days later or 6 but it passes and movement is possible. Hope is possible. Possibility is possible. To my cancer family and everyone suffering.... stay courageous. Stay strong. Stay positive. #wegotthis. #fightlikeagirl (sic)"