I had complete foot drop, it's only slightly now, but still have toe drop in both big toes. With real foot drop you will not be able to stand on your feet. This was my case 5 years ago with just chemo with high doses of taxotere, cisplatin and 5-FU, no radiation. This caused horrific side effects to nearly kill me, lost 110lbs and hospitalized me for 6 months, including paralysis of both legs, foot drop after a while, and no sensory or temperature feeling in the feet, legs. I had to learn to walk again, which took almost a year, but still required use of a walker, and now cane. I still have no true answer what was the cause. Although, I had so many life threatening illnesses, it wasn't at the top of the diagnosis list, but the inability to walk then, and still having difficulty effects me greatly since I can no longer drive or walk far. I did come across gallium barr syndrome, possibly a cause based on some symptoms, but that's my own, and difficult to prove mainly with a spinal tap.

I had Erbitux, but with taxotere, which was cut out due to causing to worsen the neuropathy, necessitating the use of a walker. My kidney doctor said great strides have been made with targeted therapy, but said one common side effect is the neuropathy, so now I wonder if it was the Erbitux.

I also noted you mention sciatica, which I had for 30 years, but only the left leg from herniated discs in L4, L5. Mine is from weight lifting. My legs are not chicken legs, more like tree trunks, and we're very strong, so that was a wake-up call when chemo knocked me down and literally out. I don't know if this pre-existing condition has any effect with chemo, but may worsen it.

So far I only spoken about the effects of chemo, but my surgeries, maybe radiation too, has caused some slight head drop, probably from my neck muscle being removed, and atrophy of the left trap, and nerve damage to the brachial plexus.

As mentioned, your best bet is to see about physical therapy. I was doing it, but right now I have other issues, cancer treatment related, to deal with that it's not a priority,

I also wear socks 24/7, which hold the toe in place, so it doesn't catch on the ground, even sheets, except when getting out of the shower. I do still have hand and foot stocking syndrome, neuropathy, so the socks help with that too. Idk if a sturdy stocking would help with the foot drop, but PT would know best.

Good luck