How long does it take for hair to grow back after radiation therapy?

Not applicable. Generally radiation dose not cause hair loss, only during brain radiation. This is usually an issue with chemotherapy after chemotherapy it usually takes 3 weeks to notice hair growth, but several months to "regain" your hair.
If permanent loss. Due to higher dose (> 50 gy), and after lower doses, for instance, prophylactic brain treatment in small cell (25 gy), I cousel my patients that peach fuzz in 3-4 months, and full return in 6 months.

Related Questions

How long will it take for hair to grow back after receiving radiation therapy on the head?

Yes. Radiation or chemotherapy drugs are toxic to cells that are rapidly dividing. This means they specifically target cancer cells, but they also kill healthy cells that grow quickly. This includes hair cells (causing baldness/alopecia) and stomach cells (causing nausea or mucositis). Once the chemo or radiation is stopped, the side effects go away and hair should grow back.
Depends on the dose. The scalp hair follicles generally regrow hair if the dose they received was less than 45 gy. Your radiation oncologist can determine the actual dose delivered to the scalp by reviewing the plan. If the hair is going to grow back, it usually starts within a few weeks to a couple of months after treatment.

Will my facial hair grow back after radiation therapy?

Depends on dose/type. Depending on what disease is being treated, radiation is given in between 2 weeks to 7 weeks in standard fractionations. Near 7 weeks of radiation we expect no further hair growth. About 2-4 weeks, we can expect recovery of hair growth. I am assuming you are talking about x-ray/therapeutic radiation for cancer. There are other types of radiation that the above answer may or may not hold true.
Possibly. Assuming you lost the hair from treatment for a cancer in the oral cavity or pharynx, it would depend on the technique. These days most radiation doctors use imrt for head and neck cancers. This distributes the radiation widely and therefore less dose directly to the skin versus older methods. Often in this case the hair will grow back but sometimes more sparsely.
Depends. Do you want it to? This is dose dependent and time dependent to some extent. If you had lymphoma treatment, it is likely. High doees head and neck treatment, probably not.

How long does it take to start growing hair back after radiation therapy?

Varies. It varies depending on the location of the radiation and other therapies; usually have noticed hair recovery in about 2-3 months after completion of therapy unless there has been permanent damage to hair follicles with radiation on scalp;.
Weeks, Months. Some patients have hair regrowth in a few weeks to months. Others, depending on the area treated may never have hair regrowth.