How many radiation therapy sessions does prostate cancer usually take?

One or up to 45. External image guided radiation is the most costly at 40-45 sessions. Radiosurgery is 5 sessions, no long term results published costs 1/2 as much. One session of inserting radioactive seeds is literally just one time and costs 1/5. They all have the same effectiveness. It would be worth it to fly to a specialist who does seeds get a one session seed procedure versus taking 45 sessions.
40-45 fractions. With modern day image guided radiation therapy (igrt), the dose is pushed to or above 81 gray. This is about 40-45 fractions. This is the next generation to intensity modulated radiation therapy (imrt). Ulternative radiation (low number of fractions) using cyberknife for early stage prostate cancer can be given as low as 4 fractions. This is the spectrum of external beam radiation.
Around 35. This depends on the radiation oncologist but the standard external beam radiation to the prostate takes around 7 weeks with 5 treatments per week. The number may go up or down somewhat based of the individuals tolerance to the treatment and if the treatment was intensity modulated or 3d conformal.
Why variation? Today's radiation doctors can deliver more radiation to the prostate with lower side effects. Not everyone can get brachytherapy (gland size, disease risk outside capsule), and shorter courses with very high technology are offered. The number of treatments vary because of doctor's beliefs..Toxicity worries, control disease worries, and frankly some are business first folks. Trust someone 1st!