Radiation is prescribed as a daily dosage to the prostate given for a certain number of days = the total dosage.
A typical treatment course I give is 180 centiGray each day, given for 45 daily treatments, = 8100 centiGrays total (180 cGy x 45 = 8100 cGy). You can also express dose this in Grays: 1.8 Gy daily x 45 days = 81 Gy total. I prefer using centiGrays. These value are in the metric system. They are units of energy, basically how much radiation energy you are putting into a unit of tissue.
The most common dosage that I use is 180 cGy daily x 45 days = 8100 cGy. This is the highest radiation dosage that has been used in clinical studies with modern equipment and has been found to be safe. I believe in giving the highest safe dose, as I’d rather tend to overkill the cancer then underkill it.
We do tend to use standard recipes in radiation. Sure, your cancer might only need 180 cGy a day for 40 days = 7200 cGy, but there is no way to know that. So, that’s why there is not a lot of individualization of dosage. We simply don’t have any tests to tell us exactly how much dose your cancer needs, so we generally use the highest dose that can be safely given.
One study has used a dose of 180 cGy x 48 days = 8640 cGy, for aggressive cancers. That seems to be the highest dose that is sometimes used.
I have recently presented a study at the 2012 annual conference of ASTRO, our radiation oncology organization. In that study I proposed giving the cancerous parts of the prostate gland a daily dose of 200 cGy, so that parts of the prostate gland would receive 9000 cGy.
Twenty years ago when I was in training we typically used a dose of 200 cGy x 33 days = 6600 cGy. The equipment and targeting was much more basic, and that was the highest dose that could be safely used back then. There were a lot more treatment failures with that dose.
Although we most commonly use 45 treatments, there is some individualization of the dose. Here are some examples:
- 180 cGy x 48 days = 8640 cGy. Rarely used. May use in certain aggressive cancer cases
- 180 cGy x 45 days = 8100 cGy. The standard dose.
- 180 cGy x 42 days = 7560 cGy. If there has been a recent TURP (surgical widening of the urine passage), or if the cancer is early and patient may be unusually susceptible to side effects.
- 180 cGy x 39 days = 7020 cGy. Dose used following prostate removal, i.e. after a radical prostatectomy.
- 180 cGy x 28 days = 5040 cGy. We use this dose if we are combining a radioactive seed implant with the radiation therapy.
Q) Can the treatment be done faster?
A) We give a proven safe dose of 180 cGy per day. Some research studies have looked at giving a higher dosage per day for fewer total days.
Q) Do you use an aggressive dose?
A) Yes, we try to give the highest radiation dose that can safely be given.