I think it would be wise to read a bit about dosimetry before rushing in and trying to calculate dose. There are a couple of online early versions of Faiz m. Khan text "The Physics of Radiation Therapy" which have an excellent reading section on dosimetry. These have a good description of dosimetric calculations just can't remember which is the better download.

http://ucrfisicamedica.files.wordpress.com/2010/10/phys-of-radiation-therapy-3-edicion-khan.pdf

http://medicalphys.files.wordpress.com/2010/12/faiz-khans-01.pdf

1: try to find out the depth dose distribution DDD.

2: fix the point by depth d where you want to specify your dose.

3. Learn to know the dose rate in the maximum of depth dose distribution DRmax, that means the dose per minute.

4. Find out the relative factor DRmax to DR(d) = f from the DDD

5. You wanted Dose shall be Dwant(d)

The time will be calculated by: Time t = Dwant/(DRmax*f)

Example: DRmax = 2 Gy/min

Depth d = 10 cm water

wanted dose  = 1,5  Gy

rel. DR in  is 50% (field size 10x10 cm2)

Factor f = 0.5

time t = 1.5 Gy/(*2 Gy/min*0.5) = 1.5 min

Hi, I send 2 attachment for improve your information abuot Radiation treatment.

Sis you can consult the Bible of Raditherapy Physics (Faiz M. Khan's "The Physics of Radiation Therapy") 

There are two technique.

1.       SSD

2.       SAD

1 SSD,   

treatment time for Co60 = Prescribe daily dose/(PDD(x,y)%  X  BSF(x,y)  X  Machine Output rate(x,y) X (802/80.52))

2 SAD,

treatment time for Co60 = Prescribe daily dose /(TAR(x,y) X machine Output rate(x,y) )

x- Field width

y- Field high

It takes a fair bit of background in radiation sciences to get to this point, at least some heavy reading as suggested.

https://www.slideshare.net/InochiAshFull/radiotherapy-calculation

Dear all

I want to calculate the cost of radiation therapy per gray. But I cannot find information about the quantity of Cobalt 60 source contains in terms of gray. Can you help me?

Thanks

how to calculate dose rate cobalt?

linac machine pdf would you help me?