How Is Dose Calculated in High Dose Rate Brachytherapy for Esophageal Cancer?

[Jhon81]

Homework Statement

Consider a high dose rate brachytherapy treatment to the esophagus using the
following conditions:
Activity: 10 Ci
Active length: 10 cm
Number of dwell positions: 20
Gamma constant: 4.7 Rcm2/(mCi*hr)
That is, the centre of the source will dwell at distances-4.75,-4.25, ..., 4.75 cm from the centre of the treatment region.
1.Use a point source model to calculate the dose at a distance of 1 cm from the centre of
the active region giving a constant dwell time of 10 s at each dwell position.
2.Calculate the dose at a distance of 1 cm directly opposite one of the most distal dwell positions (i.e.±4.75)

Homework Equations

Dose rate= (gamma constant * exposure rate constant * activity)/d^2
the total dose= dose rate * time

The Attempt at a Solution

I used the equations mentioned above for the first part
the second part i did not know how to calculate it? any help?

 

[anathema]

For the second part, you can use the same equation but with a different distance value. Since the dwell positions are at ±4.75 cm, the distance from the centre of the active region to the opposite position would be 10 cm (10 cm active length - 4.75 cm dwell position = 5.25 cm remaining distance). So, you can plug in 10 cm for the distance in the equation to calculate the dose at that position.