Monte Carlo calculation of correction factors for dosimetry in radiotherapy using the correlated sampling method

In the present work, the correlated sampling technique in Monte Carlo calculations related to diamond dosimetry and graphite calorimetry will be described. The egs_chamber and DOSRZnrc user-codes included in the EGSnrc package are used. Egs_chamber is already provided with routines enabling the use of correlated sampling while an in-house implementation of this technique was made in the original version of DOSRZnrc. Both codes have been used for calculating perturbation factors needed for absorbed dose measurements in radiotherapy dosimetry. Correlated sampling turned out to be a reliable method, allowing to determine, in reasonable times, accurate correction factors, even in unfavourable conditions as when absorbed dose is scored in very small volumes.