Contribution of electron contamination to the skin dose in teletherapy with Co-60 gamma-rays.

The contribution of electron contamination to the dose received by the skin and the underlying tissues during teletherapy with 60Co gamma-rays has been determined by an indirect method. First, the distribution of dose under the skin due to an uncontaminated beam of 60Co gamma-rays was determined using the Monte Carlo method without any major assumption. This distribution was then subtracted from the measured distribution of total dose available in the literature, to get the required dose distribution due to electron contamination. The distribution as determined in this work has been compared with that determined by some other workers, who relied on the dose distribution due to an uncontaminated beam calculated under some assumptions. It was found that the dose due to electron contamination was overestimated by them in the middle depths. This was as expected, because with their assumptions in the calculation of the dose distribution due to an uncontaminated beam, this dose is underestimated in the middle depths.