This manuscript describes a parameter modification to the Radcalc software model such that it would be able to provide a valid check to the predicted radiation doses from the Monte Carlo treatment planning system. Thus the polynomial correction model obtained provides a simple but robust and empirically sound correction to the Radcalc commercial software such that monitor unit calculations from the Monte Carlo TPS may by verified for post mastectomy chest wall irradiation cases. This provides the medical physicist confidence that any persistent differences should be investigated as possibly due to an actual systematic error unassociated with a failure of the predictive model.