What is true about the primary dose in a patient when part of the beam is blocked?

When part of the beam is blocked, the primary dose in the region that remains unblocked stays nearly the same because the primary radiation, which is the initial beam that comes directly from the radiation source, is not altered in intensity by the blockage.

In the unblocked area, the primary dose reflects the intensity of the radiation as it was originally delivered from the source, as only the section of the beam that is obstructed is affected by the blockage. This means that the dose distribution in the regions that receive direct exposure remains consistent, assuming that other factors, such as tissue density and positioning of the patient, are constant.

Moreover, any variations in dose predominantly occur in the blocked regions where the radiation does not penetrate. Therefore, while the dose may be affected in the areas that are blocked, it does not significantly change in areas that continue to receive the direct beam, underscoring the correctness of the assertion that the primary dose remains almost the same under the unblocked region.