Final answer:
Using a grid is part of precision techniques to concentrate radiation on a tumor and minimize exposure to surrounding tissue, but devices like collimators and shielding more directly reduce extrafocal radiation.
Step-by-step explanation:
The use of a grid in external beam radiotherapy does not directly reduce extrafocal radiation itself, but it is part of a broader set of techniques used to focus radiation therapy on well-defined tumors. A geometric technique involves rotating a radiation source such as 60Co y-radiation around the patient such that the common crossing point is within the tumor, thus concentrating the dose there. High precision in targeting radiation maximizes the therapeutic ratio by delivering a higher dose to the tumor while minimizing exposure to surrounding healthy tissue. Shielding also plays a critical role in protecting other areas from stray radiation, and collimation helps to narrow the beam of radiation to further reduce unwanted exposure.
Nevertheless, when discussing the reduction of extrafocal or scatter radiation, using devices like collimators and shielding are more directly associated with such reduction. Collimators can improve the beam's focus and reduce the volume of tissue exposed to unnecessary radiation. Shielding, whether from materials or distance, is essential for absorbing radiation and protecting other areas apart from the target site.