What adjustment should be made when radiographing an ankle in a dry plaster cast?

When radiographing an ankle in a dry plaster cast, it is essential to adjust the exposure factors to account for the increased density introduced by the cast material. In this situation, increasing the milliampere-seconds (mAs) by two times is appropriate. Dry plaster casts are denser than soft tissue and can absorb more of the X-ray beam.

By increasing the mAs, the amount of radiation produced is doubled, which enhances the overall exposure to ensure adequate penetration and detail in the final image. This adjustment compensates for the additional density of the cast material, allowing for clearer visualization of the ankle's structures despite the obstruction created by the cast.

Other options would not provide the necessary adjustments for the presence of the cast. Adjusting the kilovolt peak (kVp) down or maintaining the same factors would likely result in underexposure or insufficient detail in the radiographs, potentially leading to misinterpretation or missed pathologies.