Which of the following could lead to oxidation of tin in sestamibi?

The oxidation of tin in sestamibi primarily occurs due to exposure to moisture. Sestamibi, which contains tin as part of its chemical structure, is sensitive to environmental conditions. When tin comes in contact with moisture, it can lead to a chemical reaction that results in the formation of tin oxides, compromising the radiopharmaceutical's quality and efficacy.

Maintaining proper environmental conditions, including preventing moisture exposure, is crucial in the handling and storage of radiopharmaceuticals to ensure their stability and effectiveness. Excessive heating can also affect stability but doesn't specifically lead to the oxidation of tin in the same direct way that moisture does. Improper storage may lead to degradation, and inadequate shielding pertains more to protection from radiation rather than affecting chemical properties like oxidation. Thus, moisture exposure is the most relevant factor in this context.