Which scenario does NOT typically require a portfilm check?

In medical dosimetry, a portfilm check is used to verify the accuracy of treatment delivery by ensuring that the radiation is targeting the intended area effectively. The scenarios that typically require a portfilm check are ones where precision is critical due to the proximity of critical structures or the treatment area to the skin.

In the case of targeting structures distant from the treatment area, the need for a portfilm check is less critical. This is because the likelihood of errors in positioning or alignment affecting distant structures is inherently lower, as these areas are not as influenced by small shifts or changes in skin or patient positioning. Thus, the focus on ensuring precise treatment delivery using portfilm checks reduces significantly in such scenarios where critical structures are far removed from the treatment field.

In contrast, the other scenarios involve situations where shifts—whether through patient movement, changes in skin marks, or treatments specifically targeting areas near the skin surface—are more likely to impact treatment accuracy and require checks to safeguard against potential errors.