Which of the following can lead to irradiation of a volume other than the CTV during treatment?

Irradiation of a volume other than the Clinical Target Volume (CTV) can occur due to patient movement during treatment. When a patient shifts or moves, even slightly, it can alter the position of the tumor relative to the planned radiation beam. This means that the radiation may end up affecting surrounding healthy tissues or organs instead of solely targeting the intended CTV. The precision required in radiation therapy is critical, as even minimal deviations in patient positioning can compromise the treatment's effectiveness and increase the risk of side effects.

In contrast, consistent treatment setup, proper internal organ alignment, and the use of the same isocenter are practices that help ensure accurate targeting of the CTV. A consistent treatment setup and effective alignment techniques are designed specifically to maintain the desired positioning of the patient and target volume throughout the course of treatment. Using the same isocenter helps create a fixed reference point for radiation delivery, thereby improving treatment accuracy and minimizing the potential for irradiating unwanted areas.