What is a key consideration when verifying the location of the PTV during treatment planning?

When verifying the location of the Planning Target Volume (PTV) during treatment planning, the proximity to external landmarks is critical because it provides practical and reliable reference points for accurate positioning during treatment delivery. External landmarks help the treatment team ensure that the patient is correctly aligned for each session, thereby maintaining the precision of the radiation treatment.

Using external references, such as tattoos or marks on the skin that correspond with imaging taken during planning, is essential. It allows for reproducibility in patient setup and helps to ensure that the radiation beams are directed at the target area consistently throughout the treatment course. This is especially important, as even slight deviations can affect the dose distribution and potentially compromise treatment efficacy or increase the risk of side effects.

In contrast, while the relationship of the PTV to Organs At Risk (OARs) is indeed crucial for protecting healthy tissues, this consideration is secondary to ensuring that the treatment is delivered to the correct anatomical location. Comparing the size of the PTV to critical organs or considering its histological type are important in the overall treatment planning process but do not serve as primary factors for verifying positioning during treatment sessions.