Final answer:
The field positioning light and the actual radiation field must match within 2% of the SID, which is vital for the precision of radiation therapy in targeting tumors.
Step-by-step explanation:
The field positioning light and the actual radiation field cannot vary by more than 2% of the SID. The field positioning light and the actual radiation field must match within 2% of the SID, which is vital for the precision of radiation therapy in targeting tumors.
This requirement is crucial for the accuracy of radiation therapy treatments, where precise targeting of the cancerous tissue is necessary to avoid damage to surrounding healthy tissues. Regulatory standards are in place to ensure that radiation therapy machines are properly calibrated and maintained to deliver treatment within these stringent tolerances.