Which organization is recognized as the oldest professional radiation organization established in 1920?

The American Society of Radiologic Technologists (ASRT) is recognized as the oldest professional organization in the field of radiation, having been established in 1920. Its founding was pivotal in promoting the advancement of radiologic technology and ensuring high standards of practice in the profession. The ASRT provides continuing education, professional development resources, and advocates for the interests of radiologic technologists, which has contributed to its longevity and influence in the field. It serves as a central hub for the community of professionals, facilitating networking and sharing best practices among its members. The ASRT's extensive history underscores its commitment to enhancing the profession and supporting the workforce in radiologic sciences.

In contrast, the other organizations listed were established later and serve different, though related, roles within the healthcare and education sectors. Thus, the ASRT’s historical significance and foundational role in radiologic technology distinguish it as the correct answer.