Isodose curve mappings measured while undergoing rotation for quality assurance testing of a 137Cs irradiator.

To enable accurate and reproducible dosimetry for biological sample irradiation in a 137Cs irradiator, routine quality assurance of the dose rate and isodose distributions should be considered. Our previous work demonstrated a means for accurate dose rate quality assurance and for quality assurance of isodose distributions of non-rotational samples. This work presents a means to accurately and cost effectively measure dose distributions within a 137Cs irradiator using rotational geometry, which geometry represent a more typical use of these irradiators. A simple apparatus was developed to hold radiochromic film and was constructed of polymethyl methacrylate. The rotational quality assurance device allowed the comparison of measured radiochromic film vs. manufacturer provided isodose distributions. A good agreement was discovered between the two data sets along the central vertical axis of rotation in the 137Cs irradiator, but a 40-50% smaller 100% isodose region in the horizontal direction. These findings may lead to limiting the overall size of a sample capable of being uniformly irradiated by the 137Cs irradiator at this research institution. The authors propose the construction and use of a simple rotational quality assurance device for routine quality assurance of 137Cs irradiators.