Dosimetry Formalism and Implementation of a Homogenous Irradiation Protocol to Improve the Accuracy of Small Animal Whole-Body Irradiation Using a 137Cs Irradiator

Abstract

Shielded 137Cs irradiators are routinely used in pre-clinical radiation research to perform in vitro or in vivo investigations. Without appropriate dosimetry and irradiation protocols in place, there can be large uncertainty in the delivered dose of radiation between irradiated subjects that could lead to inaccurate and possibly misleading results. Here, a dosimetric evaluation of the JL Shepard Mark I-68A 137Cs irradiator and an irradiation technique for whole-body irradiation of small animals that allows one to limit the between subject variation in delivered dose to ±3% are provided. Mathematical simulation techniques and Gafchromic EBT film were used to describe the region within the irradiation cavity with homogeneous dose distribution (100% ±5%), the dosimetric impact of varying source-to-subject distance, and the variation in attenuation thickness due to turntable rotation. Furthermore, an irradiation protocol and dosimetry formalism that allows calculation of irradiation time for whole-body irradiation of small animals is proposed, that is designed to ensure a more consistent dose delivery between irradiated subjects. To compare this protocol with the conventional irradiation protocol suggested by the vendor, high-resolution film dosimetry measurements evaluating the dose difference between irradiation subjects and the dose distribution throughout subjects was performed, using phantoms resembling small animals. Based on these results, there can be considerable variation in the delivered dose of > ±5% using the conventional irradiation protocol for whole-body irradiation doses below 5 Gy. Using the proposed irradiation protocol this variability can be reduced to within ±3% and the dosimetry formalism allows for more accurate calculation of the irradiation time in relation to the intended prescription dose.

Study logistics that can impact medical countermeasure efficacy testing in mouse models of radiation injury

“…Beyond the actual setup, other confounders that should be considered are: (1) whether the animals are exposed to radiation from a c source in a unilateral, simultaneous bilateral or sequential bilateral configuration, and (2) whether a rotating table is used, since rotational devices have been shown to maintain a more accurate and consistent dose distribution by helping to minimize radiation hotspots in the radiation field ( Brady et al 2012 ; Brodin et al 2016 ).…”

Comparison and calibration of dose delivered by 137Cs and x-ray irradiators in mice

“…Irradiators 2.1.1. 137 Cs irradiator (Mark I-68) The Mark I-68 (JL Shepherd and Associates, San Fernando, CA) (figure 1) is a gamma irradiation device used in many institutions primarily for biomedical research, including small-animal studies (Brady et al 2009, Brodin et al 2016, as well as for blood sterilization to avoid fatal complications during transfusions (Kitchen et al 1989). It is a self-shielded unit with an interior cavity that contains a rotating turntable, the cylindrical source guide, and an active source cylinder unit that may be translated into the source guide to deliver a radiation dose to the cavity and its contents.…”

BAIRDA: a novel in vitro setup to quantify radiobiological parameters for cervical cancer brachytherapy dose estimations

“…We therefore performed experiments using a Cs-137 commercial irradiator (JL Shepherd and Associates, San Fernando, CA), to enable comparison to the dose responses observed using Ir-192 sources in clinical BT afterloaders. The Cs-137 irradiator's sources (source activity of 1089 Ci at the time of experiments) are pneumatically raised into position in a shaft, covered with a brass filter, at the back of the irradiation chamber (Brodin et al 2016). Over the period of the study, the dose rate at the center of the irradiator was 0.74-0.77 Gy min −1 .…”