In vivo Dosimeter Array for Accurate Irradiation of Preclinical Models
Abstract
Purpose
Preclinical studies with small animals require precise control to yield conclusive results. Small animal irradiations differ from clinical irradiations and can push dose calculation algorithm to their limits: small volumes, small fields, superficial treatments. In vivo dosimetry can ascertain dose calculation and delivery accuracy, but a single measurement point can’t detect all problems, especially in high gradients. Our purpose is thus to control preclinical irradiation accuracy with an unobtrusive detector array.
Methods
A base plan of two parallel opposed tangent beams was made using a clinical treatment planning system (TPS; Varian Eclipse) with the goal of delivering 45 Gy to the skin of a murine model with 6 MV beams and 15 mm square fields. The animals were placed in a cylindrical water-equivalent holder that acted as buildup material. An array of 4 plastic scintillation dosimeters (PSD) from Medscint was embedded in that holder, above the skin. Online measurements were performed at 1 Hz. Twelve animals were treated then images with CBCT was acquired. The base plan was copied onto each CBCT and dose to the skin and to the location of each PSD was calculated.
Results
PSD array reproducibility was tested with the holder filled with a homogeneous phantom. The reproducibility for each PSD was 0.2% and the day-to-day variability was 0.9% on average for 500 cGy. Measurements were consistent between animals for 3 of the 4 PSDs with variations within 3.7%. The fourth PSD was positioned near the edge of the fields and exhibited larger variability (22%). Compared to TPS, measurements were systematically lower by 9% which is due to challenging dose calculation conditions.
Conclusion
In vivo measurements with a PSD array represent a stable and reproducible method for validating the accuracy of dose delivery to preclinical models in challenging irradiation conditions.