Commissioning and performance characteristics of a pre-clinical image-guided radiotherapy system

Abstract

Characteristics of a small-animal radiotherapy device, the X-RAD SmART, are described following commissioning of the device for pre-clinical radiotherapy research. Performance characteristics were assessed using published standards and compared with previous results published for similar systems. Operational radiation safety was established. Device X-ray beam quality and output dose-rate were found to be consistent with those reported for similar devices. Output steadily declined over 18 months though remained within tolerance levels. There is considerable variation in output factor across the international installations for the smallest field size (varying by more than 30% for 2.5 mm diameter fields). Measured depth dose and profile data was mostly consistent with that published, with some differences in penumbrae and generally reduced flatness. Target localisation is achieved with an imaging panel and with automatic corrections for panel flex and device mechanical instability, targeting within 0.2 mm is achievable. The small-animal image-guided radiotherapy platform has been implemented and assessed and found to perform as specified. The combination of kV energy and high spatial precision make it suitable for replicating clinical dose distributions at the small-animal scale, though dosimetric uncertainties for the narrowest fields need to be acknowledged.

Keywords: Commissioning; Dose delivery; Image guidance; Pre-clinical; Small animal radiotherapy.

Fig. 1

X-RAD device components

Fig. 2

The location of the 11 survey points investigated during radiation safety survey. Point 11 remained aligned with the X-ray tube cathode–anode axis (gantry angle indicated)

Fig. 3

Output constancy with time at 225 kV, 13 mA. Error bars represent an estimated combined (baseline and constancy measurement) uncertainty of ± 1%

Fig. 4

Linearity curve: charge versus beam-on time for multiple beam currents

Fig. 5

PDD data points for a range of field sizes, measured with EBT3 film

Fig. 6

Relative output factors (measured, calculated and from the literature)

Fig. 7

Effective offset of the source from isocentre in the x and y plane

Fig. 8

a Flex map in the u-axis (orthogonal to the axis of rotation). b Flex map in the v-axis (parallel to the axis of rotation of the system)

Fig. 9

(Left) Projected point against gantry angle with stage tracking off. (Right) Projected point against gantry angle with stage tracking turned on