Adaptation of a small animal radiation research platform for pre-clinical microbeam irradiations

Microbeam radiotherapy (MRT) was introduced as a method to widen the therapeutic window compared to standard radiotherapy treatments. Studies have shown the normal tissue sparing effects of MRT, whilst maintaining the tumor control of standard broad beam radiotherapy.

To create and test a microbeam (MB) delivery system compatible with a small animal radiation research platform (SARRP, Xstrahl), which would allow the machine to be easily adapted to deliver MB irradiations without making any permanent changes to the system.

A MB collimator was designed, that fits in with the existing SARRP infrastructure and can easily be removed to revert the machine back to a normal broad beam delivery system. A translatable mousebed was developed to reduce the source-to-surface distance (SSD) for MB delivery, allowing the target position to be moved between imaging and treatment. Gafchromic film was used to test the accuracy of the positioning, and to determine the dose rates achievable in a solid water phantom.

At 1 mm depth in solid water, a peak-to-valley dose ratio (PVDR) of 46 was achieved when the target was placed directly under the collimator, whilst a PVDR of 29 was reached when a 10.5 mm air gap was introduced between the collimator and target. Integral dose rates at 1 mm depth for these setups were 0.93 ± 0.04 and 0.94 ± 0.01 Gy/min, respectively. Conversion between broad beam and microbeam setup was found to take less than 5 min.

Our adaptations enable any SARRP machine to be converted into a MB delivery system, with feasibility studies confirming MB delivery in a solid water phantom. The system is now routinely used to deliver MBs for in vivo studies.