Room: Exhibit Hall
Purpose: Electron beams from clinical linear accelerator (linac) can potentially offer a higher dose rate than photon beams by several orders of magnitude, which could be used in many pre-clinical studies that require ultra-high dose rate. We investigate the feasibility of utilizing small multileaf-collimator (MLC)-defined fields generated by a linac for pre-clinical irradiation.
Methods: 18MeV electron beams were modeled in EGSnrc for a 2100 Varian Clinac and validated through water tank measurements for a 30x30cmÂ² MLC and jaw defined field. Dosimetry was investigated for square fields defined by a single or double leaf-pairs at a source-to-surface distances (SSD) ranging from 59-69cm. Simulated results were compared to film measurements at an SSD of 60cm for a 3x3 and 6x6mmÂ² field. Finally, a 360Â° arc treatment was simulated on a mouse phantom using a source-to-axis distance of 67cm and a 3.3x3.3mmÂ² field.
Results: The simulated small field depth dose profiles diverge from the typical electron beam and share a closer profile to a kilovoltage photon beam. Specifically, maximum dose (dmax) occurs within the first several millimeters, with 80% and 50% of the maximum dose occurring at approximately 15 and 25mm for a 6x6mmÂ² field at SSD 60cm. These depths shift towards the surface approximately 5mm for the 3x3mmÂ² field. Little variation in depth dose was observed when increasing the SSD, with slight increase in the low dose fall-off for increasing SSD. The simulated arc treatment was compact with d80% and d50% covers a sphere with radius of approximately 4 and 8mm, respectively.
Conclusion: Preliminary work has shown that the combination of small field high energy electron beams and reduced SSD is well suited for pre-clinical applications with shallow dmax and sufficient fall-off to target centrally located legions. Future work will involve development of a pre-clinical system and further investigation of dosimetric characteristics.