# Incorporating Clinical Imaging into the Delivery of Microbeam Radiation Therapy  
[PERSON]  
1 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; [EMAIL_ADDRESS]  
[PERSON]  
1 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; [EMAIL_ADDRESS]  
[PERSON]  
1 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; [EMAIL_ADDRESS]  
[PERSON]  
1 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; [EMAIL_ADDRESS]  
[PERSON]  
1 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; [EMAIL_ADDRESS]  
[PERSON]  
5 [EMAIL_ADDRESS]  
[PERSON]  
the high dose rate that comes with synchrotron MRT [12; 13]. The instantaneous dose rate within each microbeam can exceed 5000 Gy s\({}^{-1}\), posing additional challenges in dosimetric characterisation and real-time imaging [14; 15; 16; 17]. Together with knowing the radiation dose delivered, it is equally important to know where the dose is being deposited. Thus, it is necessary to validate the position of a patient's internal anatomy in relation to the radiation beam. A robust patient positioning process must be accurate, repeatable and deliver minimal additional dose [18]. In a clinical context, external beam radiotherapy employs an image-guided patient positioning technique that relies on high-resolution pre-treatment imaging (for accurate identification of tumours) and imaging at the time of treatment to ascertain the position of those tumours relative to the treatment beam. Previous small animal MRT studies (involving patients without tumours) have aligned patients manually [19], using optical cameras based on external anatomy [20], or using the modified synchrotron beam to find anatomical structures [21; 22]. Other MRT studies involving tumour-bearing rats have used visual targeting relative to the midsagittal plane [8] and using X-ray fluorescent radiography relating anatomical markers to the known location of tumour inoculation [5]. MRI imaging provides clearly distinguishable tumour volumes, although its use in image guidance tasks for synchrotron generated MRT is yet to be demonstrated. MRI imaging has been utilized in MRT studies where radiosensitizing nanoparticles are employed, particularly to optimise the timing between the injection of radiosensitizing agents and the treatment delivery to maximise patient survival [23]. MRI imaging has also been used after MRT irradiation to monitor tumour growth [21; 24]. However, to date, no small animal study has employed MRI imaging for image guidance in synchrotron delivered radiotherapy. Much progress has been made on the ID17 biomedical beamline of the European Synchrotron Radiation Facility. Studies here have provided great insight into tumour vessel response using MRI before and after MRT. However, this study did not use the MRI for patient alignment, instead aligning patients using optical cameras with all patients targeted equidistant from their mediolateral line as identified by external anatomy [3; 25]. The ID17 beamline also presented the first protocol for precise patient alignment for use with larger animals, using fiducial markers to align CT images with X-ray projection images acquired on the treatment stage, demonstrating target alignment error of <=2 mm [26] and has been used for alignment in more recent studies [27]. Further work on this beamline introduced a new method for contrast-enhanced tumour tomography using a modified wiggler field as described by [PERSON], 2010 [21] was used in developing a protocol for the alignment of small animals [28]. Reconstructed tomographic images produced a 10 mm vertical volume clearly showing the location of the tumour, allowing for tumour identification and alignment on the treatment stage. More recently, SyncMRT, an image guidance program, developed for synchrotron radiotherapy, was demonstrated on IMBL [29].