Table 3.

Potential imaging biomarkers of treatment response to be acquired using an MR Linac.

Candidate imaging biomarkers	Candidate imaging metric	Tumours site with diagnostic significance	Example clinical series showing clinical significance of imaging changes during radiation therapy
Diffusion-weighted imaging [53]	ADC	Primary brain Rectal adenocarcinoma Head and Neck Pancreatic adenocarcinoma Cervical Prostate Liver	Rectal adenocarcinoma [54,55] High-grade glioma [56] Pancreatic adenocarcinoma [57] Cervical cancer [58] Prostate [59] Liver [60]
IVIM [61]	Perfusion fraction Dslow Dfast	Primary brain Rectal adenocarcinoma Head and neck Pancreatic adenocarcinoma Cervical Prostate Liver Oesophageal	Rectal cancer [62] Head and neck [63,64] Cervical cancer [65,66] Bone metastases [67] Oesophageal [68]
DCE-MRI [69],a	KTrans ve vp Blood flow IAUC	Primary brain Secondary brain Bone metastases Rectal adenocarcinoma Head and neck Pancreatic adenocarcinoma Cervical cancer Prostate Pancreatic adenocarcinoma	Head and neck [70] Prostate [71] Secondary brain tumours [72] High-grade glioma [73] Liver [74]
Relaxometry [75]	T1 map T2 map BOLD	Primary brain Secondary brain Pancreatic adenocarcinoma	N/A
CEST [76]	Metabolite maps	Primary brain Secondary brain	High-grade glioma [77–79]

IVIM, intravoxel incoherent motion; MRI, magnetic resonance imaging; DCE, dynamic contrast-enhanced; CEST, chemical exchange saturation transfer; ADC, apparent diffusion coefficient; BOLD, blood oxygen level dependent; IAUC, initial area under the curve.

^aLimited by the need for exogenous contrast agents.