The Potential of Photoacoustic Imaging in Radiation Oncology

Abstract

Radiotherapy is recognized globally as a mainstay of treatment in most solid tumors and is essential in both curative and palliative settings. Ionizing radiation is frequently combined with surgery, either preoperatively or postoperatively, and with systemic chemotherapy. Recent advances in imaging have enabled precise targeting of solid lesions yet substantial intratumoral heterogeneity means that treatment planning and monitoring remains a clinical challenge as therapy response can take weeks to manifest on conventional imaging and early indications of progression can be misleading. Photoacoustic imaging (PAI) is an emerging modality for molecular imaging of cancer, enabling non-invasive assessment of endogenous tissue chromophores with optical contrast at unprecedented spatio-temporal resolution. Preclinical studies in mouse models have shown that PAI could be used to assess response to radiotherapy and chemoradiotherapy based on changes in the tumor vascular architecture and blood oxygen saturation, which are closely linked to tumor hypoxia. Given the strong relationship between hypoxia and radio-resistance, PAI assessment of the tumor microenvironment has the potential to be applied longitudinally during radiotherapy to detect resistance at much earlier time-points than currently achieved by size measurements and tailor treatments based on tumor oxygen availability and vascular heterogeneity. Here, we review the current state-of-the-art in PAI in the context of radiotherapy research. Based on these studies, we identify promising applications of PAI in radiation oncology and discuss the future potential and outstanding challenges in the development of translational PAI biomarkers of early response to radiotherapy.

3D Ultrasound-Guided Photoacoustic Imaging to Monitor the Effects of Suboptimal Tyrosine Kinase Inhibitor Therapy in Pancreatic Tumors

“…Both oxygenated and deoxygenated Hb exhibit a molar extinction coefficient that is at least one order of magnitude greater than other common chromophores such as lipids at wavelengths between 650 and 900 nm, and spectral unmixing of photoacoustic measurements made with at least two wavelengths within this wavelength range can quantitatively approximate StO 2 values ( 28 ). PAI has the potential to be a scalable tool to enable patient stratification and monitor therapy response ( 29 ). Given the wide utility of ultrasound (US) in clinical imaging of pancreatic tumors, we believe that ultrasound-guided photoacoustic imaging (US-PAI) can simultaneously provide structural (tumor volume and shape) and functional (vascular StO 2 ) information of pancreatic tumors ( 28 , 30 , 31 ).…”

Nanoprobe-based molecular imaging for tumor stratification

“…151 Higher oxygen saturation (sO 2 ) could predict tumor response to single-dose radiotherapy, and the sensitivity and early treatment response of some PAI-based radiotherapy were under clinical evaluation (NCT04428515, NCT04110249, and NCT04437030). 152 3.2.2. ÁOH.…”

Proton pump inhibitors display anti‐tumour potential in glioma

“…Hypoxia always happens in late‐stage tumours. Hypoxic tumours are found to be highly aggressive and resistant to chemoradiotherapy because hypoxic tumours require triple the normal radiation dose to achieve the desirable cell death effect as a normal irradiating dose which means that hypoxia is also a key factor in determining the growth of tumour‐induced by MDR 87,88 . Previous studies have revealed that oxygenation in glioma is 10 mmHg compared with normal brain tissue which is 40 mmHg and which may arise from radiation resistance.…”