University of Michigan researchers have developed what they say is a precise, three-dimensional imaging method that enables the real-time tracking of radiation treatment during cancer therapy, in turn allowing for safer and more effective treatment of cancer.
"Ionizing radiation acoustic imaging (iRAI) allows online monitoring of radiation's interactions with tissues during radiation therapy, providing real-time, adaptive feedback for cancer treatments," the researchers discussed in Nature Biotechnology (2023; https://doi.org/10.1038/s41587-022-01593-8).
As the authors noted, radiation therapy has been shown to improve the outcomes of patients with cancer and provide palliation of related symptoms, but successful RT hinges on the ability to administer the intended sufficient radiation dose to the tumor while sparing surrounding normal tissue. Achieving such a desired therapeutic ratio, or maximizing tumor control while minimizing toxicity, requires that the planned radiation dose is delivered accurately.
To aid radiation therapy's efficacy, advanced image-guided delivery technologies have been proposed and developed, the researchers pointed out, adding that technologies such as intensity-modulated radiation therapy and volumetric modulated arc radiation therapy can offset some of the limitations linked to 3D conformal radiation therapy.
"However, targeting of moving lesions remains challenging," the investigators wrote. "Several studies have highlighted discrepancies between planned and delivered [radiation therapy] and their impact on tumor control. These differences are exacerbated by setup errors [and] organ motion, as well as anatomical deformations, which may markedly alter the intended doses delivered to the target or adjacent normal tissues over the course of treatment."
The team of investigators described an iRAI volumetric imaging system that allows the mapping of 3D radiation dose distribution in a complex clinical radiotherapy. The method relies on a 2D matrix array transducer and a matching multi-channel preamplifier board, the authors wrote, noting that the feasibility of imaging temporal 3D dose accumulation was first validated in a tissue-mimicking phantom.
"Next, semiquantitative iRAI relative dose measurements were verified in vivo in a rabbit model," the research abstract explained. "Finally, real-time visualization of the 3D radiation dose delivered to a patient with liver metastases was accomplished with a clinical linear accelerator."
"These studies demonstrate the potential of iRAI to monitor and quantify the 3D radiation dose deposition during treatment, potentially improving radiotherapy treatment efficacy using real-time adaptive treatment," the researchers wrote. In contrast to other dose mapping methods, they added that iRAI is directly proportional to the radiation dose absorbed by the targeted tissue.
"To further develop iRAI and promote its clinical translation, in this study we demonstrate a clinically ready iRAI system for real-time volumetric imaging of radiation dose with high sensitivity and high spatial resolution," the authors noted. Using this imaging system, iRAI was successfully performed with a lard phantom, an in vivo rabbit model and patients with cancer undergoing radiotherapy on a clinical LINAC system. "This study realized 3D semiquantitative mapping of X-ray beam delivery deep into the body during cancer treatment."
The underlying hypothesis for this study was "that ultrasound sound waves generated due to irradiation interaction with the cancer targeted region can be used to reconstruct the deposited radiation dose map in real time with 2D matrix array transducers. Thus, this image-guidance technology is termed ionizing radiation acoustic imaging," said Issam El Naqa, PhD, Chair of Machine Learning at Moffitt Cancer Center, and a co-author of the study.
"The ability to localize where and when the radiation is being deposited in real-time by iRAI would allow quantifying the accuracy of the preplanned radiation delivery and potentially correct for any deviations," he continued. "Radiation is a double-edged sword; it can kill the cancer if targeted properly, but it can cause harm if misplaced and [delivered] to healthy organs instead. The iRAI technology can help mitigate this risk."
This research represents the first recorded visualization of a radiation deposition map in a living being and a cancer patient, El Naqa said.
"This ability to image radiation dose in real-time would allow to safeguard its implementation and would enable application of online adaptive radiotherapy technologies with feedback systems, as well as enabling safer implementation of risky but potentially better treatment. Radiation modalities such as ultra-high dose rate (FLASH) could improve treatment quality by reducing side effects if guided properly, as offered by the iRAI technology."
Mark McGraw is a contributing writer.