Welcome Physics World  July 2021

Technologies team up for clinical benefit

Welcome to this Physics World Medical Physics Briefing, which showcases the latest innovations in radiation treatment techniques and biomedical imaging modalities. But as the field of medical physics continues to evolve, these areas are becoming less and less distinct, with many recent developments bringing together diverse technologies for the benefit of the patient. 

The ability to visualize the tumour and surrounding healthy tissues during radiotherapy helps to ensure highly targeted cancer treatments with minimal collateral damage. MRI is ideal for this task, and has been integrated into commercial photon-based radiotherapy systems. But operating an MRI scanner in a proton beam was long considered impossible. Now, having demonstrated that it is technically feasible to combine the two and that interference effects can be compensated for, a team at OncoRay in Dresden is planning to build the world’s first whole-body proton therapy system that can track moving tumours with MRI during actively scanned proton therapy (‘One step closer to real-time MRI in proton therapy’). 

As well as imaging the patient during radiotherapy, it’s also possible to image the treatment beam itself. Researchers in the US are using the Cherenkov light generated within irradiated tissues to visualize the shape of the treatment beam on the skin’s surface (‘Visualizing the beam enhances radiotherapy delivery’). These Cherenkov images can be overlaid on the patient in real time, providing surrogate maps of surface dose that can be used to visually verify the beam delivery and patient positioning throughout each treatment fraction.

In the field of nuclear medicine, meanwhile, a team headed up at TU Delft in the Netherlands is combining prompt gamma imaging with positron emission tomography (PET) to enable sub-millimetre-resolution preclinical PET (‘Prompt gammas allow high-resolution multi-tracer PET’). The idea is to use the prompt gamma photons emitted by many of the radioisotopes used as PET tracers to increase the image resolution. What’s more, while all PET isotopes create annihilation photons with equal energy, making it tricky to image more than one tracer at a time, the prompt gammas that they emit have different energies, paving the way towards multi-tracer PET imaging.

Researchers are also investigating novel combinations of emerging therapeutic techniques. In a case study led by Benhua Xu at Fujian Medical University Union Hospital in China, a patient with advanced lung cancer and multiple metastases was treated with LATTICE radiotherapy, a spatially fractionated method, and immunotherapy (‘LATTICE radiotherapy teams up with immunotherapy’). This dual approach dramatically shrank a large metastatic mass in one month, with a complete local response within five months. The effectiveness of this combined treatment led to the development of further clinical studies.