Navigating Proton and Photon Techniques for Locoregional Recurrence

Management of locoregional recurrence presents one of the most complex challenges in radiation oncology, requiring a delicate balance between therapeutic efficacy and the preservation of previously irradiated healthy tissue. During the 2026 American College of Radiation Oncology (ACRO) Summit, J. Isabelle Choi, MD, associate attending radiation oncologist at Memorial Sloan Kettering Cancer Center, discussed the evolving landscape of reirradiation, highlighting how clinicians can achieve high-precision outcomes even in the absence of proton therapy.

While proton therapy remains a powerful tool for reducing integral dose to critical structures like the heart, lungs, and brachial plexus, Choi emphasized that advanced photon techniques—specifically intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT)—serve as robust alternatives. By leveraging these conformal modalities alongside rigorous image guidance and a comprehensive analysis of cumulative dose plans, clinicians can mitigate risks to organs at risk while targeting recurrent disease.

Central to this process is a standard for clinical target volume delineation. In the setting of distorted anatomy or bulky recurrence, Choi advocated for a multidisciplinary, data-driven approach. This involves integrating diagnostic PET, CT, and MRI scans from the time of initial presentation and collaborating closely with surgical oncologists and radiologists to map out microscopic disease and lymphatic drainage patterns.

Transcript:

For clinicians at centers without proton access, are there specific photon techniques that you believe can safely bridge the gap for locoregional recurrences?

Proton therapy can be helpful in reducing integral dose and reducing doses to some of the critical organs that are nearby, such as the heart, lungs, and sometimes that brachial plexus. Certainly, there are advanced photon techniques that we can also apply. Those include IMRT, intensity modulated radiation therapy; or VMAT, volumetric modulated arc therapy. Those are conformal techniques that [can] mitigate excess doses to those same organs at risk. Also, combining those techniques, along with robust image guidance and achieving a lot of precision there and looking at the cumulative dose plan between the first and second radiation courses in the setting of reirradiation is key to ensure that we are creating the optimal plan.

In the setting of advanced disease, where anatomy may be distorted by previous surgeries or bulky recurrence, what is your 'gold standard' for clinical target Volume delineation to ensure you aren't missing microscopic disease at the edges of the fields?

Whenever we are creating our radiation treatment volumes, we take into consideration any piece of information that we have available. A lot of times, that will include using any diagnostic imaging that’s available, whether that’s a PET, CT, or MRI scan, especially at the time of presentation before any additional therapies are given, so that we understand the extent of the disease at the time of presentation. We should be working closely with our surgical oncologists and our radiologists to understand, from their expert point of views, where the areas are at risk for harboring residual disease if they’re after other therapies like surgery or systemic therapy. Then, [we are] also taking into consideration what we know about patterns of lymphatic drainage or spread of disease and ensuring that we’re encompassing all those areas in our training plan.