One of the sessions at this year’s Society of Interventional Oncology (SIO) meeting (24–28 March, San Francisco, USA) comprised four debates moderated by David Breen (University Hospital Southampton, Southampton, UK) and William Rilling (Medical College of Wisconsin, Milwaukee, USA). One of the key takeaways from the session was that radiation oncology has seen much innovation, and that this must continue in order to provide the best outcomes for patients into the future. Another was that “response assessment [can be] challenging”.
Peripheral colorectal lung metastases: SBRT vs. ablation
Abraham Wu (Memorial Sloan Kettering Cancer Center, New York, USA) and Thierry de Baere (Institut Gustav Roussy, Villejuif, France) took to the podium in turn—Wu as a proponent of stereotactic body radiation therapy (SBRT), and de Baere of thermal ablation, as a means of treating peripheral colorectal lung metastases.
“SBRT has really ushered in a revolution in radiation oncology.” Wu began his side of the argument by dubbing SBRT a “new standard for early-stage inoperable lung cancer”, citing the therapy as particularly successful in metastatic tumours.
Wu proceeded to highlight the non-invasive benefit of SBRT—there is “no cutting, needles, pain, nor a need for anaesthesia.” Furthermore, there are no medical contraindications, with patients free to continue on anticoagulant drugs alongside receiving SBRT. The toxicity profile, Wu assured, is also “favourable”, with “essentially no mortality risk” associated with using the therapy to treat peripheral lesions, including when treating multiple lesions, and retreating the same one.
It is also easily adaptable to large tumour sizes, and complicated tumour shapes and locations, Wu emphasised. The convenience of the therapy is also a draw when it comes to SBRT, now that it is available relatively widely in “most modern radiation facilities”.
Wu’s bottom line is that “high-level control is achievable with a sufficient dose”, which is safe for peripheral lesions. He contended that “SBRT is the preferred treatment” for peripheral colorectal lung metastases, stating that there is a larger and longer-term evidence base when compared to ablation.
De Baere began his counterargument by explaining that he “fully [agreed] with the previous speaker in that what matters is local tumour control”. However, defining local tumour control is another matter entirely. He argued that ablation sees total control in the longer term, when compared to SBRT, which, de Baere suggested “puts some smoke around the tumour”, then making it difficult to have local response criteria. Where it may be tempting to look at imaging for two years post-SBRT and declare a complete response, he underlined the need to “look past two years”, and once one does that, in the case of SBRT, he believes that it is “always the same story”—the tumour is still growing, just very slowly.
One can get a more reliable picture of the ongoing success of treating via ablation, de Baere highlighted, as it can be obtained with pathology, as opposed to the imaging that indicates in SBRT cases whether it is working.
De Baere brought nuance to his side of the debate, acknowledging that different types of cancer, for example, primary vs. metastatic, warranted different treatment approaches. Likewise, the observed success of a particular approach depends on the dosage given. It is perfectly possible, de Baere admitted, that a tumour can continue to grow after ablation, if you “mistarget with cryotherapy” or give “too low a dose”. However, he maintained that while SBRT may seem low-toxicity in the short term, in the middle or long term, “it is a different story” and one starts to see a decrease in lung function.
Given the opportunity to answer his opponent’s comment, Wu thanked de Baere for a “strong and thoughtful response”, agreeing that “response assessment with SBRT is challenging” and that it is a “limitation” of the treatment when compared to other modalities. Wu went on to outline that administering a sufficient radiation dose can resolve the issues with SBRT that de Baere pointed to, but, given his chance for rebuttal, de Baere doubled down on his preference for ablation—that a high enough dose may well “kill the tumour [with SBRT], but maybe you will also kill the patient or the lung.”