Editor’s Picks: Highlight Radiotherapy Physics Paper
Interview with the co-author, Andreas Smolders
What was your motivation for initiating this study?
When I started my PhD, I was surprised to learn how often imaging was used in adaptive therapy. When I asked about the risks, I was told that the imaging dose was much lower than the therapeutic dose. This is indeed true, and I put the issue aside. However, 1.5 years later, during a meeting with several stakeholders from the clinic, the issue of imaging dose was brought up again. On the one hand, I was happy to hear that I was not alone in my concern. On the other hand, I also wanted to convince people to use adaptive therapy in the clinic. I decided, therefore, to analyse it more rigorously, hoping to provide solid proof that online adaptation could be performed safely.
What were the main challenges during the work?
The main challenge was the accurate simulation of the imaging dose. The calculation of secondary cancer risk in our work required voxel-wise doses. While therapy doses could be easily obtained from the treatment planning system, no model or prior experience existed at our institute to simulate imaging doses. Therefore, I had to start from scratch, without the help of anybody with the necessary experience to confirm that I was on the right track. In the end, the Monte Carlo simulations we used were not overly complicated, but navigating the process without certainty was a significant challenge.
What is the most important finding of your study?
We found that, for most patients, a 1mm reduction in the set-up margin compensated for the additional secondary cancer risk that was introduced by the performance of daily cone beam CT or direct CT imaging. This finding applies to patients with head-and-neck cancer, and in follow-up work, we will investigate a larger and broader patient cohort.
What are the implications of this research?
Although there is no consensus yet on the set-up margin for adaptive proton therapy, most sources in the literature confirm that a 1mm reduction compared with conventional therapy for head-and-neck cancer is feasible. This suggests that the secondary cancer risk during the application of adaptive therapy will actually be lower than that caused by conventional radiotherapy, and this adds to other, better-established benefits. Our work therefore disproves one of the main arguments against the use of online adaptation, and we hope it will convince people to introduce the use of online adaptation in their clinics.
Andreas Smolders
Centre for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland
Department of Physics, ETH Zurich, Zurich, Switzerland
Andreas.smolders@psi.ch
Reference
Smolders, A., Czerska, K., Celicanin, Z., Lomax, A., & Albertini, F. (2024). The influence of daily imaging and target margin reduction on secondary cancer risk in image-guided and adaptive proton therapy. Physics in Medicine & Biology, 69(22), 225004.
URL: https://iopscience.iop.org/article/10.1088/1361-6560/ad8da3