4DCT is long overdue for improvement

摘要

Technology innovation has always been one of the main drivers for the evolution of the radiation oncology field. New commercial devices are emerging at a fascinating speed, that is, Magnetic Resonance Imaging (MRI)-based linac, Positron Emission Tomography (PET)-based linac, FLASH ultra-high dose rate delivery, ring gantry with double stacked multi-leaf collimators (MLC), etc. Meanwhile, technology that has already been widely adopted and used for many patients seems to have stagnated. 4DCT was first introduced in 2003, exactly 20 years ago,1 aiming to reconstruct “dynamic volumetric imaging” or “respiration-correlated CT”. It adds a temporal dimension to the traditional 3DCT and provides visualization of target motion. Subsequent clinical trials for anatomy sites pertaining to moving targets imposed a vastly reduced planning target margin using 4DCT.2, 3 The entire field has benefited from the addition of this technology, with informed knowledge of its limitations, that is, motion uncertainties and image artifacts resulted from the irregularity of patients' breathing patterns. From a clinical physicist's point of view, 20 years have gone by, and the developments on 4DCT seem to be mostly on paper, with minimum to none being incubated to mature commercial products. We cannot help but wonder should we call for vendors' attention to devote resources in innovating 4DCT technology since it is long overdue for commercial developments, or should we be made aware that incremental developments have been trialed out, but fundamental limitations of 4DCT are hard to be overcome? We are now passing these questions to two experienced physicists with expertise in motion management and 4DCT. Dr. Erik Tryggestad argues for the proposition that “4DCT is long overdue for improvement” while Dr. Heng Li argues against it. Dr. Erik Tryggestad is an Associate Professor and Consultant of Medical Physics in the Department of Radiation Oncology at Mayo Clinic, Rochester (MN), having recently marked 10 years working at Mayo's Proton Beam Therapy Center. Prior to his faculty positions at Mayo, he was an Assistant Professor at Johns Hopkins University in the Department of Radiation Oncology. Dr. Tryggestad earned his PhD in experimental nuclear physics from Michigan State University's National Superconducting Cyclotron Laboratory in 2001 and ultimately transitioned to medical physics as a post-doctoral research fellow at the end of 2004 at Johns Hopkins University. Dr. Tryggestad works in the clinic covering proton therapy and Gamma Knife radiosurgical procedures. His research and translational interests include motion management, image guidance, and aspects of radiotherapy workflow automation (especially AI-based autosegmentation). Dr. Tryggestad has contributed to over 75 peer-reviewed publications in scientific journals. Dr. Heng Li is an Associate Professor in the Department of Radiation Oncology and Molecular Radiation Sciences at Johns Hopkins University and is a fellow of the American Association of Physicists in Medicine. He serves as the Chief Proton Physicist of the Johns Hopkins Proton Therapy Center, located at the Sibley Memorial Hospital, Washington DC. He completed his PhD in Electrical and Computer Engineering at the University of Virginia, Charlottesville, VA in 2006, and received postdoctoral fellowship and therapeutic medical physics residency training at the University of Texas MD Anderson Cancer Center. His research interests include proton therapy physics, motion management in radiotherapy, global health, and AI application in radiation oncology. He has published over 70 scientific papers in peer-reviewed academic journals and authored 9 book chapters. I entered the field at the tail end of 2004, taken under the wing as a post-doctoral fellow by one of our most impactful image-guided radiotherapy (IGRT) innovators, Dr. John W. Wong (FAAPM, Quimby Awardee), just as 4DCT was being translated clinically. Synergistically (no pun intende