I joined the Department of Physics and Astronomy at the University of Kentucky as a graduate student in the fall of 1993. I arrived there after a gap of about four years after my undergraduate studies. I graduated from the University of Bucharest, Romania, in 1989, the year of the great transformations in Eastern Europe that followed the fall of the Berlin Wall. Before that time, the very idea of studying abroad was an inaccessible dream for most people in my country because of the near complete interdiction to travel abroad imposed by the dictatorship. So, the simple fact that I found myself in Lexington, KY, USA, on a university campus to embark on Ph.D. studies, felt very special and almost miraculous to me. 

I had a broad interest in theoretical high-energy physics, but I was not really focused on a particular topic. After some exploration, I settled on a project in supersymmetry under the supervision of Professor Shapere. This work provided the first complete canonical derivation of the central charge and BPS equations of the low-energy effective action for N = 2 SU(2) Yang-Mills theory, based on the construction of the superalgebra generators and the evaluation of their anticommutators. In a famous 1994 paper, Seiberg and Witten stated the central charge formula, based on indirect arguments that satisfied particular cases. However, our complete derivation found that the formula for the central charge includes additional terms that depend on the core structure of charged solitons.

I left Lexington and moved to beautiful British Columbia, Canada, in 2000, while I was in the thesis writing phase, and I returned for my PhD defense the following year. Due to various circumstances, I made a rather abrupt move to the field of medical physics, so, in 2001, I joined the Department of Radiation Therapy at the British Columbia Cancer Agency. They operate six integrated cancer centers in the province. I started with a residency at the center in Victoria and then, in 2004, I joined the Vancouver cancer center, where I am a now a Senior Medical Physicist. As a teaching hospital, we are academically affiliated with the University of British Columbia (UBC), where I am an Adjunct Professor in the Department of Physics and Astronomy. In my UBC position, I supervised several PhD students and I teach the graduate level course in radiation physics and radiation dosimetry for medical applications. A situation where my past familiarity with quantum field theory comes in handy is when I present in class the modern derivation, in the QED framework, of the Klein-Nishina cross section for Compton scattering, which is the dominant interaction mode in the energy range of radiotherapy beams.

One of the main tasks of a medical physicist is to ensure the accuracy and precision of the dose distribution delivery by radiation to cancer patients. Among other aspects, this requires a dose calculation verification that has to be done entirely independently of the commercial treatment planning system. Since we cannot measure directly the energy deposited in a deep-seated tumor in a real patient, Monte Carlo simulations represent an essential tool to accomplish this independent verification. The major Monte Carlo codes used in radiotherapy are Geant4, MCNP, EGSnrc, and a few others derived from them. My work uses the EGSnrc code, to which I have made several contributions, and I am happy that these are now in the public domain, as part of the official distribution. 

One of these contributions is a new technique for Monte Carlo simulations of continuously variable beam configurations, with arbitrary degrees of freedom. This work introduced a much-needed ‘time dimension’ in the EGSnrc code, allowing the simulation to synchronize the motion of dynamic, beam-shaping, components in the treatment machine, the variable beam motion around the patient with different degrees of freedom, and the motion in the patient anatomy (such as breathing). I have also developed a new phase space format that ‘captures’ the particles exiting the patient in all directions during treatment, including their associated time variable. After suitable coordinate transformations, these particles can be used as input for a further downstream Monte Carlo simulation into a portal imaging detector that captures the radiation transmitted through the patient. By deploying such a portal imager during treatment and comparing its measured data with the Monte Carlo prediction, we obtain real-time evidence of the accuracy of beam delivery, which is analyzed in conjunction to the simulated patient dose distribution. 

Our fully automated, Monte Carlo based, patient-specific quality assurance system has attracted significant interest and is currently at various stages of implementation at other institutions in North America, Europe, Asia, and Australia. In conjunction with this, I had the opportunity to give dozens of invited talks and lectures in many places around the world, from Havana to Beijing, and from Melbourne to Tampere.

My two most recent papers were on Monte Carlo calculations of patient dose-rate distributions, which are relevant to the emerging and very promising field of ultra-high dose-rate irradiation (known as ‘FLASH’), and on inverse treatment planning for MR-linacs (radiotherapy machines that have an on-board MRI scanner, allowing visualization of the anatomy in real time and therefore the possibility of adaptive treatment).

In addition to my Monte Carlo work, I have served for many years as the lead physicist of the Total Body Irradiation Program, which supports the Bone Marrow Transplant Program of British Columbia. My other area of clinical expertise is in pediatric cranio-spinal irradiation to treat cancers of the central nervous system.

I have very fond memories of the years I spent at the University of Kentucky (well, we were all younger, weren’t we?). Those were really intellectually formative years, when I got as close as I ever could to a glimpse into the great phenomena of the universe. I want to take this opportunity to salute and send my best wishes to my professors: my advisor Al Shapere, Joe Straley, Terry Draper, Isaac Shlosman, Keh-Fei Liu, and remember the late, distinguished, Clasine van Winter, and really appreciate the invitation to write this piece for the newsletter. I have not returned to Lexington in many years, but I would love to do so one day.