Looking back on the early days of image-guided radiotherapy (IGRT), I am struck by how much our instruments and our clinical philosophy have evolved. What began as a discipline guided by skin markings and grainy X-rays that were developed manually while the patient waited on the table has transformed into a sophisticated world of volumetric imaging, surface guidance, and daily adaptive adjustments. Witnessing this evolution as a radiation therapist (RTT) has been both an educational and an exhilarating experience.
From Skin Markings to 3D Anatomy
Before 1990,"simulation" (in the literal sense of rehearsing treatment) involved using 2D X-rays to determine an approximate treatment position. When CT entered the workflow, everything changed; for the first time, we could visualise internal anatomy instead of relying solely on external surrogates. This shift allowed us to move from the use of broad radiation fields with generous margins to precisely defined 3D target volumes.
At that time, reproducibility depended on physical lines or tattoo dots. These markings had to withstand showering and daily life, yet it was common for a patient to require multiple lines within the first week. It was a practical system for the time, but far from elegant.
The Era of Manual Adjustments
When I started, megavoltage (MV) imaging was our primary verification tool. The images were grainy and showed little more than basic bone structure. We were delighted by the introduction of the electronic portal imaging device, simply because we no longer had to develop physical films!
However, calculating shifts remained a laborious, manual process: measuring, calculating, averaging, and adjusting. To implement these shifts, we had to walk back into the bunker to physically move the treatment table. I remember recalculating shifts at the bedside, navigating coordinate systems in which a small negative correction required entering values such as "999.7". Every manual movement required a new control image, and this situation extended treatment times and tested the patience of both staff and patients.
The Rise of 3D Precision
The introduction of kilovoltage (kV) imaging and, later, cone beam CT (CBCT) was revolutionary. By using bony structures or fiducials as surrogates, we moved from guessing to verifying. While early CBCT systems were still manual — I recall often having to run back into the treatment room because I’d forgotten to click the "fan" into place — the reward was extraordinary: a complete 3D image of the patient’s anatomy before treatment.
Remote table movements, automatic panel retraction, and improved image quality streamlined our workflows. For the first time, we could visualise the soft tissue rather than just the bones. While daily imaging wasn't yet the norm for every case, we eventually transitioned in 2023 to daily CBCT for all indications, driven by the conviction that better guidance leads to better outcomes.
The MV Panel Strikes Back
Interestingly, the MV panel found a new purpose just as it seemed it might become obsolete. It was calibrated to display dose and it became the backbone of portal dosimetry program since 2016. With the advent of volumetric modulated arc therapy, traditional diode measurements were no longer feasible; portal dosimetry and gamma analysis allowed us to verify complex fluence patterns with unprecedented detail. Similarly, kV imaging saw a revival for intra-fractional monitoring in prostate stereotactic body radiation therapy (SBRT). It taught me a lasting lesson: accuracy and knowing exactly where the beam lands never go out of style.
The Synergy of Surface-guided radiation therapy (SGRT) and IGRT
In 2017, SGRT marked another turning point, as it did away with skin markings and complemented IGRT. Combined with 6D treatment tables, SGRT allowed us safely to apply smaller margins and higher doses. This enabled RTTs to use SBRT and radiosurgery as everyday practices.
SGRT also improved the patients’ experiences. I still remember the smile of a patient who had previously had a mechanical frame screwed into her skull for cerebral metastasis treatment but now wore a less invasive, open-face mask. IGRT has not only impacted clinical outcomes but also the dignity we can give the patient in the care we provide.
The Human Element and the Future
Despite these advances, patients are not rigid objects; their anatomy changes daily. Adapting these variations is a constant balancing act between target coverage and sparing organs at risk. My experiences have underscored the need for standardised procedures and structured training, such as through the courses offered by ESTRO. Technology guides us, but human judgement ensures safe care.
Today, CT-based adaptive workflows on modern linacs are a reality. We are moving from geometric precision to dosimetric accuracy. If I had known when I began what I know now, I would have embraced that technical uncertainty with more confidence. Every leap in technology has simply brought us closer to what matters most: treating the patient in front of us exactly as they present today.
Wim Vingerhoed
RTT, Department of Radiotherapy
Iridium Netwerk
Antwerp, Belgium
Wim.vingerhoed@zas.be