ESTRO Course report
1-5 December 2025, Delft, The Netherlands
The Dutch city of Delft was where Willem van Oranje laid the foundations of the Dutch Republic in the 16th century, where Antoni van Leeuwenhoek perfected the microscope around 1700, and today is home to the Van Swinden Laboratory, the Dutch Primary Standard Laboratory, which safeguards the SI units in the Netherlands. It was therefore fitting that the VSL was home to the ESTRO training course on dosimetry audits in December.
In the Netherlands, audits focused on reference dosimetry are relatively common, but more advanced audits, such as those involving a more clinical set-up for, e.g., intensity-modulated radiation therapy/volumetric-modulated arc therapy, are far less routine. For me, a senior medical physics engineer with over 20 years of experience in radiotherapy and a former member of The Netherlands Commission on Radiation Dosimetry subcommittee on dosimetry audits (2010), this course offered a welcome opportunity to re-immerse myself in the world of dosimetry audits.
Audits are indispensable, and this was evident in the programme right from the start. Yes, it may feel like stating the obvious, and although major errors are, I hope, a thing of the past, significant discrepancies are still regularly uncovered. After setting the stage and describing phantoms and measurement tools suited for audits, things quickly became even more interesting: how do you validate an audit? How do you define tolerances and uncertainties? What pitfalls should you watch out for?
Later in the course, we moved into practical sessions, which offered a welcome change of pace after the lectures. They covered treatment planning system workflows, phantoms, film dosimetry and small fields, and even included a role-playing exercise in which we had to channel our inner detectives to uncover errors hidden in a stack of audit data. I maintain that the teachers should have worn Sherlock Holmes hats and monocles during that session.
A key takeaway from this course for me was the continued necessity of audits, despite the high levels of quality and expertise already present in our field. The course also highlighted the value of well-designed phantoms and the convenience of readily available audit frameworks. At the same time, it underscored the complexity of validating an audit and the challenge of selecting the right tools and software to do so effectively.
Together with the other Dutch attendees, we are already planning to organise a more advanced audit in the Netherlands. This course provided exactly the information we needed, ensuring that we don’t have to reinvent the wheel. But most of all, it provided us with the motivation to set up an audit. Not only because it is necessary, but also because it will be a lot of fun!
For anyone who has not yet attended an ESTRO course, this was my third, and I can highly recommend joining one. You will learn a great deal, not only from the excellent lectures but also from the interactions with faculty and fellow participants, sharing experiences both formally and informally. You will certainly return home full of new ideas and motivated to put them into practice!
Thijs Perik MSc
Physicist
The Netherlands Cancer Institute
Amsterdam, The Netherlands
t.perik@nki.nl