Online

WCB 2021 - Online

Session Item

Friday
May 07
08:45 - 10:00
Brachytherapy physics 2030 – Enhanced application and in-vivo treatment verification
0150
Symposium
09:03 - 09:21
Update by the ESTRO task group on in vivo dosimetry in brachytherapy
Jacob Johansen, Denmark
SP-0055

Abstract

Update by the ESTRO task group on in vivo dosimetry in brachytherapy
Authors: Jacob Johansen(Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Gabriel P. Fonseca(Maastricht University Medical Centre, Department of Radiation Oncology, Maastricht, The Netherlands), Ryan L. Smith(Alfred Health, Melbourne, Alfred Health Radiation Oncology, Melbourne, Australia), Luc Beaulieu(Université Laval, Department of Physics, Engineering Physics & Optics and Cancer Research Center, Quebec, Canada), Sam Beddar(The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston, USA), Gustavo Kertzscher(Aarhus University Hospital, Department of Oncology, Aarhus, Denmark), Frank Verhaegen(Maastricht University Medical Centre, Department of Radiation Oncology, Maastricht, The Netherlands), Kari Tanderup(Aarhus University Hospital, Department of oncology, Aarhus, Denmark)
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Abstract Text

The steep dose gradient is one of the benefits of brachytherapy as it enables delivery of high doses to the target while sparing healthy tissues leading to excellent clinical outcome. At the same time, it also puts high constraints on the treatment accuracy. This, together with the several manual steps involved in brachytherapy, makes it important to perform treatment delivery verification. The most direct way to verify the dose delivery is through in vivo dosimetry, where the dose is measured during delivery. The steep dose gradient puts high constraints on both the internal and positional accuracy of any in vivo dosimetry system. Currently, there are no commercially available system that has the sufficient accuracy and treatment delivery verification is not routinely available in brachytherapy. This has led, in some cases, to systematic errors going unnoticed for years.

In 2017, an ESTRO task group was established to investigate how to enhance the clinical implementation of in vivo dosimetry in both external beam radiotherapy and brachytherapy. This presentation will report on the findings of the brachytherapy part of this task investigation.

it was found that the likelihood of detecting deviations from the treatment plan increases significantly with time-resolved methods. Time–resolved methods could interrupt a treatment avoiding gross errors which is not possible with time-integrated dosimetry. In addition, lower experimental uncertainties can be achieved by using more advanced techniques such as source-tracking instead of direct dose measurements, fig. 1. However, the detector position in relation to the patient anatomy remains a main source of uncertainty.

Several time-resolved systems have been developed and tested in laboratories, but only few are used clinically. The development was found to be driven by research groups and small start-up companies. These new systems use different techniques such as point detectors, flat panels and pin-hole detectors. All with their own pros and cons. It is of utmost importance that the sensitivity to different types of errors is well understood for each system as this will enable the end-users to select the most suitable method for their needs.

The many new developments within dosimetry systems for brachytherapy bodes well for the future use of in vivo dosimetry. The next steps towards clinical implementation of in vivo dosimetry will require clinical trials and systematic reporting of errors and near-misses.

 

Figure 1: Feedback levels and corresponding necessary measurement inputs.