The Secondary Standards Dosimetry Laboratory, Department of Medical Physics,
Maria Sklodowska-Curie National Research Institute of Oncology, Warsaw, Poland
Laboratory accredited by the Polish Centre for Accreditation, accreditation No. AB 1499*
* an actual scope of accreditation No. AB 1499 is available on the PCA website: www.pca.gov.pl
Page 1
New dosimetry audit in Poland –
pilot study for
helical radiotherapy systems
Wioletta Ślusarczyk-Kacprzyk, Iwona Grabska, Agnieszka Walewska, Marcin Szymański
RAP25-91
Page 2
Dosimetry audit in radiotherapy is a key element of quality assurance (QA).
Ensuring the quality of radiotherapy is a major goal at every stage of treatment. Dosimetry audit in radiotherapy aims primarily to ensure safe treatment for patients and improves quality. This is an independent, external dosimetry audit.
This audit makes it possible to check:
Such an audit also indirectly allows one to evaluate the competence of dosimetry teams at the centers.
Introduction
RAP25-91
Page 3
The basis for performing a dosimetry audit in radiotherapy in Poland is the determination of absorbed dose to water by thermoluminescent dosimetry method.
In Poland dosimetry audit in radiotherapy is performed by the Secondary Standards Dosimetry Laboratory (SSDL) in Warsaw accredited by the Polish Centre of Accreditation.
Introduction
RAP25-91
Note: The accreditation No. AB 1499 granted on 9 April, 2014 covers the determination of absorbed dose to water for X-ray beams in the range of accelerating potentials of 4 MV to 25 MV and for electron beams in the energy range of 4 MeV to 22 MeV.
Page 4
In recent years, there have been huge advances in radiotherapy techniques, equipment and treatment planning allowing patients to be treated more efficiently and safely. Modern accelerators allow therapy to be tailored to individual patient needs, increasing treatment effectiveness and minimizing side effects. The continuous development of radiotherapy devices and irradiation techniques requires existing dosimetry audits to be adapted to them.
One advanced form of radiotherapy is helical radiotherapy system like TomoTherapy or Radixact. During this therapy, a linear accelerator rotates around the patient delivering radiation in a manner similar to a helical CT scan, allowing precise irradiation of the tumour from different directions. Simultaneous movement of the therapy table while irradiating the patient allows significant areas to be irradiated without the need to combine fields. This is particularly desirable for irradiating gynecological tumours, soft tissue tumours and bone tumours and for implementing special techniques such as HBI (Half Body Irradiation), TBI (Total Body Irradiation) and TMI (Total Marrow Irradiation).
Introduction
RAP25-91
Page 5
Introduction
RAP25-91
At present, there are 5 Radixact and 1 TomoTherapy devices installed in Poland and further installations are expected in the coming years. The increase in the number of helical radiotherapy systems in Poland was the impetus for the development of a dosimetry audit methodology for these type of devices.
Page 6
Material and methods
RAP25-91
A pilot dosimetry audit for tomotherapy was performed on the RADIXACT (Accuray) installed at the Maria Sklodowska-Curie National Research Institute of Oncology in Warsaw in 2022.
All measurements were performed with a dedicated dosimetry kit including TomoElectrometer and an A1SL type ionization chamber.
TomoElectrometer
A1SL type ionization chamber
Standard holder and holder adapted - cut from the bottom
Page 7
Material and methods
RAP25-91
Reference dose was measured in agreement with reference conditions for the determination of absorbed dose to water in high energy photon beams on tomotherapy machines according (TRS 483):
Page 8
Material and methods
RAP25-91
QA for helical tomotherapy: Report of the AAPM Task Group 148
Page 9
Material and methods
RAP25-91
Fifteen TLD Li-F MT-F type (Institute of Nuclear Physics, Cracow, Poland) capsules were irradiated in five batches.
TLD capsule irradiation conditions was the same as reference conditions for the determination of absorbed dose to water on Tomotherapy machines according to TRS 483.
The detectors were irradiated with a dose equivalent to 12 seconds of beam on time (BOT), i.e. 204.41 cGy (in this case).
Set of reference detectors was irradiated with known doses close to 200.0 cGy at the SSDL in Co-60 beam.
All detectors' signals were read in SSDL using a Fimel PCL-3 TLD reader.
Fimel PCL 3 TL reader
Page 10
Material and methods
RAP25-91
Page 11
Results
RAP25-91
Page 12
The results allow us to expand the scope of dosimetry audits in Poland to include tomotherapy.
This expansion will allow for the inclusion of a larger group of modern devices for advanced radiotherapy techniques in dosimetry audits.
Conclusions
Thank you for your attention.
RAP25-91
References