Page 89 - ARNM-2-3

Advances in Radiotherapy
& Nuclear Medicine OrthoCT experimental proof of concept

that this background has a more pronounced impact national funds and FEDER, in accordance with Parceria
on orthogonal ray imaging measurements due to the PT2020 LIP - FIS/50007.
utilization of very small irradiation fields (5 mm × 5 mm).
Although impossible to eliminate entirely, the impact of this Conflict of interest
background on the obtained profiles has been significantly The authors declare that they have no competing interests.
reduced. This was achieved through the utilization of
approximately 315 kg of shielding material, consisting of Author contributions
Cerrobend and lead. The necessity for such a substantial Conceptualization: Hugo Simões & Paulo Crespo
amount of shielding material was also influenced by the Investigation: All authors
geometry of the system. Building a more compact system, Methodology: All authors
using, for example, silicon photomultipliers directly Writing–original draft: Hugo Simões
coupled to the scintillation crystals, will decrease the
quantity of shielding material needed. Writing–review & editing: All authors
Obtaining background-subtracted profiles improved Ethics approval and consent to participate
the ability to discriminate the air cavity placed at the Not applicable.
center of the PMMA phantom. This work experimentally
demonstrated the capability of OrthoCT to obtain 2D Consent for publication
images of the morphology of targets in the region of
interest without the need to rotate the linac around them. Not applicable.
To ensure sufficient statistics, the 2D images were acquired Availability of data
with an irradiation time of 45 s per phantom position. This Data are available from the corresponding author upon
was due to the dead time of the acquisition system and the use reasonable request.
of the absolute maximum amplitude of each detected event
to create the corresponding profiles. For example, analyzing References
the signals in the current integration mode can enhance the
statistical significance of the collected data. This is because 1. Berger T, Seppenwoolde Y, Pötter R, et al. Importance of
it integrates a signal that is correlated with the energy of all technique, target selection, contouring, dose prescription,
and dose-planning in external beam radiation therapy for
events detected by the system. Simulation results indicate cervical cancer: Evolution of practice from EMBRACE-I to II.
that 10 mGy is sufficient for obtaining OrthoCT images. Int J Radiat Oncol Biol Phys. 2019;104(4):85-94.
10
Therefore, in the current integration mode, similar images
to those shown in Figure 16 can be obtained with a total doi: 10.1016/j.ijrobp.2019.03.020
irradiation time of only 1.3 s. This statement is based on the 2. De Crevoisier R, Tucker SL, Dong L, et al. Increased risk
fact that the TrueBeam linac delivers approximately 10 of biochemical and local failure in patients with distended
mGy every 100 ms, and the images were obtained from 13 rectum on the planning CT for prostate cancer radiotherapy.
vertical beam positions. Int J Radiat Oncol Biol Phys. 2005;62(4):965-973.
doi: 10.1016/j.ijrobp.2004.11.032
Acknowledgments
3. Thieke C, Malsch U, Schlegel W, et al. Kilovoltage CT
The authors gratefully acknowledge the staff from the detector using a linac-CT scanner combination. Br J Radiol.
laboratory and mechanical workshop of the laboratory of 2006;79(1):S79-S86.
instrumentation and experimental particle physics (Alberto doi: 10.1259/bjr/88849490
Blanco, Rui Alves, Nuno Dias, Carlos Silva, Douglas Lima,
Américo Pereira, Orlando Cunha, and Nuno Carolino) 4. Lee C, Langen KM, Lu W, et al. Evaluation of geometric
for their support in the construction and assembly of the changes of parotid glands during head and neck cancer
detector prototype. The authors also acknowledge Andreas radiotherapy using daily MVCT and automatic deformable
registration. Radiother Oncol. 2008;89(1):81-88.
Wagner (Institute of Radiation Physics Helmholtz-Zentrum
Dresden-Rossendorf, Dresden, Germany) for lending some doi: 10.1016/j.radonc.2008.07.006
of the electronics modules used in data acquisition. 5. Serduc R, van de Looij Y, Francony G, et al. Characterization
and quantification of cerebral edema induced by
Funding synchrotron x-ray microbeam radiation therapy. Phys Med

This study was partly funded by Project POCI-01-0145- Biol. 2008;53(5):1153.
FEDER-0073334, supported through FCT/MCTES doi: 10.1088/0031-9155/53/5/001

Volume 2 Issue 3 (2024) 12 doi: 10.36922/arnm.4099