Several techniques that account and compensate for lung tumor motion have been proposed, investigated and implemented into clinical

practice for imaging, treatment planning and dose delivery. Consequently, it is necessary to verify such respiration management techniques and investigate the

related dosimetric improvements under realistic clinical treatment scenarios. For this purpose a respiratory motion phantom, i.e. the Advanced Radiation Dosimetry

System (ARDOS), was developed and a prototype was realized. This phantom can be used in clinical practice and research to verify dose delivery and image quality of

lung cancer patients on a quantitative and reproducible basis. The purpose of this work was to investigate the performance, versatility and usability of the ARDOS for

dosimetry and imaging to pave the way for real-time tumor-tracking radiotherapy.

The financial support by the Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development is gratefully acknowledged.

http://www.meduniwien.ac.at/hp/radonc

Advanced Radiation Dosimetry System (ARDOS) – A novel breathing phantom for radiation therapy

Corresponding author: natalia.kostiukhina@meduniwien.ac.at

Figure1) 1)

Advanced Radiation Dosimetry System (ARDOS)

the anthropomorphic phantom represents an average human torso with a movable tumor insert and comprises a chest wall, ribs, and lungs (Figure 1),

these parts consist of tissue-equivalent materials,

Dose Verification

The tumor insert enables dose measurements with films, pinpoint ionization chamber (IC) and thermoluminescent dosimeters (TLD)

Clinical lung cancer treatment plans based on stereotactic protocols using high-energy photon beams (10 MV and 10 MV FFF) were created on 3D- and 4D-CT image datasets

“Breathing” scenarios implemented to investigate clinical realistic impact of respiration-induced motion included:

Purpose

Material and Methods

Results

Conclusion

Dosimetric investigation

Figure 2 – Dose difference depending on the motion of the phantom

Differences in the delivered dose:

between static (M0) and chest wall (M1) or ribs (M2) motion is - up to 1.2% - for films and IC, and - up to 3.6 % - for TLD and between static (M0) and combined (M4) or tumor (M3) motion is - up to 4.5% - for films, IC, and TLD

Overall the results demonstrated that in the case of an adapted treatment plan for mitigation of the motion the delivered doses can differ from the planning dose by a maximum of 5%.

Image Registration Software Verification

Real-time 2D/3D Fast Image Registration software (FIRE) was verified using 4D-CT image data of the phantom in the combined motion mode (Fig. 3).

The study will be extended • using simultaneous kV/MV stereoscopic fluoroscopy and • tumors with more challenging tumor shape and tissue

composition (Fig. 4).

PET/CT pilot study

Especially developed inserts were inserted with [18F]-FDG of two different concentrations.

We performed measurements: a) of the tumor inserts only, b) of the phantom with tumor inserts in static mode, and c) of the phantom with tumor inserts in moving mode

Reconstructions of the PET images were performed using a standard algorithm for all acquisitions. For the moving mode a summed image as well as a gated image using the breathing trigger signals were reconstructed. Examples of the reconstructed images are shown in Figure 5.

The data was evaluated by means of recovery coefficients (RC) reflecting the ratio of measured activity in the PET/CT system to the actual activity in the spherical cavity.

The anthropomorphic phantom (ARDOS) can be used in all investigated modalities and is able to provide realistic conditions for

simulating breathing motion. Therefore, it is a promising tool for state of the art research and for advanced quality assurance of motion tracking and compensation

techniques. Further work is planned to test its usability in ion-beam therapy and for the development of 4D quality control procedures.

Preliminary results: • concentration didn’t affect on the resulting RCs, • RC were similar for the cases (c)-gated and (b), and • lower for the case (c)-ungated.

Figure 1 – Advanced radiation dosimetry system (ARDOS): (a) Phantom setup. (b) Construction sketch. (c) Topogram

Natalia Kostiukhina1,2,3, Andrej Sipaj1, Sofia Rollet1, Peter Kuess2,3, Hugo Furtado3,4, Piotr Andrzejewski2,3, Elisabeth Steiner2,3, Ivo Rausch4, Hunor Kertész2,3, Dietmar Georg2,3

¹ AIT Austrian Institute of Technology GmbH, Health & Environment Department, Biomedical Systems, Vienna, Austria ² Division Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna / AKH Vienna, Vienna, Austria

³ Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria ⁴ Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria

Structure / Tissue type Tissue-equivalent material Density of the material, g/cm3

Lungs / Lung tissue High density balsa wood 0.30

Chest wall / Soft tissue Solid water 1.05

Ribs / Bone tissue Bone representing material 1.40

• M0 Static • M1 Chest wall motion

Figure 3 – Extracted from the FIRE tumor motion along cranial-caudal direction (blue) in comparison with reference motion (black)

Figure 5 – PET/CT fused images for the cases: (a) phantom in static mode, (b) moving phantom, ungated, and (c) moving phantom, gated

reconstruction

Figure 4 – 3D-printed tumor insert (c) with its prototype (a), 3D model (b) and appearance on CT images (d)

Cross section view of rib cage cylinder

Outside torso cylinder, allowing skin expansion

The phantom lungs

Inside cylinder consists of soft and lung tissue material

Lung cylinder, used for tumor 3D motion

phantom’s motion:

• translational, for all of the parts individually: • Lung expansion - up to 4 cm, • Ribs - up to 10 cm, • Tumor translational - up to 10 cm,

• rotational, for the cylinder containing the tumor insert • Tumor rotational - up to 360 degrees

• M2 Ribs motion • M3 Tumor motion • M4 combined motion: chest wall, ribs & tumor

a b c

EBT3 films

Pinpoint IC

TLD

X-ray number

Dis

pla

cem

ent

(mm

)

a

b

c d

a b c