The stability of motion compensated cone-beam CT (MC CBCT) during radiotherapy for

locally advanced lung cancer

A. van der Reijden

M. van Herk

M.M.G. Rossi

J.S.A. Belderbos

J.-J. Sonke

Introduction

People treated for lung cancer breath freely during treatment. Consequently the tumor moves. When imaging the lung tumor, we end up with a blurred tumor. We call this ‘motion blur’ and it makes it hard to detect the tumor.

Blurry tumor

Introduction

In this study we evaluate the use of motion compensated cone-beam scanning with an a-priori motion model. The motion model is extracted from the (4D) planning CT and required the breathing motion to be the same during treatment.

3D cone beam CT Motion compensated CBCT

Materials and methods

We test our method on 9 locally advanced lung cancer patients, treated for at least 17 days.

We compared the actual tumor movement on the scans with the residual tumor movement (after applying the motion model).

We evaluated the scans in the first and the last week of treatment.

Schematic overview of the methods

• 9 NSCLC patients• CBCT in first and last treatment week

3D CBCT 4D CBCT 3D MC CBCT

Here’s an example of a patients’ scan. The 3D CBCT is blurry. We usually make a 4D CBCT scan, but that takes long and the quality is not that fantastic. We can make a 4D MC CBCT involving the motion model to evaluate the motion model and if the model works fine, we can make a 3D MC CBCT in the same time as a 3D CBCT with much better image quality.

4D MC CBCT

Results

We compared the actual tumor motion amplitudes with the residual tumor motion amplitudes and the latter one are significantly smaller in both the first and the last week.

The residual tumor amplitudes are significantly increasing between the first and the last week.

Schematic overview of the results

Actual motion

1.50 ± 0.49 cm

Residual motion

0.42 ± 0.1 cm

Actual motion

1.0 ± 0.51 cm

Residual motion

0.6 ± 0.7 cm

First Week Last Week

P < 0.01 P = 0.02

P < 0.01

n = 9

Tumor amplitudes in Cranial - Caudal direction

Discussion / Conclusion

• Residual motion always smaller than actual motion.

• Residual motion increases over time -> update of motion model beneficial.

• Only 9 patients with big amplitudes included.

• We are currently performing a bigger study with 100 patients and different amplitudes