Dr. Claus F. Behrens Profile

Dr. Claus F. Behrens

at Herlev Hospital

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Proceedings Article | 20 March 2014 Paper

Determining inter-fractional motion of the uterus using 3D ultrasound imaging during radiotherapy for cervical cancer

Mariwan Baker, Jørgen Jensen, Claus Behrens

Proceedings Volume 9040, 90400Y (2014) https://doi.org/10.1117/12.2043173

KEYWORDS: Bone, Uterus, Computed tomography, Radiotherapy, Tissues, Cervical cancer, Ultrasonography, Tumors, Bladder, Imaging systems

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Uterine positional changes can reduce the accuracy of radiotherapy for cervical cancer patients. The purpose of this study was to; 1) Quantify the inter-fractional uterine displacement using a novel 3D ultrasound (US) imaging system, and 2) Compare the result with the bone match shift determined by Cone- Beam CT (CBCT) imaging.Five cervical cancer patients were enrolled in the study. Three of them underwent weekly CBCT imaging prior to treatment and bone match shift was applied. After treatment delivery they underwent a weekly US scan. The transabdominal scans were conducted using a Clarity US system (Clarity® Model 310C00). Uterine positional shifts based on soft-tissue match using US was performed and compared to bone match shifts for the three directions. Mean value (±1 SD) of the US shifts were (mm); anterior-posterior (A/P): (3.8±5.5), superior-inferior (S/I) (-3.5±5.2), and left-right (L/R): (0.4±4.9). The variations were larger than the CBCT shifts. The largest inter-fractional displacement was from -2 mm to +14 mm in the AP-direction for patient 3. Thus, CBCT bone matching underestimates the uterine positional displacement due to neglecting internal uterine positional change to the bone structures. Since the US images were significantly better than the CBCT images in terms of soft-tissue visualization, the US system can provide an optional image-guided radiation therapy (IGRT) system. US imaging might be a better IGRT system than CBCT, despite difficulty in capturing the entire uterus. Uterine shifts based on US imaging contains relative uterus-bone displacement, which is not taken into consideration using CBCT bone match.

Proceedings Article | 12 March 2014 Paper

Optical surface scanning for respiratory motion monitoring in radiotherapy: a feasibility study

Susanne Lise Bekke, Faisal Mahmood, Jakob Helt-Hansen, Claus Behrens

Proceedings Volume 9036, 90360I (2014) https://doi.org/10.1117/12.2042850

KEYWORDS: Motion measurement, Radiotherapy, Heart, Motion estimation, Breast cancer, Visualization, Radio optics, Skin, Error analysis, Cameras

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Purpose. We evaluated the feasibility of a surface scanning system (Catalyst) for respiratory motion monitoring of breast cancer patients treated with radiotherapy in deep inspiration breath-hold (DIBH). DIBH is used to reduce the radiation dose to the heart and lung. In contrast to RPM, a competing marker-based system, Catalyst does not require an objectmarker on the patient’s skin.

Materials and Methods. Experiment 1: a manikin was used to simulate sinusoidal breathing. The amplitude, period and baseline (signal value at end-expiration) were estimated with RPM and Catalyst. Experiment 2 and 3: the Quasar phantom was used to study if the angle of the monitored surface affects the amplitude of the recorded signal.

Results. Experiment 1: we observed comparable period estimates for both systems. The amplitudes were 8 ± 0.1 mm (Catalyst) and 4.9 ± 0.1 mm (RPM). Independent check with in-room lasers showed an amplitude of approximately 8 mm, supporting Catalyst measurements. Large baseline errors were seen with RPM. Experiment 2: RPM underestimated the amplitude if the object-marker was angled during vertical motion. This result explains the amplitude underestimation by RPM seen in Experiment 1. Experiment 3: an increased (fixed) surface angle during breathing motion resulted in an overestimated amplitude with RPM, while the amplitude estimated by Catalyst was unaffected.

Conclusion. Our study showed that Catalyst can be used as a better alternative to the RPM. With Catalyst, the amplitude estimates are more accurate and do not depend on the angle of the tracked surface, and the baseline errors are smaller.

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