Publications by authors named "Fabian Hennings"

5 Publications

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Potential and pitfalls of 1.5T MRI imaging for target volume definition in ocular proton therapy.

Radiother Oncol 2021 01 3;154:53-59. Epub 2020 Sep 3.

Paul Scherrer Institut (PSI), Center for Proton Therapy, Switzerland.

Introduction: Ocular proton therapy (OPT) for the treatment of uveal melanoma has a long and remarkably successful history. This is despite that, for the majority of patients treated, the definition of the eye anatomy is based on a simplified geometrical model embedded in the treatment planning system EyePlan. In this study, differences in anatomical and tumor structures from EyePlan, and those based on 1.5T magnetic resonance imaging (MRI) are assessed.

Materials And Methods: Thirty-three uveal melanoma patients treated with OPT at our institution were subject to eye MRI. The target volumes were manually delineated on those images by two radiation oncologists. The resulting volumes were geometrically compared to the clinical standard. In addition, the dosimetric impact of using different models for treatment planning were evaluated.

Results: Two patients (6%) presented lesions too small to be visible on MRI. Target volumes identified on MRI scans were on average smaller than EyePlan with discrepancies arising mostly from the definition of the tumor base. Clip-to-tumor base distances measured on MRI models exhibited higher discrepancy to ophthalmological measurements than EyePlan. For 53% of cases, treatment plans optimized for lesions identified on MRI only, failed to achieve sufficient target coverage for EyePlan volumes.

Discussion: The analysis has shown that 1.5T MRI might be more susceptible to misses of flat tumor extension of the clinical target volume than the current clinical standard. Thus, a proper integration of ancillary imaging modalities, leading to a better characterization of the full lesion, is required.
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http://dx.doi.org/10.1016/j.radonc.2020.08.023DOI Listing
January 2021

Technical Note: Benchmarking automated eye tracking and human detection for motion monitoring in ocular proton therapy.

Med Phys 2020 Jun 10;47(5):2237-2241. Epub 2020 Mar 10.

Paul Scherrer Institut (PSI), Center for Proton Therapy, 5232, Villigen PSI, Switzerland.

Purpose: Ocular proton therapy is an effective therapeutic option for patients affected with uveal melanomas. An optical eye-tracking system (ETS) aiming at noninvasive motion monitoring was developed and tested in a clinical scenario.

Materials And Methods: The ETS estimates eye position and orientation at 25 frames per second using the three-dimensional position of pupil and cornea curvature centers identified, in the treatment room, through stereoscopic optical imaging and infrared eye illumination. Its capabilities for automatic detection of eye motion were retrospectively evaluated on 60 treatment fractions. Then, the ETS performance was benchmarked against the clinical standard based on visual control and manual beam interruption.

Results: Eye-tracking system detected eye position successfully in 97% of all available frames. Eye-tracking system-based eye monitoring during therapy guarantees quicker response to involuntary eye motions than manual beam interruptions and avoids unnecessary beam interruptions.

Conclusions: Eye-tracking system shows promise for on-line monitoring of eye motion. Its introduction in the clinical workflow will guarantee a swifter treatment course for the patient and the clinical personnel.
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http://dx.doi.org/10.1002/mp.14087DOI Listing
June 2020

Automated Treatment Planning System for Uveal Melanomas Treated With Proton Therapy: A Proof-of-Concept Analysis.

Int J Radiat Oncol Biol Phys 2018 07 13;101(3):724-731. Epub 2018 Feb 13.

Centre for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland.

Purpose: By precalculation of an entire set of planning solutions for protons, penalizing them and providing a graphical navigator tool (Automated Treatment Planning [ATP]), we aim to improve the efficiency of the planning procedure for uveal melanoma (UM) and make it independent of treatment planner experience.

Methods And Materials: A phase space of plans is evaluated by transforming the eye model in each gaze angle, calculating cumulative dose-volume histograms for each position, and defining a dose-volume constraint for each considered structure. The final result is a map of the plan phase space, displaying how many criteria are fulfilled for each gaze angle.

Results: To test its usability and performance, ATP was used retrospectively on 48 UM patients treated with protons. In 36 of 48 cases (75%), the planning result was either the same (13 of 48, 27%) or comparable (23 of 48, 48%). In 11 of 48 evaluated cases (23%), ATP plans showed improvements. In 1 case (2%) the patient's visual acuity had been impaired, and an optimization was not possible.

Conclusions: We have developed a dose calculation and planning engine that prepares a set of treatment plans covering a wide range of theoretical clinically feasible gaze angles for a given patient, by precalculating the dose distributions for each gaze angle. By considering different structures and adapting their constraints, the identification of the optimal gaze angle can be realized. With a better understanding of the dose-volume constraints and the development of strategies to react to the trade-offs between considered structures, ATP may lead to a complete automation of the planning process for UM treated with proton therapy.
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http://dx.doi.org/10.1016/j.ijrobp.2018.02.008DOI Listing
July 2018

Noninvasive eye localization in ocular proton therapy through optical eye tracking: A proof of concept.

Med Phys 2018 May 23;45(5):2186-2194. Epub 2018 Mar 23.

Center for Proton Therapy, Paul Scherrer Institut, Villigen, PSI, 5232, Switzerland.

Purpose: Over the last four decades, Ocular Proton Therapy has been successfully used to treat patients affected by intraocular lesions. For this, treatment geometry verification is routinely performed using radiographic images to align a configuration of fiducial radiopaque markers implanted on the sclera outer surface. This paper describes the clinical application of an alternative approach based on optical eye tracking for three-dimensional noninvasive and automatic eye localization. An experimental protocol was designed to validate the optical-based eye referencing against both radiographic imaging system and the clinically used EYEPLAN treatment planning system.

Methods: The eye tracking system (ETS) was installed in the OPTIS 2 treatment room at PSI to acquire eye motions during the treatment of nine patients. The pupil position and the cornea curvature center were localized by segmenting the pupil contour and corneal light reflections on the images acquired by a pair of calibrated optical cameras. After calibration of the ETS, a direct comparison of radiopaque markers position, and consequentially eye position and orientation, provided by the ETS, radiographs and EYEPLAN was performed.

Results: Nineteen out of thirty total monitored fractions were excluded from the study due to poor visibility of corneal reflection, resulting in a success rate of acquisition of 37%. For these data, overall median agreement between ETS-based and x-ray-based markers position assessment were 0.29 mm and 0.94° for translations and rotations, respectively. Small discrepancies were also measured in the eye center estimates of the ETS and EYEPLAN. Conversely, variations in measured eye orientation were higher, with interquartile range (IQR) between 4.39° and 7.58°. Nonetheless, dosimetric evaluation of the consequence of ETS uncertainties showed that the target volume would still be covered by more than 95% of the dose in all cases.

Conclusion: An ETS was successfully installed in a clinical ocular proton therapy treatment room and used to monitor eye position and orientation in a clinical scenario. First results show the potential of such a system as an eye localization device. However, the low success rate prevents straightforward clinical application and needs further improvements aimed at increasing corneal reflection visibility.
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http://dx.doi.org/10.1002/mp.12841DOI Listing
May 2018

With Gaze Tracking Toward Noninvasive Eye Cancer Treatment.

IEEE Trans Biomed Eng 2016 09 4;63(9):1914-1924. Epub 2015 Dec 4.

We present a new gaze tracking-based navigation scheme for proton beam radiation of intraocular tumors and we show the technical integration into the treatment facility. Currently, to treat a patient with such a tumor, a medical physicist positions the patient and the affected eye ball such that the radiation beam targets the tumor. This iterative eye positioning mechanism requires multiple X-rays, and radio-opaque clips previously sutured on the target eyeball. We investigate a possibility to replace this procedure with a noninvasive approach using a 3-D model-based gaze tracker. Previous work does not cover a comparably extensive integration of a gaze tracking device into a state-of-the-art proton beam facility without using additional hardware, such as a stereo optical tracking system. The integration is difficult because of limited available physical space, but only this enables to quantify the overall accuracy. We built a compact gaze tracker and integrated it into the proton beam radiation facility of the Paul Scherrer Institute in Villigen, Switzerland. Our results show that we can accurately estimate a healthy volunteer's point of gaze, which is the basis for the determination of the desired initial eye position. The proposed method is the first crucial step in order to make the proton therapy of the eye completely noninvasive.
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http://dx.doi.org/10.1109/TBME.2015.2505740DOI Listing
September 2016
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