CLIPLESS POSITIONING FOR OCULAR PROTON THERAPY

International Journal of Particle Therapy, vol. 21, pp. 101885

Abstract

Background and Aims: Proton beam therapy (PBT) is, alongside brachytherapy, a main eye-preserving treatment for uveal melanoma (UM).Currently, PBT requires surgical placement of scleral clips for tumor localization and patient positioning.We propose a novel clipless positioning workflow for ocular PBT.Methods: In the clipless workflow, patients will receive an MRI and CT scan in an in-house developed immobilization setup, consisting of a personalized double shell mask with integrated gaze guidance.To establish the feasibility of this workflow, several evaluations were performed.First, stability of the immobilization setup between supine (imaging) and sitting (treatment) position was evaluated in 15 subjects.From the CT-images, Digital Reconstructed Radiographs (DRR) are generated for bone-match-based positioning at the Eye Treatment Room (ETR).Second, a prospective end-to-end evaluation was performed using 3D-printed a head phantom, developed to simulate the clinical workflow, with tantalum clips placed on the eye.Finally, we evaluated the accuracy of using bony anatomy instead of clips for positioning at the ETR by retrospectively analyzing X-Ray images 60 consecutive UM patients, using the second fraction as a reference for manual matching of the third and fourth fractions.Results: The immobilization setup showed minimal deformation between supine and sitting treatment position (LR: -0.06±0.19mm; FH: 0.16±0.20 mm; AP: 0.15±0.28mm).The end-to-end test showed a residual error of 0.4 mm, 0.1 mm and 0.1 mm, in the LR, FH and AP directions respectively.The retrospective evaluation of the bone-match positioning method showed negligible (<0.06 mm) systematic errors and sub-milli-meter random deviations with respect to the clips (SD: LR:0.33 mm, FH:0.33 mm, AP:0.46 mm). Conclusions:The proposed clipless positioning workflow is feasible and is currently being prospectively validated in the COPTER trial.

Authors 7

1. Martijn Hol Aachen Radiation Oncology

   Leiden University Medical Center · Holland Particle Therapy Center

   Affiliation as printed

   HollandPTC, Delft, Netherlands

   Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands

2. Elefhteria Astreinidou Aachen Radiation Oncology

   Leiden University Medical Center

   Affiliation as printed

   Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands

3. Lisa Klaassen Aachen Ophthalmology Radiation Oncology Radiology

   Leiden University Medical Center · Holland Particle Therapy Center

   Affiliation as printed

   HollandPTC, Delft, Netherlands

   Ophthalmology, Leiden University Medical Center, Leiden, Netherlands

   Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands

   Radiology, Leiden University Medical Center, Leiden, Netherlands

4. Marina Marinkovic Aachen Ophthalmology

   Leiden University Medical Center

   Affiliation as printed

   Ophthalmology, Leiden University Medical Center, Leiden, Netherlands

5. T.H. Khanh Vu Aachen Ophthalmology

   Leiden University Medical Center

   Affiliation as printed

   Ophthalmology, Leiden University Medical Center, Leiden, Netherlands

6. Coen RN. Rasch Aachen Radiation Oncology

   Leiden University Medical Center · Holland Particle Therapy Center

   Affiliation as printed

   HollandPTC, Delft, Netherlands

   Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands

7. Jan-Willem Beenakker