Influence of eye movement on lens dose and optic nerve target coverage during craniospinal irradiation

Bianca A W Hoeben; Enrica Seravalli; Amber M L Wood; Mirjam Bosman; Witold P Matysiak; John H Maduro; Astrid L H M W van Lier; Matteo Maspero; Gijsbert H Bol; Geert O Janssens

doi:10.1016/j.ctro.2021.08.009

Influence of eye movement on lens dose and optic nerve target coverage during craniospinal irradiation

Clin Transl Radiat Oncol. 2021 Aug 29:31:28-33. doi: 10.1016/j.ctro.2021.08.009. eCollection 2021 Nov.

Authors

Bianca A W Hoeben^{1

2}, Enrica Seravalli¹, Amber M L Wood^{2

3}, Mirjam Bosman¹, Witold P Matysiak⁴, John H Maduro^{2

4}, Astrid L H M W van Lier¹, Matteo Maspero¹, Gijsbert H Bol¹, Geert O Janssens^{1

2}

Affiliations

¹ Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, the Netherlands.
² Princess Máxima Center for Pediatric Oncology, Utrecht, the Netherlands.
³ Radboud University, Nijmegen, the Netherlands.
⁴ Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.

Abstract

Purpose: Optic nerves are part of the craniospinal irradiation (CSI) target volume. Modern radiotherapy techniques achieve highly conformal target doses while avoiding organs-at-risk such as the lens. The magnitude of eye movement and its influence on CSI target- and avoidance volumes are unclear. We aimed to evaluate the movement-range of lenses and optic nerves and its influence on dose distribution of several planning techniques.

Methods: Ten volunteers underwent MRI scans in various gaze directions (neutral, left, right, cranial, caudal). Lenses, orbital optic nerves, optic discs and CSI target volumes were delineated. 36-Gy cranial irradiation plans were constructed on synthetic CT images in neutral gaze, with Volumetric Modulated Arc Therapy, pencil-beam scanning proton therapy, and 3D-conventional photons. Movement-amplitudes of lenses and optic discs were analyzed, and influence of gaze direction on lens and orbital optic nerve dose distribution.

Results: Mean eye structures' shift from neutral position was greatest in caudal gaze; -5.8±1.2 mm (±SD) for lenses and 7.0±2.0 mm for optic discs. In 3D-conventional plans, caudal gaze decreased Mean Lens Dose (MLD). In VMAT and proton plans, eye movements mainly increased MLD and diminished D98 orbital optic nerve (D98_OON) coverage; mean MLD increased up to 5.5 Gy [total ΔMLD range -8.1 to 10.0 Gy], and mean D98_OON decreased up to 3.3 Gy [total ΔD98_OON range -13.6 to 1.2 Gy]. VMAT plans optimized for optic disc Internal Target Volume and lens Planning organ-at-Risk Volume resulted in higher MLD over gaze directions. D98_OON became ≥95% of prescribed dose over 95/100 evaluated gaze directions, while all-gaze bilateral D98_OON significantly changed in 1 of 10 volunteers.

Conclusion: With modern CSI techniques, eye movements result in higher lens doses and a mean detriment for orbital optic nerve dose coverage of <10% of prescribed dose.

Keywords: 3D-conventional; COM, center of mass; CSI, craniospinal irradiation; CTVvoxelwise min, voxelwise minimum CTV; Craniospinal irradiation; D98OON, D98 orbital optic nerve; ITVoptic disc, internal target volume around optic discs; Lens; MLD, mean lens dose; OON, orbital optic nerve; Optic nerve; PBS, pencil-beam scanning; PRVlens, planning organ-at-risk volume around lenses; Proton; SIOPE, European International Society for Paediatric Oncology; VMAT; sCT, synthetic CT.