| Schedule | Constraint | Source |
|---|---|---|
| Conventional fractionation 70 Gy / 35 fx definitive · 60–66 Gy / 30–33 fx post-op | D0.03 cc ≤6 Gy (ideal), ≤15 Gy (acceptable) | Lee 2019 NPC guideline |
Quoted from eviQ 5049, checked 2026-09-24. Full table with references →
The transparent lens of each eye, behind the iris.
The clear lens behind the iris focuses light onto the retina. Clouding of the lens is a cataract.
The lens is one of the most radiosensitive tissues in the body: modest doses can cause cataract. Its limits are low compared with other head and neck organs, and they matter for nasopharynx, sinonasal and orbital targets. In whole-brain treatment the lateral beams run just behind the eyes, so beam divergence toward the lenses is a routine planning check.
The EPTN 2018 atlas describes the lens as a clearly visible, biconvex structure up to 10 mm across, between the vitreous and the iris, which is easy to contour on CT. It notes that the lens can move during treatment unless the patient is told where to look.
Brouwer 2015 does not contour the lens on its own — it is included in the anterior segment of the eyeball.
The European Particle Therapy Network contouring atlas for brain organs at risk on CT and MRI, with anatomical descriptions and boundaries. Citation checked against Crossref.
Consensus CT delineation guidelines for head and neck organs at risk from eight cooperative groups, with anatomical descriptions and example images. Citation checked against Crossref; content not yet reviewed by DoseLab.