30 years of ocular proton therapy, the Nice view

International audiencePurposeRadiotherapy with protons (PT) is a standard treatment of ocular tumors. It achieves excellent tumor control, limited toxicities, and the preservation of important functional outcomes, such as vision. Although PT may appear as one homogenous technique, it can be performed using dedicated ocular passive scattering PT or, increasingly, Pencil Beam Scanning (PBS), both with various degrees of patient-oriented customization.Materaial and methodsMEDICYC PT facility of Nice are detailed with respect to their technical, dosimetric, microdosimetric and radiobiological, patient and tumor-customization process of PT planning and delivery that are key. 6684 patients have been treated for ocular tumors (1991–2020). Machine characteristics (accelerator, beam line, beam monitoring) allow efficient proton extraction, high dose rate, sharp lateral and distal penumbrae, and limited stray radiation in comparison to beam energy reduction and subsequent straggling with high-energy PBS PT. Patient preparation before PT includes customized setup and image-guidance, CT-based planning, and ocular PT software modelling of the patient eye with integration of beam modifiers. Clinical reports have shown excellent tumor control rates (∼95%), vision preservation and limited toxicity rates (papillopathy, retinopathy, neovascular glaucoma, dry eye, madarosis, cataract).ResultsAlthough demanding, dedicated ocular PT has proven its efficiency in achieving excellent tumor control, OAR sparing and patient radioprotection. It is therefore worth adaptations of the equipments and practice.ConclusionsSome of these adaptations can be transferred to other PT centers and should be acknowledeged when using non-PT options

Dose-response and normal tissue complication probabilities after proton therapy for choroidal melanomas

Purpose Normal tissue complication probability (NTCP) models could aid the understanding of dose-dependence of radiation-induced toxicities after eye-preserving radiotherapy of choroidal melanomas. We performed NTCP-modelling and established dose-response relationships for visual acuity deterioration and common late complications after treatments with proton therapy (PT). Design Retrospective study from single large referral centre. Subjects We considered patients diagnosed with choroidal melanoma and primarily treated with hypo-fractionated PT (52 Gy physical dose in 4 fractions). 1020 patients had complete visual acuity deterioration information, 991 patients had complete information on late complications. Methods Treatment details and dose-volume histograms (DVHs) for relevant anatomical structures and patient and tumour characteristics were available from a dedicated ocular database. Lasso variable selection was used to identify variables with the strongest impact on each endpoint, followed by multivariable Cox regressions and logistic regressions to analyse the relationship between dose, clinical characteristics and clinical outcomes. Dose-response relationships were estimated, adjusting for relevant clinical variables. Main Outcome Measures Dose-response relationship for visual acuity deterioration and late complications Results Dose metrics for several structures (i.e. optic disc, macula, retina, globe, lens, ciliary body) correlated with clinical outcome. The near-maximum dose to the macula (macula D2%) showed the strongest correlation with visual acuity deterioration. Retina D20% was the only variable with clear impact on the risk of developing maculopathy; optic disc D20% had the largest impact on optic neuropathy; cornea D20% had the largest impact on neovascular glaucoma; ciliary body D20% had the largest impact on ocular hypertension; the volume of the ciliary body receiving 26 Gy (ciliary body V26Gy) was the only variable associated with the risk of cataract; and retina V52Gy was associated with the risk of retinal detachment. Optic disc-tumour distance was the only variable associated with dry eye syndrome in the absence of DVH for the lachrymal gland. Conclusions Visual acuity deterioration and specific late complications demonstrated dependence on dose delivered to normal structures in the eye after PT for choroidal melanoma. Visual acuity deterioration depended on dose to a range of structures, while more specific complications were primarily related to dose metrics for specific structures