Radiation-induced optic neuropathy after pencil beam scanning proton therapy for skull-base and head and neck tumours.

OBJECTIVE

To assess the radiation-induced optic neuropathy (RION) prevalence, following high dose pencil beam scanning proton therapy (PBSPT) to skull base and head and neck (H&N) tumours.

METHODS

Between 1999 and 2014, 216 adult patients, median age 47 years (range, 18-77), were treated with PBS PT for skull base or H&N malignancies, delivering ≥45 Gy to the optic nerve(s) (ON) and/or optic chiasma (OC). The median administered dose to the planning target volume was 74.0 Gy (range, 54.0-77.4). The median follow-up was 5.3 years (range, 0.8-15.9).

RESULTS

RION was observed in 14 (6.5%) patients at a median time of 13.2 months (range, 4.8-42.6) following PBSPT. Most (92.9%) of RION were symptomatic. Most affected patients (11/14; 79%) developed unilateral toxicity. Grade 4, 3, 2 and 1 toxicity was observed in 10, 2, 1 and 1 patients, respectively. On univariate analyses, age (<70  ≥70 years; < 0.0001), hypertension ( = 0.0007) and tumour abutting the optic apparatus ( = 0.012) were associated with RION. OC's V60 Gy was of border line significance ( = 0.06). None of the other evaluated OC-ON dose/volume metrics (Dmax, Dmean, V40-60) were significantly associated with this complication.

CONCLUSION

These data suggest that high-dose PBS PT for skull base and H&N tumours is associated with a low prevalence of RION. Caution should be however exercised when treating elderly/hypertensive patients with tumours abutting the optic apparatus.

ADVANCES IN KNOWLEDGE

This is the first study reporting the risk of developing RION following proton therapy with PBS technique, demonstrating the safety of this treatment.