Session Item

To report acute and early late toxicities and early clinical outcomes following proton beam therapy (PBT) for paediatric/adolescent head and neck (HN) malignancies treated at our institute.

We retrospectively analysed prospectively maintained electronic records for all patients <25 years of age treated with PBT at our institute for HN malignancies between 2018-2020. All patients were treated with pencil beam scanning PBT with daily cone-beam CT (CBCT). Toxicity was assessed weekly on treatment and then at regular follow-up and graded according to CTCAE v5. All patients had post-treatment imaging to assess response at 12 weeks and repeat imaging was performed in those with suspicion of clinical recurrence.

48 patients <25 years of age were treated with PBT at our institute for HN malignancies during the study period. The median age at treatment was 14 years (range: 1-25 years). Patient, disease, and treatment characteristics are highlighted in table 1. After a median follow-up of 18 months (Range: 8-34 months), the actuarial 1-year overall survival, local control, and distant control rates for the entire cohort were 92%, 89%, and 94%, respectively. Five patients experienced an isolated local failure (3 RMS, 1 ES, and 1 other). Only 1 patient had a nodal recurrence and was surgically salvaged. Isolated distant failure was seen in 2 patients (1 RMS and 1 ES) and 1 (RMS) experienced a combined local and distant failure. A total of 5 patients had died and all of them due to their disease. For the NPC cohort the actuarial 1-year overall survival, local control, and distant control rates were 100%, 100%, and 100%.

Grade 2 or worse acute skin and mucosal toxicities were seen in 81% (grade 3- 6%) and 60% (Grade 3- 17%) patients respectively. Acute grade 2 or worse dysphagia rates were 50% (Grade 3 - 10%). Weight loss >5% was seen in 17% of patients. Approximately half of the patients (54%) had a prophylactic feeding tube put in prior to PBT and 6% required reactive tube placement due to weight loss. Weight loss did not correlate with prophylactic tube placement in this cohort (p=0.22).

None of the patients experienced any grade 2 or worse late skin toxicity. Grade 2 or worse late xerostomia rates were 10% and Grade 3 dysphagia rates were 2% (feeding tube dependence). Other late toxicities (Grade 3) included hypothyroidism (6%), pituitary insufficiency (4%), neurocognitive deficits (2%), vision loss (2%), and hearing loss (6%). Acute and late toxicities are highlighted in table 2.

Pencil beam scanning PBT with daily CBCT is associated with excellent local control rates and low rates of acute and early late toxicities similar to historical controls. Longer follow-up is required to determine ongoing disease response and evolving late toxicities.