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Most patients with p16-positive oropharynx cancer (p16+OPC) receive elective nodal radiation therapy that improves regional control but increases acute and long-term toxicity. We evaluated the efficacy and toxicity profile of a reduced contralateral elective nodal volume in patients with p16+OPC receiving definitive or adjuvant radiation therapy. Patients with newly diagnosed p16+OPC without contralateral nodal involvement treated with primary proton or photon-based (chemo)radiation therapy or adjuvant (chemo)radiation therapy following transoral robotic surgery (TORS) were eligible for enrollment. The reduced contralateral nodal volume included high-risk regions of levels II and III1. The primary endpoint was elective out-of-field contralateral nodal failure. Dosimetric studies comparing standard versus reduced elective nodal volumes were analyzed with the t-test. Acute toxicity was collected using CTCAE v4.0. Fifty-two patients were enrolled of which 36 (69.2%) received definitive (chemo)radiation therapy. Sixteen (30.8%) patients underwent adjuvant radiation therapy following TORS of which 5 (31.2%) received concurrent chemotherapy. Proton therapy was used in 38 (73.1%) of patients. There were no elective nodal failures at a median follow up of 15 months (range 1-24 months). For the first 20 patients enrolled, dosimetric comparison of the reduced contralateral elective nodal volume to a consensus elective nodal volume demonstrated a decrease in mean dose (14.1 Gy to 18.5 Gy [p<0.05]) and V30 Gy (11.6% to 21.3% [p<0.01]) of the contralateral parotid gland. Significant differences were independent of radiation modality or technology. Acute grade 3 toxicity was observed in 13 (25%) patients including 6 (11.5%) who received a gastrostomy tube during treatment. There were no grade 4-5 acute toxicities, and no patients with 6 months of follow up retained gastrostomy tube. Precise delivery of radiation therapy to high-risk areas for contralateral nodal disease results in excellent regional control regardless of treatment approach. Dose to contralateral organs at risk and toxicity profile were favorable. Longer follow-up is needed to further support this de-intensification strategy. [ABSTRACT FROM AUTHOR]

• Cutaneous squamous cell carcinoma involving the parotid remains an aggressive clinical entity despite modern multimodal therapy. • Pathologic involvement of neck nodes significantly increases recurrence, even with radiation. • Radiation therapy is routinely indicated, and modern techniques have improved side effects. • Pencil beam scanning proton therapy offers lower doses to midline and contralateral structures. • Dry mouth, taste changes, and treatment-related weight loss seem to be improved with proton therapy. We sought to describe outcomes for locally advanced cutaneous squamous cell carcinoma (SCC) involving the parotid treated with volumetric modulated arc therapy (VMAT) versus pencil beam scanning proton beam therapy (PBT). Patients were gathered from 2016 to 2022 from 5 sites of a large academic RT department; included patients were treated with RT and had parotid involvement by: direct extension of a cutaneous primary, parotid regional spread from a previously or contemporaneously resected but geographically separate cutaneous primary, or else primary parotid SCC (with a cutaneous primary ostensibly occult). Acute toxicities were provider-reported (CTCAE v5.0) and graded at each on treatment visit. Statistical analyses were conducted. Median follow-up was 12.9 months (1.3 – 72.8); 67 patients were included. Positive margins/extranodal extension were present in 34 cases; gross disease in 17. RT types: 39 (58.2 %) VMAT and 28 (41.8 %) PBT. Concurrent systemic therapy was delivered in 10 (14.9 %) patients. There were 17 treatment failures (25.4 %), median time of 168 days. Pathologically positive neck nodes were associated with locoregional recurrence (p = 0.015). Oral cavity, pharyngeal constrictor, and contralateral parotid doses were all significantly lower for PBT. Median weight change was −3.8 kg (-14.1 – 5.1) for VMAT and −3 kg (-16.8 – 3) for PBT (p = 0.013). Lower rates of ≥ grade 1 xerostomia (p = 0.002) and ≥ grade 1 dysguesia (p < 0.001) were demonstrated with PBT. Cutaneous SCC involving the parotid can be an aggressive clinical entity despite modern multimodal therapy. PBT offers significantly lower dose to organs at risk compared to VMAT, which seemingly yields diminished acute toxicities. [ABSTRACT FROM AUTHOR]