Simple Summary: In this study, we have explored the impact of a promising new cancer treatment modality called proton therapy (PT) and compared it to traditional X-ray based photon therapy (XRT) for head and neck cancers. Proton therapy is effective because it can be delivered with precision, thus causing fewer side effects. We demonstrate in this study that, when using proton therapy, there was a significant reduction (75%) in the production of small extracellular vesicles, commonly known as exosomes, from cancer cells, which usually suppress the immune system. XRT did not reduce exosome production. Exosomes from both PT and XRT had similar inhibitory effects on immune cells. Our findings suggest that proton therapy might be better at reducing the immune-suppressing effects of cancer exosomes by producing fewer of them. Proton therapy (PT) is emerging as an effective and less toxic alternative to conventional X-ray-based photon therapy (XRT) for patients with advanced head and neck squamous cell carcinomas (HNSCCs) owing to its clustered dose deposition dosimetric characteristics. For optimal efficacy, cancer therapies, including PT, must elicit a robust anti-tumor response by effector and cytotoxic immune cells in the tumor microenvironment (TME). While tumor-derived exosomes contribute to immune cell suppression in the TME, information on the effects of PT on exosomes and anti-tumor immune responses in HNSCC is not known. In this study, we generated primary HNSCC cells from tumors resected from HNSCC patients, irradiated them with 5 Gy PT or XRT, and isolated exosomes from cell culture supernatants. HNSCC cells exposed to PT produced 75% fewer exosomes than XRT- and non-irradiated HNSCC cells. This effect persisted in proton-irradiated cells for up to five days. Furthermore, we observed that exosomes from proton-irradiated cells were identical in morphology and immunosuppressive effects (suppression of IFN-γ release by peripheral blood mononuclear cells) to those of photon-irradiated cells. Our results suggest that PT limits the suppressive effect of exosomes on cancer immune surveillance by reducing the production of exosomes that can inhibit immune cell function. [ABSTRACT FROM AUTHOR]