Iain MacEwan, MD
Associate Medical Director

With over a decade of experience at multiple proton therapy institutions, Dr. MacEwan is a leading expert in proton therapy, utilizing modern pencil beam scanning techniques for adult and pediatric cancer patients.

Iain MacEwan, MD is an Associate Professor in the Division of Radiation Oncology at UC San Diego School of Medicine and serves as the Associate Medical Director at the California Proton Therapy Center, an affiliate of the UC San Diego Health Cancer Network. He also holds a joint appointment in the UC San Diego Department of Pediatrics. During his time at California Proton Cancer Therapy Center, he has treated thousands of patients with tumors in various sites, including brain, head and neck, breast, liver, and pelvic regions (anal, rectal, prostate, gynecologic, and more). He is particularly dedicated to safely delivering radiation therapy to pregnant cancer patients using proton therapy. Early in his career, Dr. MacEwan focused on pediatric oncology, pioneering a novel proton therapy approach for children with medulloblastoma. This technique reduces radiation dose to spinal vertebrae, minimizing bone growth abnormalities and toxicity, and has since become the standard of care. He has also participated in the creation of National Comprehensive Cancer Network (NCCN) guidelines for Wilms Tumor treatment. Passionate about education, Dr. MacEwan teaches proton therapy techniques to medical students, residents, and oncologists. He has been invited to lecture on proton therapy at prestigious institutions, including UCLA, UC Irvine, Cedars-Sinai, UCSF, and Kaiser Los Angeles. In his free time, Dr. MacEwan enjoys surfing, golfing, and exploring the American West. He is a proud father of two daughters.