Status: Providers

Interventional Cardiologist

Dr. Nathan Riddell is a board-certified interventional cardiologist with Merrimack Valley Cardiology Associates, serving patients in Lowell and the greater Merrimack Valley community. Driven by a belief in the power of personal connection, Dr. Riddell takes a tailored approach to patient care, recognizing that no two patients are alike and that the most meaningful outcomes come from understanding the full picture of a patient’s life and health goals.

Dr. Riddell earned his medical degree from St. George’s University School of Medicine and completed his internal medicine residency at UMass Memorial Medical Center, followed by fellowships at St. Elizabeth’s Medical Center with a focus on cardiovascular disease and interventional cardiology.

His clinical expertise spans a broad range of cardiovascular conditions, with particular experience in aortic stenosis, acute myocardial infarction, interventional cardiac procedures, vascular medicine, and peripheral vascular disease. Dr. Riddell is affiliated with Lowell General Hospital and Tufts Medical Center.

Dr. Riddell also serves as part of the interventional care team at the Tufts Medicine, Lowell General Hospital Vascular + Vein Center in Lowell, MA, where he collaborates with vascular and interventional specialists to deliver comprehensive, patient-centered care to the greater Merrimack Valley community.

Dr. Andrew Lazar, a board-certified vascular and general surgeon, joined The Vascular Care Group in Darien, Connecticut, after completing his vascular surgery fellowship at New York University. With a deep foundation in patient-centered vascular care, academic research, and medical education, he brings a comprehensive and innovative approach to diagnosing and treating vascular disease.

Dr. Lazar earned his medical degree from Weill Cornell Medical College and completed his general surgery residency at Morristown Medical Center. He also completed a postdoctoral research fellowship at Columbia University Medical Center, where he studied cardiovascular disease and vascular surgery outcomes.

He has co-authored numerous peer-reviewed publications in leading medical journals, with research spanning carotid revascularization, health equity in vascular access, peripheral arterial disease, and telehealth adoption in surgical care. Dr. Lazar has also contributed to national vascular surgery meetings and served as both a host and guest contributor for the Audible Bleeding podcast series.

A dedicated educator and advocate for system improvement, Dr. Lazar has been recognized with multiple teaching and humanitarian awards. He remains actively involved in clinical education, surgical curriculum development, and mentorship initiatives. He is a member of the Society for Vascular Surgery, the Society for Clinical Vascular Surgery, and the American College of Surgeons.

Fluent in conversational Spanish and passionate about community health, Dr. Lazar is committed to delivering exceptional, inclusive vascular care. Outside the clinic, he is a devoted husband and father who enjoys spending time with his family, playing soccer, kayaking, and cooking.

Dr. Justin Yu joined The Vascular Care Group’s offices on Cape Cod following his Vascular Surgery Fellowship at the Ochsner Clinic Foundation in New Orleans. During his fellowship training he treated a broad range of pathologies including aortic aneurysms, carotid disease, peripheral arterial disease, and venous insufficiency. He brings a strong foundation in both clinical practice and academic research. Dr. Yu earned his Medical Degree from The Warren Alpert Medical School of Brown University and holds a Master of Science degree from Columbia University, where he conducted advanced research in metabolic disease. He completed his General Surgery Residency at the Zucker School of Medicine at Hofstra/Northwell in New York.

Throughout his career, Dr. Yu has demonstrated a strong interest in improving outcomes for patients with vascular disease, particularly those undergoing dialysis access procedures and peripheral arterial disease. He has published in peer-reviewed journals and presented nationally on topics including frailty, sex disparities in hemodialysis access and the impact of delayed care on amputation rates.

Dr. Yu is a member of the Society for Vascular Surgery, the Vascular and Endovascular Surgery Society, and the Gulf Coast Vascular Surgery Society. His approach to care emphasizes thoughtful, patient-centered decision-making and a dedication to evidence-based surgical practice.

Outside of the clinic, Dr. Yu brings a research-driven perspective and enthusiasm for mentorship and education. He is committed to delivering compassionate vascular care while advancing innovation in the field.

Dr. Allan I. Hoffman, MD, is a highly accomplished interventional radiologist and healthcare executive with over two decades of clinical and administrative leadership. He earned his MD magna cum laude in 1992, followed by internship in General Surgery, Radiology Residency and Vascular and Interventional Radiology Fellowship training at Brown University School of Medicine. He served as Chief Resident and Chief Fellow.

Dr. Hoffman has dedicated his career to advancing vascular care and interventional radiology (IR). He has been a practicing Interventional Radiologist at major institutions on the North Shore and in the Merrimack Valley. He served as Chief of Vascular and Interventional Radiology at Lowell General Hospital and North Shore Medical Center as well as Medical Director of Vein Specialists of the North Shore. 

A recognized leader in the field, Dr. Hoffman serves as President and Board Chair of Commonwealth Radiology Holdings, LLC, and previously led Commonwealth Radiology Associates as its president for over 18 years. Nationally, he chairs the Private Practice Advisory Council and co-chairs the Business Institute for the Society of Interventional Radiology. Elected a Fellow of the Society of Interventional Radiology in 2021, he is repeatedly recognized by his peers as a Boston Magazine “Top Doctor.”

Vascular & Interventional Radiologist

Dr. Gregg Franco brings a passion for minimally invasive medicine and a strong academic foundation to his work as a board-certified interventional and diagnostic radiologist at Commonwealth Radiology Associates (CRA). 

Since joining CRA in 2013, he has built a reputation for clinical excellence and collaborative care across northeastern Massachusetts.

Dr. Franco completed his medical training at Drexel University College of Medicine, followed by an internal medicine internship at Newark Beth Israel Medical Center and a diagnostic radiology residency at Boston Medical Center. He refined his subspecialty skills through a fellowship in vascular and interventional radiology at Emory University School of Medicine, earning board certification from the American Board of Radiology in 2011.

A respected voice in both his institution and the broader vascular and interventional radiology community, Dr. Franco is the Chief of Interventional Radiology at Lowell General Hospital, runs the Hepatobiliary multidisciplinary conference, elected member of medical executive committee and is an active member of two national committees for the Society of Interventional Radiology. 

He has been recognized with the Lowell General Hospital Outstanding Interdisciplinary Collaboration Award and holds academic appointments as a Clinical Assistant Professor at Tufts University School of Medicine and Adjunct Professor at multiple regional institutions.

Dr. Franco is part of the care team at the Tufts Medicine, Lowell General Hospital Vascular + Vein Center in Lowell, MA offering patient-centered vascular and interventional radiology care to the Merrimack Valley community. 

Dr. Ammar Humayun, a board-certified general surgeon, joined The Vascular Care Group’s Worcester office following his vascular fellowship at the University of Connecticut/Hartford Hospital. He brings a strong foundation in complex vascular and general surgery, along with extensive clinical research experience and a passion for academic advancement in vascular care.

Dr. Humayun completed his medical education at Dow Medical College in Pakistan before pursuing postdoctoral research at Mayo Clinic Florida. He trained in general surgery at Hahnemann University Hospital and Crozer-Chester Medical Center, where he gained broad operative and critical care experience across a range of surgical subspecialties.

Throughout his career, Dr. Humayun has remained actively engaged in clinical research. He has co-authored multiple peer-reviewed publications on topics ranging from endovascular interventions and orthopedic trauma to cancer care and critical illness. His presentations at national vascular surgery conferences, including the Society for Clinical Vascular Surgery and the Eastern Vascular Society, highlight his commitment to innovation and clinical excellence.

Dr. Humayun is fluent in Urdu. He enjoys building rapport with diverse patient populations and is committed to delivering thoughtful, evidence-based vascular care.

Outside of medicine, he is an avid tennis and squash player and enjoys spending time outdoors with his family.

Dr. Laura Boitano is a board-certified vascular surgeon who provides comprehensive vascular and endovascular care to patients across Wellesley and Framingham, Massachusetts, and the surrounding communities. She offers expertise in both minimally invasive and open vascular surgical procedures, with a focus on aortic aneurysms, carotid disease, peripheral artery disease, including chronic limb-threatening ischemia, and venous conditions. Dr. Boitano is also skilled in cosmetic procedures for the treatment of spider and varicose veins.

She graduated summa cum laude from Georgetown University with a degree in Human Science and earned her medical degree from Northwestern University’s Feinberg School of Medicine. Dr. Boitano completed an integrated vascular surgery residency at Massachusetts General Hospital, where she conducted two years of vascular research and earned a Master of Public Health in Clinical Effectiveness from the Harvard T.H. Chan School of Public Health. She also holds a Registered Physician in Vascular Interpretation (RPVI) certification.

Prior to joining The Vascular Care Group, Dr. Boitano served as Assistant Professor of Surgery at the University of Massachusetts Medical School and Medical Director of the UMass Program for Aortic Screening and Surveillance. In this role, she advanced care for patients with aneurysmal disease and led community outreach efforts to improve access to vascular services.

A dedicated researcher and educator, Dr. Boitano has published widely in peer-reviewed journals, presented nationally, and is active in several regional and national societies. She is a member of the Society for Vascular Surgery’s Resident and Student Outreach Committee (2024–2027). She remains committed to advancing limb preservation strategies and improving outcomes for women with vascular disease, an area often underrepresented in research, while maintaining her broader commitment to delivering high-quality, patient-centered care to all individuals.

Above all, Dr. Boitano takes a collaborative, patient first approach, striving to deliver compassionate, expert care tailored to each person’s unique needs.

Dr. Swati Chaparala is a board-certified vascular surgeon with advanced training in both open and endovascular techniques. She brings a wealth of expertise to The Vascular Care Group, with clinical interests that include peripheral arterial disease, limb salvage, dialysis access, and complex aortic pathology.

Dr. Chaparala earned her medical degree from Northeast Ohio Medical University and completed her advanced training in vascular and endovascular surgery at the Mayo Clinic in Rochester, Minnesota. Immediately prior to joining The Vascular Care Group, she served as an Assistant Professor in the Division of Vascular Surgery at the University of Maryland School of Medicine, where she also led the medical student clerkship program in vascular surgery.

She has authored multiple peer-reviewed publications and presented her research at national and international vascular conferences. Dr. Chaparala is an active member of the Society for Vascular Surgery and the Alpha Omega Alpha Honor Medical Society. She is passionate about improving access to care and advancing the field through education and innovation.

In addition to her clinical work, Dr. Chaparala speaks Spanish at a working level, helping her communicate effectively with a diverse patient population. She is committed to delivering compassionate, patient-centered vascular care in a collaborative outpatient setting.

Dr. Alison Messina is a Board-certified vascular surgeon who joined The Vascular Care Group’s Hyannis, MA office following her vascular fellowship at Temple University Hospital in Philadelphia, PA. She has received several recognitions as a skilled surgeon and is enthusiastic about surgical techniques and innovations. Dr. Messina is committed to lifelong learning and has been involved in numerous research projects and publications.

After studying healthcare management, Dr. Messina earned her medical degree from the University of Connecticut Health Center in Farmington, CT, and completed her general surgery residency at Mount Sinai South Nassau in Oceanside, NY.

Dr. Messina is dedicated to providing compassionate, patient-centered care and believes in a multidisciplinary approach to treatment, working closely with other specialists to ensure the best outcomes for her patients. She promotes preventative care and empowering patients to better understand their health.

Outside of the operating room, Dr. Messina values spending quality time with her husband and growing family, as well as exploring the outdoors with their retriever. She enjoys cooking, golf, and skiing, leading a busy, well-rounded life.

She is excited to join Drs. Gorin, Rosen, and Phillips, and the team in Hyannis and looks forward to serving the community with the highest level of vascular care.