(P033) Acute Toxicity and Dose Sparing of Organs at Risk Using SBRT for Orbital Tumors

April 15, 2016

Acute toxicity is common after SBRT for orbital tumors but is short-lived and mild. Chronic toxicity will be reported with further follow-up.

Anthony G. Ricco, BS, Sarah Thornton, BS, Rachelle Lanciano, MD, John Lamond, MD, Jun Yang, PhD, Stephen Arrigo, MD, Luther Brady, MD; Sidney Kimmel Medical College, Thomas Jefferson University; Philadelphia CyberKnife

INTRODUCTION: Radiation therapy (RT) of orbital tumors is challenging due to surrounding radiosensitive structures. We review our experience with stereotactic body RT (SBRT) for orbital tumors, to describe doses to organs at risk (OARs) and acute toxicity.

METHODS: Between August 2006 and August 2014, a total of 41 patients (43 orbits) treated with SBRT for orbital tumors were reviewed. Primary tumor included lymphoma/leukemia (n = 15), recurrent nonmelanoma skin cancer with orbital invasion (n = 9), recurrent melanoma (n = 10), breast metastases (n = 5), and primary lacrimal gland cancer (n = 2). SBRT was delivered utilizing the CyberKnife system with a median dose of 20 Gy (range: 13.5–35 Gy), 5 fractions (range: 3–5), 146 beams (range: 40–227), and clinical target volume (CTV) of 14.8 cm3 (range: 2.3–104.8 cm3). Acute toxicity type and grade within 3 months of SBRT as per the Radiation Therapy Oncology Group (RTOG) guidelines were recorded.

RESULTS: The median CTV maximum dose was 27.6 Gy (range: 19.2–48.6). The median optic nerve maximum dose was 14.4 Gy (range: 2.2–36.5 Gy), optic chiasm maximum dose was 5.3 Gy (range: 0.92–28.8 Gy), brain/brainstem maximum dose was 12.5 Gy (range: 1.3–25.5 Gy), lens maximum dose was 16.5 Gy (range: 1.75–28.4 Gy), and globe maximum dose was 20.4 Gy (range: 0.3–44.6 Gy). Thirty-four patients were evaluable for acute toxicity within 3 months of SBRT. Eleven patients noted no acute toxicity (32.4%). Eleven patients experienced conjunctivitis (32.4%); six patients noted foreign body sensation/irritation of eye (17.6%); five patients had acute periorbital edema (14.7%); four had increased tearing (11.8%); two experienced hair loss (5.9%); two developed dry eye (5.9%), with one requiring eye drops; and one experienced pain (2.9%). Only three patients required oral steroids for treatment of acute toxicity. The rate of RTOG grades 1 and 2 acute toxicity was 67.6%. No patients had RTOG acute grade ≥ 3 toxicity. All acute toxicities recorded resolved by 3 months of follow-up. There was no correlation between acute toxicity and CTV maximum dose or CTV.

CONCLUSIONS: Acute toxicity is common after SBRT for orbital tumors but is short-lived and mild. Chronic toxicity will be reported with further follow-up.

Proceedings of the 98th Annual Meeting of the American Radium Society -americanradiumsociety.org