Head and Neck Cancer

PV QA 2 - Poster Viewing Q&A 2

MO_32_2759 - Neutron Radiation Therapy and Gamma Knife Radiosurgery Boost for Locally Advanced Adenoid Cystic Carcinoma With Skull Base Invasion

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Neutron Radiation Therapy and Gamma Knife Radiosurgery Boost for Locally Advanced Adenoid Cystic Carcinoma With Skull Base Invasion
A. Lui1, U. Parvathaneni2, G. E. Laramore2, J. K. Rockhill2, L. M. Halasz2, and J. J. Liao3; 1University of Washington, Seattle, WA, 2University of Washington, Department of Radiation Oncology, Seattle, WA, 3University of Washington Medical Center Department of Radiation Oncology, Seattle, WA

Purpose/Objective(s): Adenoid cystic carcinoma (ACC) is a relatively radioresistant malignant salivary gland histology with a predilection for perineural spread and skull base invasion. High LET radiation with neutron therapy (NRT) provides a radiobiologic advantage over x-rays, which translates into improved local control, especially in unresectable disease. However, full NRT dose is not possible in patients with skull base invasion due to proximity of tumor to critical structures. We previously showed that the addition of a single fraction stereotactic boost to the skull base with Gamma Knife (GK) after NRT provides improved local control. We report updated longer-term follow up of this approach.

Materials/Methods: From 2001-2015, 77 patients underwent NRT followed by GK boost for ACC with skull base invasion, of these 70 were primary therapy and 7 were treated for recurrent disease. The majority had advanced T4 tumors. Demographics: median age 52 (range 20-85), male (31), female (46). Primary tumor site was nasopharynx (15), sinonasal (31), parotid (7), oral cavity (15), other (9). 28 underwent initial surgical resection or debulking: 13 GTR/R1, 15 STR/R2. Median neutron dose was 18.4 Neutron Gy (range 16 – 19.2). Median GK dose was 12 Gy (range 8-18) in a single fraction, encompassing areas of reduced neutron dose coverage close to or involving the base of skull, due to brainstem, temporal lobe or optic structure tolerance.

Results: Median follow up is 43 months (0 – 177), 35 patients are alive, 35 have died, and 7 are lost to follow up. 34 recurrences have been observed (3 of which were in those treated for recurrence), including 26 local, 18 distant and 9 both local and distant. KM-estimated OS was 2-year 87%, 3-year 77%, 5-year 59%. KM-estimated local control for those undergoing primary therapy was 2-year 80%, 3-year 71%, and 5-year 61%. 5-year local control was significantly higher in patients who had R1 resection compared with no surgery or R2 resection (89% vs 55%, log-rank p=0.05). R2 resection did not appear to improve local control compared to patients who did not have surgery. Treatment was well tolerated with few cases of temporal lobe edema seen on imaging, generally asymptomatic.

Conclusion: ACC presenting with skull base invasion or perineural spread with intracranial extension is a challenging disease to treat both due to relative radioresistance and proximity to critical normal structures. NRT combined with GK boost to the skull base offers encouraging rates of local control in this challenging patient population, which compares favorably with our historical experience with NRT alone and with reported x-ray based series with acceptable toxicity profile. Late local failures and distant metastases remain a problem.

Author Disclosure: A. Lui: None. U. Parvathaneni: None. G.E. Laramore: Professor and Chair of Department of Radiation Oncology; University of Washington. J.K. Rockhill: None. L.M. Halasz: Research Grant; Fred Hutch/Univ of Washington Cancer Consortium. J.J. Liao: None.

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