Improved Outcomes For Patients Treated With Neutron Radiotherapy And Gamma Knife For Salivary Gland Neoplasms With Base Of Skull Invasion





Keywords: gamma knife, salivary gland, skull base, radiotherapy, cancer

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Abstract

       Malignant skull base tumors can pose great management challenges.
     Our purpose was to evaluate the effect on local control and survival of a Gamma Knife boost added to Neutron radiotherapy for salivary gland neoplasms with base of skull invasion.
     Patients had the following characteristics: median age 54; female: male ratio 1.4:1; all had TNM stage III or IV disease; 95% had evidence of gross residual disease. Sites of disease included: parotid -26; nasopharynx - 31; paranasal sinuses - 50; oral cavity- 15; oral pharynx -2; lacrimal gland- 6; auditory canal- 3; miscellaneous sites - 5. Histologies included: adenoid cystic carcinoma 114; adenocarcinoma 8; mucoepidermoid 8; squamous cell carcinoma 2; basaloid 1; other carcinomas NOS 5.
     One-hundred thirty eight patients having salivary gland neoplasms with base of skull invasion were treated with neutron radiotherapy ± Gamma Knife boost at the University of Washington. All patients were treated with neutron radiotherapy with a neutron dose of 18.4 – 19.2 nGy. 6Sixty-two patients were treated with neutron radiotherapy while the remaining 76 were treated with the addition of a Gamma Knife boost (median dose 12 Gy to 50% isodose line; median isocenters 18; median treated volume 13.9 cm3, median conformity index 1.6; and median target coverage of 96%). The median follow-up for the entire group was 25.5 months; non-boosted group 28.5 months and 24 months for the GK boosted group. 
     The Kaplan Meier (KM) 5-year projected local control of the non-GK boosted patients was 17 months. The KM 5-year projected local control of the GK boosted group was 62% (p = 0.001). The median time to failure in the non-boosted group was 18 months. The median time to failure in the GK boosted group has not been reached. The KM estimated overall 5-year survival was 71% in the boosted group compared to 14% in the non-boost group (p = 0.05). Side effects were similar in both groups with the exception of temporal lobe changes found on T2 MRI in over 50% of patients in the boosted group. The majority of patients with MRI changes were asymptomatic.
     This was a retrospective study
     A GK boost added to Neutron radiotherapy for patients having salivary gland neoplasms with base of skull involvement markedly improves 5-year local control and survival with acceptable complications.
     A GK boost added to Neutron radiotherapy should be the recommended therapy for such patients.


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