Utilize the input text as a context reference, choose the right relationship between Elekta and Gamma Knife from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

This relates especially to Elekta Unity and Leksell Gamma Knife products for which we have a global installation teams.

Answer: product_or_material_produced