We have three reportable segments. Last year, we had orders of right at $3 billion. Oncology Systems, just over $2 billion, represents about 75% of the company, X-ray Products $0.5 billion at about 15%, with the remainder coming in our other category, which includes our Security and Inspection Products business, our Proton Therapy business, and our central research facility, which is the Ginzton Technology Center.
Moving into Oncology Systems, which is obviously the largest part of the company, about two-thirds of all patients today receive radiation therapy as part of their course of a cancer treatment. We have been focused on becoming the technology leader and we are today a one stop shop for all radiation therapy needs, including all of the hardware, all of the software, the service, and all of the accessories that go along with that.
The name of the game in radiation therapy is deliver as much dose or radiation as you can to the tumor, so that you can kill the cancer cells, while at the same time minimizing the radiation to healthy tissue, so that you can avoid complication. And we are the technology leader in this. This business is growing. The oncology total business is growing in the high single-digits with mid single-digit growth in the U.S. along with mid-teens growth in the international markets, as well as low-to-mid teens in our service business. And what's driving this growth are several initiatives. Really, there's a three-legged stool to oncology.
The first is driving a replacement market. The second is, moving into emerging markets, where there’s an absolute need for equipment. Third, is the service business, which I'll come back and touch on. And then we just added a fourth leg to this stool with last month announcing a partnership that we have now with Siemens Corporation. The replacement market, we have about 6,800 installed base of machines. And those machines are getting a little long in the tooth, particularly in the U.S. where we have approximately 3,500 machines. And we estimate that the average age today is somewhere over 10 years or older.