Massachusetts General Hospital is due to open a cancer treatment center at Cooley Dickinson Hospital in Northampton by next year. The center will give cancer patients in western Massachusetts access to clinical trials, genetic screening and other advanced oncology treatments. The Cooley Dickinson says it's raised $2.4 million of the $5 million required for the project. Officials of the two hospitals say the center will provide access to clinical trials headed by Mass General. Patients also will get the latest Mass General chemotherapy and radiation therapy treatment protocols and access to genetic screening and counseling.