Sen. Edward Kennedy, midway through six weeks of radiation and chemotherapy treatments for brain cancer, is doing well aside from some fatigue, his wife says.

In an e-mail to family and friends sent Wednesday, Vicki Kennedy said her husband has been exercising each morning before heading to Boston for treatment at Massachusetts General Hospital. By afternoon, he's back at his family's compound in Hyannis Port.

The e-mail was obtained by The Associated Press on Monday from a Kennedy friend.

"The only side effect is fatigue, and that word has never been in Teddy's vocabulary before," Vicki Kennedy wrote. "But he's learning to cope with it. As I have mentioned to many of you, he is tackling cancer with his trademark grit and determination, and he is doing everything he needs to do to regain his strength and health."