prostate cancer, joint pain issue with going off vitamin e?

my dad, who has taken vitamin E for years, recently was diagnosed with prostate cancer and told by his doctor to stop taking it - due to the recent research. Since then, he has been in pain: excruciating joint pain which has left him unable to exercise. He is 76 years old and in very good shape due to daily walks and doing karate several times a week. The doctors are thrilled about that as it is so important with his treatment and recovery as he goes through radiation this winter. But he can barely move and takes ibuprofin all day. Has anyone out there had this issue with going off vitamin e? The doctors seem baffled and for now suggest that he eat foods rich with it. Could vitamin e have been masking arthritis that started during the time he was taking it? Help!