Any prisoner who is otherwise eligible for parole under the provisions of this article, except that his mental condition is deemed by the Probation, Pardon and Parole Board to be such that he should not be released from confinement may, subject to approval by the Veterans Administration, be released to the custody of the Veterans Administration or to a committee appointed to commit such prisoner to a Veterans Administration Hospital. Such a special parole shall be granted in the sole discretion of the Board and, when so paroled, a prisoner shall be transferred directly from his place of confinement to a Veterans Administration Hospital which provides psychiatric care. When any prisoner paroled for psychiatric treatment is determined to be in a suitable condition to be released, he shall not be returned to penal custody except for a subsequent violation of the conditions of his parole.