Section 4R. (a) For the purposes of this section, the following words shall have the following meanings:
''Prosthesis'', an artificial appliance used to replace a lost natural structure; provided, however, that prosthesis shall include, but not be limited to, artificial arms, legs, breasts, scalp hair or glass eyes.
''Scalp hair prosthesis'', an artificial substitute for scalp hair.
(b) Any subscription certificate under an individual or group medical service agreement, except certificates which provide supplemental coverage to medicare or other governmental programs, that shall be delivered, issued or renewed within the commonwealth, and which provides coverage for any other prosthesis, shall provide, as benefits to all individual subscribers or members within the commonwealth and to all group members having a principal place of employment within the commonwealth, coverage for expenses for scalp hair prostheses worn for hair loss suffered as a result of the treatment of any form of cancer or leukemia; provided, however, that such coverage shall be subject to a written statement by the treating physician that the scalp hair prosthesis is medically necessary; and provided, further, that such coverage shall be subject to the same limitations and guidelines as other prostheses. Scalp hair prosthesis coverage pursuant to this section shall not exceed an amount of $350 per year.