How often can I have cosmelan MD step 1 treatment?

I had my first cosmelan MD step 1 treatment Jan. 2016, followed by the step 2. I am on cosmelan 2 maintenance treatment after the step 2. Per my assessment I still need to have another treatment. My melasma in my bilateral cheeks slightly fade away , but the brown spots in the area of my forehead and temple were still lingering. I wanted to know if I can have another treatment of step 1 & 2 by next year. Your expertise/opinion is highly appreciated. Thank you.