Yes, this is possible. You will need to discuss with your therapist to ask if they will want you to pay to hold your weekly slot when you are on vacation to avoid you forfeiting the slot, or to arrange phone or Skype sessions during those weeks you are away. It's likely however that the therapist will simply just book your next session for the next date you are available as long as this is discussed in advance, with more than 48 hours notice.