How can i calculate the sample size in this situation?

#1
I am designing a RCT between two interventions (two closure techniques of abdomen after an operation) to assess their safety, the safe intervention will have the less percentage of outcome (dehiscence). The problem is that i know the outcome of one intervention (p1): 0.2 % while for the other intervention i do not know any p2. However the maximum reported proportion for the outcome is 1.17%. While still the average reported by whole literature is 0.7%

i know p1 = 0.2 %, Now what should i do?

1. p2 as the maximum?
2. Have some arbitrary p2 like risk reduction to 30% etc?
3. p2 as the average?
4. Anything else i am missing?

I am using this sample size calculator: http://www.stat.ubc.ca/~rollin/stats/ssize/b2.html

I am not an expert in these things and googled the sample size community and found you? :)