Evaporate propylene glycol
Let me reword the question:  

Does $\Delta^9$-tetrahydrocannabinol (THC) significantly degrade when its solution in propylene glycol is heated to 115-123 °C?

This was somewhat answered in a study by Michael A. Repka et al. (DOI) on the stability of THC embedded in a  hydroxypropylcellulose polymer matrix. When heating this system to 120 °C for 75-90 min, about 2.7% of the initial THC degraded. With other words, 97.20% remained unchanged.

Heating to higher temperatures did not lead to significantly higher degradation, but among the degradation products, the amount of cannabinol (CBN), the oxidation product of THC, was much higher here.

Technically, heating to ~120 °C seems to be no problem.

You might want to check the reference given, have a look at the articles cited, compare toxicological data of THC and CBN and decide for yourself.