Dear Ken Yang,
Many thanks for your question.
As it was also explained in the post you have linked (Strange LET shape for 800 keV protons in LiF), LETd defined in literature is derived from fluence (see equation 2). To evaluate the numerator in the equation you should use the fluscw.f routine so as to weight the scored fluence with the requested power of the stopping power. The comscw.f is used instead to weight deposited energy, stars or residual nuclei.
Please have a look and do not hesitate to come back to us in case of further questions.
Best,
Davide