As far as needing a new mark with the weight loss, it doesn't really go by the amount of weight lost, but the mask fit, which can be related. Some just don't lose as much weight in the face, initially, some do, and I guess what type weight, how lost, etc. comes into play. I lost 40lbs during my first radiation treatment, I gained from the 110lbs lost just from chemo, a year earlier, and didn't need a new mask, so your techs will see, and RO will decide. Hopefully not, since you will need to have a new mask, another CT simulation, probably have a new treatment plan with the IMRT, which takes time.