A Combined Breath Hold and Free Breathing Protocol Is not Feasible for Locoregional Radiation Therapy of Left-Sided Breast Cancer

mean and median doses to the parotid grand compared to the SIB technique under the same HI. It is well known that a head and neck tumor often shrinks and thus the SIB may cause more late toxicity to the parotid grand without an indication in the calculated DVH. It is anticipated that the combination of the two-step adaptive technique and the 5-mm low transmission MLC may reduce complication to the parotid grand while maintaining the tumor control. Author Disclosure: A. Sakumi: None. K. Yamamoto: None. A. Haga: None. K. Okuma: None. H. Igaki: None. Y. Iwai: None. K. Yoda: None. K. Nakagawa: None.