International Journal of Radiation Oncology Biology Physics
head-and-neck cancer. Int J Radiat Oncol Biol Phys 2013;87: 676-682. 2. Han C, Chen YJ, Liu A, et al. Actual dose variation of parotid glands and spinal cord for nasopharyngeal cancer patients during radiotherapy. Int J Radiat Oncol Biol Phys 2008;70:1256-1262.
and our study found that only a minority of patients (31% and 11%, respectively) had differences between the planned and actually delivered doses that were higher than this “noise.” Adaptive replanning aiming to reduce delivered doses back to planned levels are not likely, therefore, to gain measurable improvements in salivary output in the majority of cases. Following the data we presented (1), the challenge is how to predict as early as possible during the course of therapy who are the minority of patients at risk of increase in parotid gland doses beyond the “noise,” to identify those who may benefit from adaptive replanning.
In Reply to Ren et al To the Editor: We thank Ren et al for their comments on our article (1, 2). The reasons for the differences between the planned and the actually delivered parotid doses are related to reduced parotid volumes during therapy, as noted by Ren et al and by many previous published studies, and to complex setup deviations that could not be fully addressed by the translational corrections that are typically used in image guided radiation therapy. Despite using different treatment equipment and quality assurance procedures, the results reported in our article and in the letter by Ren et al are surprisingly similar: small median differences between planned and delivered mean parotid gland doses, 0.66 Gy (Ren et al) versus 0.92 Gy (Hunter et al). The most important finding of our study was the spread of the dose/saliva output data points. We have demonstrated that for both the planned doses and the actually delivered doses, the “noise” in the data, measured by their standard deviations, was in the range of 3 to 4 Gy, suggesting that smaller differences between the planned and delivered parotid doses may not be clinically relevant. Both Ren et al
James Balter, PhD Avraham Eisbruch, MD Department of Radiation Oncology University of Michigan Ann Arbor, Michigan http://dx.doi.org/10.1016/j.ijrobp.2014.01.028
References 1. Hunter KU, Fernandes LL, Vineberg KA, et al. Parotid glands doseeffect relationships based on their actually delivered doses: Implications for adaptive replanning in radiation therapy of head and neck cancer. Int J Radiat Oncol Biol Phys 2013;87:676-682. 2. Ren G, Ma L, Xu S. In regard to Hunter et al. Int J Radiat Oncol Biol Phys 2014;88:1213-1214.