NTCP model guided whole brain radiation re-planning to reduce risk of acute xerostomia and dry eye.

INTRODUCTION: Previous work has shown that whole brain radiation (WBRT) can lead to acute xerostomia and dry eye from dose delivered to the parotid and lacrimal glands, respectively. We performed a retrospective study to assess whether a previously developed normal tissue complication probability (NTCP) model could guide planning to reduce the risk of these complications. We also evaluate if the use of VMAT/IMRT instead of 3D planning can reduce the risk of side effects while maintaining dose to the brain. METHODS: We identified 11 patients who had previously received WBRT to 30 Gy in 10 fractions using 3D-conformal radiation therapy without prospective delineation of the parotid or lacrimal glands. For each patient, these structures were contoured and new 3D and IMRT plans were created to limit the V20 to the parotid glands and the V15 to the lacrimal glands while maintaining the dose to the brain. A previously developed relative seriality (RS) NTCP model was used to assess the reduction in xerostomia and dry eye risk relative to the original plan that was achieved with the new plans. RESULTS: The 3D re-plans significantly (p < 0.001) reduced the estimated risk of xerostomia, by 12.2 ± 4.5%, but did not significantly (p > 0.025) reduce the risk of dry eye. The IMRT re-plans significantly (p < 0.001) reduced the risk of xerostomia, by 20.6 ± 7.2%, and dry eye by 11.0 ± 3.8%. Both re-plans maintained target coverage. CONCLUSION: By using parameter values obtained from NTCP models, we were able to create whole brain plans that lowered the estimated risk of xerostomia and dry eye while maintaining target coverage.