Analysis of parotid and lacrimal gland radiation dose in hippocampal-voiding whole brain radiation therapy
International Journal of Radiation Oncology • Biology • Physics
Purpose/Objective(s): Hippocampal avoidance (HA) has become a standard of care following the publication of NRG CC-001. This technique decreases neurocognitive sequelae of conventional whole brain radiation therapy (C-WBRT). It has previously been reported that C-WBRT planned with opposed lateral fields causes clinically significant acute lacrimal gland (LG) and parotid gland (PG) toxicity. There remains uncertainty regarding the dosimetric impact of HA-WBRT. We hypothesized that intensity modulation utilized for HA-WBRT may unintentionally lead to higher integral doses to nearby at-risk structures while delivering WBRT, specifically the LGs and PGs. Materials/Methods: We performed a retrospective analysis of C-WBRT and HA-WBRT plans from patients treated at a single institution using conventionally fractionated radiation therapy with palliative intent. We retrospectively contoured the parotid and lacrimal glands for each patient. Dose-volume histograms were generated for the LGs and PGs. We then performed comprehensive dosimetric analysis comparing parameters between patients who received C-WBRT versus HA-WBRT. Factors evaluated included: mean parotid dose, mean lacrimal dose, maximum parotid dose, maximum lacrimal dose, and V2Gy through V38Gy at increments of 2 Gy. DMean and DMax were compared with a Mann-Whitney U test with Bonferroni correction for multiple hypotheses testing. Results: Dose to the PGs and LGs was retrospectively evaluated for 14 patients, 8 of whom were treated using HA-WBRT and 6 of whom were treated using traditional WBRT with opposed lateral fields. In general, the HA-WBRT plans were noted to deliver higher low-dose and lower highdose to the LGs and PGs. There were no statistically significant differences in DMean and DMax between the two groups of patients in any of the evaluated structures. The V26, V28, and V30 for the bilateral PGs were lower with HA-WBRT. Conclusion: Dose to the LGs and PGs were similar between patients treated with C-WBRT and HA-WBRT, with a reduction in clinically significant parotid gland doses with HA-WBRT. Prospective avoidance of these structures with HA-WBRT may afford the ability to further reduce dose and potentially decrease toxicity. Further work will explore this opportunity.
Grzywacz VP, Levitin R, Porter E, Siddiqui ZA, Thompson A, Grills IS, Chinnaiyan P, Guerrero TM. Analysis of Parotid and Lacrimal Gland Radiation Dose in Hippocampal-avoiding Whole Brain Radiation Therapy. International Journal of Radiation Oncology, Biology, Physics. 2020 Nov 1;108(3):e368-9.