Author: Michael Evan Chaga, Timothy Chen, Darra M. Conti, Shabbar Danish, Jing Feng, Wenzheng Feng, Joseph Hanley, Tingyu Wang 👨🔬
Affiliation: Hackensack Meridian Health, Jersey Shore University Medical Center 🌍
Purpose: ZAP-X is the newest cranial stereotactic radiosurgery (SRS) platform. Small-volume structures usually found in the head and neck may be susceptible to dose-volume averaging, which has not been studied for ZAP-X. The impact of calculation grid size on dose distribution is investigated for ZAP-X SRS using the two available grid sizes in the treatment planning system, 0.5- and 1-mm.
Methods: An SRS plan was generated for a single Acoustic Neuroma patient and dose was optimized and calculated using the 1-mm grid size. Dose was then calculated for the plan using the 0.5-mm grid. Dose parameters were obtained for the gross target volume (GTV) and organs-at-risk (OARs) such as maximum pixel dose (Dmax), mean pixel dose (Dmean), maximum dose to 0.035 cm3 (D0.035cm3), volume receiving 1590 cGy (V1590cGy), conformity index (CI), gradient index (GI), and homogeneity index (HI).
Results: The dose parameters obtained at 1-mm grid were: GTV Dmax = 3169.01 cGy, GTV Dmean = 2497.23 cGy, CI = 1.39, HI = 1.76, GI = 2.93 cGy, Cochlea Dmax = 1483.82 cGy, Cochlea D0.035cm3 = 972.89 cGy, Brainstem Dmax = 1646.21 cGy, Brainstem D0.035cm3 = 900 cGy, Brainstem V1590cGy = 0 cm3. The dose parameters obtained at 0.5-mm grid were: GTV Dmax = 3169.19 cGy, GTV Dmean = 2512.26 cGy, CI = 1.40, HI = 1.76, GI = 2.91 cGy, Cochlea Dmax = 1465.56 cGy, Cochlea D0.035cm3 = 957.09 cGy, Brainstem Dmax = 1655.22 cGy, Brainstem D0.035cm3 = 893.71 cGy, Brainstem V1590cGy = 0 cm3. The greatest dose differences occurred for Cochlea Dmax (difference = 18.26 cGy) and Cochlea D0.035cm3 (difference = 15.80 cGy).
Conclusion: ZAP-X grid size minimally impacts dose distribution, but careful consideration is warranted for small OAR structures like the Cochlea.