ESTRO 2024 - Abstract Book

S892

Clinical - CNS

ESTRO 2024

minimizing beam-on time (BOT) and Gradient Index (GI), in this order of importance. Also, the maximum doses (D0.03cc) to critical structures (brainstem and optic pathways) were calculated. Finally, the normal brain receiving 12 Gy (V12Gy) was calculated for all cases, while the V20Gy and V24Gy were calculated for 3 or 5 fractions, respectively. Plan quality metrics and delivery parameters between GK and each of the other platforms (CK, VMAT, MRL, and ZAP X) were compared for all patients using a paired Wilcoxon signed rank test (p<0.05) to evaluate for statistical significance.

Results:

The average largest linear dimension and volumes of treated volumes (GTVs or CTVs) were 3.90 ± 1.37 cm and 7.66 ± 5.22 cc, respectively. All GK plans satisfied clinical goals with a median PCI [Interquartile range] of 0.93 [0.90-0.93], median GI of 2.52 [2.48-2.60], median brain Dmean dose of 2.45 Gy [1.30-3.35 Gy], and a median D0.03cc dose within the GTV/CTV of 52.5 Gy [51.1-54.6 Gy]. PCIs of GK plans (0.93 [0.90-0.93]) were significantly higher than ZAP-X (0.90 [0.86-0.92]; p<0.01), significantly lower than VMAT plans (0.96 [0.94-0.96]; p<0.01) and MRL plans (0.94 [0.93 0.95]; p<0.05), but not significantly different than CK (0.93 [0.89-0.94]; p>0.05). GIs of GK plans (2.52 [2.48-2.60]) were significantly lower than CK (2.94 [2.80-3.21]; p<0.01) and MRL plans (3.22 [3.14-3.55]; p<0.01) and higher than ZAP-X (2.35 [2.33-2.45]; p<0.01); not statistically significantly different when compared to VMAT plans (2.54 [2.44 2.69]; p=0.60). The average normal brain volume receiving 20 Gy (V20Gy) for intact brain metastases with GK (14.42 ± 9.61 cc) was significantly lower as compared to CK, and MRL plans (17.05 ± 9.95 cc and 16.91 ± 10.82 cc; p<0.05), while no statistical significance was found in comparison to VMAT (14.66 ± 9.41 cc; p=0.65) and ZAP-X (14.63 ± 9.36 cc; p=0.17). The average normal brain volume receiving 24 Gy (V24Gy) for postoperative brain metastases cavities with GK (33.39 ± 10.04 cc) was significantly lower as compared to CK plans (37.29 ± 11.43 cc; p<0.01), significantly higher than VMAT (32.23 ± 9.58 cc; p<0.05), while no statistically significant difference was found in comparison to MRL (35.59 ± 11.40 cc; p=0.06) and ZAP-X (33.20 ± 10.17 cc; p=0.96). The average normal brain volume receiving 12 Gy (V12Gy) for the total of cases with GK (48.08 ± 29.63 cc) was also significantly lower as compared to CK, VMAT, and MRL (57.18 ± 35.67 cc, 50.34 ± 30.05 cc, and 68.28 ± 41.64 cc, respectively; p<0.05), and not statistically significantly different as compared to ZAP-X plans (49.03 ± 31.51 cc; p=0.68). Median GK BOT (33.55 min [29.00 35.74 min] @2.5Gy/min) was significantly longer than CK, VMAT, and MRL (26.00 min [23.00-29.00 min], 2.98 min [2.50-3.43 min], and 4.13 min [3.38-7.04 min], respectively; p<0.01) and shorter than ZAP-X (46.44 min [35.88-54.22 min]; p<0.05). No significant difference was noted when comparing the maximum doses (D0.03cc) to several OARs, such as the brainstem or optic pathway between GK and other platforms.