Dosimetric impact of reduced nozzle-to-isocenter distance in intensity-modulated proton therapy of intracranial tumors in combined proton-carbon fixed-nozzle treatment facilities

Table 2 Planning target volume coverage for treatment plans prepared in two different room positions

Dosimetric index	d_ISO	d_ISO-40	p
D_min [Gy(RBE)]	46.4 (44.9÷47.6)	46.0 (43.9÷47.1)	0.791
D_near-min [Gy(RBE)]	48.5 (48.4÷48.9)	48.6 (48.5÷48.9)	0.068
D_mean [Gy(RBE)]	50.4 (50.3÷50.5)	50.4 (50.2÷50.5)	0.204
D_near-max [Gy(RBE)]	52.2 (51.8÷52.6)	52.1 (51.7÷52.3)	0.021*
D_max [Gy(RBE)]	53.8 (53.1÷55.7)	54.3 (53.1÷55.4)	0.126
CI_95% [−]	0.69 (0.45÷0.81)	0.70 (0.49÷0.83)	0.042*
CI_50% [−]	0.30 (0.19-0.41)	0.36 (0.22-0.47)	0.002*

Values are median (range) of patient cohort.
Abbreviations: RBE relative biological effectiveness, D_(near-)min (near) minimum dose, D_(near-)max (near) maximum dose, D_mean mean dose, CI_X% conformity index of PTV coverage with X% of prescription dose, d_ISO nozzle-to-treatment-isocenter 100 cm (treatment at room isocenter), d_ISO-40 nozzle-to-treatment-isocenter 60 cm.
* statistically significant difference (p < 0.05 two-tailed Wilcoxon signed-rank test).

ISSN: 1748-717X