By mimicking the experimental setup in RayStation TPS, proton dose calculations were performed using pencil beam (RS-PB) and Monte Carlo (RS-MC) dose calculation algorithms. 
RayStation TPS
By mimicking the experimental setup in RayStation TPS, proton dose calculations were performed using pencil beam (RS-PB) and Monte Carlo (RS-MC) dose calculation algorithms.  The calculated spot sizes (RS-PB and RS-MC) were then compared against the measured spot sizes.  For the 0 cm air gap, the agreement between the TPS-calculated (RS-PB and RS-MC) and measured spot sizes were within ± 0.1 mm.  For the 35 cm air gap, the RS-PB overpredicted spot sizes by 0.3-0.8 mm, whereas the RS-MC computed spot sizes were within ± 0.3 mm of measured spot sizes.  The comparison between the TPS calculated and measured spot sizes showed that the RS-MC is more accurate (within ± 0.3 mm), whereas the RS-PB overpredicted (up to 0.8 mm) the spot sizes when a range shifter (7.5 cm WET) and large air gaps are encountered in the proton beam path.
RS-PB
By mimicking the experimental setup in RayStation TPS, proton dose calculations were performed using pencil beam (RS-PB) and Monte Carlo (RS-MC) dose calculation algorithms.  The calculated spot sizes (RS-PB and RS-MC) were then compared against the measured spot sizes.  For the 0 cm air gap, the agreement between the TPS-calculated (RS-PB and RS-MC) and measured spot sizes were within ± 0.1 mm.  For the 35 cm air gap, the RS-PB overpredicted spot sizes by 0.3-0.8 mm, whereas the RS-MC computed spot sizes were within ± 0.3 mm of measured spot sizes.  The comparison between the TPS calculated and measured spot sizes showed that the RS-MC is more accurate (within ± 0.3 mm), whereas the RS-PB overpredicted (up to 0.8 mm) the spot sizes when a range shifter (7.5 cm WET) and large air gaps are encountered in the proton beam path.
RS-MC