ESTRO 2024 - Abstract Book

S1832

Clinical - Mixed sites, palliation

ESTRO 2024

For the plan quality metrics, our results demonstrated a reduced value in D mean and D 95% by 4.3% (signed-rank p <0.001) and 4.6% (signed-rank p <0.001) respectively when using the MC algorithm for lung cases. There was also a decrease in D max value but the difference was not significant. The results implied that FSPB plans overestimated D mean and D 95% as expected. The ratio of the plan quality parameters of the MC plans to that of FSPB plans was also computed in our study. The ratio of the target coverage and CI index was less than 1 (0.95 and 0.83 respectively), which implied a lower index of the MC plans. Our results indicated that there was a loss in target coverage and conformity for the MC plans. The HI index also decreased but the difference was not significant. For the dose falloff outside the PTV, a lower GI index was observed for the MC plans with a ratio of 0.84 (signed-rank p <0.001). R 10% increased in the MC plans with a ratio of 1.05 (signed-rank p<0.001). It was deduced that a slower dose falloff in the MC plans. No significant changes in D max,2cm and R 50% . For dose-volume constraints to the lung, there was a significant increase in V 12.5Gy and D mean, lung . No significant changes in V 13.5Gy and V 20Gy . Brain cases were also studied to compare D mean, brain computed by the two algorithms. There was also a significant increase in D mean, brain by 10.1% (signed-rank p=0.006). The results matched our previous result of having a slower dose falloff in the MC plans than in the FSPB plans.

Conclusion:

To conclude, our study showed that the FSPB algorithm overestimated the target dose for lung cases. It reflected a loss in target coverage and conformity when using the MC algorithm. MC plans also had a slower dose falloff outside the PTV which implied a higher dose to the lung. These factors should be taken into account when choosing the dose calculation algorithm. This study sheds light on providing the oncologist, radiation therapist, medical physicist and medical dosimetrist a more comprehensive picture of dosimetric differences when choosing different dose calculation algorithms for the MLC-equipped CyberKnife System.

Keywords: MLC Cyberknife, Monte Carlo and FSPB Algorithms

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