ESTRO 2024 - Abstract Book

S4653

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Results:

Dosimetric objectives were met with both techniques for all plans, with exception of the ribs dose at 2cm3, which constraint was exceeded in 2 IMPT plans and 13 VMAT plans out of 20. The IMPT dose delivered to the chest wall, ribs, and lungs in relation to constraint were considerably less than those delivered by VMAT plans. Generally, the biological effective dose (BED) of the organs at risk (alpha/beta=3 Gy) decreased by 15.3 Gy for chest wall D70cm3 (P<0.001), by 36.2 Gy for chest wall D2cm3 (P=0.020), and by 43.5 Gy for ribs D2cm3 (P<0.001). The average volume of the lungs-less-ITV fulfilling the (BED3 equivalent of) V20Gy constraint lowered from 3.0% to 1.3% (P<0.001). Prescription isodoses covered more than 95% of CTV volume in all plans for both IMPT and VMAT (mean values are 95.3%±0.8% for IMPT and 98.6%±1.6% for VMAT; P<0.001). CTV D95% average value of all scenarios for IMPT and VMAT plans was respectively 93.6% and 98.6% of prescription dose, indicating adequate and robust target coverage. No statistically significant differences were observed in terms of CI and GI between IMPT and VMAT plans.

Conclusion:

Comparing IMPT plans to VMAT plans, the former offered a significant dose reduction to the organs at risk, with special attention to the maximum dose to the ribs, all without compromising target coverage. In a robust evaluation, passing rate scenarios for target coverage produced sufficiently high results even in the robust and PTV-less optimization process used for IMPT plans. These findings confirm the possibility of a reduction in late toxicities in patients with lung diseases receiving SBRT. Further analysis on normal tissue complications is necessary in order to evaluate the clinical implications of these outcomes.

Keywords: IMPT, lung SBRT, collimated active spot-scanning