ESTRO 2024 - Abstract Book

S6013

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

50 Gy in 25 fractions, without simultaneous integrated boost. The planning goals were based on established protocols, and both MF and RO approaches had the same OAR planning goals [24-26]. The MF approach involved the creation of a virtual bolus and a pseudo-PTV, while the RO approach accounted for uncertainties related to chest wall motion, breast swelling, and positioning errors [2,27]. To evaluate plan robustness, organ motion uncertainties were simulated using the RayStation treatment planning system. The plan robustness was quantified by measuring the volume/dose difference between the nominal and worst scenarios (ΔV/ΔD) for each CTV and OARs parameter with a smaller difference representing more robust. Statistical analysis was conducted with SPSS Statistics 28, and a paired sample t-test was used to compare the average robustness values of the MF and RO plans [28-33].

Results:

The RO approach demonstrated smaller ΔV/ΔD values for all parameters (except CTV ΔD98%) when compared to the MF approach. Additionally, the differences in ΔV/ΔD values between the RO and MF plans were statistically significant (p<0.001-0.012) for all CTV parameters, except CTV ΔV95%, ΔD98%, and heart ΔDmean. Table 1 presents the ΔV/ΔD values. The results of our study confirmed the superiority of the RO approach over the MF approach. Specifically, the RO plans exhibited better target coverage, high-dose control, and cardiac sparing. However, the RO approach had a weakness regarding CTV underdose, as represented by CTV ΔD98%. Nonetheless, both approaches could generate clinically acceptable plans, as demonstrated in Table 2, which shows the nominal dose statistics of plans created by MF and RO approaches, respectively.