ESTRO meets Asia 2024 - Abstract Book

S393

RTT – Treatment planning, OAR and target definitions

ESTRO meets Asia 2024

- Plan_2: Optimization with "No entry+exit".

- Plan_3: Optimization with "No entry".

- Plan_4: Exclusion segments.

Plans 2, 3, and 4 were tested to reduce dose either only to the heart, only to the lungs, or to both the heart and lungs.

As this was a retrospective study, prescriptions and dosimetric objectives remained constant across the plans.

Results:

When attempting to simultaneously reduce dose to both the heart and lungs using any of the optimization tools, a negative impact on tumor dose is observed because it becomes overly restrictive, preventing the expected dose from reaching the tumor. Similarly, when avoiding radiation entry and exit through the organ (Plan_2), it was discarded due to these reasons. After discarding Plan_2, an attempt was made to minimize dose to each organ separately. Better results were achieved by avoiding direct entry (Plan_3) rather than manually selecting exclusion segments (Plan_4).

Figure 1. DVH

Furthermore, when comparing the doses received by both organs and the PTV when avoiding entry through the heart or only through the lungs, a reduction in dose to both organs compared to the reference plan is achieved, while maintaining PTV coverage. Comparing plans that avoid entry through the heart versus only through the lungs yields similar results, indicating that both strategies are equivalent.

Conclusion:

The results indicate that in all patients, dosimetric differences were observed in the heart and lungs. This led to the conclusion that the best optimization tool to minimize dose to these organs at risk is the "no entry" option of "Avoidance Structures". With this tool, the mean dose to the heart and lungs can be reduced by up to 10% without affecting the coverage, conformity, or homogeneity of the PTV.

Finally, it is suggested as future research to expand the sample size of patients to investigate which organ is better to avoid direct beam entry (heart or lungs) and to test this optimization tool for a wider range of pathologies.

Keywords: VMAT, breast, optimization tools

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