ESTRO 2024 - Abstract Book

S5985

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Proton therapy for breast cancer has become a new and accessible option for patients who are concerned about the long-term side effects of conventional breast irradiation with photon.[1] Proton beams are sensitive to anatomical changes, so a good beam angle arrangement can enhance the treatment plan’s robustness and reduce uncertainty.[2] In recent years, the development of automated treatment planning has flourished, offering consistent high-quality plans and reducing the clinical workload. [3] For breast cancer, beam angle arrangement is relatively straightforward, with primarily en face beams applied. This simplicity makes automated treatment planning more feasible. This feature makes treatment plan automation more feasible. This study aims to examine the feasibility of automated beam angle arrangement for breast cancer proton therapy and to compare the dose differences between plans using manually selected angles and automatically selected angles. The goal is to provide a high-quality reference treatment plan for beginners in proton therapy planning.

Material/Methods:

This emulation study used images and structures of 10 breast cancer patients, with five left-sided and five right-sided tumors. The in-house developed ESAPI program automatically selected the beam angles for the automated plans based on the largest target projection area. The human planners manually selected the beam angles for the manual plans based on their own experience. Each plan applied two beam angles and used a robust optimization method with 5 mm setup uncertainty and 3.5% range uncertainty. The dose distributions of the two sets of plans were compared in terms of dose differences in the target volume and organs at risk. The conformity and homogeneity indices were applied to evaluate the target dose coverage. [4,5]

Results:

The manual plans and automated plans had similar dose distributions. The dose homogeneity and conformity of the target volume were 1.16 and 0.65 for manual plans and 1.16 and 0.63 for automated plans, respectively. The organs at risk, such as lungs, heart, and contralateral breast, showed no significant dose differences. Table 1 summarizes the dosimetry parameter between the human-selected angles plans and automated-selected angles plans.

Table 1. Dosimetry parameters comparison between the human-selected angles plans and automated-selected angles plans.

Manual

plans

Automated

plans

Parameters

( Average (Range))

( Average (Range))

CTV Conformity Inedx

0.65 (0.54-0.85)

0.63 (0.51-0.83)

CTV Homogeneity index

1.16 (1.03-1.20)

1.16 (1.03-1.20)

Heart Dmean(cGy)

43.57 (0.73-161.25)

44.07 (0.71-161.25)

Ipsilateral Lung V20Gy(%)

8.97 (3.5-22.5)

8.93(3.45-23.56)

Contralateral Breast Dmax(cGy)

99.2 (0-307.01)

95.54(0-344.29)

Conclusion: