Identifying Surrogates for Heart and Ipsilateral Lung Dose to Guide Field Placement and Treatment Modality Selection...

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Virtual simulation (VSim) is used for tangential photon field localization in breast radiotherapy.
• Accurate prediction of heart and ipsilateral lung dose is essential to avoid exceeding tolerance limits and potential treatment pathway delays.
• Current methods lack early predictive surrogates for organ doses during the VSim phase.

Purpose of the Study:

• To identify predictive surrogates for heart and ipsilateral lung dose during VSim for breast radiotherapy.
• To aid in optimal field placement and treatment modality selection.
• To prevent exceeding organ tolerance doses and streamline pre-treatment pathways.

Main Methods:

• Retrospective analysis of computed tomography data from 50 patients undergoing left breast/chest wall radiotherapy.
• Calculation of percentage of heart-in-field (%HIF) and ipsilateral lung-in-field (%ILF) during VSim.
• Correlation of %HIF with mean heart dose (MHD) and %ILF with ipsilateral lung V18Gy using linear regression models.
• Validation of the predictive model in a separate cohort including anterior supraclavicular fossa and internal mammary nodes.

Main Results:

• Strong positive correlations were found between %HIF and MHD (r² = 0.97) and %ILF and ipsilateral lung V18Gy (r² = 0.99).
• The predictive model was validated in cases with anterior supraclavicular fossa and internal mammary node inclusion.
• Calculated threshold values for %HIF and %ILF provide clinically relevant dose predictions.

Conclusions:

• Percentage of heart-in-field and ipsilateral lung-in-field are reliable surrogates for predicting organ doses during VSim.
• These surrogates facilitate accurate dose prediction early in the pre-treatment pathway.
• This approach helps ensure tolerance doses are not exceeded and guides selection of appropriate radiotherapy techniques.