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Comparison of Setup Error of Chestwall and Heart Using AlignRT-Guided Vs. RPM-Guided DIBH in Left Breast Radiotherapy

W Lu1*, G Li1, L Hong1, E Gillespie1, E Yorke1, S Berry1, J Mechalakos1, S Powell1, X Tang1,2, (1) Memorial Sloan Kettering Cancer Center, New York, NY, (2) Yale New Haven Hospital, New Haven, CT

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To compare the setup accuracy of chestwall and heart with AlignRT-guided vs. RPM-guided DIBH for left breast radiotherapy.

Methods: Fourty left breast or chest wall patients (20 tangential fields, 20 VMAT; ten of each with AlignRT- or RPM-guided DIBH) were retrospectively evaluated. Weekly MV portal images and daily orthogonal kV images were taken. Setup errors were measured as the difference of the following parameters in MV or kV images vs. planing DRR: For tangential patients (1) Central Lung Distance (CLD) and (2) Heart Shadow to Field Edge Distance (HFD); For VMAT patients (1) Sternum to ISO Distance (SID), (2) Spine to Rib Edge Distance (SRD) and (3) Heart Shadow to Central Axis (CAX) Distance (HCD). The setup errors of chestwall and heart were compared between AlignRT-guided DIBH and RPM-guided DIBH.

Results: In tangential patients, the mean absolute setup errors of RPM vs. AlignRT were 0.17 vs. 0.14 cm in CLD, and 0.51 vs. 0.28 cm in HFD. Heart moved closer to the field edge on average by 0.48 cm with RPM vs. 0.08 cm with AlignRT. In VMAT patients, the setup errors of RPM vs. AlignRT were 0.21 vs. 0.16 cm in SID, 0.23 vs. 0.25 cm in SRD, and 0.71 vs. 0.83 cm in HCD. Heart moved on average 0.71 cm closer to field CAX with RPM, whereas 0.56 cm further away CAX with AlignRT.

Conclusion: The setup errors of chestwall were small and similar between RPM- or AlignRT-guided DIBH. The setup errors of heart with AlignRT-guided DIBH were smaller in tangential patients and not significantly different in VMAT patients, compared to RPM-guided DIBH. Furthermore heart motion was in a favorable direction with AlignRT-guided DIBH. These results suggested that AlignRT-guided DIBH may lead to more reproducible heart position and better heart dose reduction than RPM-guided DIBH.

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Funding Support, Disclosures, and Conflict of Interest: This work was supported in part through the NIH/NCI Cancer Center Support Grant P30 CA008748.

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