Reproducibility of Chestwall and Heart Position Using AlignRT-Guided Vs. RPM-Guided DIBH Radiotherapy for Left Breast Cancer
W Lu*, G Li, L Hong, E Yorke, X Tang, J Mechalakos, P Zhang, L Cervino, S Powell, S Berry, Memorial Sloan Kettering Cancer Center, New York, NY
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PO-GePV-M-216 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To compare the reproducibility of chestwall and heart position using AlignRT-guided vs. RPM-guided deep inspiration breath hold (DIBH) radiotherapy for left breast cancer.
Methods: Forty patients were studied retrospectively. Pretreatment MV portal images for tangential patients and orthogonal kV images for VMAT patients were acquired. Breath hold reproducibility were measured as the displacements in Central Lung Distance (CLD) and Heart Shadow to Field Edge Distance (HFD) between MV images and planning DRR for tangential patients; Sternum to ISO Distance (SID), Spine to Rib Edge Distance (SRD) and Heart Shadow to Central Axis (CAX) Distance (HCD) between kV images and planning DRR for VMAT patients. These displacements were compared between AlignRT-guided DIBH and RPM-guided DIBH, using ANOVA test for repeated measurements.
Results: In tangential patients, the mean absolute displacements of AlignRT vs. RPM guidance were 0.19 vs. 0.23 cm in CLD, and 0.33 vs. 0.62 cm in HFD. With respect to planning DRR, heart appeared closer to the field edge by 0.04 cm with AlignRT vs. 0.62 cm with RPM. In VMAT patients, the displacements of AlignRT vs. RPM guidance were 0.21 vs. 0.15 cm in SID, 0.24 vs. 0.19 cm in SRD, and 0.72 vs. 0.41 cm in HCD. Heart appeared 0.41 cm further away from CAX with AlignRT, whereas 0.10 cm closer to field CAX with RPM. None of the differences between AlignRT and RPM guidance was statistically significant.
Conclusion: The displacement of chestwall were small and comparable with RPM- or AlignRT-guided DIBH. Though not statistically significant, the position deviation of heart with AlignRT-guided DIBH was in a favorable direction and smaller in tangential patients but larger in VMAT patients, compared to RPM-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 in tangential patients.
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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