Improving the reproducibility of voluntary deep inspiration breath hold technique during adjuvant left-sided breast cancer radiotherapy

Abstract

Background: Adjuvant radiotherapy (RT) of left-sided breast cancer (LSBC) with voluntary deep inspiration breath hold (vDIBH) technique reduces the cardiac dose. In this study, the effect of marker block position and the efficacy of breath hold level (BHL) correction based on lateral kV setup images are evaluated to improve the daily reproducibility. Material and methods: A total of 148 consecutive LSBC patients treated with vDIBH RT were included in this study. The real-time position management (RPM) marker block was placed on the abdominal wall in 63 patients (group A) and on the sternum in 85 patients (group S). Acquired 900 (group A) þ 1040 (group S) orthogonal image pairs were retrospectively analyzed. The actual BHL was determined from the lateral kV images. The height of the BHL gating window in RPM was corrected if errors of the actual BHL exceeded 4 mm. Setup margins were calculated for the chest wall and for bony surrogates of the lymph node regions. Results: The sternal marker block reduced the random residual errors in the actual BHL (p < 0.05). The BHL correction was required for 26/63 patients in group A and for 26/85 patients in group S. Correction of the BHL window significantly reduced both the systematic and the random residual error in both groups. In patients with lymph node irradiation, the effect of both marker placement and BHL window correction was significant in the superior-inferior direction. Correction of the BHL reduced the mean cardiac dose by 0.5 Gy (p < 0.01) in group A and 0.6 Gy (p < 0.05) in group S. Conclusions: Reproducibility of the BHL can be improved by placing the marker block on the sternum and correcting the height of the BHL window based on lateral kV setup images. Acquisition of lateral kV images in the first 3 fractions and once a week during RT is recommended.

Technical Note: Issues related to external marker block placement for deep inspiration breath hold breast radiotherapy

“…Placement of the RPM block directly on the breast or chest wall has been shown to improve breath hold level reproducibility for left‐sided breast cancer DIBH patients . We investigated three specific concerns when placing the RPM external marker block directly on the breast: (a) surface dose effects; (b) system accuracy with lateral block tilt; and (c) optimal block location on the breast surface.…”

“…Erythema commonly occurs following doses of 3000–4000 cGy to the skin; therefore, for a typical breast dose of 5000 cGy placement of the marker block in the primary beam could lead to increased incidence of erythema. There have been two patient studies where the (two‐dot) RPM marker block has been placed in the primary radiation field: one reported that there were no observed skin reactions resulting from the marker block for 31 patients; the other did not report on the incidence of skin reactions …”

“…We found that superior and mid‐breast positions were strongly correlated with internal chest wall position, whereas the inferior surface contour was only moderately correlated with internal chest wall position. The inferior breast location as defined in this study was close to the xiphoid process; therefore, our results are consistent with other studies concluding that sternal placement of the marker block will result in improved chest wall position reproducibility …”

“…Lutz et al found a statistically significant reduction of the inter‐field random shift and an overall tendency for smaller setup errors, shifts, and chest wall motion with the marker block placed medially on the inferior part of the sternum when compared to marker block placement 5 cm to the right at the level of the xiphoid process. Similarly, a recent prospective trial examined the effect of two‐dot marker block location on daily breath hold position reproducibility for 148 consecutive left‐breast DIBH patients. It was found that sternal marker placement (4 cm above the xiphoid process) significantly reduced the residual errors in breath hold level when compared to placement on the upper abdomen (4 cm below the xiphoid process).…”

Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy

“…This was likely due to the effect of C‐C breathing motion. If the A‐P BHL is lower than planned, it is more likely that positional errors also occur in the C‐C direction 14. Thus, if in 2D image guidance the match of lateral image is performed with a compromise between the sternum and spine, but prioritizing the sternum, then the C‐C residual error of the spine is likely connected with the altered breathing motion.…”