Reproducibility of chestwall and heart position using surface-guided versus RPM-guided DIBH radiotherapy for left breast cancer

Abstract

This study compared the reproducibility of chestwall and heart position using surface-guided versus RPM (real-time position management)-guided deep inspiration breath hold (DIBH) radiotherapy for left sided breast cancer. Forty DIBH patients under either surface-guided radiotherapy (SGRT) or RPM guidance were studied. For patients treated with tangential fields, reproducibility was measured as the displacements in central lung distance (CLD) and heart shadow to field edge distance (HFD) between pretreatment MV (megavoltage) images and planning DRRs (digitally reconstructed radiographs). For patients treated with volumetric modulated arc therapy (VMAT), sternum to isocenter (ISO) distance (StID), spine to rib edge distance (SpRD), and heart shadow to central axis (CAX) distance (HCD) between pretreatment kV images and planning DRRs were measured. These displacements were compared between SGRT and RPM-guided DIBH. In tangential patients, the mean absolute displacements of SGRT versus RPM guidance were 0.19 versus 0.23 cm in CLD, and 0.33 versus 0.62 cm in HFD. With respect to planning DRR, heart appeared closer to the field edge by 0.04 cm with surface imaging versus 0.62 cm with RPM. In VMAT patients, the displacements of surface imaging versus RPM guidance were 0.21 versus 0.15 cm in StID, 0.24 versus 0.19 cm in SpRD, and 0.72 versus 0.41 cm in HCD. Heart appeared 0.41 cm further away from CAX with surface imaging, whereas 0.10 cm closer to field CAX with RPM. None of the differences between surface imaging and RPM guidance was statistically significant. In conclusion, the displacements of chestwall were small and were comparable with SGRT- or RPM-guided DIBH. The position deviations of heart were larger than those of chestwall with SGRT or RPM. Although none of the differences between SGRT and RPM guidance were statistically significant, there was a trend that the position deviations of heart were smaller and more favorable with SGRT than with RPM guidance in tangential patients.

Keywords: breast cancer; comparison; deep inspiration breath hold; real-time position management; surface imaging.

FIGURE 1

Example tangential patient. Central lung distance (CLD) and heart shadow to field edge distance (HFD) measured in DRRs (a), (c), and MV portal images (b), (d), respectively. Yellow contour in (c) is heart (including pericardial fat if presented). ΔCLD = 3.55–3.61 = ‐0.06 cm and ΔHFD = 0.50–0.60 = −0.10 cm

FIGURE 2

Example volumetric modulated arc therapy (VMAT) patient. Sternum to ISO distance (StID), Spine to Rib Edge Distance (SpRD), and Heart Shadow to Central Axis Distance (HCD) measured in DRRs (a), (c), (e), and AP/LAT kV setup images (b), (d), (f), respectively. ΔStID = 1.59–1.63 = −0.04 cm, ΔSpRD = 8.87–8.84 = 0.03 cm, and ΔHCD = 1.47–2.12 = −0.65 cm

FIGURE 3

Box plots of ΔCLD and ΔHFD with RPM‐ and AlignRT‐guided deep inspiration breath hold (DIBH). The central line/marker indicates the median/mean, and the box indicates the 25th and 75th percentiles

FIGURE 4

Correlation between (a) CLD_DRR and CLD_PORT and between (b) HFD_DRR and HFD_PORT in tangential patients. The dashed line is the identity line.

FIGURE 5

Box plots of ΔStID, ΔSpRD, and ΔHCD. The central line/marker indicates the median/mean, and the box indicates the 25th and 75th percentiles

FIGURE 6

Correlation between (a) StID_DRR and StID_PORT, (b) SpRD_DRR and SpRD_PORT, and (c) HCD_DRR and HCD_PORT in volumetric modulated arc therapy (VMAT) patients