Comparison of set-up errors by breast size on wing board by portal imaging

Abstract

Aim

To quantify and compare setup errors between small and large breast patients undergoing intact breast radiotherapy.

Methods

20 patients were inducted. 10 small/moderate size breast in arm I and 10 large breast in arm II. Two orthogonal and one lateral tangent portal images (PIs) were obtained and analyzed for systematic (Σ) and random (σ) errors. Effect of no action level (NAL) was also evaluated retrospectively.

Results

142 PIs were analyzed. Σ(mm) was 3.2 versus 6.7 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.41) in the mediolateral (ML) direction, 2.1 versus 2.9 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.06) in the craniocaudal (CC) and 2.2 versus 3.6 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.08) in the anteroposterior (AP) direction in small and large breast, respectively. σ(mm) was 3.0, 3.3 and 3.3 for small breast and 4.1, 3.7 and 3.2 for large breast in the ML, CC and AP direction (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.07, 0.86, 0.37), respectively. 3 D Σ(mm) was 2.7 versus 4.2 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.01) and σ(mm) was 2.5 versus 3.2 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.14) in arm I and II, respectively. The standard deviation (SD) of variations (mm) in breast contour depicted by central lung distance (CLD) was 5.9 versus 7.4 (p[[ce:hsp sp="0.25"/]]<[[ce:hsp sp="0.25"/]]0.001), central flash distance (CFD) 6.6 versus 10.5 (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.002), inferior central margin (ICM) 4 versus 4.9 (p[[ce:hsp sp="0.25"/]]<[[ce:hsp sp="0.25"/]]0.001) in arm I and II, respectively. NAL showed a significant reduction of systematic error in large breast in the mediolateral direction only.

Conclusion

Wing board can be used in a busy radiotherapy department for setting up breast patients with a margin of 1.1[[ce:hsp sp="0.25"/]]cm, 0.76[[ce:hsp sp="0.25"/]]cm and 0.71[[ce:hsp sp="0.25"/]]cm for small breasts and 1.96[[ce:hsp sp="0.25"/]]cm, 1.12[[ce:hsp sp="0.25"/]]cm and 0.98[[ce:hsp sp="0.25"/]]cm for large breast in the ML, AP and CC directions, respectively. The large PTV margin in the mediolateral direction in large breast can be reduced using NAL. Further research is needed to optimize positioning of large breasted women.