[Factors influencing clinical target volume delineation of intact breast in intensity-modulated radiotherapy for breast cancer].

BACKGROUND & OBJECTIVE: In patients with breast cancer who underwent breast conservation treatment, intensity-modulated radiotherapy (IMRT) has been approved to hold better dosimetric advantages and improbable future. Target delineation is the most important process, which determines the accuracy of planning and application of IMRT. However, there is no consensus criterion for the delineation of clinical target volume (CTV) of intact breast. This study was to investigate the factors influencing the delineation of CTV of intact breast in IMRT for breast cancer.

METHODS

The CTV of intact breast in 6 patients was delineated by 4 radiation oncologists and 1 radiologist individually, and reference CTV was determined by group consensus. The extent of variation in CTV delineation was quantified by the ratio of common volumes (Vco) of all CTVs to the maximum volume encompassing all CTVs (Vmax). The deviation in the extent of CTV from the extent of reference CTV was quantified in each orthogonal direction to find the origins of variations. In addition, all central lung distances (CLD) in tangential fields, which were designed based on CTVs, were measured.

RESULTS

The ratios of Vco to Vmax were low (0.660 and 0.651, respectively) in 2 patients with low glandular density. Among the other 4 patients with high glandular density, the ratio was relatively higher in 2 patients with radio-opaque marks than in the other 2 patients with no marks (0.799, 0.769 vs. 0.735, 0.752, respectively). Compared with reference CTVs, the patients' average deviations of the extent of CTVs were 0 in anterior direction, (1.2+/-3.4) mm in posterior direction, (1.5+/-2.1) mm in cranial direction, (0.7+/-4.1) mm in caudal direction, (0.6+/-3.3) mm in medial direction, and (0.8+/-0.8) mm in lateral direction. The most obvious variations were observed in the area of breast axillary part and primary tumor bed after surgery. The mean CLD in 4 patients exceeded over the conventional limitation of 2 cm.

CONCLUSION

The variability between CTVs of intact breast delineated by different radiation oncologists is strongly related to individual glandular density, the extent of breast axillary part, the primary tumor bed after surgery, and the different understanding for lung sparing limitations.