Unintended irradiation of internal mammary chain – Is that enough?

Abstract

Aim

To evaluate the unintentional coverage of the internal mammary chain (IMC) with tangential fields irradiation to the breast, and its relation with the type of surgery employed.

Background

The dose distribution in regions adjacent to the treatment targets (mammary gland or chest wall), with incidental irradiation of the IMC, could translate into clinical benefit, due to the proximity of these regions.

Materials and methods

One hundred and twelve consecutive conformal radiotherapy plans were correlating the average dose to the IMC with the type of surgery employed, the extent of disease and the irradiation techniques.

Results

The mean doses to IMC after modified radical mastectomy (MRM), modified radical mastectomy with immediate reconstruction (MRM[[ce:hsp sp="0.25"/]]+[[ce:hsp sp="0.25"/]]R), and breast conservative surgery (BCS) were 30.34[[ce:hsp sp="0.25"/]]Gy, 30.26[[ce:hsp sp="0.25"/]]Gy, and 18.67[[ce:hsp sp="0.25"/]]Gy, respectively. Significant differences were identified between patients who underwent MRM or MRM[[ce:hsp sp="0.25"/]]+[[ce:hsp sp="0.25"/]]R over BCS (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.01 and 0.003, respectively), but not between MRM and MRM[[ce:hsp sp="0.25"/]]+[[ce:hsp sp="0.25"/]]R (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.88). Mean doses to IMC were greater in patients with T3–T4 tumors when compared with more initial stages (≤T2) (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.0096). The lymph node involvement also correlated with higher average doses to IMC (node positive: 26.1[[ce:hsp sp="0.25"/]]Gy[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]node negative: 17.8[[ce:hsp sp="0.25"/]]Gy, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.0017).

Conclusions

The moderate dose level to the IMC in the unintentional irradiation scenario seems to be insufficient to treat the subclinical disease, although it could have an impact in patients undergoing mastectomy.