Evaluation of the liver load index as a predictor of liver exposure in right breast radiotherapy.

BACKGROUND

To compare doses deposited to the liver during right breast radiotherapy with static and dynamic radiotherapy techniques. The second aim was to introduce the liver load index (LLI), a novel index developed to estimate radiation exposure to the liver prior to treatment selection.

MATERIALS AND

METHODS

We prepared radiotherapy treatment plans for ten patients with right breast cancer. Plans were created for conventional 3D conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT) with and without dose optimisation to liver, and hybrid 3D-CRT/volumetric modulated arc therapy (VMAT). Dosimetric evaluation was based on dose-volume histogram (DVH) parameters. The Wilcoxon test was used to assess differences between treatment plans. Spearman's rank correlation was used to determine the correlation between the LLI and the radiation dose to the liver.

RESULT: IMRT plans resulted in significantly higher Dmean (p = 0.0051), V5Gy (p = 0.0051), and V10Gy (p = 0.0051) liver values than 3D-CRT. Compared to non-optimised IMRT [liver not included as an organ at risk (OAR)], liver parameters: V5Gy, V10Gy, V20Gy (p = 0.0051) andV30Gy (p = 0.0152) were significantly lower when the IMRT plan was optimised (IMRTopt), with no increase in doses to other OAR. Compared to standard 3D-CRT, hybrid 3D-CRT/VMAT significantly reduced the V30Gy (p = 0.0209), V40Gy (p = 0.0077). The LLI was significantly correlated with liver Dmean for 3D-CRT (rS = 0.8909, p = 0.0005) and IMRT (rS = 0.8303, p = 0.0029), and also with liver D200 for 3D-CRT (rS = 0.8024, p = 0.0052) and IMRT (rS = 0.8545, p = 0.0016).

CONCLUSION

The LLI provides an accurate estimation of liver exposure to radiation during right breast radiotherapy. This index, which is calculated prior to treatment planning, is highly accurate, as evidenced by the strong correlation between the LLI and the mean liver dose.