Can proton therapy improve the therapeutic ratio in breast cancer patients at risk for nodal disease?

OBJECTIVES

Regional node irradiation in patients with invasive breast cancer often results in increased radiation exposure to organs at risk. We evaluated the potential advantages of 3-dimensional conformal photon+proton therapy (3DCX+PT) in treating regional nodes versus photon-electron (3DCRT) or intensity-modulated radiotherapy (IMRT).

MATERIALS AND

METHODS

Ten left-sided breast cancer patients underwent radiation treatment planning. 3DCX+PT, 3DCRT, and IMRT plans were generated for each patient.

RESULTS

There was no significant difference in target coverage between 3DCX+PT and IMRT. However, coverage of level II axillary lymph nodes was inferior with 3DCRT with a median D95 of 45 versus 50 Gy with either IMRT (P=0.0006) or 49.5 CGE with 3DCX+PT (P=0.0033). Internal mammary nodes coverage was also inferior with 3DCRT (median D95 was 42 Gy) compared with 47 Gy with IMRT (P=0.043) or 48.5 CGE with 3DCX+PT (P=0.0068).With 3DCX+PT, left lung V20 and V5 were 31% and 50% versus 36% (P=0.0368) and 70% (P=0.0007) with 3DCRT and 30% (P=0.7328) and 81% (P=0.0002) for IMRT. 3DCX+PT resulted in heart V20 and heart V5 of 0% and 7%, respectively, versus 4% (P=0.0067) and 24% (P=0.0002) with 3DCRT and 21% (P=0.0001), 50% (P=0.0001) with IMRT. The IMRT plans produced significantly higher integral, contralateral lung, and breast doses.

CONCLUSIONS

Regional node target coverage was inferior with 3DCRT compared with either IMRT or 3DCX+PT. Organs at risk were exposed to less radiation with 3DCX+PT compared with 3DCRT or IMRT. Proton treatment offered both improved coverage of the regional lymph nodes and decreased dose to the heart, lung, and contralateral normal tissue.