Comparison of modulated electron radiotherapy to conventional electron boost irradiation and volumetric modulated photon arc therapy for treatment of tumour bed boost in breast cancer

Background and purpose

To compare few leaf electron collimator (FLEC)-based modulated electron radiotherapy (MERT) to conventional direct electron (DE) and volumetric modulated photon arc therapy (VMAT) for the treatment of tumour bed boost in breast cancer.

Materials and methods

Fourteen patients with breast cancer treated by lumpectomy and requiring post-operative whole breast radiotherapy with tumour bed boost were planned retrospectively using conventional DE, VMAT and FLEC-based MERT. The planning goal was to deliver 10 Gy to at least 95% of the tumour bed volume. Dosimetry parameters for all techniques were compared.

Results

Dose evaluation volume (DEV) coverage and homogeneity were best for MERT (D₉₈ = 9.77 Gy, D₂ = 11.03 Gy) followed by VMAT (D₉₈ = 9.56 Gy, D₂ = 11.07 Gy) and DE (D₉₈ = 9.81 Gy, D₂ = 11.52 Gy). Relative to the DE plans, the MERT plans predicted a reduction of 35% in mean breast dose (p < 0.05), 54% in mean lung dose (p < 0.05) and 46% in mean body dose (p < 0.05). Relative to the VMAT plans, the MERT plans predicted a reduction of 24%, 36% and 39% in mean breast dose, heart dose and body dose, respectively (p < 0.05).

Conclusions

MERT plans were a considerable improvement in dosimetry over DE boost plans. There was a dosimetric advantage in using MERT over VMAT for increased DEV conformity and low-dose sparing of healthy tissue including the integral dose; however, the cost is often an increase in the ipsilateral lung high-dose volume.