Simultaneous integrated boost in breast conserving treatment of breast cancer: A dosimetric comparison of helical tomotherapy and three-dimensional conformal radiotherapy

Background and purpose: To evaluate the dosimetry of helical tomotherapy (HT) and three-dimensional conformal radiotherapy (3D-CRT) in breast cancer patients undergoing whole breast radiation with simultaneous integrated boost (SIB) of the tumor bed. Material and methods: Thirteen patients with breast cancer treated by lumpectomy and requiring whole breast radiotherapy with tumor bed boost were planned using both HT and 3D-CRT using the field-in-field technique. The whole breast and tumor bed were prescribed 50.68 Gy and 64.4 Gy, respectively, in 28 fractions. Dosimetries for both techniques were compared. Results: Coverage of the whole breast was adequate with both techniques (V95% = 96.22% vs. 96.25%, with HT and 3D-CRT, respectively; p = 0.64). Adequate tumor bed coverage was also achieved, although it was significantly lower with HT (V95% = 97.18% vs. 99.72%; p < 0.001). Overdose of the breast volume outside the tumor bed was significantly lower with HT (V54.23Gy = 12.47% vs. 30.83%; p < 0.001). Ipsilateral lung V20Gy (6.34% vs. 10.17%; p < 0.001), V5Gy (16.54% vs. 18.53%; p < 0.05) and mean dose (4.05 Gy vs. 6.36 Gy; p < 0.001) were significantly lower with HT. In patients with left-sided tumors, heart V30Gy (0.03% vs. 1.14%; p < 0.05) and mean dose (1.35 Gy vs. 2.22 Gy; p < 0.01) were significantly lower with HT, but not V5Gy. Contralateral breast V5Gy (0.27% vs. 0.00%; p < 0.01) and maximum dose were significantly increased with HT. Conclusions: In breast cancer treated with SIB, both HT and 3D-CRT provided adequate target volume coverage and low heart doses. Tumor bed coverage was slightly lower with HT, but HT avoided unnecessary breast overdosage while improving ipsilateral lung dosimetry.