3D-CRT Techniques for Simultaneously Integrated Boost in Breast Conserving Radiation Therapy

Aim: To evaluate the dosimetric outcomes of two different three dimensional conformal radiation therapy (3D-CRT) of concomitant boost delivery to the intact breast. Methods: Ten patients were evaluated using two standard opposed tangents conformal to the whole breast PTV, plus a pair of wedged fields conformal to the boost PTV; all fields have the same isocenter, placed in the whole breast planning target volume (PTV) (WBI) or located in the boost (BI) PTV. Dose Volume Histograms were calculated and analysed for the difference in maximum and minimum doses; also mean doses and volumes receiving 90% and 107% of the prescribed dose. Lung irradiation was analysed in terms of maximum and mean doses. Results: For breast PTV coverage, significant differences were observed only in the maximum doses (62.3Gy Vs. 61Gy, p=0.003) and higher Dose Homogeneity Index DHI (0.66 Vs. 0.64, p=0.003) in favour WBI. For boost PTV coverage, a significant difference between the two techniques with maximum dose (62.6 versus 60.87, p=0.003) as well the DHI (0.97 Vs. 0.94, p=0.002) in favour of WBI. The Conformity Index CI was significantly better in WBI (0.87 Vs. 0.64, p=0.001). Dose to lung or healthy tissue was not statistically significant difference between the two methods. Conclusion: This study shows a dosimetrical superiority of using the whole breast isocenter technique over boost isocenter technique in whole breast PTV coverage, dose homogeneity index and boost PTV coverage. The clinical significance of this difference needs further clinical studies.