Dosimetric comparison of conventional and field-in-field techniques in early-stage breast cancer radiotherapy

Breast conserving surgery followed by adjuvant whole breast radiotherapy is the accepted treatment in early-stage breast cancer. Due to breast irregularities, it is difficult to achieve homogenous dose distribution with conventional techniques. Currently, it is possible to use varied breast irradiation techniques such as field-in-field (FIF) that is claimed to produce more homogenous distribution of doses within the target volumes while sparing the organs at risk, leading to a better treatment outcome. The present study aimed to compare the conventional and the FIF techniques dosimetrically.

Twenty patients with early-stage breast cancer underwent computed tomography. Two different treatment plans were created for each patient: the wedge-based (conventional) plan and the FIF plan. Dosimetric parameters and monitor units were compared with paired sample t-test.

FIF technique obtained significantly lower dose homogeneity index, lower maximum doses and higher median doses in PTV (P<0.05). Similarly, the conformity index, and mean doses were higher in the FIF technique but the differences were not significant (P>0.05). In ipsilateral lungs, FIF significantly reduced the maximum and mean doses (P<0.05), and showed a tendency to reduce V20 (P>0.05). In patients with left-sided breast cancer, minimum and maximum doses and V40 of heart were significantly decreased in FIF plans (P<0.05). Doses to the contralateral lungs did not differ significantly.

These results along with significantly less monitor units required for therapy in FIF suggest that this technique may be more advantageous during breast irradiation.