Dosimetric Comparison of Irregular Surface Compensator and Field-in-Field for Whole Breast Radiotherapy.

Purpose: The purpose of the present study was to evaluate the dosimetric benefits of the irregular surface compensator (ISC) technique for whole breast radiotherapy compared with the field-in-field (FIF) technique.

Materials and Methods: Radiotherapy was planned using both techniques in 50 breast cancer patients (25 left sided and 25 right sided). The Eclipse treatment planning system (Varian Medical Systems) was used for dose calculations. For the FIF technique, subfields were added to the main fields to reduce hot and cold regions; for the ISC technique, the fluence editor application was used to extend the optimal fluence. Planning target volume dose, dose homogeneity index (DHI), maximum dose, ipsilateral lung, and heart doses for the left breast irradiation and monitor unit (MU) counts required for treatment were compared between the two techniques.

Results: Compared with the FIF technique, the ISC technique significantly decreased DHI values and volumes receiving >105% of the prescription dose, and increased volumes receiving >95% of the dose and MU count ( P < 0.01 for all comparisons). For the heart and ipsilateral lung, the FIF technique significantly reduced volumes receiving >5 Gy compared with the ISC technique ( P < 0.01); however, volumes receiving >10, 20, and 30 Gy and the values of a mean dose did not differ significantly between the techniques ( P > 0.05).

Conclusions: The ISC technique is preferred over the FIF technique.