Can field-in-field technique replace wedge filter in radiotherapy treatment planning: a comparative analysis in various treatment sites.

The aim of the study was to show whether field-in-field (FIF) technique can be used to replace wedge filter in radiation treatment planning. The study was performed in cases where wedges are commonly used in radiotherapy treatment planning. Thirty patients with different malignancies who received radiotherapy were studied. This includes patients with malignancies of brain, head and neck, breast, upper and lower abdomen. All the patients underwent computed tomography scanning and the datasets were transferred to the treatment planning system. Initially, wedge based planning was performed to achieve the best possible dose distribution inside the target volume with multileaf collimators (Plan 1). Wedges were removed from a copy of the same plan and FIF plan was generated (Plan 2). The two plans were then evaluated and compared for mean dose, maximum dose, median dose, doses to 2% (D2) and 98% (D98) of the target volume, volume receiving greater than 107% of the prescribed dose (V > 107%), volume receiving less than 95% of the prescribed dose (V< 95%), conformality index (CI) and total monitor units. FIF gives equivalent dosimetric results as wedge based treatment planning. It is better than wedge planning in terms of maximum dose, D2, V >107% and CI for most of the sites with statistically significant reduction in monitor units. FIF results in better dose distribution in terms of homogeneity in most of the sites. It is feasible to replace wedge filter with FIF in radiotherapy treatment planning.