A comparison of different intensity modulation treatment techniques for tangential breast irradiation

Several intensity modulation (IM) treatment techniques for tangential breast irradiation were evaluated in terms of dose uniformity in the treated breast volume, contralateral breast dose, and treatment irradiation time.

Contralateral breast dose was measured via TLD chips, and the dose uniformity was calculated on two anthropomorphic phantoms. IM was applied to all beams or to the lateral-medial (LM) beam only. The techniques evaluated include (a) IM via "step & shoot" multileaf collimator (MLC), (b) IM via intensity modulator (compensator), (c) virtual wedge, and (d) physical wedge. A dose optimization algorithm was used for the first two techniques.

Collimator-generated IM techniques (MLC-IM and the virtual wedge) produced 50% (average) less contralateral breast dose than the conventional two-wedge technique. When the compensator or the physical wedge was used, contralateral breast dose was reduced 30% (average) by leaving the ML beam open.

The treatments generated by dose optimization algorithm and delivered via the compensator and MLC techniques offered superior dose uniformity. Single-beam IM techniques in general use less irradiation time without significant degradation of dose uniformity. The MLC-IM technique in this study required the longest treatment irradiation time, while the virtual wedge and compensator IM techniques required the least.