Improved Breast Irradiation Techniques Using Multistatic Fields or Three Dimensional Universal Compensators

Han, Youngyih; Cho, Jae Ho; Park, Hee Chul; Chu, Sung Sil; Suh, Chang Ok

Abstract

PURPOSE: In order to improve dose homogeneity and to reduce acute toxicity in tangential whole breast radiotherapy, we evaluated two treatment techniques using multiple static fields or universal compensators.
MATERIALS AND METHODS
1) Multistatic field technique : Using a three dimensional radiation treatment planning system, Adac Pinnacle 4.0, we accomplished a conventional wedged tangential plan. Examining the isodose distributions, a third field which blocked overdose regions was designed and an opposing field was created by using an automatic function of RTPS. Weighting of the beams was tuned until an ideal dose distribution was obtained. Another pair of beams were added when the dose homogeneity was not satisfactory. 2) Universal compensator technique : The breast shapes and sizes were obtained from the CT images of 20 patients who received whole breast radiation therapy at our institution. The data obtained were averaged and a pair of universal physical compensators were designed for the averaged data. DII (Dose Inhomogeneity Index : percentage volume of PTV outside 95-105% of the prescribed dose), Dmax (the maximum point dose in the PTV) and isodose distributions for each technique were compared.
RESULTS
The multistatic field technique was found to be superior to the conventional technique, reducing the mean value of DII by 14.6% ( p value<0.000) and the Dmax by 4.7% ( p value<0.000). The universal compensator was not significantly superior to the conventional technique since it decreased Dmax by 0.3% ( p value=0.867) and reduced DII by 3.7% ( p value=0.260). However, it decreased the value of DII by maximum 18% when patients' breast shapes fitted in with the compensator geometry.
CONCLUSION
The multistatic field technique is effective for improving dose homogeneity for whole breast radiation therapy and is applicable to all patients, whereas the use of universal compensators is effective only in patients whose breast shapes fit inwith the universal compensator geometry, and thus has limited applicability.