Improvement in dose homogeneity with electronic tissue compensation over IMRT and conventional RT in whole brain radiotherapy.

摘要

BACKGROUND AND PURPOSE: To perform a dosimetric analysis of whole brain radiotherapy using electronic tissue compensation (ECOMP) with dynamic multileaf collimation (dMLC) and its comparisons with inverse-planned intensity modulated radiation therapy (IMRT) with optimization constraints and conventional whole brain radiotherapy (WBRT). MATERIALS AND METHODS: Ten patients (6 adult, 4 pediatric) who were treated at our institution were selected for this study. WBRT fields were defined using opposed lateral fields directed at the intracranial contents and MLC leaves were used to block the critical normal structures. A two-field inverse-planned IMRT plan was then developed using sliding window technique and two optimization constraints. Finally, a dMLC plan with electronic tissue compensation (ECOMP) was developed using identical beam and collimator angles and blocking strategy; the fluence map was generated based on tissue compensation and no additional constraints were given for optimization purposes. This tissue compensation based fluence map was applied to deliver a homogenous dose to the intracranial contents. Radiation dose was identically prescribed to the isocenter (30.0Gy in 10 fractions) for all the cases. A dosimetric comparison was then performed for each method in our patient population. RESULTS: ECOMP significantly reduced the mean maximum dose (D(max)) to the intracranial contents as compared to both WBRT (103.9% vs. 112.4%, p<0.0001) and IMRT (106.1%, p=0.02). ECOMP also reduced the intracranial volume receiving greater than 103% of the prescribed dose (2.6% vs. 54.9%, p<0.0001) and the intracranial volume receiving greater than 105% of the prescribed dose (0% vs. 26%, p<0.0001) as compared to WBRT; there was no statistical difference in these two parameters between ECOMP and IMRT. The mean number of monitor units was increased, however, using both ECOMP and IMRT as compared to WBRT (870 and 860 vs. 318, p<0.0001). CONCLUSIONS: Dynamic multileaf collimation with electronic tissue compensation(ECOMP) leads to improved dose homogeneity with less 'hot spots' as compared to conventional and inverse-planned intensity modulated whole brain radiotherapy. At our institution, ECOMP is being used in all pediatric patients or select adult patients with a long life expectancy requiring cranial radiotherapy.