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

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 (30.0 Gy 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.

Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis.

BACKGROUND: Radiosurgery can deliver a single, large radiation dose to a localized tumor using a stereotactic approach and hence, requires accurate and precise delivery of radiation to the target. Of the extracranial organ targets, the spine is considered a suitable site for radiosurgery, because there is minimal or no breathing-related organ movement. The authors studied spinal radiosurgery in patients with spinal metastases to determine its accuracy and precision. METHODS: The spinal radiosurgery program was based on an image-guided and intensity-modulated, shaped-beam radiosurgical unit. It is equipped with micromultileaf collimators for beam shaping and radiation intensity modulation and with a noninvasive, frameless positioning device that uses infrared, passive marker technology together with corroborative image fusion of the digitally reconstructed image from computed tomography (CT) simulation and orthogonal X-ray imagery at the treatment position. These images were compared with the port films that were taken at the time of treatment to determine the accuracy of the isocenter position. Clinical feasibility was tested in 10 patients who had spinal metastasis with or without spinal cord compression. The patients were treated with fractionated external beam radiotherapy followed by single-dose radiosurgery as a boost (6-8 grays) to the most involved portion of the spine or to the site of spinal cord compression. RESULTS: The accuracy for the isocenter was within 1.36 mm +/- 0.11 mm, as measured by image fusion of the digitally reconstructed image from CT simulation and the port film. Clinically, the majority of patients had prompt pain relief within 2-4 weeks of treatment. Complete and partial recovery of motor function also was achieved in patients with spinal cord compression. The radiation dose to the spinal cord was minimal. The maximum dose of radiation to the anterior edge of the spinal cord within a transverse section, on average, was 50% of the prescribed dose. There was no acute radiation toxicity detected clinically during the mean follow-up of 6 months. CONCLUSIONS: Image-guided, shaped-beam spinal radiosurgery is accurate and precise. Rapid clinical improvement of pain and neurologic function also may be achieved. The results indicate the potential of spinal radiosurgery in the treatment of patients with spinal metastasis, especially those with solitary sites of spine involvement, to increase the prospects of long-term palliation.