Results of a multi-institutional benchmark test for cranial CT/MR image registration.

PURPOSE: Variability in computed tomography/magnetic resonance imaging (CT/MR) cranial image registration was assessed using a benchmark case developed by the Quality Assurance Review Center to credential institutions for participation in Children's Oncology Group Protocol ACNS0221 for treatment of pediatric low-grade glioma. METHODS AND MATERIALS: Two DICOM image sets, an MR and a CT of the same patient, were provided to each institution. A small target in the posterior occipital lobe was readily visible on two slices of the MR scan and not visible on the CT scan. Each institution registered the two scans using whatever software system and method it ordinarily uses for such a case. The target volume was then contoured on the two MR slices, and the coordinates of the center of the corresponding target in the CT coordinate system were reported. The average of all submissions was used to determine the true center of the target. RESULTS: Results are reported from 51 submissions representing 45 institutions and 11 software systems. The average error in the position of the center of the target was 1.8 mm (1 standard deviation = 2.2 mm). The least variation in position was in the lateral direction. Manual registration gave significantly better results than did automatic registration (p = 0.02). CONCLUSION: When MR and CT scans of the head are registered with currently available software, there is inherent uncertainty of approximately 2 mm (1 standard deviation), which should be considered when defining planning target volumes and PRVs for organs at risk on registered image sets.

Hybrid IMRT for treatment of cancers of the lung and esophagus.

PURPOSE: To report on a hybrid intensity-modulated radiation therapy (IMRT; static plus IMRT beams treated concurrently) technique for lung and esophageal patients to reduce the volume of lung treated to low doses while delivering a conformal dose distribution. METHODS: Treatment plans were analyzed for 18 patients (12 lung and 6 esophageal). Patients were treated with a hybrid technique that concurrently combines static (approximately two-thirds dose) and IMRT (approximately one-third dose) beams. These plans were compared with conventional three-dimensional (3D; non-IMRT) plans and all IMRT plans using custom four- and five-field arrangements and nine equally spaced coplanar beams. Plans were optimized to reduce V13 and V5 values. Dose-volume histograms were calculated for the planning target volume, heart, and the ipsilateral, contralateral, and total lung. Lung volumes V5, V13, V20, V30; mean lung dose (MLD); and the generalized equivalent uniform dose (gEUD) were calculated for each plan. RESULTS: Hybrid plans treated significantly smaller total and contralateral lung volumes with low doses than nine-field IMRT plans. Largest reductions were for contralateral lung V5, V13, and V20 values for lung (-11%, -15%, -7%) and esophageal (-16%, -20%, -7%) patients. Smaller reductions were found also for 3D and four- and five-field IMRT plans. MLD and gEUDs were similar for all plan types. The 3D plans treated much larger extra planning target volumes to prescribed dose levels. CONCLUSIONS: Hybrid IMRT demonstrated advantages for reduction of low-dose lung volumes in the thorax for reducing low dose to lung while also reducing the potential magnitude of dose deviations due to intrafraction motion and small field calculation accuracy.

Hybrid IMRT plans--concurrently treating conventional and IMRT beams for improved breast irradiation and reduced planning time.

PURPOSE: To evaluate a hybrid intensity modulated radiation therapy (IMRT) technique as a class solution for treatment of the intact breast. METHODS AND MATERIALS: The following five plan techniques were compared for 10 breast patients using dose-volume histogram analysis: conventional wedged-field tangents (Tangents), forward-planned field-within-a-field tangents (FIF), IMRT-only tangents (IMRT tangents), conventional open plus IMRT tangents (4-field hybrid), and conventional open plus IMRT tangents with 2 anterior oblique IMRT beams (6-field hybrid). RESULTS: The 4-field hybrid and FIF achieved dose distributions better than Tangents and IMRT tangents. The volume of tissue outside the planning target volume receiving > or =110% of prescribed dose was largest for IMRT tangents (average 158 cc) and least for 6-field hybrid (average 1 cc); the FIF and 4-field hybrid were comparable (average 15 cc). Heart volume > or =30 Gy averaged 13 cc for all techniques, except Tangents, for which it was 32 cc. Average total lung volume > or =20 Gy was 7% for all. Contralateral breast doses were < 3% for all. Planning time for hybrid techniques was significantly less than for conventional FIF technique. CONCLUSIONS: The 4-field hybrid technique is a viable class solution. The 6-field hybrid technique creates the most conformal dose distribution at the expense of more normal tissue receiving low dose.

A systematic benchmark method for analysis and comparison of IMRT treatment planning algorithms.

Tools and procedures for evaluating and comparing different intensity-modulated radiation therapy (IMRT) systems are presented. IMRT is increasingly in demand and there are numerous systems available commercially. These programs introduce significantly different software to dosimetrists and physicists than conventional planning systems, and the options often seem initially overwhelmingly complex to the user. By creating geometric target volumes and critical normal tissues, the characteristics of the algorithms may be investigated, and the influence of the different parameters explored. Overall optimization strategies of the algorithm may be characterized by treating a square target volume (TV) with 2 perpendicular beams, with and without heterogeneities. A half-donut (hemi-annulus) TV with a "donut hole" (central cylinder) critical normal tissue (CNT) on a CT of a simulated quality assurance phantom is suggested as a good geometry to explore the IMRT algorithm parameters. Using this geometry, the order of varying parameters is suggested. First is to determine the effects of the number of stratifications of optimized intensity fluence on the resulting dose distribution, and selecting a fixed number of stratifications for further studies. To characterize the dose distributions, a dose-homogeneity index (DHI) is defined as the ratio of the dose received by 90% of the volume to the minimum dose received by the "hottest" 10% of the volume. The next step is to explore the effects of priority and penalty on both the TV and the CNT. Then, choosing and fixing these parameters, the effects of varying the number of beams can be looked at. As well as evaluating the dose distributions (and DHI), the number of subfields and the number of monitor units required for different numbers of stratifications and beams can be evaluated.