Computer optimization of noncoplanar beam setups improves stereotactic treatment of liver tumors.

PURPOSE: To investigate whether computer-optimized fully noncoplanar beam setups may improve treatment plans for the stereotactic treatment of liver tumors. METHODS: An algorithm for automated beam orientation and weight selection (Cycle) was extended for noncoplanar stereotactic treatments. For 8 liver patients previously treated in our clinic using a prescription isodose of 65%, Cycle was used to generate noncoplanar and coplanar plans with the highest achievable minimum planning target volume (PTV) dose for the clinically delivered isocenter and mean liver doses, while not violating the clinically applied hard planning constraints. The clinical and the optimized coplanar and noncoplanar plans were compared, with respect to D(PTV,99%), the dose received by 99% of the PTV, the PTV generalized equivalent uniform dose (gEUD), and the compliance with the clinical constraints. RESULTS: For each patient, the ratio between D(PTV,99%) and D(isoc), and the gEUD(-5) and gEUD(-20) values of the optimized noncoplanar plan were higher than for the clinical plan with an average increase of respectively 18.8% (range, 7.8-24.0%), 6.4 Gy (range, 3.4-11.8 Gy), and 10.3 Gy (range, 6.7-12.5). D(PTV,99%)/D(isoc), gEUD(-5), and gEUD(-20) of the optimized noncoplanar plan was always higher than for the optimized coplanar plan with an average increase of, respectively, 4.5% (range, 0.2-9.7%), 2.7 Gy (range, 0.6-9.7 Gy), and 3.4 Gy (range, 0.6-9.9 Gy). All plans were within the imposed hard constraints. On average, the organs at risk were better spared with the optimized noncoplanar plan than with the optimized coplanar plan and the clinical plan. CONCLUSIONS: The use of automatically generated, fully noncoplanar beam setups results in plans that are favorable compared with coplanar techniques. Because of the automation, we found that the planning workload can be decreased from 1 to 2 days to 1 to 2 h.

Left-sided breast cancer radiotherapy with and without breath-hold: does IMRT reduce the cardiac dose even further?

PURPOSE: In radiotherapy for left-sided breast cancer, Active Breathing Control enables a decrease of cardiac and Left Anterior Descending (LAD) coronary artery dose. We compared 3D-Conformal (3D-CRT) to Intensity Modulated Radiotherapy (IMRT) treatment plans based on free-breathing (FB) and breath-hold (BH). We investigated whether IMRT enables an additional decrease of cardiac dose in radiotherapy plans with and without BH. METHODS AND MATERIALS: Twenty patients referred for whole breast irradiation were included. The whole breast, heart and LAD-region were contoured. Four treatment plans were generated: FB_3D-CRT; FB_IMRT; BH_3D-CRT; BH_IMRT. Several doses were obtained from Dose Volume Histograms and compared. Results were compared statistically using the Wilcoxin Signed Rank Test. For heart and LAD-region, a significant dose reduction was found in BH (p<0.01). For both BH and FB, a significant dose reduction was found using IMRT (p<0.01). By using IMRT an average reduction of 5% was noted in the LAD-region for the volume receiving 20Gy. In 5 cases, the LAD-region remained situated in the vicinity of the radiation portals even in BH. Nevertheless, with IMRT the LAD dose was reduced in these cases. CONCLUSION: IMRT results in a significant additional decrease of dose in the heart and LAD-region in both breath-hold and free-breathing.

MRI- versus CT-based volume delineation of lumpectomy cavity in supine position in breast-conserving therapy: an exploratory study.

PURPOSE: To examine magnetic resonance imaging (MRI) and computed tomography (CT) for lumpectomy cavity (LC) volume delineation in supine radiotherapy treatment position and to assess the interobserver variability. METHODS AND MATERIALS: A total of 15 breast cancer patients underwent a planning CT and directly afterward MRI in supine radiotherapy treatment position. Then, 4 observers (2 radiation oncologists and 2 radiologists) delineated the LC on the CT and MRI scans and assessed the cavity visualization score (CVS). The CVS, LC volume, conformity index (CI), mean shift of the center of mass (COM), with the standard deviation, were quantified for both CT and MRI. RESULTS: The CVS showed that MRI and CT provide about equal optimal visibility of the LC. If the CVS was high, magnetic resonance imaging provided more detail of the interfaces of the LC seroma with the unaffected GBT. MRI also pictured in more detail the interfaces of axillary seromas (if present) with their surroundings and their relationship to the LC. Three observers delineated smaller, and one observer larger, LC volumes comparing the MRI- and CT-derived delineations. The mean ± standard deviation CI was 32% ± 25% for MRI and 52% ± 21% for CT. The mean ± standard deviation COM shift was 11 ± 10 mm (range 1-36) for MRI and 4 ± 3 mm (range 1-10) for CT. CONCLUSIONS: MRI does not add additional information to CT in cases in which the CVS is assessed as low. The conformity (CI) is lower for MRI than for CT, especially at a low CVS owing to greater COM shifts for MRI, probably caused by inadequate visibility of the surgical clips on magnetic resonance (MR) images. The COM shifts seriously dictate a decline in the CI more than the variability of the LC volumes does. In cases in which MRI provides additional information, MRI must be combined with the CT/surgical clip data.

Magnetic resonance imaging- versus computed tomography-based target volume delineation of the glandular breast tissue (clinical target volume breast) in breast-conserving therapy: an exploratory study.

PURPOSE: To examine MRI and CT for glandular breast tissue (GBT) volume delineation and to assess interobserver variability. METHODS AND MATERIALS: Fifteen breast cancer patients underwent a planning CT and MRI, consecutively, in the treatment position. Four observers (two radiation oncologists and two radiologists) delineated the GBT according to the CT and separately to the MR images. Volumes, centers of mass, maximum extensions with standard deviations (SD), and interobserver variability were quantified. Observers viewed delineation differences between MRI and CT and delineation differences among observers. RESULTS: In cranio-lateral and cranio-medial directions, GBT volumes were delineated larger using MRI when compared with those delineated with CT. Center of mass on MRI shifted a mean (SD) 17% (4%) into the cranial direction and a mean 3% (4%) into the dorsal direction when compared with that on the planning CT. Only small variations between observers were noted. The GBT volumes were approximately 4% larger on MRI (mean [SD] ratio MRI to CT GBT volumes, 1.04 [0.06]). Findings were concordant with viewed MRI and CT images and contours. Conformity indices were only slightly different; mean conformity index was 77% (3%) for MRI and 79% (4%) for CT. Delineation differences arising from personal preferences remained recognizable irrespective of the imaging modality used. CONCLUSIONS: Contoured GBT extends substantially further into the cranio-lateral and cranio-medial directions on MRI when compared with CT. Interobserver variability is comparable for both imaging modalities. Observers should be aware of existing personal delineation preferences. Institutions are recommended to review and discuss target volume delineations and to design supplementary guidelines if necessary.