PubMed · 10254619
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INTRODUCTION: The treatment of midline tumors in the head and neck by conventional radiotherapy almost invariably results in xerostomia. This study analyzes whether a simple three-dimensional conformal radiotherapy (3D-CRT) technique with beam intensity modulation (BIM) (using a 10-MV beam of the MM50 Racetrack Microtron) can spare parotid and submandibular glands without compromising the dose distribution in the planning target volume (PTV). METHODS: For 15 T2 tumors of the tonsillar fossa with extension into the soft palate (To) and 15 T3 tumors of the supraglottic larynx (SgL), conventional treatment plans, consisting of lateral parallel opposed beams, were used for irradiation of both the primary tumor (70 Gy) and the elective neck regions (46 Gy). Separately, for each tumor a 3-D conformal treatment plan was developed using the 3-D computer planning system, CadPlan, and Optimize, a noncommercial program to compute optimal beam profiles. Beam angles were selected with the intention of optimal sparing of the salivary glands. The intensity of the beams was then modulated to achieve a homogeneous dose distribution in the target for the given 3D-CRT techniques. The dose distributions, dose-volume histograms (DVHs) of target and salivary glands, tumor control probabilities (TCPs), salivary gland volumes absorbing a biologically equivalent dose of greater than 40 or 50 Gy, and normal tissue complication probabilities (NTCPs) of each treatment plan were computed. The parameters of the 3D-CRT plans were compared with those of the conventional plans. RESULTS: In comparison with the conventional technique, the dose homogeneity in the target volume was improved by the conformal technique for both tumor sites. In addition, for the SgL conformal technique, the average volumes of the parotid glands absorbing a BED of greater than 40 Gy (V40) decreased by 23%, and of the submandibular glands by 7% (V40) and 6% (V50). Consequently, the average NTCPs for the parotid and submandibular glands were reduced by 7% and 6%, respectively. For the To conformal techniques, the V40 of the parotid glands was decreased on average by 31%, resulting in an average reduction of the NTCP by 49%. Both the average V50 and the NTCP of the submandibular glands were decreased by 7%. CONCLUSION: For primary tumors of the oropharynx, the parotid glands could be spared to a considerable degree with the 3D-CRT technique. However, particularly the ipsilateral submandibular gland could not be spared. For primary tumors of the larynx, the 3D-CRT technique allows sparing of all salivary glands to a considerable and probably clinically relevant degree. Moreover, the conformal techniques resulted in an increased dose homogeneity in the PTV of both tumor sites.
PURPOSE: To investigate the clinical importance and feasibility of a 3-D portal image analysis method in comparison with a standard 2-D portal image analysis method for pelvic irradiation techniques. METHODS AND MATERIALS: In this study, images of 30 patients who were treated for prostate cancer were used. A total of 837 imaged fields were analyzed by a single technologist, using automatic 2-D and 3-D techniques independently. Standard deviations (SDs) of the random, systematic, and overall variations, and the overall mean were calculated for the resulting data sets (2-D and 3-D), in the three principal directions (left-right [L-R], cranial-caudal [C-C], anterior-posterior [A-P]). The 3-D analysis included rotations as well. For the translational differences between the three data sets, the overall SD and overall mean were computed. The influence of out-of-plane rotations on the 2-D registration accuracy was determined by analyzing the difference between the 2-D and 3-D translation data as function of rotations. To assess the reliability of the 2-D and 3-D methods, the number of times the automatic match was manually adjusted was counted. Finally, an estimate of the workload was made. RESULTS: The SDs of the random and systematic components of the rotations around the three orthogonal axes were 1. 1 (L-R), 0.6 (C-C), 0.5 (A-P) and 0.9 (L-R), 0.6 (C-C), 0.8 (A-P) degrees, respectively. The overall mean rotation around the L-R axis was 0.7 degrees, which deviated significantly from zero. Translational setup errors were comparable for 2-D and 3-D analysis (ranging from 1.4 to 2.2 mm SD and from 1.5 to 2.5 mm SD, respectively). The variation of the difference between the 2-D and 3-D translation data increased from 1.1 mm (SD) for zero rotations to 2.7 mm (SD) for out-of-plane rotations of 3 degrees, due to a reduced 2-D registration accuracy for large rotations. The number of times the analysis was not considered acceptable and was manually adjusted was 44% for the 2-D analysis, and 6% for the 3-D analysis. CONCLUSION: True 3-D analysis of setup errors for a group of 30 patients with prostate cancer demonstrated that setup rotations are rather small. The deformation of the projected anatomy in portal images caused by out-of-plane rotations leads to a reduced 2-D registration accuracy. For rotations larger than 3 degrees this effect can be quite pronounced, making 3-D registration the preferred method. Furthermore, the automatic 3-D registration has a higher success rate, most likely because this technique uses more information compared to the 2-D method.
BACKGROUND: CT simulation systems provide integration of CT-based planning target volumes, which allows to operate without the conventional simulator. The aim of our study was the quantitative assessment of the accuracy of field alignment and isocenter position using the new virtual simulation system AdvantageSim 4.1. for different treatment regions. PATIENTS AND METHODS: Twenty-seven patients with prostate cancer, 23 patients with head and neck cancer and 30 lung cancer patients were included in this prospective trial. CT-based virtual simulation was performed to define treatment isocenter position. The linear discrepancies of the digitally reconstructed beam's eye views were compared with the conventional simulation and first treatment verification images. RESULTS: Among all patients the mean difference of isocenter position between conventional and virtual simulation was 3.5 mm. The isocenter displacements ranged from 0 to 6 mm. There was no significant difference in isocenter accuracy between the different treatment regions. CONCLUSIONS: Virtual simulation with AdvantageSim 4.1. is feasible in daily routine and allows to replace conventional simulation for different target volumes with a reliable accuracy of isocenter and field alignment. The beam's eye views allow the precise evaluation of the coverage of the planning target volume and the shielding of organs at risk.