Overall, excellent agreement was observed in TrueBeam commissioning data. This set of multi-institutional data can provide comparison data to others embarking on TrueBeam commissioning, ultimately improving the safety and quality of beam commissioning.
Purpose-To evaluate the feasibility of using tomotherapy to deliver whole brain radiotherapy (WBRT) with hippocampal avoidance, hypothesized to reduce the risk of memory function decline, and simultaneously integrated boost to brain metastases to improve intra-cranial tumor control.Methods and Materials-Ten patients treated with radiosurgery and WBRT were replanned on tomotherapy using original CT scans and MR-CT fusion defined target and normal structure contours. The individually contoured hippocampus was used as dose-limiting structures (<6Gy); the whole brain dose was prescribed at 32.25 Gy to 95% in 15 fractions and simultaneous boost doses to individual brain metastases were 63 Gy to lesions ≥ 2.0cm in maximum diameter, and 70.8 Gy to lesions < 2.0cm. Plans were generated with a field width (FW) of 2.5cm, and in five patients with FW of 1.0cm. Plans were compared regarding conformation number (CN), prescription isodose to target volume (PITV) ratio, target coverage (TC), homogeneity index (HI), and mean normalized total dose (NTD mean ).Results-A 1.0cm compared with 2.5cm FW significantly improved the dose distribution. Mean CN number improved from 0.55±0.16 to 0.60±0.13. Whole brain homogeneity improved by 32% (p<0.001). NTD mean to the hippocampus were 5.9±1.3 and 5.8±1.9 Gy 2 , for 2.5 and 1.0cm FW, respectively. Mean treatment delivery time for 2.5 and 1.0cm FW plans were 10.2±1.0 and 21.8±1.8 minutes.Conclusions-Composite tomotherapy plans achieved 3 objectives: homogeneous whole brain dose distribution equivalent to conventional WBRT; conformal hippocampal avoidance; radiosurgically-equivalent dose distributions to individual metastases.
Purpose
To assess patient setup corrections based on daily megavoltage CT (MVCT) imaging for four different anatomical treatment sites treated on tomotherapy.
Method and Materials
Translational and rotational per-fraction setup corrections, based on registration of daily helical MVCT to planning CT images, were analyzed for 1179 brain and head and neck (H&N), 1414 lung, and 1274 prostate tomotherapy treatment fractions. Frequencies of 3D vector lengths, overall distributions of setup corrections, and patient-specific distributions of random and systematic setup errors were analyzed.
Results
Brain and H&N had lower magnitude positioning corrections and smaller variations in setup errors in the translational directions, but were comparable in roll rotations. 3D vector translational shifts of larger magnitudes occurred more frequently for lung and prostate than for brain and H&N treatments, yet this was not observed for roll rotations. The global systematic error for prostate was 4.7 mm in the vertical direction, most likely due to couch sag caused by large couch extension distances. Patient-to-patient variations in systematic errors and magnitudes of random translational errors ranged from 1.6-2.6 mm for brain and H&N and 3.2-7.2 mm for lung and prostate while roll rotational errors ranged from 0.8-1.2° for brain and H&N and 0.5-1.0° for lung and prostate.
Conclusions
Differences in setup were observed between brain, H&N, lung, and prostate treatments. Patient setup can be improved if daily imaging is performed. This analysis can assess the utilization of daily image guidance and allows for further investigation into improved anatomical site-specific and patient-specific treatments.
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