Purpose/Objective(s): Few treatment options exist for recurrent GBM. HFSRT has been used as a salvage treatment strategy. Gross tumor volume (GTV) is usually based on pretreatment contrast enhanced T1-weighted (T1-contrast pre ) MR image. T2-FLAIR pre may detect additional subtle signal of tumor infiltration. This study aimed to investigate the patterns of recurrence following salvage HFSRT using T2-FLAIR image in addition to T1-contrast in target delineation for HFSRT. Materials/Methods: We retrospectively examined 13 patients with recurrent GBM treated with HFSRT from 2015 to 2017 who had local recurrence following HFSRT. A median dose of 30 (25-35) Gy in 5 to 10 fractions was delivered. The median time between HFSRT and recurrence after HFSRT was 178 (48-259) days. Diagnostic MRI was performed before and 4 weeks after HFSRT, and then every 4 -8 weeks. Separate GTVs using T1-contrast pre only, T2-FLAIR pre only, or T1 pre +-T2 pre , were contoured blindly by a single radiation oncology physician. Recurrence volume was delineated on the post-treatment T1-contrast (T1-contrast post ) MRI at the time of progression. The volume overlapping between pretreatment GTV and recurrence volume was calculated. The centroid distance between pre-and post-treatment volumes was measured as well. Wilcoxon test was used to assess the statistical significance of differences. Results: The median volumes overlapping between T1-contrast pre , T2-FLAIR pre , T1 pre +T2 pre and T1-contrast post were 18% (range: 0-100%, Q1: 12%, Q3: 40%), 52% (range: 0-90%, Q1: 24%, Q3: 59%) and 53% (range: 0-100%, Q1: 26%, Q3: 77%), respectively. The recurrent volume overlapping with T1 pre +T2 pre was significantly larger than the overlap with T1-contrast pre (pZ0.003). The median volume difference between T1-contrast pre and T2-FLAIR pre volumes resided in the recurrence volume was 3.9 cm 3 (range: 0-11.5 cm 3 , Q1: 0.2 cm 3 , Q3 5.6 cm 3 ). The centroid distance between volumes did not show significant difference. The median centroid distances between recurrence volume and T1-contrast pre volume, T2-FLAIR pre volume, and T1 pre +T2 pre volume were 1.3 cm (range: 0.3-4.9 cm, Q1: 0.8, Q3: 2.00), 1.3 cm (range: 0.3-4.7 cm, Q1: 0.8 cm, Q3: 2 cm) and 1.2 cm (range: 0.2-1.2 cm, Q1: 0.7 cm, Q3: 2.1 cm), respectively. Conclusion: A significant volume of recurrence occurred in the T1 pre +T2 pre region beyond the T1-contrast pre region. Further studies to investigate techniques incorporating T2-FLAIR pre region may improve GTV delineation for salvage HFSRT.Purpose/Objective(s): The impact of rotational deviations is investigated for single fiducial tumor tracking. The hypothesis is that the yaw rotation of a single fiducial will increase the uncertainty parameter in the tracking system. Materials/Methods: When treating a moving target, tumor tracking can be employed using a single fiducial. However, tracking using a single fiducial is limited to linear chasing and does not track rotation. A mini ball cube with 3, gold fiducials on its surface was placed insi...
the CSRS workspace can be cumbersome. Higher modulation in CSRS led to lower CI and GI values and lower OAR doses without affecting planning times. For complex lesions for which iPlan was not adequate, both VMAT TPSs yielded highly conformal treatment plans that satisfied OAR constraints, however CSRS was faster to plan, gave more homogeneous dose distributions and used less MUs.
Total skin electron beam therapy (TSEBT) has been used in the treatment of cutaneous T-cell lymphoma or mycosis fungoides. The Stanford technique or six-dual field technique is to irradiate the entire skin by irradiating six ports electron beams while changing the body direction, positions of arms and legs while the patient is standing. This method is by far the most commonly used method, but it is difficult for the patient to maintain the same posture for a fairly long period of time. As noted in several papers, the reason for maintaining dose uniformity is due to the nature of TSEBT. It is not easy to use the latest treatment techniques to investigate uniform doses of irregular whole body skin of a patient while minimizing dose to the internal organ. It is certain that if the patient is in a lying position, he or she can make treatment possible for patients with mobility discomfort. On the other hand, it is difficult to ensure dose uniformity of areas where radiation is difficult to be irradiated unless artificially placed arms and legs such as between arm and body (underarm), between legs and legs (groin). In this study, we tried to improve the dose uniformity of TSEBT patients using 3 ports instead of 6 ports. Materials/Methods: We performed TSEBT using a LINAC and High dose rate electron (HDRE) mode was used to shorten treatment time. To improve the rotation and position accuracy of patients during TSEBT, a dedicated patient set up system for TSEBT was also used. The effect of Xray on spoiler on dose uniformity was quantitatively evaluated by Monte Carlo simulation. Since we use only 3 ports, we used a human phantom to optimize the incidence angle of MUs and LPO and RPO beam for each beam port. In-vivo dosimetry was performed while applying the optimized treatment set up with Monte Carlo simulation and phantom experiment. Results: We distinguished dose distribution by the X-ray distribution from the acryl spoiler and by the primary electron distribution with Monte Carlo simulation. In the experiment using the anthrophomorphic phantom, it was verified that 84 w 112 cGy was contained in the field area including the side when PA 100 MU and 60 LPO / RPO 1400 MU were irradiated. The shield was installed on the acryl panel to cover the field above and below the light field interface. Based on the results of MC simulation and phantom measurement, we performed the first treatment according to MU and set up per port, and performed in vivo dosimetry. The dose distribution was 91.5 w 117.8 cGy, showing dose uniformity within 10% during treatment. Conclusion: We performed TSEBT on the limited region using 3 ports instead of the traditional 6 ports and found the optimized set up condition through MC simulation and phantom experiment to maintain dose uniformity that is clinically usable.
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