• The Journal of Korean Society for Radiation Therapy
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• v.35
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• pp.33-39
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• 2023

Purpose: The purpose of this study is to find out the dose variation according to thickness of the air gap between the patient's body surface and immobilization device in the treatment plan. Materials and Methods : Four conditions were created by adjusting the air gap thickness using 5 mm bolus, ranging from 0 mm to 3 mm bolus. Immobilization was placed on top in each case. And computed tomography was used to acquire images. The treatment plan that 430 cGy (Relative Biological Effectiveness,RBE) is irradiated 6 times and the dose of 2580 cGy (RBE) is delivered to 95% of Clinical Target Volume (CTV). The dose on CTV was evaluated by Full Width Half Maximum (FWHM) of the lateral dose profile and skin dose was evaluated by Dose Volume Histogram (DVH). Result: Results showed that the FWHM values of the lateral dose profile of CTV were 4.89, 4.86, 5.10, and 5.10 cm. The differences in average values at the on the four conditions were 3.25±1.7 cGy (RBE) among D_95% and 1193.5±10.2 cGy (RBE) among D_95% respectively. The average skin volume at 1% of the prescription dose was 83.22±4.8%, with no significant differences in both CTV and skin. Conclusion: When creating a solid-type immobilization device for carbon particle therapy, a slight air gap is recommended to ensure that it does not extend beyond the dose application range of the CTV.

• The Journal of Korean Society for Radiation Therapy
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• v.23 no.1
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• pp.31-39
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• 2011

Purpose: Helical Tomotherapy allows only coplanar beam delivery because it does not allow couch rotation. We investigated a method to introduce non-coplanar beam by tilting a patient's head for Tomotherapy. The aim of this study was to compare intrafractional movement during Tomotherapy between coplanar and non-coplanar patient's setup. Materials and Methods: Helical Tomotherapy was used for treating eight patients with intracranial tumor. The subjects were divided into three groups: one group (coplanar) of 2 patients who lay on S-plate with supine position and wore thermoplastic mask for immobilizing the head, second group (non-coplanar) of 3 patients who lay on S-plate with supine position and whose head was tilted with Variable Axis Baseplate and wore thermoplastic mask, and third group (non-coplanar plus mouthpiece) of 3 patients whose head was tilted and wore a mouthpiece immobilization device and thermoplastic mask. The patients were treated with Tomotherapy after treatment planning with Tomotherapy Planning System. Megavoltage computed tomography (MVCT) was performed before and after treatment, and the intrafractional error was measured with lateral(X), longitudinal(Y), vertical(Z) direction movements and vector ($\sqrt{x^2+y^2+z^2}$) value for assessing overall movement. Results: Intrafractional error was compared among three groups by taking the error of MVCT taken after the treatment. As the correction values (X, Y, Z) between MVCT image taken after treatment and CT-simulation image are close to zero, the patient movement is small. When the mean values of movement of each direction for non-coplanar setup were compared with coplanar setup group, X-axis movement was decreased by 13%, but Y-axis and Z-axis movement were increased by 109% and 88%, respectively. Movements of Y-axis and Z-axis with non-coplanar setup were relatively greater than that of X-axis since a tilted head tended to slip down. The mean of X-axis movement of the group who used a mouthpiece was greater by 9.4% than the group who did not use, but the mean of Y-axis movement was lower by at least 64%, and the mean of Z-axis was lower by at least 67%, and the mean of Z-axis was lower by at least 67%, and the vector was lower by at least 59% with the use of a mouthpiece. Among these 8 patients, one patient whose tumor was located on left frontal lobe and left basal ganglia received reduced radiation dose of 38% in right eye, 23% in left eye, 30% in optic chiasm, 27% in brain stem, and 8% in normal brain with non-coplanar method. Conclusion: Tomotherapy only allows coplanar delivery of IMRT treatment. To complement this shortcoming, Tomotherapy can be used with non-coplanar method by artificially tilting the patient's head and using an oral immobilization instrument to minimize the movement of patient, when intracranial tumor locates near critical organs or has to be treated with high dose radiation.

• Radiation Oncology Journal
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• v.20 no.2
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• pp.165-171
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• 2002

Purpose : In order to perform craniospinal irradiation (CSI) in the supine position on patients who are unable to lie in the prone position, a new simulation technique using a CT simulator was developed and its availability was evaluated. Materials and Method : A CT simulator and a 3-D conformal treatment planning system were used to develop CSI in the supine position. The head and neck were immobilized with a thermoplastic mask in the supine position and the entire body was immobilized with a Vac-Loc. A volumetrie image was then obtained using the CT simulator. In order to improve the reproducibility of the patients' setup, datum lines and points were marked on the head and the body. Virtual fluoroscopy was peformed with the removal of visual obstacles such as the treatment table or the immobilization devices. After the virtual simulation, the treatment isocenters of each field were marked on the body and the immobilization devices at the conventional simulation room. Each treatment field was confirmed by comparing the fluoroscopy images with the digitally reconstructed radiography (DRR)/digitally composite radiography (DCR) images from the virtual simulation. The port verification films from the first treatment were also compared with the DRR/DCR images for a geometrical verification. Results : CSI in the supine position was successfully peformed in 9 patients. It required less than 20 minutes to construct the immobilization device and to obtain the whole body volumetric images. This made it possible to not only reduce the patients' inconvenience, but also to eliminate the position change variables during the long conventional simulation process. In addition, by obtaining the CT volumetric image, critical organs, such as the eyeballs and spinal cord, were better defined, and the accuracy of the port designs and shielding was improved. The differences between the DRRs and the portal films were less than 3 mm in the vertebral contour. Conclusion : CSI in the supine position is feasible in patients who cannot lie on prone position, such as pediatric patienta under the age of 4 years, patients with a poor general condition, or patients with a tracheostomy.