• Radiation Oncology Journal
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• v.25 no.2
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• pp.134-144
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• 2007

[ $\underline{Purpose}$ ]: Immobilization devices that improve the setup reproducibility of pelvic cancer patients and that provide comfort to patients during radiotherapy were designed and the feasibility of the devices was evaluated. $\underline{Materials\;and\;Methods}$: A customized device was designed to immobilize a knee, thigh, and foot of a patient. Sixty-one patients with prostate cancer were selected and were divided into two groups-with or without devices. The setup errors were measured with respect to bony landmarks. The difference between digitally reconstructed radiographs (DRR) and simulation films, and the differences between DRR and portal films were measured. $\underline{Results}$: The left-right (LR), anterior-posterior (AP) and craniocaudal (CC) errors between the DRR and simulation films were $1.5{\pm}0.9\;mm$, $3.0{\pm}3.6\;mm$, and $1.6{\pm}0.9\;mm$, respectively without devices. The errors were reduced to $1.3{\pm}1.9\;mm$, $1.8{\pm}1.5\;mm$ and $1.1{\pm}1.1\;mm$, respectively with the devices. The errors between DRR and portal films were $1.6{\pm}1.2\;mm$, $4.0{\pm}4.1\;mm$, and $4.2{\pm}5.5\;mm$, respectively without the devices and were reduced to $1.0{\pm}1.8\;mm$, $1.2{\pm}0.9\;mm$, and $1.2{\pm}0.8\;mm$, respectively, with the devices. The standard deviations among the portal films were 1.1 mm, 2.1 mm, and 1.0 mm at each axis without the devices and 0.9 mm, 1.6 mm and 0.8 mm with the devices. The percentage of setup errors larger than 3 mm and 5 mm were significantly reduced by use of the immobilization devices. $\underline{Conclusion}$: The designed devices improved the setup reproducibility for all three directions and significantly reduced critical setup errors.

• Progress in Medical Physics
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• v.21 no.1
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• pp.86-92
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• 2010

The purpose of this study was to measure curvature contour skin dose using radiochromic film and TLD for a conventional open field. We also attempted to quantify the degradation of skin sparing associated with use of immobilization devices for high energy photon beams and to calculate the skin dose with a help of Monte Carlo (MC) simulation. To simulate head-and-neck and shoulder treatment, a cylindrical solid water phantom 11 cm in diameter was irradiated with 6 MV x-rays using $40{\times}40\;cm^2$ field at 100 cm source axis distance (SAD) to the center of the phantom. Aquaplastic mesh mask was placed on the surface of the cylindrical phantom that mimicked relevant clinical situations. The skin dose profile was obtained by taking measurements from $0^{\circ}$ to $360^{\circ}$ around the circumference of the cylindrical phantom. The skin doses obtained from radiochromic film were found to be 47% of the maximum dose of $D_{max}$ at the $0^{\circ}$ beam entry position and 61% at the $90^{\circ}$ oblique beam position without the mask. Using the mask (1.5 mm), the skin dose received was 59% at $0^{\circ}$ incidence and 78% at $80^{\circ}$ incidence. Skin dose results were also gathered using thin thermoluminescent dosimeters (TLD). With the mask, the skin dose was 66% at $0^{\circ}$ incidence and 80% at $80^{\circ}$ incidence. This method with the mask revealed the similar pattern as film measurement. For the treatments of the head-and-neck and shoulder regions in which immobilization mask was used, skin doses at around tangential angle were nearly the same as the prescription dose. When a sloping skin contour is encountered, skin doses may be abated using thinner and more perforated immoblization devices which should still maintain immoblization.