| Evaluation of a Water-based Bolus Device for Radiotherapy to the Extremities in Kaposi's Sarcoma Patients |
| Seung Kwon Ahn, Yong Bae Kim, Ik Jae Lee, Tae Soo Song, Dong Min Son, Yung Jae Jang, Jung Hee Cho, Joo Ho Kim, Dong Wook Kim, Jae Ho Cho, Chang Ok Suh |
1Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University Medical School, Seoul, Korea. jjhmd@yuhs.ac
2Institute of Physics and Applied Physics, Yonsei University, Seoul, Korea.
3Department of Rehabilitation Medicine, Rehabililtaion Hospital, Yonsei University Medical School, Seoul, Korea. |
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| ABSTRACT |
PURPOSE:
We designed a water-based bolus device for radiation therapy in Kaposi's sarcoma. This study evaluated the usefulness of this new device and compared it with the currently used rice-based bolus.
MATERIALS AND METHODS:
We fashioned a polystyrene box and cut a hole in order to insert patient's extremities while the patient was in the supine position. We used a vacuum-vinyl based polymer to reduce water leakage. Next, we eliminated air using a vacuum pump and a vacuum valve to reduce the air gap between the water and extremities in the vacuum-vinyl box. We performed CT scans to evaluate the density difference of the fabricated water-based bolus device when the device in which the rice-based bolus was placed directly, the rice-based bolus with polymer-vinyl packed rice, and the water were all put in. We analyzed the density change with the air gap volume using a planning system. In addition, we measured the homogeneity and dose in the low-extremities phantom, attached to six TLD, and wrapped film exposed in parallel-opposite fields with the LINAC under the same conditions as the set-up of the CT-simulator.
RESULTS:
The density value of the rice-based bolus with the rice put in directly was 14% lower than that of the water-based bolus. Moreover, the value of the other experiments in the rice-based bolus with the polymer-vinyl packed rice showed an 18% reduction in density. The analysis of the EDR2 film revealed that the water-based bolus shows a more homogeneous dose plan, which was superior by 4.0~4.4% to the rice-base bolus. The mean TLD readings of the rice-based bolus, with the rice put directly into the polystyrene box had a 3.4% higher density value. Moreover, the density value in the case of the rice-based bolus with polymer-vinyl packed rice had a 4.3% higher reading compared to the water-based bolus.
CONCLUSION:
Our custom-made water-based bolus device increases the accuracy of the set-up by confirming the treatment field. It also improves the accuracy of the therapy owing to the reduction of the air gap using a vacuum pump and a vacuum valve. This set-up represents a promising alternative device for delivering a homogenous dose to the target volume. |
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