Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_3_3145 - Monte Carlo Simulation and Measurement for Improving Dose Uniformity of Total Skin Electron Beam Therapy with Three Ports

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Monte Carlo Simulation and Measurement for Improving Dose Uniformity of Total Skin Electron Beam Therapy with Three Ports
S. Ahn1, J. Choi2, H. Lee1, K. Park1, C. O. Suh2, and J. Kim1; 1Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Yonsei University Health System, Seoul, Korea, Republic of (South), 2Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South)

Purpose/Objective(s): 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 X-ray 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 ~ 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 ~ 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.

Author Disclosure: S. Ahn: None. J. Choi: None.

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TU_3_3145 - Monte Carlo Simulation and Measurement for Improving Dose Uniformity of Total Skin Electron Beam Therapy with Three Ports



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