Program Information
Additional Exposure On Out-Of-Target Lesion Due to Dynamic Tumor Tracking Irradiation
N Hayashi1*, M Kokawaji2 , M Kobayashi3 , Y Katsuragawa3 , K Kimura4 , C Nakagami3 , Y Ueshima3 , Y Takada5, S Tanahashi5(1) School of Health Sciences, Fujita Health University, Toyoake, Aichi, JPN. (2) Fujita Health University Hospital, Toyoake, Aichi, JPN. (3) Fujita Health University, Toyoake, Aichi, JPN. (4) Nagoya Tokushu-kai Hospital, Kasugai, Aichi, JPN(5)Ogaki Tokushu-kai Hospital, Ogaki, Gifu, Aichi, JPN.
Presentations
SU-I-GPD-J-88 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Dynamic tumor tracking irradiation (DTI) cannot only provide accurate high dose to target with respiratory motion but also decrease internal margin. However, the technique requires continuous orthogonal X-rays during therapeutic X-ray delivery. The purpose of this study is to make sure additional exposure out-of-target lesion due to DTI.
Methods: The DTI plan was created for demonstrative tumor with respiratory motion in anthropomorphic phantom. The prescription dose of 12 Gy was set to demonstrative target with diameter of 5 cm. For tumor tracking, two implant markers were inserted into the phantom. Sine wave and patient respiration-like wave were applied for the phantom. To evaluate entrance skin dose (ESD) at both lens and chest wall during DTI, radiochromic film or parallel-state chamber was placed on the phantom. Following DTI plan, the procedure of radiation delivery including 4D modeling was carried out. To evaluate radiation quality, the half-value layer of orthogonal X-ray was calculated by specific semiconductor detector.
Results: Radiation quality of orthogonal X-ray during DTI was 2.60±0.07 mm (HVL). The additional exposure on patient respiration-like wave was higher than that on sine wave. The ESD measurements on chest wall during 4D modeling and actual therapeutic X-ray delivery were 40.54 mGy and 270 mGy, respectively. The ESD measurements on lens during 4D modeling and actual therapeutic X-ray delivery were 0.25 mGy and 9.22 mGy. As one of the reasons, tolerance setting of 4D modeling was depended on treatment time. If suitable setting for 4D modeling was defined, the additional exposure might be further lower than this result.
Conclusion: The additional exposures on lens and chest wall during DTI technique were less than 12 mGy and 320 mGy even though 4D modeling procedure was included. These dose were not effective for clinical strategy but non-negligible for patient with hyper-fractioned curative radiotherapy.
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