Physics·Biology·Technique
Dosimetric effect of set-up errors on nasal NK/T cell lymphoma based on dose reconstruction
Wang Zhanyu, Tan Junwen, Long Yusong, He Xiantao, Li Gang, Feng Yongfu, Liang Weixue
Published 2019-11-15
Cite as Chin J Radiat Oncol, 2019,28(11): 849-853. DOI: 10.3760/cma.j.issn.1004-4221.2019.11.011
Abstract
ObjectiveTo evaluate the dosimetric effects of set-up errors on nasal NK/T cell lymphoma by introducing set-up errors into the radiotherapy planning system for dose reconstruction.
MethodsTen patients with nasal NK/T cell lymphoma were recruited. A non-coplanar volumetric modulated arc therapy plan was designed for CT image and clinical target area of each patient. After the completion of the plan, the set-up errors were introduced into the radiotherapy plan by changing the ISO of the treatment, and dose calculation was performed to reconstruct the dose distribution.
ResultsWith the increase of system set-up errors, the dose of target was decreased and the order affected by set-up errors in different directions was: left-right direction> head-foot direction> front-rear direction. When the translational set-up errors in each direction were -3 mm to 3 mm and the rotating set-up errors were -3° to 3°, the range of dose change in all targets was less than ±3%. When the set-up errors in all directions were ≤ 3 mm, the dose of organ at risk was less than or similar to the prescribed dose. When the set-up errors were> 3 mm, the doses of lens, spinal cord, parotid gland and optic nerve gradually exceeded the prescribed dose. Only when the rotating set-up errors were ≥ 3°, the dose of lens exceeded the prescribed dose. Special attention should be paid to the influence of the greater set-up errors in the left and right direction on lens, spinal cord and parotid gland, as well as on the spinal cord due to the larger set-up errors in the front and rear direction. After the actual set-up errors were introduced from our department, it exerted slight effect on the irradiation dose of GTV and CTV, which was less than ±2%. In a few cases, the dose of organ at risk potentially exceeded the prescribed dose limit, and special attention should be diverted to overdose of the lens and optic nerve.
ConclusionsThe set-up errors will result in target dose deficiency and overdose of organ at risk in nasal NK/T cell lymphoma, especially upon the set-up errors in the left and right direction. The effect of 3 mm and 3° set-up errors on target and organ at risk is limited. Therefore, it is recommended to maintain the single direction set-up errors within 3 mm and 3°. The actual set-up errors introduced from our department exert little effect on the target dose, but a small number of organs are at risk of exceeding the prescribed dose limit. It is necessary to increase the evaluation of the extension region of organ at risk.
Key words:
Nasal natural killer/T-cell lymphoma; Set-up error; Dosimetry
Contributor Information
Wang Zhanyu
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
Tan Junwen
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
Long Yusong
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
He Xiantao
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
Li Gang
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
Feng Yongfu
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China
Liang Weixue
Department of oncology, Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China