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Journal of Peking University (Health Sciences) ›› 2022, Vol. 54 ›› Issue (1): 182-186. doi: 10.19723/j.issn.1671-167X.2022.01.029

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Dosimetric effect of patient arm position on Cyberknife radiosurgery for spinal tumors

LI Jun1,LIU Xu-hong2,3,WANG Gong1,CHENG Cheng1,ZHUANG Hong-qing1,YANG Rui-jie1,△()   

  1. 1. Department of Radiation Oncology, Peking University Third Hospital, Beijing 100191, China
    2. Yunnan Cancer Hospital, Kunming 650018, China
    3. The Third Affiliated Hospital of Kunming Medical University, Kunming 650018, China
  • Received:2021-02-23 Online:2022-02-18 Published:2022-02-21
  • Contact: Rui-jie YANG E-mail:ruijyang@yahoo.com
  • Supported by:
    National Natural Science Foundation of China(81372420);Beijing Municipal Commission of Science and Technology Collaborative Innovation Project(Z201100005620012);Natural Science Foundation of Beijing(7202223)

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Abstract:

Objective: To assess the potential dosimetric effects of arms movement in patients with Cyberknife spine tumors. Methods: In the study, 12 patients with thoracic and lumbar tumors were retrospectively selected respectively. The contour of the patient’s arms was sketched and the CT density was modified to be equivalent to air in order to simulate the extreme case when the arm was completely removed from the radiation fields. The dose of simulated plan was re-calculated with the original beam parameters and compared with the original plan. The changes of V100, D95, and D90, conformity index (CI) and heterogeneity index (HI) in planning target volume (PTV), as well as Dmax, D1cc and D2cc in the spinal cord, stomach, esophagus, and intestines were analyzed by comparing with the original plans. Results: Compared with the original treatment plan, V100, D95, D90 and CI of PTV for the simulated plan was increased by 0.86%, 2.02%,1.97% and 0.80% respectively, the difference was statistically significant (P<0.05). Dmax, D1cc and D2cc of spinal cord was increased by 2.35%, 0.59% and 1.49% on average, compared with the original plan, the difference was statistically significant (P<0.05). The difference was statistically significant only in average D2cc of stomach, which was increased by 1.70%, compared with the original plan (P<0.05). There was no significant difference in dose change of eso-phagus and intestine between the original and simulated plans. Conclusion: This study analyzed the most extreme arm position in spinal tumor of radiation therapy based on Cyberknife. It was found that the change of arm position had little effect on dosimetry. In addition, with the change of arm position, the dose in PTV and organ at risk (OAR) increased, but the increase was relatively small. Therefore, in some special cases where the patient really can’t keep the arm position consistent during treatment, reasonable adjustment can be accepted. However, in order to ensure accurate radiotherapy, patient position should be as stable and consistent as possible.

Key words: Cyberknife, Position of arm, Spinal tumor, Dosimetry

CLC Number: 

  • R739.92

Figure 1

Radiotherapy simulation plan for spinal tumor patient A, the manual outline of the arms; B, the beams of simulation plan same as the original plan."

Figure 2

Comparison of dose distribution and DVH between original plan and simulation plan for thoracic vertebral tumor A, axial dose distribution of the original plan; B, axial dose distribution of the simulation plan; C, DVH comparison between the original plan and the simulation plan. PTV, planning target volume; DVH, dose-volume histogram."

Figure 3

Comparison of dose distribution and DVH between original plan and simulation plan for lumbar vertebral tumor A, axial dose distribution of the original plan; B, axial dose distribution of the simulation plan; C, DVH comparison between the original plan and the simulation plan. PTV, planning target volume; DVH, dose-volume histogram."

Table 1

Comparison of dosimetric parameters of two plans for target at different arm positions ($\bar{x}\pm s$)"

PTV Original plan Simulation plan 95%CI t value P value
V100 93.84%±0.80% 94.65%±1.40% 0.902(0.225-1.781) 3.319 0.004
D95/Gy 27.59±4.86 28.15±5.13 1.075(0.526-1.924) 5.740 <0.001
D90/Gy 28.93±5.12 29.50±5.57 1.161(0.631-2.388) 5.960 <0.001
CI 0.75±0.16 0.76±0.13 0.027(0.001-0.055) 2.781 0.020
HI 1.32±0.67 1.31±0.06 0.008(0.014-0.029) 1.000 0.330

Table 2

Comparison of dosimetric parameters of two plans for organ at risk at different arm positions ($\bar{x}\pm s$)"

Organ Parameters Original plan Simulation plan 95%CI t value P value
Spinal cord/cauda equina
Dmax/Gy 23.86±4.65 24.42±4.90 1.347(0.720-2.521) 4.573 <0.001
D1cc/Gy 20.02±4.85 20.54±4.97 1.282(0.579-2.577) 5.280 <0.001
D2cc/Gy 18.74±5.21 19.02±5.32 1.019(0.486-3.219) 2.796 0.017
Esophagus
Dmax/Gy 22.37±4.24 22.53±4.70 0.260(0.109-0.670) 1.918 0.061
D1cc/Gy 18.39±4.13 18.48±4.22 0.535(0.068-2.059) 1.873 0.073
D2cc/Gy 15.63±5.38 15.70±5.58 0.231(0.085-0.765) 1.540 0.082
Stomach
Dmax/Gy 10.33±3.35 10.50±3.27 0.313(0.114-1.082) 2.018 0.058
D1cc/Gy 8.36±3.10 8.43±3.22 0.073(0.034-0.283) 1.185 0.251
D2cc/Gy 7.63±2.93 7.76±2.85 0.460(0.244-1.319) 2.273 0.035
Bowel
Dmax/Gy 9.98±3.77 10.02±3.83 0.047(0.022-0.189) 1.350 0.193
D1cc/Gy 8.90±3.64 8.93±3.56 0.043(0.028-0.239) 1.255 0.225
D2cc/Gy 7.61±3.37 7.63±3.84 0.064(0.049-0.191) 1.748 0.097
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