Abstract
PurposeTo assess the setup errors in radiation therapy for thoracic tumors patients of different somatotypes, and to seek an individualized mathematical basis for defining the planning target volume (PTV).MethodsSixty patients with thoracic tumors were divided into four somatotypes according to their body mass index (BMI), and their body positions were setup by two groups of technicians independently. CT simulations were performed and the reconstructed radiography was digitally generated as reference images for location verification and error measurement. By setting positioning error ranges, the within‐range positioning correction rate was compared among groups.ResultsPosition setups for patients in the emaciated group, moderate group, and overweight group were relatively stable (with minor setup error differences between the two groups of technicians). In emaciated group, moderate group, overweight group, and obese group, setup errors in the right–left direction (R‐L) were 2.2 ± 1.3 mm, 2.2 ± 1.6 mm, 3.9 ± 3.1 mm, and 8.8 ± 3.5 mm, respectively; whereas the setup errors in the four groups in the superior–inferior(S‐I) direction were 2.4 ± 1.8 mm, 2.1 ± 1.9 mm, 3.2 ± 2.6 mm, and 5.4 ± 3.5 mm, and in the anterior–posterior (A‐P) direction were 2.2 ± 1.7 mm, 1.9 ± 1.9 mm, 3.2 ± 2.9 mm, and 6.2 ± 4.2 mm, respectively. Moreover, in the moderate group, the positioning correction rate in the three directions (R‐L, S‐I, and A‐P) was 20%, 9%, 8% within the error range of 5–10 mm, and 3%, 0%, 1% with a more than 10 mm error range. However, in overweight group and obese group, the positioning correction rate in these three directions (also with a more than 10 mm error range) was 23%, 27%, 19% and 21%, 16%, 23%, respectively.ConclusionsIn radiation therapy for patients with thoracic tumors, the definition of PTV should be individualized. Meanwhile, with the increase in BMI, positioning correction rate has a tendency to rise too.
Highlights
With the development of radiotherapy, intensity-modulated radiation therapy (IMRT) has become the mainstream method in modern radiotherapy technology with its obvious dosimetric advantage.[1,2,3] The accurate positioning and setup are needed with the increasing use of IMRT
Patients were divided into four groups according to Chinese standard based on their body mass index (BMI) value: patients with BMI < 18.5 kg/m2 were allocated into the emaciated group, patients with BMI within the range of 18.5–24.0 kg/m2 were allocated into moderate group, with BMI between 24.0–28.0 kg/m2 were assigned into overweight group, whereas patients with BMI ≥ 28 kg/m2 were grouped into the obesity group
When compared with the moderate group, the emaciated group showed no significant difference in patient setup errors
Summary
With the development of radiotherapy, intensity-modulated radiation therapy (IMRT) has become the mainstream method in modern radiotherapy technology with its obvious dosimetric advantage.[1,2,3] The accurate positioning and setup are needed with the increasing use of IMRT. Due to the factors such as respiratory, body weight, skin traction, arm lift, etc, the repeatability of whole-treatment process is poor.[4] There are a variety of factors influencing the setup errors in radiation therapy for patients with thoracic tumors.[5,6,7] In order to reduce these setup errors, many researchers tried to improve setup accuracy by improving the fixation of patients.[8,9,10] In the study of Wang Wei etc.,[11] it was shown that BMI was positively correlated with total error, indicating that BMI was an important factor in the setup errors. Our study measured the setup errors in radiation therapy for thoracic tumors patients of different somatotypes, and compared the impact of positioning correction rate on setup accuracy within different error ranges. We aim to provide evidence for the patient-specific definition of PTVs in radiation therapy
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