Evaluation of the Treatment Field Deviations in Different Set-up Positions During Thoracic Radiotherapy in Lung Cancer Patients

OBJECTIVE The purpose of the study was to evaluate the treatment field deviations in lung cancer patients treated with thoracic radiotherapy (RT) performed using different immobilization devices into three different set-up positions and the influencing factors. METHODS Thirty lung cancer patients having palliative thoracic RT indication were randomized into three different set-up positions using different immobilization devices (Group I: arm along the body, Group II: lung board, and Group III: arm supported board). The treatment field center deviation was measured on sternal (X and Y axis) and axillary (z and theta axis) cross. In addition, parameters such as age, pain, pulmonary function test, set-up time, the temperature difference between the treatment room and the outside environment, and patient education level that may cause set-up were evaluated. RESULTS Mean intra-fraction field center deviations of 5.66 +/- 4.15 mm were observed in the right (z) axis (p=0.049) and 5.53 +/- 4.81 mm in the left (z) axis (p=0.015) in Group II which were statistically significantly larger than the deviations in other groups. A statistically significant correlation was found between the indoor and outdoor temperature difference and set-up time. CONCLUSION Both set-up positions of Groups I and III, gave better results than the position of Group II. According to our results, if a lung board will be used, adding the arm supporting accessory will be necessary. Random errors can be minimized and the set-up quality improved by using appropriate immobilization devices, minimizing the total set-up time and balancing the in and outdoor temperature by air conditioning system.