Evaluating the impact of treatment table and immobilization device in IMRT planning accuracy / 国际生物医学工程杂志

ABSTRACT

Objective To investigate the influence of treatment table with C-arm and immobilization device in IMRT planning accuracy, and to explore methods to solve this problem.Methods The solid water slabs and the ionization chamber was scanned and images were transmitted to the treatment planning system (TPS).Beam parameters in the TPS were set with 6 MV beam and 100 MU exposures were used.Measurements were performed at two different sizes of 5 cm×5 cm and 10 cm×10 cm.The gantry was rotated through angles from 0° to 180° with measurements taken at 5° increments.The measure point was set at center of the ionization chamber' measure point, which was also the central point of planning.The center axis of Matrix was aligned with the center of couch and was irradiated in accordance with the same conditions.OmniPro-FmRT software was used to compare and analyze the dose distribution of the radiation field of measurement and the treatment planning system output.Using the function of add constant value to find the appropriate coefficient to improve the plan total dose.The dose distributions for each beam in IMRT plans which was increased or unincreased total dose were measured for 6 patients with pelvic tumor respectively.Results In radiation therapy, treatment couch and immobilization device may attenuate radiotherapy dose.The impact of the incident range from 65°-70° and 115°-125° were the largest.Increasing the total dose of the treatment plan by 2％ could compensate the attenuation of the treatment table and immobilization device.Conclusions In radiation therapy, the impact of the incident range from 65°-70°, 115°-125° and another side of 290°-295° and 230°-245° should be avoided.The attenuation should not be neglected in the TPS and dose should be compensated by adjusting beams' MU.