Application of dosimetric verification in intensity-modulated pan-pelvis radiation therapy for cervix cancer / 解放军医学杂志

ABSTRACT

Objective To evaluate the intensity-modulated radiation therapy(IMRT)for the whole pelvis in the treatment for cervix cancer with the method of ionization chamber verification and fluence map verification.Methods IMRT plan was designed with Pinnacle 7.0 inversed treatment planning system,and the planning parameter was copied to the solid water phantom.The dose of the reference points in the phantom was calibrated with ionization chamber,and compared with those in IMRT plan.Then the gantry angle was set as 0 degree.The solid water phantom was irradiated with film,and the actual fluence maps were obtained 2cm below the phantom surface,and then the delivered films were compared with those fluence maps in plan.Results The error percentage at 4 points was less than 3% in absolute dose calibration,at 2 points was less than 5%,at another 2 points was less than 5%,at 1 point was over 10%,and at another 1 point was over 15%.It was found that the last two calibrated points were set in a region with a high dose gradient,resulting in high error.In fact they were impertinent.So another two points were chosen in uniformity area of dose distribution.The percentage of error were both less than 3%.The fluence maps between films and plan were consistent.Conclusion It is feasible to evaluate IMRT plan for whole pelvis in the treatment of cervix cancer with the method of ionization chamber verification and fluence map verification.The results can meet the clinical requirement.