The preliminary study of setup errors' impact on dose distribution of image guide radiation therapy for head and neck cancer

Abstract

Objective To measure the set-up errors of patients with head and neck (HN then to further investigate the necessity of adjustment online for H&N cancer during IMRT treatment.Methods Cone-beam CT (CBCT) scanning of thirty patients with H&N cancer were acquired by once weekly with a total of 6 times during IMRT treatment.The CBCT images and the original planning CT images were matched by the bony structure and worked out the translational errors of the x,y,z axis,as well as rotational errors.The dose distributions were recalculated based on the data of each setup error.The dose of planning target volume (PTV) and organs at risk were calculated in the replanning,and than compared with the original plan by paired t-test.Results The mean value of x,y,z axis translational set-up errors were ( 1.06 ± 0.95 ) mm,( 0.95 ± 0.77 ) mm and ( 1.31 ± 1.07 ) mm,respectively.The rotational error of x,y,z axis were ( 1.04 ±0.791 ),( 1.06 ±0.89) and (0.81 ±0.61 ),respectively.PTV 95％ volume dose ( D95 ) and PTV minimal dose of replanning for 6 times set-up were lower than original plan (6526.6 cGy:6630.3 cGy,t =3.98,P =0.000 and 5632.6 cGy:5792.5 cGy,t =- 2.89,P =0.007).Brain stem received 45 Gydose volume ( V45 ) and 1％ brain stem volume dose ( D01 )were higher than original plan ( 3.54％:2.75％,t =3.84,P =0.001 and 5129.7 cGy:4919.3 cGy,t =4.36,P =0.000).Conclusions The set-up errors led to the dose of PTV D95 obviously insufficient and significantly increased V45,D01 of the brainstem.So,adjustment online is necessary for H&N cancer during IMRT treatment. Key words: Set-up error; Dosimetry; Head and neck neoplasms/image guide radiotherapy