[Dosimetric comparison of non-small cell lung cancer treatment with multi fields dynamic-MLC IMRT]

We compared the dosimetric differences between the target and surrounding tissues/organs of the 5-field and 7,9-field (Hereinafter referred to as F5, F7, F9) treatment plan in non-small cell lung cancer (NSCLC) by the dynamic intensity-modulated radiotherapy (dIMRT), to provide reference for clinical application.

Using Varian planning system (Eclipse 7.3), we randomly selected 30 cases of patients who received dIMRT to study, all patients were 5, 7, 9 fixed field dynamics intensity-modulated radiotherapy plans to meet the target prescription requirements (95% dose curve enveloping 100% of the PTV), by comparing dose-volume histogram DVH evaluation, and the maximum dose D(max), the minimum dose D(min), and the mean dose D(mean), and conformal index CI of PTV,organs at risk of spinal cord the maximum dose D(max), lung V(5), V(10), V(20), V(30), heart V(30) and esophageal V(50), V(60) of F5,F7 and F9 dIMRT plans,and compare the mu of the three treatment programs.

The D(max), D(min) and D(mean) values of F5's PTV are (7 203 ± 128), (5 493 ± 331), (6 900 ± 138) cGy respectively; the D(max), D(min) and D(mean) values of F7's PTV are (7 304 ± 96), (5 526 ± 296), (6 976 ± 130) cGy respectively; and the D(max), D(min) and D(mean) values of F9's PTV are (7 356 ± 54), (5 578 ± 287), (7 019 ± 56) cGy respectively. The data shows that while we increased the numbers of fields, the isodose line surrounding the target area would also promote slightly. The conformity index CI of target became better with the increase of radiation fields. The whole lung V(5) and V(10) slightly became larger with increase of fields and the V(20) showed no significant difference in three models, V(30) of double lungs slightly decreased with the increase of fields. The above date was statistically meaningless (P > 0.05). With the increase of fields esophagus V(50) were reduced by 3% and 5% respectively, V(60) of the esophagus were reduced by 6% and 11%, the average dose reduced by 5% and 10% and spinal cord D(max) decreased by 9% and 13%. In the F7 and F9, heart V5 were lower than F5 plan by 11%, 19%. The mu of them were increased with the increase of radiation fields, Treatment time of F7 and F9 plan were longer by 15% and 25%.

Through comparing the three fixed dIMRT plans, we could draw a conclusion that the three multi-field intensity-modulated radiotherapy in non-small cell lung cancer can meet the clinical target volume dose requirements. If the treatment is required to protect the patient's spinal cord, esophagus and heart, we can choose 7 or 9 fields. While other ordinary patients should be treated with 5 fields plan, to shorten the treatment time and improve the biological effects of lesions, and lower mu of plans to avoid unnecessary irradiation of normal tissues.