A study of lung protection in intensity?modulated radiotherapy with split field and fixed jaw techniques for peripheral lung cancer with mediastinal lymph node metastasis / 中华放射肿瘤学杂志

ABSTRACT

Objective To retrospectively design an intensity?modulated radiotherapy ( IMRT) plan with split field and fixed jaw techniques for peripheral lung cancer with mediastinal lymph node metastasis, to compare dosimetric characteristics between the IMRT plans with fixed jaw and dynamic jaw, and to study lung protection by the plan with split field and fixed jaw. Methods Treatment plans were collected from 12 patients with peripheral lung cancer and mediastinal lymph node metastasis who were treated with IMRT in our hospital. All plans used the dynamic jaw technique. The plans with split field and fixed jaw were designed based on the identical computed tomography images and planning target volume ( PTV) . Each jaw position in split field depended on each separate PTV. The prescription dose was 60 Gy in 30 fractions. 95%PTV was planned to receive 100% of the prescription dose. Dosimetric parameters of PTV, conformity index ( CI) , heterogeneity index ( HI) , number of monitor units ( MUs) , and dose?volume values of the lung and heart were obtained from dose?volume histogram. Comparison between the two plans was made by paired t test. Results Both plans met clinical requirements. There were no significant differences in D2 , D98 , CI, or HI of PTV between the two plans ( all P>005) . Compared with the dynamic jaw plan, the fixed jaw plan had MUs increased by 15%?20%( P=0010) . The V5 , V10 , V20 , V30 , and mean dose for the whole lungs were significantly lower in the fixed jaw plan than in the dynamic jaw plan ( P=0000, 0000, 0000, 0002,0000) . The V5 , V20 , and mean dose for the healthy lung were also significantly lower in the fixed jaw plan than in the dynamic jaw plan ( P=0000,0017,0000) . There were no significant differences in dose?volume values for the spinal cord or heart between the two plans ( all P>005) . Conclusions IMRT with split field and fixed jaw is recommended for patients with peripheral lung cancer and mediastinal lymph node metastasis. The therapy to a certain extent reduces low?dose volume for the lung and the incidence of radiation?induced pneumonitis.