[Effect of tumor volume on pulmonary dose-volume parameter by intensity-modulated radiation therapy in non-small cell lung cancer]

To explore the effectof tumor volume on pulmonary dose-volume parameters by intensity-modulated radiation therapy (IMRT) in non-small cell lung cancer (NSCLC), and to provide a basis for pulmonary dose parameters in IMRT treatment.
 Methods: A total of 204 patients with NSCLC received IMRT were retrospectively analyzed from June, 2009 to October, 2013. The prescribed dose of planning target volume (PTV) for primary tumor was 60-66Gy (2.00-2.25 Gy, 27-33 times in all). The fractional volume percent of the lung received a dose >5 or 20 Gy (V5, V20), and absolute volume of lung received a dose <5 Gy (AVS5).The mean lung dose (MLD) in normal tissues were analyzed. Regression model curve was used to analyze them along with the change of primary tumor volume.
 Results: With the increase in lung tumor volume, the V5, V20 and MLD presented quadratic equation curve, and AVS5 presented logarithmic equation. When the tumor volume, less than a certain value (294.6, 283.2, 304.9 cm3, respectively), the V5, V20 and MLD increased with tumor size and presented an increased quadratic curve; when the tumor volume was higher than a certain value (294.6, 283.2, 304.9 cm3 respectively), the V5, V20 and MLD was declined. The AVS5 was declined in a logarithmic curve along with the increase of tumor volume.
 Conclusion: With the increase in lung tumor volume, the change in rule of V5, V20, MLD and AVS5 is not completely equivalent. When the tumor volume exceeds a certain boundary value (about 300 cubic centimeter), the corresponding tumor diameter is about 7-8 cm. In addition to the focus on pulmonary V5, V20 and MLD, we should also pay more attention to AVS5 restrictions in establishment of IMRT in NSCLC.