Beam orientation optimization of pulmonary ventilation image-guided intensity modulated radiotherapy for lung cancer

Abstract

Objective To evaluate the dosimetric advantage of pulmonary ventilation image guided intensity-modulated radiotherapy (IMRT) planning in protecting functional lung with optimizing beam orientation. Methods Sixteen non-small cell lung cancer patients were included and carried out with the peak-exhale and peak-inhale CT scans, respectively. The two sets of CT images were then input to the pulmonary ventilation analysis system to acquire the three dimensional distribution of ventilation images. Then the area of better pulmonary ventilation named as functional lung was delineated automatically by the system. The pulmonary ventilation images were fused with CT images by using treatment planning system. Two kinds of IMRT plans were generated, in cluding conventional IMRT, in which the main dose constraints were applied to total lung, as well as f-IMRT, with the main dose constraints applying to functional lung. To evaluate the dosimetric changes of beam arrangement, the five equal-spaced beams and five manual optimization beams were applied to each plan. The dosimetric difference between IMRT and f-IMRT plans was compared using the paired t-test. Result In the same category of plan, all the dosimetric parameters of PTV had no significant difference (P>0.05) in the plan with FMOB, comparing with FESB. The dose delivered to spinal cord, esophagus, and heart varied in degrees, whereas only the dosimetric difference of the mean dose to esophagus and V60 to heart had statistically significance (t =4.33, -2.37, P <0.05) between the plan with FESB and plan with FMOB. For IMRT plans, compared with FESB, the volume of functional lung at more than 5, 10 and 20 Gy (FLV5, FLV10, and FLV20) decreased significantly in plan with FMOB (t=4.87, 4.74, 2.33, P <0.05). The FLV5, FLV10, and FLV20 in plan with FESB were (54.2±29.1)%, (42.5±22.1)%, (26.3±20.7)%, respectively, while in plan with FMOB were (30.2±18.5)%, (24.1±12.0)%, (17.8±8.9)%, respectively. For f-IMRT plans, compared the plan with FMOB to plan with FESB, the FLV5, FLV10, and FLV20 of the functional lung decreased significantly (t=5.30, 4.84, 2.23, P <0.05). The FLV5, FLV10, and FLV20 were (52.4±20.7)%, (37.1±12.2)%, (21.1±5.8)%, respectively in plan with FESB, while in plan with FMOB were (29.2±18.3)%, (23.0±14.8)%, (16.7±9.7)%, respectively. The dosimetric parameters of low-dose region of total lung also decreased in different degrees, with statistical significance (t=7.96-6.07, P <0.05). Conclusions The combination of pulmonary ventilation images and IMRT, with further optimizing the beam directions, can effectively reduce the radiation dose on functional lung, which is expected to reduce the incidence and severity of radiation pneumonitis and might improve the NSCLC patient′s quality of life. Key words: Lung neoplasms/radiotherapy; Four-dimensional computed tomography; Pulmonary ventilation; Plan optimization