[Application of active breathing control system to precise radiotherapy for non-small cell lung cancer]

Breathing is one major factor which affects the dose used in the treatment of non-small cell lung cancer (NSCLC). This study was to observe the influence of active breathing control (ABC) system on the motion of primary tumor of non-small cell lung cancer and investigate the effect of ABC on the reduction of radioactive damage of lungs during precise radiotherapy.

Seven patients with stage IIIA and IV peripheral lung cancer, whose pathology were either squamous cell carcinoma or adenocarcinoma, were enrolled. The patients receiving three-dimensional conformal radiotherapy controlled by ABC system held their breath when their inspiratory volume reached 80% of the maximum. The moving ranges of tumor in intra-and inter-fractions during radiotherapy were calculated respectively. The tumor moving ranges of patients who accepted repeated CT scans when breathing freely in the same position were calculated. Internal margin, V2, D(mean), volume of GTV and total volume of bilateral lung were calculated by treatment planning system and compared by t-test.

The mean ranges in left-right (X), superior-inferior (Y) and cranial-caudal (Z)directions were(0.79+/-0.45)mm, (0.98+/-0.52)mm, (0.50+/-0.75)mm in intra-fractional radiotherapy and (0.91+/-0.69)mm, (1.02+/-0.77)mm, (0.74+/-1.0)mm in inter-fractional radiotherapy respectively when patients used ABC system; while the ranges were (1.09+/-0.61)mm, (1.71+/-0.82)mm, (2.73+/-1.08)mm respectively when patients breathed freely. V20 were (10.0+/-3.7)% and (17.0+/-6.5)% (P=0.015); D(mean) were (539+/-247)cGy and (844+/-390)cGy (P=0.012); the volumes of GTV were (26.1+/-22)cm(3) and (30.0+/-23.9)cm(3) (P=0.02), and total bilateral lung volume were (3522.8+/-1020)cm(3) and (3240.7+/-876.7)cm(3) (P=0.045) respectively under ABC and free breathing condition.

The tumor moving ranges and internal margins are reduced by holding the patients' breath by ABC system, which reduces the volume of normal tissues around peripheral lung tumor during radiotherapy. In addition, total lung volumes are enlarged when patients holding their breath while inhaling, which can reduce the density of irradiated lungs, and thus the incidence of radioactive lung damage is decreased accordingly.