Study Of Dosimetry In Radiation Therapy For Intermediate And Advanced Stage NSCLC

Objective: Conventional radiotherapy(RT), three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiation therapy(IMRT) were designed for 10 patients with non-small cell lung cancer (NSCLC) and the three different kinds of radiotherapy plans were compared systematically by DVHs. Compared with conventional radiotherapy ,the advantage of 3DCRT and IMRT for patients with intermediate and advanced stage NSCLC in improving the target dose and reducing the dose of organs at risk (OARs) nearby.Methods: From May 2008 to May 2009, ten patients with intermediate and advanced stage NSCLC were treated by radiotherapy. A retrospective treatment planning study was performed to compare RT, 3DCRT and IMRT for these patients. All patients were immobilized by MED-TEC vacuum body bags when they lied supine with their hands up hold the elbows and with normal respiration, exposured to radiotherapy simulator, and marked three groups of laser lines nearby target with nine points. Repeated position and then scanned from the cricoid cartilage to the costophrenic angles on the CT (PLUS FOUR SPIRAL CT), the slice thickness was 3 to 5 mm. Using the three-dimensional radiation treatment planning systems (TPS, Topslane Venus Planning System),CT images were transformed and restructured in three dimensions. Delineated the tumor target and the organs at risk (OARs)such as lung, heart, spinal cord and esophagus on the CT cross-sectional images, combined with the recent chest-CT, or MRI, or PET / CT. The gross tumor volume (GTV), clinical target volume(CTV) and planning target volume(PTV) were delineated according to the ICRU50 Report and the ICRU62 Report. CTV was defined as the GTV plus a 7-10mm margin, and PTV as the CTV plus a 8mm margin, and then expanded the scope furthermore according to the breathing movement rang showed in the simulator and the potential set-up error, the three plans had the same target volume. Three kinds of radiation treatment plans were designed for each patient: RT plans, 3DCRT plans and IMRT plans. The RT plans were simulated on the TPS, irradiated vertically to 40Gy by 6MV-X ray, and then avoided the spinal cord adding to the total dose 66 Gy in 33 fractions. The 3DCRT plans and the IMRT plans was planned according to the dose volume histogram(DVH),and the principle was maximizing dose to the target volume and minimizing dose to the surrounding normal tissues, the best plan was selected to perform , one target volume was predefined: PTV which was given 66Gy in 33 fractions. Dose volume histograms were used to compare doses distributions for tumor and normal tissues in the three plans.Results: Target volume dosimetric distribution of IMRT were better than RT, because the doses in 95% PTV and the volume of the prescription doses of IMRT were higher than RT, all had statistical significance (P<0.05).The volume of lung V30 and lung V40 of IMRT were lower than RT and 3DCRT , had statistical significance (P<0.05),also the volume of lung V20 of the IMRT was the lowest, but the total lung volume receiving low dose radiation of IMRT improved significantly ,the volume of lung V5 of IMRT was the highest (P<0.05).The mean dose of esophageal and the volume of esophageal V45 of 3DCRT and IMRT were lower than RT. The mean dose of heart and the volume of heart V35 of 3DCRT were lower than RT, and the value of IMRT was the lowest .The maximum dose at the spinal cord were all under 45Gy in the three plans, and the dose of IMRT were higher than 3DCRT(P>0.05).Conclusions: Target volume dosimetric distribution of IMRT were better than RT and 3DCRT , the volume of lung V30,lungV40, esophageal and heart V35 of IMRT were lower than RT and 3DCRT ;the volume of lung V5 of IMRT was higher than RT and 3DCRT ;the dose at the spinal cord of IMRT was higher than 3DCRT,but lower than the minimum tolerated dose .The target volume dosimetric distribution of IMRT was more precise as compared with RT and 3DCRT.The IMRT plans decreased the surrounding normal tissues and organs radiation injury, especially the total lung volume receiving high dose radiation.