Study Of Dosimetry In Radiation Therapy For Middle And Advanced Stage Of Middle Thoracic Esophageal Cancer

Objective:To systematically compare the dose distribution of regional mediastinal lymph node partition Ⅱ-Ⅷ and adjacent volume of organs at risk for middle thoracic esophageal cancer patients treated with four different fraction mode of the three-dimensional conformal radiotherapy (3DCRT), then to explore the advantages of the different splitting mode in order to get the best treatment plan.Methods:Ten patients with intermediate and advanced stage middle thoracic esophageal cancer were treated with radiotherapy between Nov2010and Dec2011. A retrospective treatment planning study was performed to compare four different fraction mode of3DCRT 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, then exposured to radiotherapy simulator, and marked with nine points by three groups of laser lines nearby. After that, we repeated position and scanned from the cricoids cartilage to the costophrenic angles on the CT(PLUS FOUR SPIRAL CT), with the slice thickness was2.5to5mm. Using the three-dimensional radiation treatment planning system (TPS, Topslane Venus Planning System),CT images were transformed and reconstructured in three dimensions. Then, we delineated the tumor target and the organs at risk (OARs) such as lung, heart, spinal cord on the CT cross-sectional images, combined with the recent chest-CT. The gross target volume (GTV), clinical target volume (CTV) and planning target volume (PTV) were delineated according to the ICRU50Report and the ICRU62Report. Each case was designed by the following four split mode treatment plan:NO.1Two fields+two oblique field; NO.2a field+two former oblique fields; NO.3two fields+two posterior oblique; NO.4Maeno+two posterior oblique. Oblique fields angles are selected the minimum angle to avoid the spinal cord. The spinal cord dose less than40Gy. PTV was given64Gy in32fractions. Dose volume histograms were used to analyse the dose distribution of mediastinal lymph node partition Ⅱ-Ⅶ and the volume of organs at risk nearby.Results:The dose of the mediastinal lymph node partition Ⅲ region in first plan was43.3±10.5Gy, which was higher than that of second plan, third plan and fourth plan (P<0.05). The dose of the mediastinal lymph node partition Ⅳ region of the first plan was higher than that of plan3, plan four (P<0.05).The maximum dose at the spinal cord were all not exceed40Gy in the these four plans. Minimum dose of spinal cord in these four plans is plan4(24.1±5.5Gy). The plan2get the minimum dose of the mediastinal lymph node partitionVI District, right and left lung V5value, the average dose of heart, heartV30and V40value (P<0.05)Conclusions:The plan1, which obtained the maximum dose of the mediastinal lymph node partition Ⅲ and Ⅳ R District can reduce the regional lymph nodes relapse possibility, and the plan2, which get the minimum value of the Ⅵ District dose, right and left lung V5value, the average dose of heart, heart V30, V40value, can reduce the damage of lung tissue and heart tissue; The left and right lung V30values is smaller than that of other three plans, which can reduce the probability of radiation pneumonitis; The fourth plan significantly reduced the spinal cord maximum dose value result in reliable protection of the spinal cord.