Dosimetric Comparative Study of Static Gantry IMRT and 3D Conformal Radiotherapy for Organ at Risk in Adjuvant Therapy of Gastric Cancer

Background: Despite the benefits of postoperative radiotherapy for gastric cancer patients after publishing the results of the Intergroup 0116 (INT-0116) study, there are still the concerns of radiation-induced toxicity.
Aim: To determine the radiation technique that can eliminate the dose of radiation to the organ at risk (OAR) in patients postoperatively treated for gastric cancer with three-dimensional conformal radiotherapy (3D-CRT) or intensity- modulated radiotherapy (IMRT) using dosimetric analysis.
Methods: A total of 22 computerized radiation plans were reviewed. Dosimetric values for 3DCRT and IMRT technique were calculated. The following dosimetric parameters were compared for the planned target volume (PTV); the homogeneity index, maximal and minimal doses, the volumes of PTV received 95 % and 107 % of the prescribed dose. In addition, the mean dose and dose volume histogram (DVH) for the OAR as, V20 for each kidney, V30 for the liver, maximum dose (Dmax) for D1% of the spinal cord and V40 to the heart .
Results: The 3D-CRT and IMRT achieved comparable PTV coverage. However, IMRT was associated with a highly significant decrease in the mean V20 value of the right kidney by 15% (P=0.001) and left kidney by 9% (P=0.01). The IMRT significantly improved sparing of the mean irradiated volume and the V30 of the liver by 12% (P=0.01) and by 10% (P=0.02) respectively compared with 3D-CRT. On the other hand, the dosimetric parameters for the spinal cord and heart were comparable for the IMRT and 3D-CRT plans.
Conclusion: In gastric cancer patients receiving postoperative radiotherapy, IMRT provided better protection for the liver and kidneys when compared to 3D-CRT.