Dosimetric comparison of three-field and four-field 3D conformal radiation therapy ballistics for rectal cancer treatment

Abstract

The tremendous improvement made over the last ten years in radiotherapy has been achieved mainly by developing particle acceleration techniques. Three-dimensional conformal radiation therapy [3D-CRT] is crucially applied for decreasing the shape of advanced rectal tumors yet has several side consequences. Our investigation examined the dose distribution in planning target volumes (PTV), the protection of healthy organs at risk (OAR), and the quality of therapy for the two strategies based on the three fields and four fields ballistic used in treating rectal cancers. Using the Varian Linear Accelerator system (Varian Medical Systems, Inc., Palo Alto, CA, USA) integrated with an Eclipse MLC 2100 planning system including Pencil Beam Convolution PBC dose calculation algorithm. Two different treatments of rectal cancer based on the two approaches are performed. A dosimetric comparison of the parameters is made to evaluate the feasibility of each ballistic. These parameters, including the target volume coverage indicators, included average dose, conformity index (CI), and homogeneity index (HI) of planning tumor volume; OAR included the bladder and bilateral proximal femurs. The results achieved in this dosimetric comparative study advocate for the clinical application of three fields ballistic in all specialties already compared, except for the planning target volume PTV dose distribution. The study has shown that the three-field technique (an anterior and two opposing lateral fields with the portals orientation 0°, 90°, 270°) and applied energy photons of 18 MV and 6 MV provides the best bladder protection. According to the dose distribution in the target (PTV), all evaluated plans have not indicated any significant differences. The risk of morbidity in the femoral heads for all the applied methods, in a dose up to 56.396 Gy, was not a therapeutic problem. However, the three-field approach with beams orientation 0°, 120°, 240°gave the best sparing effect for femoral heads.