Clinical dosimetric impact of AAA and Acuros XB on high-density metallic implants in case of carcinoma cervix

Abstract

Background: Metallic implant in radiotherapy leads to difficulty in tumor target and critical organ delineation. Four-field box technique is conventional approach to treat pelvic malignancies. Aim of the Study: The aim of study is to evaluate the dosimetric impact of calculation algorithms in the treatment of carcinoma cervix with metallic implants. Materials and Methods: A paraffin wax-coated iron rod was used to evaluate the beam characteristics under the influence of metallic implant. Beam characteristics such as tissue phantom ratio (TPR20,10) were measured and analyzed. 15 patients with and without metallic prosthesis of carcinoma cervix were compared in the study. Planning was done for the prescription dose of 45 Gy/25 fractions. Plans were calculated using AAA algorithm and recalculated using Acuros XB (AXB) and pencil beam convolution algorithms for the same monitor units. RTOG and Quantec Protocol were used for plan evaluation. Results: Transmission and TPR20,10increases with field size and beam energy. Surface dose Dsalso increases with field size. D98%and D2%of planning target volume showed a significant difference for AAA versus AXB. 4FN (AAA) are significantly better for all the 4F plans, calculated by three algorithms in case of V15Gyof small bowel. Analyzed data indicated the significant attenuation caused by high-Z material. Analyzed value of conformity index showed that value of index comes >1 in all the cases. Conclusion: The results indicate that when creating treatment plans for cervical cancer lesions with metallic prosthesis, the AAA algorithm would be a more appropriate choice.