Evaluation of the peripheral dose and the conformity index for three stereotactic radiotherapy techniques: Arcs, noncoplanar fixed fields and intensity modulation

Abstract

Purpose: The main aim of this work is to compare the conformity index and the peripheral doses absorbed during stereotactic treatment of a brain lesion delivered using three stereotactic techniques; Arcs, noncoplanar fixed conformal fields (3DCRT) and intensity modulation (IMRT). Methods : Ten patients with brain lesions who were previously treated with Stereotaxy radiosurgery (SRS) using the cones (Arcs technique), were re-planned both non-coplanar 3D Conformal fixed fields (3DCRT) and non-coplanar intensity modulated radiotherapy fixed fields (IMRT) with the same arrangement and orientation of the fields as the Arcs technique. To facilitate direct comparison between the competing techniques, the primary planning object was to cover 95% of the volume of PTV by 95% of the prescribed dose (1200 cGy). Results: The IMRT technique shows the highest dose conformity, Arcs technique is the next homogeneity followed by 3DCRT. The differences were statistically significant among the three different techniques (P < 0.01) for PITV (defined as the ratio of the prescription isodose volume (PI) and Target Volume (TV)) and Conformal Number (CN). The mean integral dose using the 3 different techniques for all studied patients were: 2.44 ± 0.36J, 2.31 ± 0.37J and 2.6 ± 0.37J in the Arcs, IMRT and 3DCRT techniques respectively, the differences were not statistically significant (p = 0.326). The results show that Arcs technique has the lowest volume of the body that received 2 Gy, IMRT is the next followed by 3DCRT and IMRT technique has the lowest volume of the body that received 5 Gy, Arcs technique is the next followed by 3DCRT. The differences were not statistically significant p = 0.126 for V2 and p = 0.118 for V5, but these differences might be clinically significant that need more clinical discussion and investigation. IMRT plan delivery time almost has two folded more than the two others techniques, and the arc the technique has the lowest estimated time compared to both IMRT and Conformal techniques. The differences were statistically significant (P < 0.01). Conclusion : The conformity index, dose homogeneity and the outfield dose are important aspects of plan quality, although they do not always receive clinically attention. Our results have been showed that the superiority of the IMRT in conformity, dose homogeneity and the lowest volume that received 5 Gy, Arcs technique has the superiority in lower treatment delivery time than IMRT and the lowest volume that received 2 Gy. The 3DCRT don't present a significant advantage among the competing techniques. Oncologist should be alert of the possibility of significantly increasing the secondary cancer risk particularly for pediatric patients, because children are more susceptible to the risk of second cancers. --------------------------------------- Cite this article as : Ammar H, Eldebawy E, Maarouf E, Khalil W, Zaghloul MS. Evaluation of the peripheral dose and the conformity index for three stereotactic radiotherapy techniques: Arcs, noncoplanar fixed fields and intensity modulation. Int J Cancer Ther Oncol 2014; 2 (4):02042. DOI : 10.14319/ijcto.0204.2