A comparison of dosimetric variance for external-beam partial breast irradiation using three-dimensional and four-dimensional computed tomography

Abstract

PurposeTo investigate the potential dosimetric benefits from four-dimensional computed tomography (4DCT) compared with three-dimensional computed tomography (3DCT) in radiotherapy treatment planning for external-beam partial breast irradiation (EB-PBI).Patients and methods3DCT and 4DCT scan sets were acquired for 20 patients who underwent EB-PBI. The volume of the tumor bed (TB) was determined based on seroma or surgical clips on 3DCT images (defined as TB3D) and the end inhalation (EI) and end exhalation (EE) phases of 4DCT images (defined as TBEI and TBEE, respectively). The clinical target volume (CTV) consisted of the TB plus a 1.0 cm margin. The planning target volume (PTV) was the CTV plus 0.5 cm (defined as PTV3D, PTVEI, and PTVEE). For each patient, a conventional 3D conformal plan (3D-CRT) was generated (defined as EB-PBI3D, EB-PBIEI, and EB-PBIEE).ResultsThe PTV3D, PTVEI, and PTVEE were similar (P=0.549), but the PTV coverage of EB-PBI3D was significantly less than that of EB-PBIEI or EB-PBIEE (P=0.001 and P=0.025, respectively). There were no significant differences in the homogeneity or conformity indexes between the three treatment plans (P=0.125 and P=0.536, respectively). The EB-PBI3D plan resulted in the largest organs at risk dose.ConclusionThere was a significant benefit for patients when using 3D-CRT based on 4DCT for EB-PBI with regard to reducing nontarget organ exposure. Respiratory motion did not affect the dosimetric distribution during free breathing, but might result in poor dose coverage when the PTV is determined using 3DCT.

Effects of four‐dimensional simulation of boost radiation after breast conservation surgery: A prospective dosimetric and volumetric analysis

“…In the present dosimetric analysis, we observed no significant differences in target coverage or normal tissue dosimetry between the plans formed using 3‐D and 4‐D datasets. This is in partial concordance with previous studies by Guo et al., who observed no significant differences in the homogeneity index or conformity index, but reported a reduction in doses to the organs at risk with the use of 4D CT and 3D CRT planning . However, these results should be interpreted cautiously in the context of treatment delivery using 3D CRT, and might not be readily extrapolated to intensity‐modulated radiotherapy.…”

“…This is in partial concordance with previous studies by Guo et al, who observed no significant differences in the homogeneity index or conformity index, but reported a reduction in doses to the organs at risk with the use of 4D CT and 3D CRT planning. 28,29 However, these results should be interpreted cautiously in the context of treatment delivery using 3D CRT, and might not be readily extrapolated to intensity-modulated radiotherapy. Because our median conformity index of 1.7 implied that the volume receiving the desired dose is 70% greater than that of the target volume, it can be concluded from the present study that routine 4-D simulation or additional for internal target volume margin might not be necessary when…”