Assessing cumulative dose distributions in combined external beam radiotherapy and intracavitary brachytherapy for cervical cancer by treatment planning based on deformable image registration

BACKGROUND: This study aimed to validate the feasibility of deformable image registration (DIR) in assessing the cumulative dose distributions in combined external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT) for cervical cancer. METHODS: This retrospective study included 23 patients with stage IIB disease treated with combined EBRT to the whole pelvis (50.4 Gy in 28 fractions) using an intensity-modulated radiotherapy technique with 6-MV X-ray, followed by three-dimensional (3D) ICBT (28 Gy in 4 fractions). Tumor gross target volume at diagnosis (GTV-Tinit), tumor gross target volume before brachytherapy, high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV), and parametrium and organs at risk were recontoured on computed tomography images of EBRT and ICBT, respectively. The dose-volume parameters were also determined. The DIR results were reviewed using MIM Maestro (Reg Review) and modified by function (Reg Refine). To evaluate the accuracy of DIR, DIR-based cumulative dose-volume histogram (DVH) parameters and simple DVH parameter addition were compared using Wilcoxon rank-sum tests. RESULTS: The cumulative dose distributions of EBRT and four ICBT sessions were successfully illustrated using DIR. The mean tumor diameters were 68.35 cm(3) at diagnosis and 29.63 cm(3) at ICBT initiation. The mean tumor regression was 56.6%. The median minimum dose covering 90% (D90) of HR-CTV, GTV-Tinit, IR-CTV, and parametrium were 69.58±4.94, 68.81±7.98, 59.28±3.78, and 60.97±1.1 Gy(α/β)=10, respectively, for DIR and 69.11±5.68, 68.49±8.62, 58.89±3.59, and 61±1.49 Gy(α/β)=10, respectively, with conventional simple DVH parameter addition.No statistically significant differences in dosimetric parameters were observed between the two methods. CONCLUSIONS: Although there were limitations in the DIR accuracy, DIR-based dose accumulation was significantly beneficial in visually showing the cumulative dose distribution in the target area to clinicians in combined radiotherapy for cervical cancer in routine clinical practice.