Comparison of dose-volume analysis between standard Manchester plan and magnetic resonance image-based plan of intracavitary brachytherapy for uterine cervical cancer

Abstract

To investigate the feasibility of image-based intracavitary brachytherapy (IBICBT) for uterine cervical cancer, we evaluated the dose-volume histograms (DVHs) for the tumor and organs at risk (OARs) and compared results from the IBICBT plan and the standard Manchester system (Manchester plan) in eight patients as a simulation experiment. We performed magnetic resonance imaging (MRI) and computed tomography (CT) following MRI-adapted applicator insertion, then superimposed MR images on the planning CT images to describe the contours of high-risk clinical target volume (HR CTV) and OARs. The median volume of HR CTV was 29 cm(3) (range, 21-61 cm(3)). Median D90 (HR CTV) and V100 (HR CTV) were 116.1% prescribed doses (PD) (90.0-150.8%) and 96.7% (84.2-100%), respectively, for the Manchester plan. In comparison, we confirmed that the median D90 (HR CTV) was 100% PD in the IBICBT plan for all patients. Mean D(2cc) (bladder) was 101.8% PD for the Manchester plan and 83.2% PD for the IBICBT plan. Mean D(2cc) (rectum) was 80.1% PD for the Manchester plan and 64.2% PD for the IBICBT plan. Mean D(2cc) (sigmoid) was 75% PD for the Manchester plan and 57.5% PD for the IBICBT plan. One patient with a large tumor (HR CTV, 61 cm(3)) showed lower D90 (HR CTV) with the Manchester plan than with the IBICBT plan. The Manchester plan may represent overtreatment for small tumors but insufficient dose distribution for larger tumors. The IBICBT plan could reduce OAR dosage while maintaining adequate tumor coverage.

Figures

Fig. 1.

(a) computed tomography (CT) image of Patient 1 after insertion of treatment applicator and (b) same CT image as Fig. 1a without superimposition of MRI. (a) A magnetic resonance image (MRI) was superimposed to describe the precise contours of high-risk clinical target volume (HR CTV, white broken line). (b) It was difficult to describe the high-risk clinical target volume (HR CTV) as shown in Fig. 1a. The HR CTV described by CT imaging appears to be of larger volume than that described by MRI (black broken line).

Fig. 2.

(a−d) dose distribution curves of Patient 1. We first followed the Manchester plan (a, axial image; b, sagittal image) and administered treatment to the patient. After treatment, we followed the image-based intracavitary brachytherapy (IBICBT) plan (c, axial image; d, sagittal image). HR CTV (black line) was covered by a higher isodose line than the prescribed isodose line (white broken line) in the Manchester plan (a, b). In contrast, the IBICBT plan showed better coverage of HR CTV (black line) by the prescribed isodose line (white broken line).

Fig. 3.

Dosages that covered 90% of the HR CTV were compared between the Manchester plan (white columns) and the IBICBT plan (gray columns) for each patient. We could control the D90 (HR CTV) values of all patients to 100% PD. In contrast, median D90 (HR CTV) per fraction was 116.1% PD (90.0–150.8%) for the Manchester plan. Seven of the eight patients showed higher values in the Manchester plan than in the IBICBT plan. However, Patient 8, whose HR CTV was >61 ml, showed a lower value.

Fig. 4.

(a, b) dose distribution curves of Patient 8. We first followed the Manchester plan (a) and administered treatment to the patient. After treatment, we modified the Manchester plan and followed the IBICBT plan (b). HR CTV (black line) could not be covered by the prescribed isodose line (white broken line) in the Manchester plan (a). In the IBICBT plan, we extended the dwell time of the right ovoid applicator and enhanced the right side of HR CTV (white broken line). However, we compromised at this point to maintain the maximally irradiated 2 cm3 volume for the bladder within tolerable levels.

Fig. 5.

Percentage of prescribed doses for organs at risk were compared between the Manchester and IBICBT plans. Shown here are average values with standard deviation for the minimum dose received by the maximally irradiated 2 cm3 volume (D2cc) for bladder, rectum and sigmoid colon. Significant differences were observed between the two plans for bladder (P = 0.0008), rectum (P = 0.003) and sigmoid colon (P = 0.002).