Computed tomography-based three-dimensional dosimetry of intracavitary brachytherapy for cervical cancer

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

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.

Adaptive brachytherapy of cervical cancer, comparison of conventional point A and CT based individual treatment planning

BACKGROUND

Locally advanced cervical cancer is commonly treated with external radiation therapy combined with local brachytherapy. The brachytherapy is traditionally given based on standard dose planning with prescription of dose to point A. Dosimetric aspects when changing from former standard treatment to individualized treatment plans based on computed tomography (CT) images are here investigated.

MATERIAL AND METHODS

Brachytherapy data from 19 patients with a total of 72 individual treatment fractions were retrospectively reviewed. Standard library plans were analyzed with respect to doses to organs at risk (OARs), and the result was compared to corresponding delivered individualized plans. The theoretical potential of further optimization based on prescription to target volumes was investigated. The treatments were performed with a Fletcher applicator.

RESULTS

For standard treatment planning, the tolerance dose limits were exceeded in the bladder, rectum and sigmoid in 26%, 4% and 15% of the plans, respectively. This was observed most often for the smallest target volumes. The individualized planning of the delivered treatment gave the possibility of controlling the dose to critical organs to below certain limits. The dose was still prescribed to point A. An increase in target dose coverage was achieved when additional individual optimization was performed, while still keeping the dose to the OARs below predefined limits. Relatively low average target coverage, especially for the largest volumes was however seen.

CONCLUSION

The individualized delivered treatment plans ensured that doses to OARs were within acceptable limits. This was not the case in 42% of the corresponding standard plans. Further optimized treatment plans were found to give an overall better dose coverage. In lack of MR capacity, it may be favorable to use CT for planning due to possible protection of OARs. The CT based target volumes were, however, not equivalent to the volumes described in magnetic resonance imaging (MRI) based recommendations. Prescription and assessment of dose, when introducing such target volumes, should be evaluated and preferably compared to well known treatment regimens.