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Dosimetric comparison between 2D and 3D planned intracavitary brachytherapy for cervical cancer at Groote Schuur Hospital
Background: Intracavitary brachytherapy (ICBT) remains a vital component of curative treatment for locally advanced cervical cancer. Traditionally, two-dimensional (2D) treatment planning using orthogonal radiographs has been employed in many low- and middle-income countries (LMICs), including at Gr...
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| Format: | Thesis |
| Language: | English English |
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Division of Radiology
2026
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| Summary: | Background: Intracavitary brachytherapy (ICBT) remains a vital component of curative treatment for locally advanced cervical cancer. Traditionally, two-dimensional (2D) treatment planning using orthogonal radiographs has been employed in many low- and middle-income countries (LMICs), including at Groote Schuur Hospital (GSH) in Cape Town, South Africa. While standard 2D-based planning has historically been sufficient, it presents limitations in accurately estimating the dose to organs at risk (OARs) and the clinical target volume (CTV). The global standard of care has shifted toward three-dimensional (3D) image-based planning using CT or MRI, allowing for improved visualization of target structures and OARs, as well as optimized dose distributions through dose-volume histogram (DVH) evaluation. However, implementation in resource-constrained environments remains challenging due to limited access to imaging, trained personnel, and infrastructure. Aim: This study aimed to conduct a dosimetric comparison of 2D-based and optimized 3D-based intracavitary brachytherapy plans for cervical cancer patients treated at GSH, to evaluate whether optimized 3D planning is superior in target coverage and OAR sparing, and with the intent to support a safe transition toward a CT-based 3D brachytherapy workflow. Methods: A total of 160 CT datasets from 40 patients, each treated with 4 fractions of high dose rate (HDR) brachytherapy (7 Gy prescribed to Manchester system Point A) using a tandem-and-ovoid applicator, were retrospectively analyzed. Patients were treated with plans based on 2D planning techniques, created on CT images. In Phase 1, the target and OAR structures were retrospectively delineated, and dose distributions were evaluated. In Phase 2, 3D optimized plans were generated, prioritizing normal tissue sparing. This was achieved by manually adjusting dwell times to align with the dose planning aims. Paired samples t-tests were used to compare parameters, including D90, D100, and mean dose to the clinical target volume (CTV), as well as D0.1cc, D1cc, and D2cc for the bladder, rectum, and sigmoid. Results: Statistically significant differences (p < 0.001) were observed for all parameters when comparing 2D to 3D plans (i.e., unoptimized vs optimized). OAR mean doses showed consistent reductions in 3D plans: bladder D2cc decreased from 6.57 Gy to 4.45 Gy, rectum D2cc from 3.82 Gy to 2.36 Gy, and sigmoid D2cc from 4.80 Gy to 3.62 Gy. High dose sub-volumes such as bladder 0.1 cc, rectum 0.1 cc, and sigmoid 0.1 cc were also significantly lower in 3D plans (9.17 Gy vs 6.07 Gy for bladder; 6.54 Gy vs 3.82 Gy for rectum; 6.91 Gy vs 5.07 Gy for sigmoid). Additionally, the 7 Gy isodose volume was markedly reduced in 3D plans (109.73 cc vs. 72.31 cc), indicating improved dose conformity and sparing of normal tissue. Following a conservative approach to normal tissue sparing resulted in less optimal target coverage. The dose to Point A dropped to 5.19 Gy in optimized plans. Similarly, D90 to the CTV decreased from 5.26 Gy to 4.16 Gy, while the mean dose to the CTV dropped from 12.61 Gy to 10.25 Gy. Conclusion: This dosimetric comparison confirms the advantage of 3D image-based planning over conventional 2D-based planning, in terms of OAR sparing. Although a reduction in target coverage was observed in 3D plans, it reflects a more anatomically accurate and individualized dose delivery. A key limitation of 3D planning lies in the quality of structure delineation. Accurate contouring of the CTV and OARs is critical for plan optimization and safe dose escalation. Variability in contour quality, particularly on CT, where soft tissue contrast is limited, may influence dosimetric outcomes and must be considered when interpreting the results. |
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