Clinical acceptability of fully automated external beam radiotherapy for cervical cancer with three different beam delivery techniques

Abstract

Purpose: To fully automate CT-based cervical cancer radiotherapy by automating contouring and planning for three different treatment techniques.

Methods: We automated three different radiotherapy planning techniques for locally advanced cervical cancer: 2D 4-field-box (4-field-box), 3D conformal radiotherapy (3D-CRT), and volumetric modulated arc therapy (VMAT). These auto-planning algorithms were combined with a previously developed auto-contouring system. To improve the quality of the 4-field-box and 3D-CRT plans, we used an in-house, field-in-field (FIF) automation program. Thirty-five plans were generated for each technique on CT scans from multiple institutions and evaluated by five experienced radiation oncologists from three different countries. Every plan was reviewed by two of the five radiation oncologists and scored using a 5-point Likert scale.

Results: Overall, 87%, 99%, and 94% of the automatically generated plans were found to be clinically acceptable without modification for the 4-field-box, 3D-CRT, and VMAT plans, respectively. Some customizations of the FIF configuration were necessary on the basis of radiation oncologist preference. Additionally, in some cases, it was necessary to renormalize the plan after it was generated to satisfy radiation oncologist preference.

Conclusion: Approximately, 90% of the automatically generated plans were clinically acceptable for all three planning techniques. This fully automated planning system has been implemented into the radiation planning assistant for further testing in resource-constrained radiotherapy departments in low- and middle-income countries.

Keywords: auto-contouring; auto-planning; cervical cancer; field-in-field.

FIGURE 1

The synthetic planning target volume (PTV) structure was defined on the basis of the beam apertures for the 4‐field‐box plans. First, the geometric beam path from each beam angle was converted into a 3D binary mask, and then the volume overlapped by each mask was defined as the region of hot spot detection (RHD). Finally, the synthetic PTV was created from 7 mm shrinkage of the RHD

FIGURE 2

Workflow of the automated 3D conformal radiotherapy (3D‐CRT) system for cervical cancer. The planning target volume (PTV) was derived from the automatically generated clinical target volumes. The beam apertures were determined with a user‐defined uniform margin (7 mm in this study) around the projected PTV. The dose was calculated with a pre‐defined MU

FIGURE 3

Demonstration of the customized plans for Reviewer #1 (left) and Reviewer #2 (right) for the (a) 4‐field‐box, (b) 3D conformal radiotherapy, and (c) volumetric modulated arc therapy techniques in three patients with intermediate risk cervical cancer. The thick lines represent the planning target volume (red), 105% isodose line (pink), 100% isodose line (yellow), and 95% isodose line (green)

FIGURE 4

Boxplots for the normal structure dose metrics for the 35 volumetric modulated arc therapy plans. The median values for the dose metrics are indicated next to each boxplot

FIGURE 5

Boxplots for the normal structure dose–volume metrics for the 35 volumetric modulated arc therapy plans. The median values for the volume metrics are indicated next to each boxplot

FIGURE 6

Examples of the plans scored ≤3. The thick yellow lines represent the 100% isodose line, and the thick red lines represent the planning target volume (PTV). (a) The 4‐field‐box plan was scored as 3 because of the excessive dose to the bowel. (b) The 3D conformal radiotherapy plan was scored as 3 as the PTV (red) was not fully covered by a 100% isodose line near the bowel. (c) The volumetric modulated arc therapy plan was scored as 2 as the PTV (red) was not fully covered by a 100% isodose line near the rectum