Prog Med Phys.  2024 Dec;35(4):145-154. 10.14316/pmp.2024.35.4.145.

Intra-Fractional Dose Evaluation for Patients with Breast Cancer Using Synthetic Computed Tomography

• Ahn S
• Choi SE
• Kim JH
• Park K
• Yoon HJ

• KMID: 2564153
• DOI: http://doi.org/10.14316/pmp.2024.35.4.145

Abstract

Purpose
This study investigated the use of synthetic computed tomography (CT) images derived from cone beam CT (CBCT) scans to analyze dose changes in breast cancer patients undergoing treatment and to evaluate the optimal timing for implementing adaptive radiotherapy.
Methods
A retrospective analysis was conducted on five breast cancer patients treated with tomotherapy-based volumetric-modulated arc therapy at Yongin Severance Hospital. Each patient received 15 fractions, with doses of 320 centigray (cGy) to the high-dose planning target volume (PTV) and 267 cGy to the low-dose PTV. Planning CT images were acquired using the Aquilion scanner, and CBCT images were captured with the VersaHD linear accelerator’s on-board imager. These images were registered in RayStation using a hybrid deformable image registration method to generate synthetic CT images. Dose distributions were reanalyzed using the synthetic CT images, and dose- volume histogram parameters, including the dose to 95% of the volume (D₉₅ ) and mean dose (D_mean ) for the PTV, as well as D₉₅ , D_mean , the percentage of the volume receiving at least 5 Gy (V₅ ) and 10 Gy (V₁₀ ) for organs-at-risk (OARs), were extracted using MATLAB to assess dose changes during treatment.
Results
For the original plans, the mean D₉₅ for PTV high across all patients was 287.13±31.32 cGy, while for PTV low, it was 245.53±6.21 cGy. In contrast, the adaptive plans yielded a mean D₉₅ of 298.17±12.37 cGy for PTV High and 247.25±4.23 cGy for PTV low. The ART Plan may lead to increased dose exposure in certain structures, such as the spinal cord, while providing targeted improvements in reducing radiation exposure in specific OARs (e.g., contralateral breast and esophagus).
Conclusions
Synthetic CT images generated from CBCT scans provide a fast and efficient means of quantifying dose changes, supporting precise patient care through interfractional evaluation. Future studies will aim to apply this method to other organs and larger patient cohorts.

Keyword

Synthetic computed tomography generation; Adaptive radiotherapy; Breast cancer treatment; Dose-volumetric analysis; Cone beam computed tomography imaging

Figure

• 

  Fig. 1 Workflow for synthetic CT-based plan evaluation through DVH in breast cancer treatment. The process includes the following steps: (a) acquisition of planning CT and CBCT images, (b) image registration focusing on bone alignment, (c) deformable image registration, (d) synthetic CT generation, and (e) plan evaluation with DVH curve exportation to assess dose distribution. CT, computed tomography; CBCT, cone-beam CT; DVH, dose–volume histogram; N/A, not applicable.

• 

  Fig. 2 Overall distribution differences between the original and ART plans, showing: (a) PTV high and PTV low, (b) heart, (c) spinal cord, (d) esophagus, (e) ipsilateral lung, and (f) contralateral breast. ART, adaptive radiation therapy; PTV, planning target volume; D95, dose received by 95% of the target volume; Dmean, mean dose received by the target volume; V5 and V10, volumes of the OARs receiving 5 and 10 Gy, respectively.

• 

  Fig. 3 Dose analysis of the high-dose PTV region for Patients 1 and 4, who exhibited the lowest and highest dose differences between Original Plan and ART Plan, respectively. (a, b) D95 and Dmean of the high-dose PTV region for Patients 1. (c, d) D95 and Dmean of the high-dose PTV region for Patients 4. PTV, planning target volume; ART, adaptive radiation therapy; D95, dose received by 95% of the target volume; Dmean, mean dose received by the target volume.

• 

  Fig. 4 Dose analysis of OARs, particularly the heart and ipsilateral lung, for Patients 1 and 4 comparing D95 between the original and adaptive treatment plans over treatment fractions. (a, b) D95 of the heart and ipsilateral lung for Patients 1. (c, d) D95 of the heart and ipsilateral lung for Patients 4. OARs, organs-at-risk; D95, dose received by 95% of the target volume.

Reference

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