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Quantifying ITV instabilities arising from 4DCT: a simulation study using patient data.

Sara St James¹, Pankaj Mishra, Fred Hacker

¹Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, USA. sara.stjames@gmail.com

Physics in Medicine and Biology

|February 21, 2012

Summary

This summary is machine-generated.

Four-dimensional computed tomography (4DCT) for radiation therapy planning can create unstable internal target volumes (ITVs). This instability means the ITV may not accurately cover lung tumors during treatment, impacting patient care.

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Area of Science:

Medical Physics
Radiation Oncology
Imaging Science

Background:

Radiation therapy planning for lung cancer relies on four-dimensional computed tomography (4DCT) to account for respiratory motion.
The internal target volume (ITV) is defined on 4DCT to encompass all potential tumor locations.
Accurate ITV definition is crucial for effective radiation delivery and minimizing dose to healthy tissues.

Purpose of the Study:

To evaluate the stability and accuracy of internal target volume (ITV) generation using four-dimensional computed tomography (4DCT) in lung cancer patients.
To quantify the variability of ITV definitions due to variations in scan start times.
To assess the coverage of lung tumors by the generated ITV.

Main Methods:

Utilized gold fiducial marker locations from eight lung cancer patients to simulate tumor motion.
Generated ITVs for model tumors (10, 20, 30 mm diameter) using a simulated four-slice CT scanner.
Repeated ITV calculations with scan start times staggered by 1 second to assess variability.

Main Results:

Significant volumetric variations in ITV were observed, ranging from 46% to 127% for a 10 mm tumor diameter.
The generated ITV failed to cover the entire tumor 11% to 74% of the time for a 10 mm tumor diameter.
Instabilities in ITV definition were demonstrated, highlighting potential inaccuracies in treatment planning.

Conclusions:

4DCT-based ITV definitions can be unstable and may not consistently encompass the entire tumor volume.
Variations in scan timing can lead to substantial differences in ITV size and coverage.
These findings suggest a need for improved methods to ensure accurate ITV definition and robust tumor coverage in radiation therapy planning for lung cancer.