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Dose calculation with respiration-averaged CT processed from cine CT without a respiratory surrogate
Adam C Riegel1, Moiz Ahmad, Xiaojun Sun
1Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Medical Physics
|January 30, 2009
Summary
Respiration-averaged CT (RACT) from cine CT, without 4D-CT, accurately calculates thoracic radiotherapy doses. Increasing cine scan duration further improves dose distribution agreement, simplifying motion management in treatment planning.
Area of Science:
- Medical Physics
- Radiotherapy
- Imaging Technology
Background:
- Thoracic radiotherapy dose calculation is often done using free-breathing CT, which is prone to respiratory motion artifacts.
- Four-dimensional computed tomography (4D-CT) integrates motion data but requires specialized technology.
- Respiration-averaged CT (RACT) from 4D-CT is used for dose calculation, but a method to generate RACT directly from cine CT data could simplify the process.
Purpose of the Study:
- To evaluate if RACT generated from cine CT data can substitute for RACT from 4D-CT in radiotherapy dose calculation.
- To determine if extending the cine CT scan duration reduces differences in dose distributions.
Main Methods:
- Generated RACT from 4D-CT and from cine CT data (1, 1.5, and 2 breathing cycles) for 23 patients.
- Recalculated clinical treatment plans on each RACT dataset.
- Compared dose distributions within the planning target volume (PTV) using the gamma index (2%/1 mm criteria).
Main Results:
- Over 95% of patients in both the primary and follow-up studies achieved 100% PTV gamma index pass rates.
- Average gamma index values were consistently low, indicating excellent agreement between dose distributions.
- Increased cine CT duration generally led to improved dose agreement.
Conclusions:
- RACT derived from cine CT is a viable substitute for RACT from 4D-CT for dose calculation in thoracic radiotherapy.
- This method bypasses the need for 4D-CT reconstruction and respiratory surrogates.
- Extending cine CT acquisition time can further enhance the accuracy of dose calculations.
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