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Leaf position error during conformal dynamic arc and intensity modulated arc treatments
C R Ramsey1, K M Spencer, R Alhakeem
1Department of Radiation Oncology, Thompson Cancer Survival Center, Knoxville, Tennessee 37921, USA. cramsey@utk.edu
Medical Physics
|February 24, 2001
Summary
Dynamic arc therapy treatments like CD-ARC and IMAT can have leaf position errors due to high multileaf collimator (MLC) speeds. This study quantifies these errors and provides a formula to estimate dosimetric inaccuracies for better treatment planning.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Technology
Background:
- Conformal dynamic arc (CD-ARC) and intensity modulated arc treatments (IMAT) allow dynamic multileaf collimator (MLC) movement during gantry rotation, enabling complex dose distributions.
- Unlike fixed-gantry techniques, CD-ARC and IMAT treatments cannot utilize beam-hold delays, necessitating acceptance of some leaf position error for deliverability.
Purpose of the Study:
- To quantify the leaf position accuracy of dynamic arc therapy techniques at various MLC velocities.
- To determine the MLC velocity error coefficient and develop a formula for estimating velocity-dependent dosimetric errors.
Main Methods:
- Leaf position accuracy was measured for MLC velocities ranging from 0.3 to 3.0 cm/s.
- Least-squares linear regression analysis was performed to calculate the MLC velocity error coefficient.
- A formula was derived to estimate dosimetric error based on treatment time and MLC leaf controller data.
Main Results:
- Average leaf position errors ranged from 0.03 to 0.21 cm, increasing with MLC velocity.
- The MLC velocity error coefficient was found to be approximately 0.067-0.068 s, with no significant difference between 0 and 90-degree collimator rotations.
- A formula was developed to calculate a dosimetric error index for treatment plan evaluation.
Conclusions:
- Leaf position errors in CD-ARC and IMAT are velocity-dependent, with higher speeds leading to greater inaccuracies.
- The developed formula provides a method to estimate dosimetric errors, aiding in treatment plan evaluation and quality assurance for dynamic arc therapies.
