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A method to individualize adaptive planning target volumes for deformable targets.
Pauliina Wright1, Anthony Thomas Redpath, Morten Høyer
1Department of Medical Physics, Aarhus University Hospital, Nørrebrogade 44, DK-8000 Aarhus C, Denmark. paulwrig@rm.dk
Physics in Medicine and Biology
|November 12, 2009
Summary
This study introduces a new method for individualizing radiotherapy planning target volumes (PTVs) using computed tomography (CT) and cone beam CT (CBCT) scans for deformable targets. This approach offers improved conformity compared to standard PTVs.
Area of Science:
- Radiation Oncology
- Medical Imaging
Background:
- Accurate planning target volume (PTV) delineation is crucial in radiotherapy for deformable targets.
- Standard PTVs may not adequately account for inter-fractional motion, potentially leading to suboptimal dose delivery.
Purpose of the Study:
- To investigate a novel method for individualizing PTVs in radiotherapy by integrating a computed tomography (CT) scan with multiple cone beam computed tomography (CBCT) scans.
- To assess the feasibility and efficacy of different PTV definitions derived from combined CT and CBCT data for deformable targets.
Main Methods:
- Combined CT and up to five initial CBCT scans were used to define PTVs.
- Clinical target volumes (CTVs) in CBCTs were matched to the CTV in the CT to correct for translational motion.
- PTVs were investigated as unions, intersections, and other volume-defined structures based on CTV location frequency.
Main Results:
- At least four scans were required for reliable alternatives to standard PTVs.
- CTV unions of four or five scans achieved high volumetric coverage (64-86%) of repeat scan CTVs.
- PTVs defined by the volume occupied by the CTV in all but one scan showed clinical feasibility, covering 52-64% of repeat CBCT CTVs.
Conclusions:
- Individualized PTVs derived from combining CT and multiple CBCT scans can offer improved conformity in radiotherapy planning.
- The proposed method, particularly using CTV unions or near-complete occupancy definitions, shows promise in complementing standard PTVs for deformable targets.
- The method's success is dependent on adequate volume control, as demonstrated by its failure in one patient case due to poor bladder volume control.
