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- W4234734806 abstract "The goal of lung cancer radiotherapy is to improve tumor control without increasing toxicity and compromising quality of patient life. In this study, we used an analytic model accounting for breathing motion to evaluate the motion effect on delivered dose for lung cancer treatments with three-dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT). The gated radiotherapy in 3D-CRT and the dynamic multileaf collimator technique (where the delivered beam position changes synchronously with respect to target motion) in IMRT were investigated to optimize the treatments. Taking into account the thoracic motion and lung tumor shift independently, an analytical model has been developed to reconstruct a patient geometry during treatment based on two initial CT data taken at the inspiration and expiration phases and the chest wall motion measured using an optical motion detector. The 3D dose data for any patient geometry can be obtained from Monte Carlo simulations with EGS4/MCDOSE code. Correlation between the voxels in the inspiration geometry and the voxels in the reconstructed geometry at any point of a breathing cycle is established so that the dose to a voxel can be accumulated accurately during a treatment. For lung cancer treatments with 3D-CRT and IMRT, breathing motion effect on delivered dose to the targets and the critical structures were analyzed for different target margins. Gated radiotherapy with different thresholds and the dynamic MLC technique with different time delay of leaf movement were studied for individual patients based upon considerations of anatomy and respiratory motion. In this study, a 0.5cm chest wall movement resulted in ∼1cm change for a tumor in the top portion of the lung, and ∼1.5cm shift in the lower portion of the lung, in the superior-inferior direction. Our results show that if 1cm target margins were chosen in the 3D-CRT, the breathing motion would cause cold spots in target dose coverage for these tumors. If 2cm margins were applied, target dose coverage would not be affected by the breathing motion, however, the lung dose would increase by up to ∼60%. Gated radiotherapy applied in 3D-CRT could reduce the motion effect with suitable thresholds. However, the balance between elimination of motion effect and the treatment time should be considered in the clinic. We found that IMRT plans could improve the dose conformity to the target and reduce the lung volume (∼30%) that received a high dose compared with the 3D-CRT plans with the same gantry angles and the same number of beams. Furthermore, if we use the dynamic MLC technique including breathing motion into the MLC leaf sequencing, the dose to the adjacent normal tissues and critical structures could be greatly reduced by applying smaller treatment margins. If there was 0.1 second time delay between the breathing motion tracking system and the movement of MLC, the discrepancy would be about 2% in the target dose coverage, which was clinically acceptable. In lung cancer radiotherapy, the target dose can be improved by increasing the treatment margins, but this will result in more normal tissues inside the treatment beams. Therefore, the conventional margin increasing method is not a good solution for solving the uncertainties due to breathing motion in lung cancer treatment. Techniques to compensate or correct for organ motion should be used for lung cancer treatment. Our preliminary results suggest that dynamic beam delivery can provide both target dose conformity and normal tissue sparing with smaller treatment margins" @default.
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- W4234734806 date "2004-09-01" @default.
- W4234734806 modified "2023-09-26" @default.
- W4234734806 title "Evaluation of motion effect on lung cancer radiotherapy" @default.
- W4234734806 doi "https://doi.org/10.1016/s0360-3016(04)01913-3" @default.
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