Abstract
Introduction
Due to its time structure, the proton pencil beam scanning is more susceptible to intra-fractional motion raising concerns for its clinical deployment despite reducing dose in organs at risk, integral dose and potential neutron contamination in the field. The aim of this study was to investigate target coverage robustness in intensity modulated proton therapy(IMPT) treatments at our institution.
Material and methods
Ten mediastinal lymphoma patients treated with IMPT were evaluated. A 4DCT was acquired for treatment planning and weekly repeated 4DCTs were collected to evaluate possible deviations in target coverage. Layer repainting (5x), large airgaps (~20cm) and 3D-robust optimisation were utilised to generate clinical plans. Prior to physician approval, plan robustness was evaluated using the vox-wise min/max method for range and setup uncertainties (3%-5/6mm). In addition, treatment plan robustness prior and during the course of treatment was continuously evaluated using an in-house developed fraction-wise reconstruction of 4D-dose distribution and dose accumulation method employing weekly verification 4DCTs and patient specific planning, daily breathing motion patterns and treatment delivery log files.
Results
Average target motion was 12,3 mm (ranging from 6 to 20 mm). No clinically relevant changes in target coverage were found in the fraction-wise reconstructed 4D dose distributions. The accumulated treatment course doses showed: V95 > 99.8% and D98 > 95% for all ten patients. Moreover, D98 remained within 1% from the pre-treatment evaluations.
Conclusion
Interplay and motion effects did not result in loss of homogeneity or coverage due to our treatment planning technique. 4D reconstructions enables to do pre-treatment evaluations and are a good predictor for plan robustness.
Due to its time structure, the proton pencil beam scanning is more susceptible to intra-fractional motion raising concerns for its clinical deployment despite reducing dose in organs at risk, integral dose and potential neutron contamination in the field. The aim of this study was to investigate target coverage robustness in intensity modulated proton therapy(IMPT) treatments at our institution.
Material and methods
Ten mediastinal lymphoma patients treated with IMPT were evaluated. A 4DCT was acquired for treatment planning and weekly repeated 4DCTs were collected to evaluate possible deviations in target coverage. Layer repainting (5x), large airgaps (~20cm) and 3D-robust optimisation were utilised to generate clinical plans. Prior to physician approval, plan robustness was evaluated using the vox-wise min/max method for range and setup uncertainties (3%-5/6mm). In addition, treatment plan robustness prior and during the course of treatment was continuously evaluated using an in-house developed fraction-wise reconstruction of 4D-dose distribution and dose accumulation method employing weekly verification 4DCTs and patient specific planning, daily breathing motion patterns and treatment delivery log files.
Results
Average target motion was 12,3 mm (ranging from 6 to 20 mm). No clinically relevant changes in target coverage were found in the fraction-wise reconstructed 4D dose distributions. The accumulated treatment course doses showed: V95 > 99.8% and D98 > 95% for all ten patients. Moreover, D98 remained within 1% from the pre-treatment evaluations.
Conclusion
Interplay and motion effects did not result in loss of homogeneity or coverage due to our treatment planning technique. 4D reconstructions enables to do pre-treatment evaluations and are a good predictor for plan robustness.
| Original language | English |
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| Publication status | Published - 2020 |
| Event | 59th Particle Therapy Co-Operative Group (PTCOG) meeting - Virtual Duration: 13-Sept-2020 → 16-Sept-2020 https://www.ptcog2020online.org/ |
Conference
| Conference | 59th Particle Therapy Co-Operative Group (PTCOG) meeting |
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| Abbreviated title | PTCOG 2020 |
| Period | 13/09/2020 → 16/09/2020 |
| Internet address |