Combining rescanning and gating for a time-efficient treatment of mobile tumors using pencil beam scanning proton therapy. (July 2021)

• Record Type: Journal Article
• Authors: Gut, Pauline; Krieger, Miriam; Lomax, Tony; Weber, Damien C.; Hrbacek, Jan
• Is Part Of: Radiotherapy and oncology. Volume 160(2021)
• Page Start: 82
• Page End: 89
• Publication Date: 2021-07
• Subjects: 4D proton therapy -- Time efficiency -- Tumor coverage -- Intrafractional motion -- Pencil beam scanning -- Volumetric rescanning -- Respiratory gating; Oncology -- Periodicals; Radiotherapy -- Periodicals; Tumors -- Periodicals; Medical Oncology -- Periodicals; Neoplasms -- radiotherapy -- Periodicals; Radiotherapy -- Periodicals; Radiothérapie -- Périodiques; Cancérologie -- Périodiques; Tumeurs -- Périodiques; Electronic journals; 616.9940642
• DOI: 10.1016/j.radonc.2021.03.041
• Languages: English
• ISSNs: 0167-8140

Abstract

Highlights: Tumor movements smaller than 5 mm do not require motion mitigation. Volumetric rescanning improve CTV dose coverage for intermediate tumor motions (5–10 mm) using a dense spot grid, whilst being more time efficient than respiratory gating. Respiratory gating does not necessarily reduce dose to normal tissues for intermediate tumor motions. Respiratory gating combined with volumetric rescanning improve CTV dose coverage for tumor motions larger than 10 mm using a dense or sparse spot grid. A denser spot grid gives better CTV dose coverage. Combined rescanning and gating treatments of moving tumors with proton pencil beam can be used effectively and efficiently. Abstract: Background and purpose: Respiratory motion during proton therapy can severely degrade dose distributions, particularly due to interplay effects when using pencil beam scanning. Combined rescanning and gating treatments for moving tumors mitigates dose degradation, but at the cost of increased treatment delivery time. The objective of this study was to identify the time efficiency of these dose degradation-motion mitigation strategies for different range of motions. Materials and methods: Seventeen patients with thoracic or abdominal tumors were studied. Tumor motion amplitudes ranged from 2–30 mm. Deliveries using different combinations of rescanning and gating were simulated with a dense dose spot grid (4 × 4 × 2.5 mm 3 ) for all patients and a sparse dose spot grid (8 × 8 × 5 mm 3 ) for six patients with larger tumor movements ( > 8 mm). The resulting plans were evaluated in terms of CTV coverage and time efficiency. Results: Based on the studied patient cohort, it has been shown that for amplitudes up to 5 mm, no motion mitigation is required with a dense spot grid. For amplitudes between 5 and 10 mm, volumetric rescanning should be applied while maintaining a 100% duty cycle when using a dense spot grid. Although gating could be envisaged to reduce the target volume for intermediate motion, it has been shown that the dose to normal tissues would only be reduced marginally. Moreover, the treatment time would increase. Finally, for larger motion amplitudes, both volumetric rescanning and respiratory gating should be applied with both spot grids. In addition, it has been shown that a dense spot grid delivers better CTV dose coverage than a sparse dose grid. Conclusion: Volumetric rescanning and/or respiratory gating can be used in order to effectively and efficiently mitigate dose degradation due to tumor movement.