(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Proton pencil beam scanning treatment of mobile targets is subject to interplay effect. Various methods such as layer repainting and volumetric repainting were proposed to mitigate the interplay effect. The layer repainting method is currently supported by the DICOM standard and has been implemented by multiple proton beam delivery system vendors. However, layer repainting is generally not effective because each layer is typically delivered in much less than one respiration cycle. Volumetric repainting on the other hand can deliver the dose over different phases of respiration cycles, thus randomizing and mitigating the interplay effect. Nonetheless the volumetric repainting is not yet available in existing commercial proton systems.
Methods: A novel volumetric repainting method was first implemented by planning the total fractions as the product of the numbers of treatment fractions and volumetric repaintings. During treatment each beam was loaded and delivered multiple times via the record and verify system. However, in practice the preparation time (e.g. data transfer and beam tuning) can easily take about one minute for each delivery. An in-house program was then developed to merge the duplicate beams into a single volume-repainted beam, which is then sent to the delivery system and delivered in one beam preparation.
Results: For a three-field SBRT case with four times volumetric repainting, this merged volumetric repainting method can save about 10 minutes per fraction. It also eliminates undesired situations where the proton beam can potentially be allocated to other treatment rooms in the middle of volumetric repainting delivery, which ensures seamless treatment workflow and reduces the treatment time.
Conclusion: The novel volumetric repainting method helps mitigate the interplay effect and improve treatment workflow. Ideally this method should be implemented directly in the treatment planning system and beam delivery system, and be adopted as a DICOM standard in proton radiotherapy.
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