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Methods: VMAT plans use a whole-body phantom with a virtual tumor, prescribing dose to D95% of the PTV and evaluating 60%–80% isodose surfaces. v4DCT simulates free breathing across 10 respiratory phases to generate v4DRT dose distributions. Results identify the 60% isodose plan as optimal and compute OM of 5.6 mm (44% reduction).",{"@graph":14,"@context":73},[15,34,56],{"@type":16,"itemListElement":17},"BreadcrumbList",[18,23,27,31],{"item":19,"name":20,"@type":21,"position":22},"https://docshare.wps.com","Home","ListItem",1,{"item":24,"name":25,"@type":21,"position":26},"https://docshare.wps.com/document/","Document",2,{"item":28,"name":29,"@type":21,"position":30},"https://docshare.wps.com/document/healthcare/","Healthcare",3,{"item":32,"name":10,"@type":21,"position":33},"https://docshare.wps.com/document/margin-reduction-and-optimal-prescription-isodose-model-for-liver-stereotactic-radiotherapy-with-respiratory-motion/458125/",4,{"url":32,"name":10,"@type":35,"image":36,"author":41,"headline":10,"publisher":44,"fileFormat":47,"inLanguage":8,"description":12,"dateModified":48,"datePublished":49,"encodingFormat":47,"isAccessibleForFree":50,"interactionStatistic":51},"DigitalDocument",{"url":37,"@type":38,"width":39,"height":40},"https://docshare.wps.com/thumbnails/margin-reduction-and-optimal-prescription-isodose-model-for-liver-stereotactic-radiotherapy-with-respiratory-motion/458125.png","ImageObject",300,407,{"name":42,"@type":43},"Levi","Person",{"url":19,"name":45,"@type":46},"DocShare","Organization","application/pdf","2026-10-30","2026-09-30",true,{"@type":52,"interactionType":53,"userInteractionCount":55},"InteractionCounter",{"@type":54},"ViewAction",11,{"@type":57,"mainEntity":58},"FAQPage",[59,65,69],{"name":60,"@type":61,"acceptedAnswer":62},"What is the main goal of this study in liver SBRT planning?","Question",{"text":63,"@type":64},"To optimize PTV margins using v4DCT by balancing adequate tumor (GTV) coverage against normal-tissue sparing, guided by the DCA concept and an Optimal Margin (OM) derived from isodose plan analysis.","Answer",{"name":66,"@type":61,"acceptedAnswer":67},"How is the DCA used to evaluate respiratory motion tolerance?",{"text":68,"@type":64},"DCA is defined as the maximum respiratory amplitude at which GTV dose coverage (D100% or D99%) is maintained. This links allowable motion to dosimetric coverage requirements for margin selection.",{"name":70,"@type":61,"acceptedAnswer":71},"Which prescription isodose level was identified as optimal, and what margin reduction was achieved?",{"text":72,"@type":64},"The 60% isodose plan was identified as optimal. 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The 60%–80% isodose levels were defined relative to the maximum dose to represent alternative prescription surfaces. v4DCT simulated free-breathing conditions across 10 respiratory phases to generate virtual four-dimensional radiotherapy (v4DRT) dose distributions. The DCA was defined as the maximum respiratory amplitude at which GTV dose coverage (D100% or D99%) was maintained. Based on DCA analysis, the OM was determined as the clinically applicable margin derived from the isodose plan that satisfied the DCA condition and minimized normal tissue dose.  \nResults: DCA analysis revealed that GTV dose coverage was maintained for respiratory motion amplitudes up to 1.9–2.2 times larger than the conventional PTV margin of 10 mm. Taking into account GTV dose coverage, average GTV dose relative to the 80%-static reference, and normal-tissue dose, the 60% isodose plan was identified as the optimal prescription level. From this plan, the OM was calculated as 5.6 mm, representing a 44% reduction compared with the conventional 10-mm PTV, while maintaining GTV coverage and minimizing liver dose. This margin reduction was attributed to the steeper dose gradient associated with prescribing to a lower isodose level. The v4DCT approach enabled the generation of multiple respiratory phase images, allowing quantitative evaluation of motion-induced dose distribution and optimization of margins based on respiratory variability.  \nConclusion: The proposed v4DCT-based framework demonstrated that the 60% isodose plan provided the optimal balance between tumor coverage and normal-tissue sparing, yielding an OM of 5.6 mm (44% reduction compared with the conventional 10-mm PTV) . This approach offers a clinically applicable strategy for margin reduction in liver SBRT while maintaining robust dosimetric coverage.  \nThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.  \n© 2026 The Author(s) . Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.  \nJAppl Clin Med Phys. 2026;27:e70455 .  \n[https://doi.org/10.1002/acm2.70455](https://doi.org/10.1002/acm2.70455)  \n[wileyonlinelibrary.com/journal/acm2](wileyonlinelibrary.com/journal/acm2)  \n1 of 10  \nKEYWORDS  \n4DCT, internal margin, stereotactic body radiotherapy  \n1  INTRODUCTION  \nStereotactic body radiation therapy (SBRT) is a promising local treatment for liver cancer th","cbCaipbk0nzfpptA","https://ap.wps.com/l/cbCaipbk0nzfpptA","pdf",748546,"English","# Abstract\n## Purpose\n## Methods\n## Results\n## Conclusion\n# Introduction","[{\"question\":\"What is the main goal of this study in liver SBRT planning?\",\"answer\":\"To optimize PTV margins using v4DCT by balancing adequate tumor (GTV) coverage against normal-tissue sparing, guided by the DCA concept and an Optimal Margin (OM) derived from isodose plan analysis.\"},{\"question\":\"How is the DCA used to evaluate respiratory motion tolerance?\",\"answer\":\"DCA is defined as the maximum respiratory amplitude at which GTV dose coverage (D100% or D99%) is maintained. This links allowable motion to dosimetric coverage requirements for margin selection.\"},{\"question\":\"Which prescription isodose level was identified as optimal, and what margin reduction was achieved?\",\"answer\":\"The 60% isodose plan was identified as optimal. It yielded an OM of 5.6 mm, representing a 44% reduction compared with the conventional 10-mm PTV while maintaining GTV coverage and minimizing liver dose.\"}]","Margin reduction and optimal prescription isodose model for liver stereotactic radiotherapy with respiratory motion | PDF",1790751712,25]