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Acuros-Based Planning with Density Override for Lung SBRT by a Dynamic Conformal Arc Technique: Comparative Evaluation with AAA-Based Planning in Terms of Four-Dimensional Delivered Dose

I Yeo*, N Joyce, D Singh, M Milano, Y Chen, D Rosenzweig, University of Rochester, Rochester, NY

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To comparatively evaluate plans based on Acuros and AAA


Methods: Eight patients with a lung tumor were selected, each with a 2-4 cm lung planning target volume (PTV) surrounded by lung parenchyma. During simulation, they were imaged using a slow scan protocol, followed by four-dimensional (4D) imaging limited to the disease sites. On each phase-specific image of each patient, gross tumor volume (GTV) was contoured. Summed over all phases, integrated GTV (ITV) was generated, and copied to the slow scan. A treatment plan was created using a dynamic conformal arc technique with AAA to prescribe 60 Gy to 95% of PTV (ITV+0.5cm) and to meet constraints: chest wall: V30Gy <30 mL; lung: V20 <10%. In order to determine the delivered dose to the PTV a 4D dose was produced by copying and running the plan to each phase-specific images, after overriding the density of PTV-GTV with that of GTV (to generate a realistic delivered dose accounting for potential tumor movement within the PTV margin); calculating with Acuros (for greater accuracy); summing the phase-specific plans through organ/dose registration. Proposing to use a more accurate algorithm, Acuros, each AAA-based plan was altered by changing AAA with Acuros and overriding the density in PTV-ITV. Considering colder dose provided by Acuros, the density override with the density of ITV was considered in PTV-ITV. The 4D dose was similarly produced.


Results: The Acuros-based plan and the AAA-based plan delivered the followings: D95%=64.2 and 65.2Gy, respectively, averaged over 8 patients; V60Gy=98% of PTV for both plans, greater than the prescribed 95%. The density override for the former required less MUs than the latter, thereby delivering smaller 4D dose.


Conclusion: The Acuros plan provided closer 4D dose to the planned dose. With breathing irregularity not considered, it is uncertain how sufficient the 4D dose will be.

Keywords

Treatment Planning

Taxonomy

Not Applicable / None Entered.

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