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K. Li
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P2.02 - Poster Session/ Treatment of Localized Disease – NSCLC (ID 210)
- Event: WCLC 2015
- Type: Poster
- Track: Treatment of Localized Disease - NSCLC
- Presentations: 1
- Moderators:
- Coordinates: 9/08/2015, 09:30 - 17:00, Exhibit Hall (Hall B+C)
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P2.02-037 - Evaluation of the Dosimetric Characteristics of Salvage Lung SBRT with Image Deformable Registration Technique (ID 2915)
09:30 - 17:00 | Author(s): K. Li
- Abstract
Background:
Treatment planning for salvage radiation therapy after failing initial treatment is challenging. Many factors can contribute to local failure, including inherent aggressiveness of the tumor, target motion localization accuracy, and dose delivery variation. Especially when a patient is re-treated for local failure with repeat lung SBRT at a different institution, or using a different radiation treatment platform or software, treatment planning becomes very complex. In particular, it is crucial to create a reliable composite plan to determine the dose delivered to critical structures to prevent serious complications with repeat lung SBRT. Another factor which has not been well studied is a method to compare temporal changes in dose delivered to the target volume after initial treatment, which can surely affect local control. We present a method to compare lung SBRT treatments and analyze the dosimetric characteristics of salvage lung SBRT by applying image deformation registration techniques with dose distributions, and incorporating temporal changes in dose over time.
Methods:
A patient treated with repeat lung SBRT to a region of local failure involving the left upper lobe was used for analysis. The target volume was initially treated on a CyberKnife radiosurgery unit, and then re-treated with lung SBRT on a Varian Trilogy machine (LINAC). Dosimetric characteristics were compared for these two platforms. Indexes used for analysis include target volume dose coverage, and dose target dose conformity, which is quantified by conformity index (CI), integrated conformity index (ICI), dose spillage level outside of treatment target, and dose to the critical structure. The spillage is defined to be the ratio of maximum dose ouside of the target to the maximum plan dose.Treatment dose effect was described by Biologically Effective Dose (BED) with dose conversion by considering changes in BED over time. CyberKnife SBRT dose distribution was converted for treatment with salvage SBRT with deformable registration by MIM software.
Results:
Parameters were compared for initial CyberKnife SBRT treatment alone, salvage LINAC SBRT treatment alone, and composite sum SBRT with deformable registration. Assuming α/β=10 for the tumor, the calculated BEDs were 100, 138, and 127, respectively. The corresponding CIs were 1.03, 1.18, and 1.28. The ICIs were 0.894, 0.807, and 0.881. Dose spillages were 0.81, 0 .78, and 0.56. V20 was 4.9%, 7.2%, and 5.4% for each plan.
Conclusion:
This study provides a method to estimate the dosimetric characteristics of lung SBRT from different treatment platforms with incorporation of temporal loss of dose between initial and salvage treatments. Deformable registration accuracy and the appropriate parameters affecting local control of lung tumor need further investigation and validation.
