Premium
TH‐A‐9A‐07: Investigation of Localization Errors Using CBCT for SABR‐Based Treatment of Lung Cancer and Impact On Planning Margins and Dose Coverage
Author(s) -
Mayyas E,
GlideHurst C,
Wen N,
Snyder K,
Kumar S,
Movsas B,
Ajlouni M,
Chetty I
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4889577
Subject(s) - sabr volatility model , context (archaeology) , excursion , nuclear medicine , margin (machine learning) , residual , medicine , radiation therapy , image guided radiation therapy , mathematics , radiology , computer science , geology , algorithm , machine learning , volatility (finance) , paleontology , stochastic volatility , political science , law , econometrics
Purpose: In this study, we quantify setup errors and their impact on planning margin and dose coverage in the context of CBCT‐based IGRT for SABR of lung tumors. The effect of respiratory excursion on setup up error was also investigated. Methods: The datasets of 150 patients, divided into four groups according to tumor location: upper‐chest well seated (CWS), upper‐island, lower‐CWS, and lower‐island, were evaluated. Setup errors and planning margins were calculated and compared. Degradation of dose coverage due to setup errors was investigated for 8 patients. For each patient, 4 CBCT localizing images were used to create internal target volume (ITVCBCT), which was considered a surrogate of respiratory‐induced tumor excursion during treatment. Results: The percentage of patients showing >5 mm tumor respiratory excursion for upper‐island/lower‐island was 10.0/42.9% and for upper‐CWS/lower‐CWS was 4.2/46.7%. Without image‐guidance for patient localization, ∑interfxn and σinterfxn of the inter‐fraction setup errors were 2.2–3.9/2.9–5.0 mm and 2.3–4.2/3.0–5.1 mm for upper‐island/lower‐island and upper‐CWS/lower‐CWS, respectively. Errors were correlated to tumor excursion. Pearson coefficient for upper‐island/lower‐island was 0.36/0.60, and for upper‐CWS/lower‐CWS was 0.20/0.44. With the use of CBCT for daily image guidance, ∑residual and σresidual of the residual setup errors were 0.7–1.2/0.8–1.4 mm and 0.7–1.2/0.8–1.3 mm for upper‐island/lower‐island and upper‐CWS/lower‐CWS, respectively. The planning margin vectors (Ant./Post., Sup./Inf., Left/Right) for upper‐island/lower‐island tumor were (2.7, 2.8, 3.6)/(2.8, 3.6, 4.4) mm, and for upper‐CWS/lower‐CWS tumors were (2.4, 3.3, 3.3)/(2.8, 2.9, 3.5) mm. Average dose difference (D95) between delivered doses to ITVCBCT and planned doses was 4.5±0.9% and 7.4±1.9% with and without using CBCT for localization, respectively. Conclusion: This large cohort analysis suggests that tumor location may be predictive of tumor excursion and corresponding inter‐fraction setup errors. The use of CBCT reduces setup uncertainty substantially. 3–5 mm ITV‐to‐PTV planning margin would be adequate to compensate for residual setup errors and provide sufficient dosimetric coverage.