Dosimetric Effect of Intrafraction Tumor Motion in Lung Stereotactic Body Radiotherapy Using CyberKnife Static Tracking System

Abstract

Purpose: We investigated the dosimetric effect of intrafraction tumor motion in lung stereotactic body radiotherapy using the CyberKnife static tracking system. Methods: Four-dimensional computed tomography scans of a dynamic thorax phantom were acquired. Two motion ranges, 3 collimator sizes, and 4 treatment starting phases were investigated. Monte Carlo dose distributions were calculated on internal target volume with a treatment-specific setup margin for 6 Gy/1 fraction. Dosimetric effects of intrafractional tumor motion were assessed with Gafchromic films. γ (5%/3 mm), dose differences, and distance to agreement were analyzed. Results: With 30 mm collimator plans, the measured dose passed the criteria γ (5%/3 mm) in all tumor motion ranges. The γ passing rates of the plans using 20 mm or 20+35 mm collimators were much lower than that with 30 mm collimator, especially with the 30 mm tumor motion range. The measured dose of 10 mm tumor motion ranges all passed the 90% criteria of γ (5%/3 mm), the results being much better than those of 30 mm tumor motion ranges, which were below 80%. The results of same delivered plan but treated with different starting phases varies greatly. Conclusion: Xsight Lung Tracking technique should be used with caution in lung cancer stereotactic body radiation therapy because the temporal dose variations can be significant.

Integrating CVH and LVH metrics into an optimization strategy for the selection of Iris collimator for Cyberknife Xsight lung tracking treatment

“…Most of the CyberKnife treatment retrospective studies have focused on improving tracking accuracy and reducing the planning target volume (PTV) margins 1,7–11 . Some studies have investigated the relationship between dose uncertainty of CyberKnife Xsight Lung Tracking (XLT) treatment and the collimator diameters of XLT plan, and have shown that the intrafractional dose uncertainty can be reduced with large collimators 12,13 . However, the XLT plans with large collimators will certainly irradiate more surrounding normal tissues 5,14,15 .…”

“…At our institution, in order to improve the plan quality and time efficiency, one collimator is used for small tumors in CKS treatment and two collimator combinations (small and large) are used for the large tumors in CKS treatment 4,6,17 . We previously analyzed the intrafractional dose uncertainty in the CyberKnife XLT treatment, and found that the plan robustness is better with large collimator 12 . However, the relevance between the proposed value of the collimator diameter in the CyberKnife XLT treatment plan and the intrafractional target tracking error has not yet been investigated.…”

Evaluation of OAR dose sparing and plan robustness of beam-specific PTV in lung cancer IMRT treatment

“…Intensity-modulated radiotherapy (IMRT) can deliver conformal dose distributions to tumors. However, the inter-fractional uncertainties during treatment results in deviations between the planned and actual dose distributions [1][2][3]. These uncertainties can result in underdosing of the clinical target volume (CTV), or overdosing of organs at risk (OARs) [1].…”

Evaluation of OAR sparing and plan robustness of beam-specific PTV in lung cancer IMRT treatment

“…The intensity-modulated radiotherapy (IMRT) can deliver conformal dose distributions to the tumors. However, the inter-fractional uncertainties during the treatment result in deviations between the planned and the actual dose distributions [1][2][3]. These uncertainties can result in underdosing of the clinical target volume (CTV), or overdosing of organs at risk (OARs) [1].…”