Abstract
The aim of this study is to compare the dosimetric characteristics of robotic and conventional linac‐based SBRT techniques for lung cancer, and to provide planning guidance for each modality. Eight patients who received linac‐based SBRT were retrospectively included in this study. A dose of 60 Gy given in three fractions was prescribed to each target. The Synchrony Respiratory Tracking System and a 4D dose calculation methodology were used for CyberKnife and linac‐based SBRT, respectively, to minimize respiratory impact on dose calculation. Identical image and contour sets were used for both modalities. While both modalities can provide satisfactory target dose coverage, the dose to GTV was more heterogeneous for CyberKnife than for linac planning/delivery in all cases. The dose to 1000 cc lung was well below institutional constraints for both modalities. In the high dose region, the lung dose depended on tumor size, and was similar between both modalities. In the low dose region, however, the quality of CyberKnife plans was dependent on tumor location. With anteriorly‐located tumors, the CyberKnife may deliver less dose to normal lung than linac techniques. Conversely, for posteriorly‐located tumors, CyberKnife delivery may result in higher doses to normal lung. In all cases studied, more monitor units were required for CyberKnife delivery for given prescription. Both conventional linacs and CyberKnife provide acceptable target dose coverage while sparing normal tissues. The results of this study provide a general guideline for patient and treatment modality selection based on dosimetric, tumor and normal tissue sparing considerations.PACS numbers: 87.53.Ly, 87.55.dk.
Highlights
213 Ding et al.: Dosimetric comparison of stereotactic body radiation therapy (SBRT) for lung cancer: robotic vs. linac (GTV), must be as small as reasonably possible in respect to normal tissue tolerances, without compromising target dose coverage.A number of linac-based approaches have been described for delivery of SBRT in lung cancer patients.[3,4] Localization and interfraction setup uncertainties can be significantly reduced through the application of various image-guided methodologies including orthogonal kV X-ray imaging and cone-beam computed topography (CBCT)
The most straightforward method for compensating for tumor motion is to create internal target volume (ITV) by adding an appropriate margin to the GTV. This method may irradiate excessive normal tissue and/or miss the target by not considering the unique tumor motion in individual patients. 4D CT can provide temporal information on target and organ motion based on respiration and can be useful to in defining patient-specific ITVs.[5]. It has been reported that composite images based on 4D CT scans, such as maximum intensity projection (MIP), minimum intensity projection and average intensity (AVG), are effective for the assessment of tumor mobility and ITV delineation.[6,7] Respiratory gating[8] is an potential method for reducing ITVs, with the tradeoff of increased treatment times
The results of this study may provide a general guideline for patient and treatment modality selection based on dosimetric, tumor control and normal tissue sparing considerations
Summary
213 Ding et al.: Dosimetric comparison of SBRT for lung cancer: robotic vs. linac (GTV), must be as small as reasonably possible in respect to normal tissue tolerances, without compromising target dose coverage.A number of linac-based approaches have been described for delivery of SBRT in lung cancer patients.[3,4] Localization and interfraction setup uncertainties can be significantly reduced through the application of various image-guided methodologies including orthogonal kV X-ray imaging and cone-beam computed topography (CBCT). 4D CT can provide temporal information on target and organ motion based on respiration and can be useful to in defining patient-specific ITVs.[5] It has been reported that composite images based on 4D CT scans, such as maximum intensity projection (MIP), minimum intensity projection and average intensity (AVG), are effective for the assessment of tumor mobility and ITV delineation.[6,7] Respiratory gating[8] is an potential method for reducing ITVs, with the tradeoff of increased treatment times Methods such as breath hold, abdominal compression, and active breathing control[9,10,11] have been shown to be effective in reducing tumor motion during treatment. These methods are still under development and not in wide-spread use in most institutions, they may help to further reduce the dose to the critical tissue
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