Abstract
Objective: The jaw-tracking technique has been developed to reduce the radiation beam transmission in the regions blocked by multileaf collimator (MLC). The aim of this study is the dosimetric evaluation of the jaw-tracking technique in Volumetric Modulated Arc Therapy (VMAT). Material and Methods: 31 VMAT cases treated with the jaw-tracking technique were employed and re-planned with fixed jaw to analyze the dosimetric influences of the planning target volume (PTV) and organs at risk (OARs) volume. The treatment sites were liver, lung, and pancreas. All plans were optimized and calculated under jawtracking and fixed jaw conditions to cover the prescription dose to 95% of PTV (D95%) using the treatment planning system. The dosimetric verification of the treatment plans, the uniformity of the target dose distributions, the partial volume doses in OARs, and the low-dose volume were evaluated to verify the dosimetric impact of the jaw-tracking. Results: The jaw-tracking technique appeared to be able to provide some clinical advantages compared to the fixed-jaw technique. The dose uniformities in targets were similar between in jaw-tracking technique and in fixed jaw. It appeared that the jaw-tracking technique could significantly reduce the partial volume dose of OARs, for the kidney (p=0.008) and duodenum (p=0.028) in liver cancer cases, for the esophagus (p=0.015) in the lung cancer cases, and for the normal liver (p=0.005) and kidney (p=0.005) in the pancreatic cancer cases. The low-dose volumes with the jaw tracking technique were calculated to be smaller than those with fixed jaw setup when the effective maximum field dimension were 1.5 cm larger than the equivalent spherical diameter of the PTVs. Conclusions: The partial volume dose of OARs and the low-dose volume could be significantly reduced by application of the jaw-tracking technique without any adverse effect of the dosimetric parameter for targets in VMAT.
Highlights
In cancer treatment, the radiotherapy has been made more and more emphasis on their clinical importance and the accompanying technology has been rapidly developed
The partial volume dose of Organs at Risk (OARs) and the low-dose volume could be significantly reduced by application of the jaw-tracking technique without any adverse effect of the dosimetric parameter for targets in Volumetric Modulated Arc Therapy (VMAT)
Verification of dose delivery The 8 pairs of VMAT treatment plans were compared between jawtracking technique and fixed jaw by gamma analysis, and the correlation between the two techniques in terms of dose uniformity for planning target volume (PTV) was analyzed by using the Wilcoxon signed rank test
Summary
The radiotherapy has been made more and more emphasis on their clinical importance and the accompanying technology has been rapidly developed. Several reports have been published the VMAT plan was shown their superiorities to static IMRT for various types of cancer in term of clinical efficiency [4,5,6,7,8,9]. It is expected the nontrivial low doses due to the use of multi-directional beams and the block transmissions for MLCs can result in the increase of the chronic radiation complication probabilities [10]. It is well known that low doses delivered to normal organs can provoke secondary cancers The plans of both VMAT and IMRT could be limited by these dosimetric problems
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