Acquisition of MV-scatter-free kilovoltage CBCT images during RapidArc™ or VMAT

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• 作者：Clifton Ling^a ; ^b ; ¹ ; ^{lingc@mskcc.org"" rel=""nofollow} ; Pengpeng Zhang^b ; ¹ ; Thanos Etmektzoglou^a ; Josh Star-lack^a ; Mingshan Sun^a ; Edward Shapiro^a ; Margie Hunt^b ; ¹
• 关键词：CBCT ; RapidArc ; VMAT ; IGRT
• 刊名：Radiotherapy and Oncology
• 出版年：2011
• 出版时间：July 2011
• 年：2011
• 卷：100
• 期：1
• 页码：145-149
• 全文大小：273 K

文摘

<h4 class=""h4"">Purposeh3>To perform kilovoltage (kV) cone beam computed tomography (CBCT) imaging concomitant with the delivery of megavoltage (MV) RapidArc treatment, and demonstrate the feasibility of obtaining MV-scatter-free kV CBCT images.<h4 class=""h4"">Methods and materialsh3>

RapidArc/CBCT treatment and imaging plans are designed, and delivered on the Varian TrueBeam, using its Developer Mode. The plan contains 250 control points for MV-radiation delivery, each over an arc of 0.4–0.7^o. Interlaced between successive MV delivery control points are imaging control points, each over an arc of 0.7–1.1^o. During the 360^o gantry rotation for the RapidArc delivery, CBCT projections of a phantom are acquired at 11 frames per second. The kV projections with minimal MV-scatter are selected, based on gantry angle, and the CBCT_s image reconstructed. For comparison, a reference CBCT_r image is acquired in the normal way. In addition, to examine the effect of MV-scatter we acquire CBCT_c using the same treatment plan without the imaging control points, i.e. with continuous MV delivery during the 360^o rotation. Quantitative evaluation of image qualities is performed based on the concepts of CNR (contrast-to-noise ratio) and NSTD (normalized standard deviation).<h4 class=""h4"">Resultsh3>

The different types of CBCT images were reconstructed, evaluated, and compared. Visual comparison indicates that the image quality of CBCT_s is similar to that of the reference CBCT_r, and that the quality of CBCT_c is significantly degraded by the MV-scatter. Quantitative evaluation of the image quality indicates that MV-scatter significantly decreases the CNR of CBCT (from 7 to 3.5 in one comparison). Similarly, MV-scatter significantly increases the inhomogeneity of image intensity, e.g. from 0.03 to 0.06 in one comparison.<h4 class=""h4"">Conclusionh3>

We have developed a method to acquire MV-scatter-free kV CBCT images concomitant with the delivery of RapidArc treatment. Engineering development is necessary to improve the process, e.g. by synchronization of the MV and kV beams.