A comparative study of identical VMAT about two adjacent targets with and without fixed-jaw technique
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RESEARCH
Open Access
A comparative study of identical VMAT about two adjacent targets with and without fixed-jaw technique Kai Xie1,2, Hongfei Sun1,2, Liugang Gao1,2, Tao Lin1,2, Jianfeng Sui1,2 and Xinye Ni1,2*
Abstract Background: The radiation transmission through the multileaf collimators is undesired in modern techniques such as volumetric modulated arc therapy (VMAT). According to identical plans, in this study, we aim to investigate the dosimetric impact of jaw tracking on the VMAT plans on two adjacent targets. Methods: Two treatment plans were designed for eight pelvic (cervical) patients with two targets using the same optimization parameters. The original plan (O-plan) used automatically selected jaw positions. In the new plan (Fplan), the jaws were fixed to block two targets in two beams. The dosimetric parameters of the two plans were compared to evaluate the improvement of dose sparing for the body volume between two targets (named interOAR) in F-VMAT. Results: The mean dose of interOAR reduced significantly from 654.96 ± 113.38 cGy for O-VMAT, to 490.84 ± 80.26 cGy for F-VMAT (p = 0.018). The monitor units (MUs) in the F-plans were 1.49-fold higher than that in the O-plan. The F and O-plan performed similarly in target dose homogeneity. The differences in Dmax of spinal cord, Dmax of spinal cord planning organ at risk volume, and V20, V30, and V40 of the intestine were insignificant. Conclusions: VMAT plans with the fixed-jaw method can reduce the volume between two targets effectively. However, despite the plan quality, the method can only be used when the regular methods cannot reach the clinical requirements for critical organs because of additional MUs. Keywords: VMAT, Adjacent targets, MLC transmission, Fixed-jaw, Dosimetry
Background A multileaf collimator (MLC) is essential to realize the intensity distributions required in intensity-modulated radiotherapy (IMRT) [1, 2] and volumetric-modulated arc radiotherapy (VMAT) [3–6]. For only covered by MLC, the transmitted dose rate can be 0.90–4.40% (6 MV photon) higher than that shielded by both MLC and jaws. Without protection from jaws, the critical organs may receive doses from MLC leaf transmission and leakage. If any of the organs (such as lens, ovaries, and testicles) is extremely sensitive to low tolerance dose, then its received dose may be higher than the dosage it can tolerate.
* Correspondence: [email protected] 1 Radiotherapy Department, Second People’s Hospital of Changzhou, Nanjing Medical University, Changzhou 213003, People’s Republic of China 2 Center for Medical Physics, Nanjing Medical University, Changzhou 213003, People’s Republic of China
Generally, multiple lesions are common in radiotherapy. For targets far from each other, the planning design is carried out separately for each target; for targets close to one another, the same plan is generally used for simultaneous optimization [7–10]. Then, the design of the treatment plans is the key to radiotherapy and the focus of our study. The benefits of jaw tracking have been as
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