Single arc volumetric-modulated arc therapy is sufficient for nasopharyngeal carcinoma: a dosimetric comparison with dual arc VMAT and dynamic MLC and step-and-shoot intensity-modulated radiotherapy

Abstract

BackgroundThe performance of single arc VMAT (VMAT1) for nasopharyngeal carcinoma (NPC) on the Axesse linac has not been well described in previous studies. The purpose of this study is to assess the feasibility of VMAT1 for NPC by comparing the dosimetry, delivery efficiency, and accuracy with dual arc VMAT (VMAT2), dynamic MLC intensity-modulated radiotherapy (dIMRT), and step-and-shoot intensity-modulated radiotherapy (ssIMRT).MethodsTwenty consecutive patients with non-metastatic NPC were selected to be planned with VMAT1, VMAT2, dIMRT and ssIMRT using Monaco 3.2 TPS on the Axesse™ linear accelerator. Three planning target volumes (PTVs), contoured as high risk, moderate risk and low risk regions, were set to receive median absorbed-dose (D50%) of 72.6 Gy, 63.6 Gy and 54 Gy, respectively. The Homogeneity Index (HI), Conformity Index (CI), Dose Volume Histograms (DVHs), delivery efficiency and accuracy were all evaluated.ResultsMean HI of PTV72.6 is better with VMAT1(0.07) and VMAT2(0.07) than dIMRT(0.09) and ssIMRT(0.09). Mean HI of PTV63.6 is better with VMAT1(0.21) and VMAT2(0.21) than dIMRT and ssIMRT. Mean CI of PTV72.6 is also better with VMAT1(0.57) and VMAT2(0.57) than dIMRT(0.49) and ssIMRT(0.5). Mean CI of PTV63.6 is better with VMAT1(0.76) and VMAT2(0.76) than dIMRT(0.73) and ssIMRT(0.73). VMAT had significantly improved homogeneity and conformity compared with IMRT. There was no significant difference between VMAT1 and VMAT2 in PTV coverage. Dose to normal tissues was acceptable for all four plan groups. VMAT1 and VMAT2 showed no significant difference in normal tissue sparring, whereas the mean dose of the parotid gland of dIMRT was significantly reduced compared to VMAT1 and VMAT2. The mean delivery time for VMAT1, VMAT2, dIMRT and ssIMRT was 2.7 min, 3.9 min, 5.7 min and 14.1 min, respectively. VMAT1 reduced the average delivery time by 29.8%, 51.1% and 80.8% compared with VMAT2, dIMRT and ssIMRT, respectively. VMAT and IMRT could all be delivered accurately based on our quality assurance standards.ConclusionsIn the treatment of NPC using the Axesse™ linear accelerator, single arc VMAT has shown superiority to double arc VMAT, dIMRT and ssIMRT in delivery efficiency, without compromise to the PTV coverage. However, there is still room for improvement in terms of OAR sparing.

Potential benefits of adaptive intensity modulated proton therapy in nasopharyngeal carcinomas: a planning comparison study

“…We cannot simply compare these results with ours, but assume that even if we make the IMXT plan with the VMAT technique, the dose to the oral cavity in A-IMPT plan would have been preferential to the adaptive VMAT plan. This is because low but de nite doses are irradiated to the entire oral cavity in the VMAT plan in the Ning et al 24 . study while the anterior part of the oral cavity was spared from any irradiation in the A-IMPT plan in all the patients in this study.…”

Comparison of intensity modulated radiotherapy treatment plans between 1.5 T MR-Linac and conventional linac

“…V TV is the treatment volume of the body received the prescribed dose, V PTV is the volume of PTV, and TV PV is the target volume covered by the prescribed dose. The lower the HI value means the better the homogeneity [17]. CI is normally used to quantitatively measure the conformality of the dose distribution relative to the target volume, which denotes the ratio of reference dose received by targets and normal tissue.…”

Beam complexity and monitor unit efficiency comparison in two different volumetric modulated arc therapy delivery using automated planning

“…Studies have suggested that VMAT may be useful in a variety of treatment sites, such as BC [6][7][8] and NPC [9][10][11][12]. As well all known that high quality treatment plan relies on the skills and experience of the dosimetrist, which can vary greatly.…”