Comparative analysis of SmartArc-based dual arc volumetric-modulated arc radiotherapy (VMAT) versus intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma

The purpose of this study was to evaluate and quantify the planning performance of SmartArc‐based volumetric‐modulated arc radiotherapy (VMAT) versus fixed‐beam intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) using a sequential mode treatment plan. The plan quality and performance of dual arc‐VMAT (DA‐VMAT) using the Pinnacle3 Smart‐Arc system (clinical version 9.0; Philips, Fitchburg, WI, USA) were evaluated and compared with those of seven‐field (7F)‐IMRT in 18 consecutive NPC patients. Analysis parameters included the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), maximum and mean dose, normal tissue complication probability (NTCP) for the specified organs at risk (OARs), and comprehensive quality index (CQI) for an overall evaluation in the 11 OARs. Treatment delivery time, monitor units per fraction (MU/fr), and gamma (Γ3mm,3%) evaluations were also analyzed. DA‐VMAT achieved similar target coverage and slightly better homogeneity than conventional 7F‐IMRT with a similar CI and HI. NTCP values were only significantly lower in the left parotid gland (for xerostomia) for DA‐VMAT plans. The mean value of CQI at 0.98±0.02 indicated a 2% benefit in sparing OARs by DA‐VMAT. The MU/fr used and average delivery times appeared to show improved efficiencies in DA‐VMAT. Each technique demonstrated high accuracy in dose delivery in terms of a high‐quality assurance (QA) passing rate (>98%) of the (Γ3mm,3%) criterion. The major difference between DA‐VMAT and 7F‐IMRT using a sequential mode for treating NPC cases appears to be improved efficiency, resulting in a faster delivery time and the use of fewer MU/fr.

PACS number: 87.53.Tf, 87.55.x, 87.55.D, 87.55.dk

Single Arc Volumetric Modulated Arc Therapy of head and neck cancer

BACKGROUND

The quality of Volumetric Modulated Arc Therapy (VMAT) plans is highly dependent on the performance of the optimization algorithm used. Recently new algorithms have become available which are capable of generating VMAT plans for Elekta accelerators. The VMAT algorithm in Pinnacle is named SmartArc and its capability to generate treatment plans for head and neck cancer was tested.

METHODS

Twenty-five patients with oropharyngeal or hypopharyngeal carcinoma, previously treated with IMRT by means of Pinnacle and Elekta accelerators, were replanned with single arc VMAT. The VMAT planning objectives were to achieve clinical target coverage and sparing of the organs at risk (OAR). Comparison with the original clinically used IMRT was made by evaluating (1) dose-volume histograms (DVHs) for PTVs, (2) DVHs for OARs, (3) delivery time and monitor units (MU), and (4) treatment accuracy.

RESULTS

Equivalent or superior target coverage and sparing of OARs were achieved with VMAT compared to IMRT. Volumes in the healthy tissues receiving between 17.3 Gy and 49.4 Gy were significantly reduced and the conformity (CI(95%)) of the elective PTV was improved from 1.7 with IMRT to 1.6 with VMAT. Compared to step-and-shoot IMRT, VMAT reduced the number of MUs by 8.5% to 460+/-63 MUs per fraction, and delivered on an Elekta Synergy accelerator, the treatment time was on average reduced by 35% to 241 +/- 16s. In Delta4 measurements of the VMAT treatments, 99.6 +/- 0.5% of the detector points passed a 3 mm and 3% gamma criterion, identical to the results of IMRT.

CONCLUSIONS

The target coverages obtained in the IMRT and VMAT plans were found to be very similar. SmartArc generated single arc VMAT plans with equivalent or better target coverage and sparing of OARs compared to IMRT, while both delivery time and MUs were decreased. Very good dose accuracy results were obtained delivering the plans on an Elekta accelerator.