Volumetric modulated arc therapy for delivery of hypofractionated stereotactic lung radiotherapy: A dosimetric and treatment efficiency analysis

Abstract 

Purpose/objective(s)

Volumetric modulated arc therapy (VMAT) allows for intensity-modulated radiation delivery during gantry rotation with dynamic MLC motion, variable dose rates and gantry speed modulation. We compared VMAT plans with 3D-CRT for hypofractionated lung radiotherapy.

Materials/methods

Twenty-one 3D-CRT plans for Stage IA lung cancer previously treated stereotactically were selected. VMAT plans were generated by optimizing machine aperture shape and radiation intensity at 10° intervals. A partial arc range of 180° was manually selected to coincide with tumor location. The arc was resampled down to 5° intervals to ensure dose calculation accuracy. Identical planning objectives were used for VMAT/3D-CRT. Parameters assessed included dose to PTV and organs-at-risk (OAR), monitor units, and multiple conformity and homogeneity indices. Plans were delivered to a phantom for time comparison.

Results

Lung V_20/12.5/10/5 were less with VMAT (relative reduction 4.5%, p=.02; 3.2%, p=.01; 2.6%, p=.01; 4.2%, p=.03, respectively). Mean/maximum-doses to PTV, dose to additional OARs, 95% isodose line conformity, and target volume homogeneity were equivalent. VMAT improved conformity at both the 80% (1.87 vs. 1.93, p=.08) and 50% isodose lines (5.19 vs. 5.65, p=.01). Treatment times were reduced significantly with VMAT (mean 6.1 vs. 11.9min, p<.01).

Conclusions

Single arc VMAT planning achieves highly conformal dose distributions while controlling dose to critical structures, including significant reduction in lung dose volume parameters. Employing a VMAT technique decreases treatment times by 37–63%, reducing the chance of error introduced by intrafraction variation. The quality and efficiency of VMAT is ideally suited for stereotactic lung radiotherapy delivery.

Keywords: VMAT, Extracranial stereotactic radiotherapy, Hypofractionation, Lung cancer