Dosimetric evaluation of VMAT for palliative radiotherapy for non-small cell lung carcinoma.

OBJECTIVE::To compare the dosimetric consequences of volumetric modulated arc therapy (VMAT) for high-dose palliative thoracic radiotherapy through comparison with conventionally used isocentric parallel opposed pair (POP) of fields. METHODS::20 consecutive patients with non-small cell lung cancer who received 36 Gy in 12 fractions using a POP technique were re-planned using a single VMAT arc. Salient dosimetric parameters were compared between the plans using a paired t-test. RESULTS::VMAT demonstrated dosimetric superiority; all PTV dose parameters were significantly improved and importantly the volume of normal lung receiving a high dose was also significantly reduced (mean volume of normal lung receiving 36 Gy was 12.9% in POP vs 1.8% in VMAT, p < 0.005). CONCLUSION::The standard POP technique does not take into account tissue densities which results in higher doses to the normal tissue outside the target volume and reduced conformity to the PTV. ADVANCES IN KNOWLEDGE::With the help of modern VMAT techniques, it is possible to effectively achieve highly conformal dose delivery which may provide an opportunity to escalate the dose to the tumour in this group of patients.