Should we include SPECT lung perfusion in radiotherapy treatment plans of thoracic targets? Evidences from the literature

• Radiation therapy (RT) has a well-established role in the therapeutic approach of patients with an several thoracic malignancies.
• Currently, lung-based computed tomography (CT) dosimetric parameters are the most significant factors associated with radiation-induced lung toxicity. Up to now, three-dimensional conformal-RT (3D-CRT) and intensity modulated RT (IMRT) planning of thoracic targets are based on doses delivered to the “anatomical” lung defined on the simulation CT scan, regardless of regional difference in lung function.
• The majority of patients treated for an intra-thoracic target suffer from pre-existing lung diseases (i.e. smoking related damages, chronic pulmonary diseases, etc.), which are frequently associated with inhomogeneous lung perfusion and pulmonary functions. The presence of the tumour itself can contribute to functional inhomogeneity.
• Noteworthy, it could be important to take into account of these regional lung function variations. It has been already showed that different lung regions contribute differently to the pulmonary function, and the radiation dose delivered to non-perfused regions contributes less to functional lung radiation-induced damage. The identification (and sparing) of more functioning areas may be of major interest in order to reduce the risk of severe lung toxicities.
• The aim of the present review is to report the current use of SPECT imaging in the RT scenario for the optimization of RT of intra-thoracic targets.

PurposeTo report the available data about the potential impact of integrating lung perfusion SPECT/CT in treatment plans optimization for the irradiation of thoracic targets.Materials and methodsWe searched in the PubMed and Scopus databases, English-written articles published from 2000 to June 2015 dealing with the integration of perfusion SPECT/CT in radiotherapy.ResultsWe found and analyzed 16 research articles (10 dosimetric, 6 clinical) for a total of 578 patients. Available data suggest dosimetric and clinical improvements when perfusion SPEC/CT is integrated in the radiotherapy treatment planing of selected patients with thoracic targets. In particular, patients presenting emphysema and/or large areas of deficit of perfusion show the most important improvements. Moreover, some studies show different risk of radiation pneumonitis (RP) depending on the localization of the tumor in the lungs: patients with low-located tumors, present an increased risk of RP, and functional data could be a benefit in treatment plan optimization. Unfortunately, none of the available studies finally reports any dosimetric constraint, which could be used in the clinical practice, even if most of them used the cut-off of the 30% of the maximal perfusion value to define the well-functioning lung.ConclusionsPublished data support the integration of lung perfusion scintigraphy in some selected categories of patients. Prospective studies should be designed to define the best candidates, and to assess the clinical advantage of this kind of optimization.