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Perfusion SPECT guided dose escalation in radiation therapy for lung cancer patients Yin, Lingshu


Radiation therapy (RT) is a standard of care for patients with locally advanced inoperable non-small cell lung cancer (NSCLC). Prognosis for these patients is poor with 2-years survival below 20%. A substantial proportion of the lung cancer patients receiving RT develop symptomatic radiation pneumonitis (RP) as radiationinduced side effects. Thus, sparing of normal lung is one of the important goals for lung cancer patients receiving RT. Currently in clinical practice, the sparing of lung is assessed based on the dosevolume histogram (DVH) assuming homogeneous lung function which is clearly not valid. Lung perfusion scan using Single Photon Emission Computed Tomography (SPECT) with ⁹⁹mTc macroaggregated albumin (⁹⁹mTc-MAA) provides unique functional information (lung perfusion i.e. blood flow) about the lung and holds the potential to improve normal tissue sparing in RT. Incorporating functional information from perfusion SPECT scan into RT treatment planning allows for identifying and sparing the well perfused parts of lung, thus reducing the risk of clinically significant radiation-induced lung complications. From February 2008 to May 2011, 22 lung cancer patients in BC Cancer Agency were recruited into this ethics board approved SPECT study. The goal of this study is to establish a framework for SPECT-guided RT treatment planning and dose escalation trials. In this study, the incorporation of SPECT into RT treatment planning is carried out in a sequential manner including: 1. Reconstruction of SPECT images and investigating the metric of functional sparing for treatment planning 2. Evaluation of SPECT image registration algorithms 3. Developing the methodology of SPECT-guided intensity modulated radiation therapy (IMRT) treatment planning with a Monte Carlo based beamlets dose calculation 4. Evaluation of the effectiveness of SPECT-guided RT through a planning study comparing DVH and SPECT-driven IMRT plans. In conclusion, comparing to conventional DVH driven IMRT plans, we found that SPECT-driven IMRT plans provide better sparing of both lung function and volume. Mean lung dose and SPECT-weighted mean dose can be reduced by 10.8% and 13.1%, respectively. We suggest that the use of SPECT guided IMRT treatment planning improves the sparing of lung functionality and makes possible dose escalations in patients with non-small cell lung cancers.

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