3-D irradiated lung and heart volume predictions from 2-D datasets: Value of CT-based treatment planning in postmastectomy tangential beam radiation therapy

Abstract

11013 Background: Lung and heart complications in breast cancer treatment are directly related to the irradiated volumes, technique, total radiation dose and type of chemotherapy. 3D dose calcuations allow computation of the DVH’s & a realistic NTCP associated with breast cancer RT. 1) Study aims to evaluate the impact of the 2-D radiographic parameters on the volumetric dose of the lung and heart, for patients undergoing postmastectomy,postchemo radiation therapy. (2)To deduce the analytical equations for the quick estimation of the irradiated volume based on the distances obtained from the digitally reconstructed radiographs. Methods: Between August 2002–2006, 162 postmastectomy patients underwent 5wk course of tangential CW irradiation ± Axillary / SCL radiation to a total dose of 50gy/25#. After adequate immobilization on the CT compatable breast board, CT scans with 1cm slice intervalsof the chest were performed, covering lung apex to lung base. The ipsilateral total lung area and the lung area included within the treatment port were countered on each CT slice.It is multiplied by slice thickness, and then integrated in all CT slices to give volumes.Parameters used to deduce irradited lung volume (n=104) studied from the DRR included Central lung distance-CLD, Maximum perpendicular distance-MPD, Length of the lung-L & Parameters related to heart are measured only in left breast irradiation (n=58) included: Maximum heart distance-MHD, Maximum heart length MHL.Linear regression analysis is applied to test relationship between the percentage of ipsilateral lung volume involved and the CLD / MPD / L and similarly between MHD / MHL and the cardiac volume in irradiation. Results: Predicted irradiated volume for: Right Lung = 4.0118+6.6474(CLD) OR -5.965 + 6.827(MLD) Left Lung = 6.6395(CLD) OR 5.431(MLD) Heart = 7.325(MHD) OR 6.742(CLD) Conclusions: The conclusion of the present study, to the best of our knowledge, is the largest series reported so far in the literature. CLD and MLD deduced from the DRR, are the direct measures of the lung volumes irradiated in tangential breast irradiation ( r2=0.91 & 0.79).While MHD and CLD appear to be direct measure of the irraidiated heart volume (r2=0.98 & 0.91). No significant financial relationships to disclose.