Delineation of the cardiac substructures based on PET-CT and contrast-enhanced CT in patients with left breast cancer treated with postoperative radiotherapy

Estimating cardiac substructures exposure from diverse radiotherapy techniques in treating left-sided breast cancer

The study compares the physical and biologically effective doses (BED) received by the heart and cardiac substructures using three-dimensional conformal RT (3D-CRT), intensity-modulated radiotherapy (IMRT), and simple IMRT (s-IMRT) in postoperative radiotherapy for patients with left-sided breast cancer. From October 2008 to February 2009, 14 patients with histologically confirmed left-sided breast cancer were enrolled and underwent contrast-enhanced computed tomography (CT) simulation and 18F-FDG positron emission tomography-CT to outline the left cardiac ventricle (LV) and other substructures. The linear-quadratic model was used to convert the physical doses received by critical points of inner heart to BED.The maximal dose, minimum dose, dose received by 99% of volume (D99) and dose received by 95% of volume (D95) in target areas were significantly better using IMRT and s-IMRT when compared with 3D-CRT (P < 0.05). IMRT and s-IMRT significantly reduced the maximal cardiac dose (5038.98 vs 5346.47 cGy, P = 0.002; 5146.66 vs 5346.47 cGy, P = 0.03). IMRT reduced the maximal dose to LV by 4% (P = 0.05) in comparison with 3D-CRT. The average doses to heart and LV in 3D-CRT plan were significantly lower than those in IMRT plan (P < 0.05). The average cardiac volumes receiving ≥25 Gy (V25 Gy) in IMRT, s-IMRT, and 3D-CRT plans were 73.98, 76.75, and 60.34 cm, respectively. The average LV volumes receiving ≥25 Gy (V25 Gy) in IMRT, s-IMRT and 3D-CRT plans were 23.37, 24.68, and 17.61 cm, respectively. In the IMRT plan, the mean BED to the critical points of inner heart located within the high physical dose area were substantially lower than in 3D-CRT or s-IMRT.Compared with 3D-CRT technique, IMRT and s-IMRT had superior target dose coverage and dose uniformity. IMRT significantly reduced the maximal RT dose to heart and LV. IMRT and s-IMRT techniques did not reduce the volume of heart and LV receiving high doses.

Sparing functional anatomical structures during intensity-modulated radiotherapy: an old problem, a new solution

ABSTRACT During intensity-modulated radiotherapy, an organ is usually assumed to be functionally homogeneous and, generally, its anatomical and spatial heterogeneity with respect to radiation response are not taken into consideration. However, advances in imaging and radiation techniques as well as an improved understanding of the radiobiological response of organs have raised the possibility of sparing the critical functional structures within various organs at risk during intensity-modulated radiotherapy. Here, we discuss these structures, which include the critical brain structure, or neural nuclei, and the nerve fiber tracts in the CNS, head and neck structures related to radiation-induced salivary and swallowing dysfunction, and functional structures in the heart and lung. We suggest that these structures can be used as potential surrogate organs at risk in order to minimize their radiation dose and/or irradiated volume without compromising the dose coverage of the target volume during radiation treatment.