Quantification of doses to mediastinal lymph nodes in Hodgkin's disease

Hodgkin's disease is highly curable today. Radiotherapy (RT) is the treatment of choice in the early stages. A mantle field is often used in the RT of Hodgkin's disease, and the technique and dosimetry are quite complex. We used computerized tomography (CT)-based dosimetry to determine doses delivered to different mediastinal nodes with the commonly used technique in Hodgkin's disease that was originally described by Kaplan. We used dose-volume histograms to determine doses to various groups of nodes in nine patients. Significant inhomogeneity (30%, 30%, 35%, 35%, 30%, 40%, 35%, 35%, and 30% in the nine patients) in dose distribution was found within the mediastinum. With the advent of 3-dimensional CT-based treatment planning, we are able to quantify such inhomogeneities. The question arises whether a homogeneous, lesser dose can achieve equal results. Average doses and "effective doses" were also calculated. The "effective doses" in eight patients (for a prescribed dose of 44 Gy) with a midline posterior spinal cord block added at 20 Gy were 37.3 Gy, 34.3 Gy, 36.0 Gy, 38.4 Gy, 35.8 Gy, 38.1 Gy, 36.7 Gy, and 36.7 Gy, respectively. A homogeneous dose equivalent to effective dose may achieve the same control as an inhomogeneous dose delivery. Prospective 3-D dosimetric studies are required to confirm this concept.