Purpose: High cure rates for Hodgkin's lymphoma must be balanced with long-term treatment-related toxicity. Here we report an intensity-modulated radiation therapy (IMRT) technique that achieves adequate target coverage for mediastinal disease while minimizing high- and low-dose exposure of critical organs.
Methods and materials: Treatment plans for IMRT and conventional anteroposterior-posteroanterior (AP-PA) techniques, with comparable coverage of the planning target volume (PTV), were generated for 9 female patients with mediastinal Hodgkin's lymphoma assuming use of inclined positioning, daily breath-hold, and CT-on-rails verification. Our "butterfly" IMRT beam arrangement involved anterior beams of 300°-30° and posterior beams of 160°-210°. Percentages of normal structures receiving 30 Gy (V30), 20 Gy (V20), and 5 Gy (V5) were tabulated for the right and left breasts, total lung, heart, left and right ventricles, left anterior descending coronary artery (LAD), and spinal cord. Differences in each variable, conformity index, homogeneity index, and V107% between the two techniques were calculated (IMRT minus conventional).
Results: Use of IMRT generally reduced the V30 and V20 to critical structures: -1.4% and +0.1% to the right breast, -1.7% and -0.9% to the left breast, -14.6% and -7.7% to the total lung, -12.2% and -10.5% to the heart, -2.4% and -14.2% to the left ventricle, -16.4% and -8.4% to the right ventricle, -7.0% and -14.2% to the LAD, and -52.2% and -13.4% to the spinal cord. Differences in V5 were +6.2% for right breast, +2.8% for left breast, +12.9% for total lung, -3.5% for heart, -8.2% for left ventricle, -1.5% for right ventricle, +0.1% for LAD, and -0.1% for spinal cord. Use of IMRT significantly reduced the volume of tissue receiving 107% of the dose (mean 754 cm3 reduction).
Conclusions: This butterfly technique for IMRT avoids excess exposure of heart, breast, lung, and spinal cord to doses of 30 or 20 Gy; mildly increases V5 to the breasts; and decreases the V107%.