Purpose: Previous radiation treatment of patients with recurrent Hodgkin's lymphoma hampers attempts to give these patients further radiation treatment for their recurrence, because of the potential for serious radiation damage to critical normal structures within the treatment volume. The purpose of this paper is to present a technique we developed for treatment of recurrent Hodgkin's lymphoma in mediastinum and hilum. The technique is based on parallel-opposed electron beams with a spinal cord shield in the posterior electron beam. Methods and Materials: The patient was treated with parallel-opposed 20 MeV electron beams and the spinal cord shield was shaped in such a way that the total dose from both the anterior and posterior electron beams did not exceed 33% of the prescribed tumor dose. Wax bolus was used to obtain the desired separation for the electron beams. Results: In an electron beam, the dose under the spinal cord shield depends not only on the depth of the spinal cord but also on the width of the shield. For a given shield width, as the cord depth increases the relative dose under the shield first increases, reaches a maximum, and then decreases to approach the open field depth dose data at large depths. The depth at which the relative dose maximum occurs increases slowly with the shielded width. At a given depth, the relative dose decreases with an increasing shield width. Conclusion: Parallel-opposed electron beams with a spinal cord shield in the posterior electron beam provide a viable option in treatment of tumors enveloping the spinal cord. A high tumor dose may be prescribed with a concurrent low dose to the spinal cord obtained with an appropriately shaped spinal cord shield.
