RSNA 2009 

Abstract Archives of the RSNA, 2009


SSC17-09

Radiation Therapy for Orbital Lymphoma: Clinical and Physical Considerations

Scientific Papers

Presented on November 30, 2009
Presented as part of SSC17: Radiation Oncology and Radiobiology (Lymphoma and Pediatrics)

Participants

Wanbao Gao PhD, Presenter: Nothing to Disclose
Waleed Fouad Mourad MD, MSc, Abstract Co-Author: Nothing to Disclose
Wayne Fai Chan MD, PhD, Abstract Co-Author: Nothing to Disclose
Mike Cheng MD, Abstract Co-Author: Nothing to Disclose
Joe Salloum MD, Abstract Co-Author: Nothing to Disclose

ABSTRACT

Purpose Megavoltage photons or electrons with lens shielding have been proven to be effective in treating the orbital lymphoma. During the last few years, IMRT has become easily available, and is considered the technique of choice to treat tumors with adjacent critical structures. On the other hand, a new measurement technique for non-standard high energy electron beams was recently developed by the same group utilizing commercially available diode arrays. The new method allows the dose distributions of electron fields being monitored instantly with varying treatment parameters and, as a result, the optimal treatment parameters for each patient can be quickly determined. The aim of the present work is to help radiation oncologists to select an appropriate technique for treating orbital lymphoma between IMRT for its ability to deliver a complex dose distribution and the electron technique for its simplicity, reliability, and reproducibility. Methods The clinical case is a 57 years old male diagnosed with orbital lymphoma of the left eye. A CT scan was performed with 1mm spacing to determine the location and size of the lesion. The goal was to deliver 30.6 Gy (1.8Gy x 17) to the tumor, to minimize the dose to the lens and other critical structures. We developed three IMRT plans with 5, 7 and 9 beams, respectively, all with 6 MV photons. DVHs were generated for lenses, optical nerves, the optical chiasm, and the brain stem. For the electron planning, we used 18 MeV beam with a hanging lens block placed 7mm above patient?s eye. A 2mm plastic was also used as the beam spoiler to increase the scatter dose behind the lens block. The dose distributions were measured with a two-dimensional diode array with solid water buildups, and compared with results from ion chamber and film measurements. Results All three IMRT plans achieve superior PTV coverage comparing with the electron plan, but they give significant doses to the right lens, optical nerves and optical chiasm. It would also require a sophisticated method to keep the lens still during the treatment time, typically 15 minutes. In addition, the computer plans were optimized with a CTV to PTV margin of 3 mm, taking advantage of daily CBCT, resulting in further increases in the doses to those critical structures. Therefore, we chose to use the electron plan with dose prescribed to the 85% isodose line. Post-radiation MRI in 6 month showed significant improvement compared to the pre-radiation MRI. All sensitive ocular structures are still functioning (including lens). Conclusions: Orbital Lymphomas can be treated effectively with a simple, reliable and reproducible technique using high energy electrons. Although IMRT is an attractive option, effort must be made to keep the lens in a fixed position during treatment, and the imaging dose must be taken into account if daily CBCT scan will be used. 1

Cite This Abstract

Gao, W, Mourad, W, Chan, W, Cheng, M, Salloum, J, Radiation Therapy for Orbital Lymphoma: Clinical and Physical Considerations.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8502367.html