Blinding in Sham Radiation Therapy

The use of clinical trials in the development of new treatment techniques (pharmaceutical or otherwise) is a necessary step in demonstrating the efficacy of that treatment. The gold standard for testing new techniques is the randomised controlled trial, where participants are split up into groups that are treated (or not treated, potentially) with different techniques. The clinical results observed for groups receiving the experimental treatments are compared against the results observed for so-called ‘control’ groups, which either receive the standard treatment (where one exists), or a placebo. 

Radiation oncology treatment centres are frequently involved in multiple trials at once. These are often designed to test the effect of concurrent chemotherapy and radiation therapy. Sometimes they evaluate two different radiation therapy treatment approaches (for example, irradiating nodes in a treatment even where there is no evidence of involvement). In these cases both test and control groups receive radiation therapy.

There have been, however, a number of trials experimenting with therapeutic radiation treatments for benign conditions, where a control group does not receive radiation therapy, but a placebo in its place – ‘sham’ radiation therapy. A review by Schwarz and Christie (2008) identified 26 trials involving treatments of multiple sclerosis, coronary artery restenosis, macular degeneration and Graves’ ophthalmopathy.

The blinding of the control group patients necessitates the illusion of an active treatment. Techniques have included (Schwarz and Christie, 2008):

• the use of a pulse generator to create the sound of a linear accelerator;
• the use of headphones playing white noise;
• and the use of shielding to prevent dose deposition.

Mourits et al (2000), evaluating the use of therapeutic radiation in the treatment of Graves’ orbitopathy, delivered a 6 MV photon beam (20 Gy over 10 fractions) to the test group, while the sham-irradiation ‘treatment’ involved a 4 MeV electron beam, with closed collimators and a cerrosafe block in the accessory tray of the accelerator.

Schawz and Christie (2008) found that patients were blinded successfully (in which where it was reported) using these techniques.

References

• Mourits MP, van Kempen-Harteveld ML, Garcia MBG, Koppeschaar HP, Tick L and Terwee CB, 2000. Radiotherapy for Graves’ orbitopathy: randomised placebo-controlled study, The Lancet, 355: 1505-1509.
• Schwarz F and Christie D, 2008. Use of ‘sham’ radiotherapy in randomized clinical trials, Journal of Medical Imaging and Radiation Oncology, 52(3): 269-277.