Dosimetric Impact And Theoretical Clinical Benefits Of Fiducial Markers For Dose Escalated Prostate Cancer Radiation Treatment

UroToday.com - Dose-escalated external beam radiotherapy (EBRT) is widely accepted as an effective treatment for localized prostate cancer (1-4). From these randomized trials, it is evident that an increase in dose also means more toxicity. Thus, for dose escalation, minimizing planning target volume (PTV) margins with more precise target localization techniques is mandatory to keep the rate of late toxicity as low as possible. With better organ position verification, image-guided radiotherapy (IGRT) techniques such as fiducial markers and daily kilovoltage imaging (FM-kV) allow reduction in setup error and therefore allow PTV margins reduction.

The present study was purely dosimetric. We found that a significant number of patients planned with traditional setup in our study did not fulfill several Radiation Therapy Oncology Group (RTOG) DVH constraints. Of the 20 patients in this study, 30% would not have met three or more RTOG DVH constraints for the rectum. On average, V60Gy, V65Gy, V70Gy and V75Gy were 4.5% to 6.9% less for the rectum, and V65Gy, V70Gy and V75Gy were 5.4% to 8.4% less for the bladder when treated with FM-kV.

Our data support the fact that, for a selected radiation dose (76Gy in our case), PTV margins reduction with FM-kV should decrease the rate of late radiation toxicities, especially for the rectum but maybe not in the same magnitude as we initially thought (from 11.5% to 9%). The NTCP analysis suggests a potential increase in prostate dose of 2.1 Gy (to 78.1 Gy) while maintaining the same level of late rectal toxicity as with the traditional setup.

We believe that the reduction in setup error justifies the use of fiducial markers. Further studies are needed to ascertain whether there is concordance between the theoretical benefits and real clinical outcomes.

References:

1. Peeters ST, Heemsbergen WD, Koper PC, et al. Dose-response in radiotherapy for localized prostate cancer: results of the Dutch multicenter randomized phase III trial comparing 68 Gy of radiotherapy with 78 Gy. J Clin Oncol 2006;24:1990-1996.
2. Al-Mamgani A, van Putten WL, Heemsbergen WD, et al. Update of Dutch Multicenter Dose-Escalation Trial of Radiotherapy for Localized Prostate Cancer. Int J Radiat Oncol Biol Phys 2008.
3. Kuban DA, Tucker SL, Dong L, et al. Long-term results of the M. D. Anderson randomized dose-escalation trial for prostate cancer. Int J Radiat Oncol Biol Phys 2008;70:67-74.
4. Pollack A, Zagars GK, Starkschall G, et al. Prostate cancer radiation dose response: results of the M. D. Anderson phase III randomized trial. Int J Radiat Oncol Biol Phys 2002;53:1097-1105.