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Implanted dosimeters identify radiation overdoses during IMRT for prostate cancer, "Beyond the Abstract," by Nicholas G. Zaorsky, MD and Robert B. Den, MD

BERKELEY, CA (UroToday.com) - Intensity-modulated radiation therapy (IMRT) is currently the standard of care in radiation treatments for prostate cancer because it increases the radiation dose delivered to the tumor volume and minimizes the dose delivered to surrounding organs.[1]

Image guided radiation therapy (IGRT) is an integral component of IMRT because it improves tumor control rates and minimizes toxicity.[2] IGRT corrects for random and systematic errors that occur during treatment delivery and provides a high degree of accuracy and precision in each fraction. Cone beam CT is a common type of system used for image guidance. [3]

 This study [4] showed that even with cone beam CT there are significant anatomic changes that occur in about 15% of patients, and these changes alter dose distributions. The clinical outcome for these patients could mean incomplete treatment, recurrence of cancer, or increased gastrointestinal and genitourinary toxicity. Since the publication of the work, other simulation [5, 6] and in vivo [7, 8] studies continue to show that image-guidance systems are imperfect at delivering accurate and precise doses.

The use of image guidance systems varies widely in published studies,[1] and there are currently no clear guidelines established for their use. The published literature shows that there are a number of variables among patients, providers, and the equipment used to deliver radiation. Ultimately, these factors affect the delivered dose and the clinical outcomes. Practitioners should consider the following in treatment planning and delivery: first, since the movements of the prostate occur both interfractionally (i.e. between two RT sessions) and intrafractionally (i.e. during one RT session), are both translational (i.e. shifting of the isocenter) and rotational (i.e. around the isocenter), the selection of an IGRT modality is critical. Cone beam CT alone may be unacceptable for certain patients. Thus, perhaps these patients may benefit from real-time tracking systems,[7, 9, 10, 11] adaptive dose-deforming radiotherapy algorithms,[12, 13] and novel fiduciary markers.[14] In the future, tracking systems may use single molecules as fiduciary markers.[15] Second, unique patient attributes should be considered in order to individualize IMRT and the type of IGRT used. IMRT systems will need to account for changes in bladder and colorectal volumes, pelvic anatomy,[16] obesity,[8] and prostheses,[6] because these have all been shown to affect dose distribution. 

References: 

  1. Bauman G, Rumble RB, Chen J, Loblaw A, Warde P. Intensity-modulated Radiotherapy in the Treatment of Prostate Cancer. Clin Oncol (R Coll Radiol). Sep 2012;24(7):461-473.
  2. Zelefsky MJ, Kollmeier M, Cox B et al. Improved Clinical Outcomes With High-Dose Image Guided Radiotherapy Compared With Non-IGRT for the Treatment of Clinically Localized Prostate Cancer. Int J Radiat Oncol Biol Phys. Sep 1 2012;84(1):125-129.
  3. Wierzbicki M, Schaly B, Peters T, Barnett R. Automatic image guidance for prostate IMRT using low dose CBCT. Med Phys. Jul 2010;37(7):3677-3686.
  4. Den RB, Nowak K, Buzurovic I et al. Implanted dosimeters identify radiation overdoses during IMRT for prostate cancer. Int J Radiat Oncol Biol Phys. Jul 1 2012;83(3):e371-376.
  5. Olsen JR, Parikh PJ, Watts M et al. Comparison of dose decrement from intrafraction motion for prone and supine prostate radiotherapy. Radiother Oncol. Aug 2012;104(2):199-204.
  6. Wang B, Tward JD, Salter BJ. An evaluation of interference of inflatable penile prostheses with electromagnetic localization and tracking system. Med Phys. Aug 2012;39(8):4807-4811.
  7. Klayton T, Price R, Buyyounouski MK et al. Prostate Bed Motion during Intensity-Modulated Radiotherapy Treatment. Int J Radiat Oncol Biol Phys. Feb 11 2012.
  8. Butler WM, Morris MN, Merrick GS, Kurko BS, Murray BC. Effect of Body Mass Index on Intrafraction Prostate Displacement Monitored by Real-Time Electromagnetic Tracking. Int J Radiat Oncol Biol Phys. Aug 1 2012.
  9. Rassiah-Szegedi P, Wang B, Szegedi M et al. Individualized margins for prostate patients using a wireless localization and tracking system. J Appl Clin Med Phys. 2011;12(3):3516.
  10. Munoz F, Fiandra C, Franco P et al. Tracking target position variability using intraprostatic fiducial markers and electronic portal imaging in prostate cancer radiotherapy. La Radiologia medica. Feb 10 2012.
  11. Litzenberg DW, Balter JM, Hadley SW et al. Prostate intrafraction translation margins for real-time monitoring and correction strategies. Prostate Cancer. 2012;2012:130579.
  12. Noel CE, Santanam L, Olsen JR, Baker KW, Parikh PJ. An automated method for adaptive radiation therapy for prostate cancer patients using continuous fiducial-based tracking. Phys Med Biol. Jan 7 2010;55(1):65-82.
  13. Mohan R, Zhang X, Wang H et al. Use of deformed intensity distributions for on-line modification of image-guided IMRT to account for interfractional anatomic changes. Int J Radiat Oncol Biol Phys. Mar 15 2005;61(4):1258-1266.
  14. Thomsen JB, Arp DT, Carl J. Urethra sparing - potential of combined Nickel-Titanium stent and intensity modulated radiation therapy in prostate cancer. Radiother Oncol. May 2012;103(2):256-260.
  15. Parthasarathy R. Rapid, accurate particle tracking by calculation of radial symmetry centers. Nature Methods. Jul 2012;9(7):724-726.
  16. de Crevoisier R, Melancon AD, Kuban DA et al. Changes in the pelvic anatomy after an IMRT treatment fraction of prostate cancer. Int J Radiat Oncol Biol Phys. Aug 1 2007;68(5):1529-1536.

 

Written by: 

Nicholas G. Zaorsky, MD and Robert B. Den, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

Department of Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA, USA

Corresponding Author: 

Robert B. Den, MD
Dept. of Radiation Oncology
Thomas Jefferson University Hospital
111 South 11th St.
Philadelphia, PA 19107-5097
Voice (215) 955-0284
fax (215) 955-0412

Acknowledgements: None.

Approval/disclosures: The authors have read and approved the manuscript. We have no financial disclosures. We are not using any copyrighted information, patient photographs, identifiers, or other protected health information in this paper. No text, text boxes, figures, or tables in this article have been previously published or owned by another party.

Conflicts of Interest Notification: We have no conflicts of interests.

 

 

Implanted dosimeters identify radiation overdoses during IMRT for prostate cancer - Abstract

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