BERKELEY, CA (UroToday.com) - This work aimed at developing and evaluating an in vivo dosimetry system based on plastic scintillation detectors (PSDs). In vivo dosimetry is an increasingly important part of radiotherapy. The incredible technologic complexity of modern day treatments like IMRT has resulted in a number of severe treatment mis-administrations[1, 2, 3, 4, 5] with debilitating and even fatal outcomes. The number of less severe mis-administrations that nonetheless result in sub-optimal tumor cure or unnecessary acute or long-term side effects is unknown but presumably occurs at a higher rate than the severe mis-administrations. The primary means of addressing this situation is by developing quality assurance (QA) procedures that are highly robust and sensitive enough to detect potential errors before or as they occur, to limit adverse outcomes for patients. in vivo dosimetry represents a significant step towards this goal by verifying treatment, at the point of, or during the treatment delivery.[6, 7] If errors are detected, treatment can be halted before they play a significant role in patient outcome.
In light of this, the choice to implement in vivo dosimetry seems straightforward, but as always there is an associated cost. Detectors suitable for in vivo dosimetry are often expensive and complicated. The three most commonly used detectors, thermoluminescent detectors (TLDs), silicon diodes, and metal oxide field-effect transistors (MOSFETs) each have significant drawbacks. TLDs require expensive, dedicated read-out machinery and require at least two days after irradiation before a dose can be read, considerably lessening their utility. Silicon diodes require correction factors for the specific irradiation conditions, such as the energy of the treatment radiation used or the orientation of the radiation beam with respect to the detector etc., which makes their routine use complicated, Additionally, diodes suffer radiation damage that alters the detectors response to radiation over time. Newer detectors suffer from similar drawbacks: MOSFETs, for example, are extremely sensitive to radiation damage, rendering them essentially useless after one full course of radiation therapy treatment. Thus, each detector could only be used for one single patient treatment and additional detectors would have to be purchased and calibrated for each patient, a considerable investment of time and money. The net result is that the routine use of in vivo dosimetry has been, and still is, a controversial issue due to a questionable cost-to-benefit ratio.[8]
By implementing an in vivo system based on plastic scintillation dosimetry,[9] we are attempting to bring down that cost (both monetarily and in terms of technical expertise required for implementation). The components of a PSD are relatively inexpensive and PSDs are largely free from the need for correction factors (aside from a simple, constant correction for temperature).[10] PSDs provide results in real time such that treatment can be monitored on a beam-by-beam basis (and interrupted if errors occur) and are radiation-hard relative to other detectors, withstanding doses on the order of kilograys before exhibiting any radiation damage-induced effects.
This study was designed to illustrate those advantages. Prostate cancer was chosen as an initial site for evaluating our PSD-based in vivo dosimetry system because it allowed simultaneous monitoring of a critical organ at risk (the anterior rectal wall) and treatment verification. Furthermore, due to the high incidence of prostate cancer, this system will have broad applicability. It is our hope that demonstrating that a PSD-based system is practical to implement clinically, as well as highly accurate and precise, will foster increasing adoption of in vivo dosimetry and thus improve patient safety.
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| Figure 1: The research undertaken produced new knowledge and resulted in the conception and development of an in-vivo dosimetry system using miniature plastic scintillation detectors to monitor in real time the dose received by the rectal wall for prostate cancer patients: the OAR track system being manufactured by Radiadyne, LLC. Radiadyne is currently undergoing FDA approval. |
References:
- S. Derreumaux, C. Etard, C. Huet, F. Trompier, I. Clairand, J.-F. Bottolier-Depois, B. Aubert, and P. Gourmelon, “Lessons from recent accidents in radiation therapy in France,” Radiat. Prot. Dosim. 131, 130-135 (2008).
- International Commission on Radiological Protection, “ICRP Publication 112: Preventing accidental exposure from new external beam radiation therapy technologies,” Ann. ICRP 39(4), 1-86 (2009).
- W. Bogdanich, “Radiation offers new cures, and ways to do harm,” New York Times, January 23 2010.
- W. Bogdanich, “A pinpoint beam strays invisibly, harming instead of healing,” New York Times, December 29, 2010.
- W. Bogdanich, “As technology surges, radiation safeguards lag,” New York Times, January 26, 2010.
- B. Mijnheer, S. Beddar, J. Izewska, and C. Reft, “in vivo dosimetry in external beam radiotherapy,” Med. Phys. 40 070903 (2013).
- K. Tanderup, S. Beddar, C.E. Andersen, G. Kertzscher, and J.E. Cygler, “in vivo dosimetry in brachytherapy,” Med. Phys. 40 070902 (2013)
- C. Edwards, and P. Mountford, “Characteristics of in vivo radiotherapy dosimetry,” Brit. Jour. Radiol. 82 881-883 (2009)
- Beddar AS. Plastic scintillation dosimetry and its application to radiotherapy. Radiat Meas 41:S124-S133, 2007
- Wootton L, Beddar S. Temperature dependence of BCF plastic scintillation detectors. Phys Med Biol 58(9):2955-2967, 5/7/2013. e-Pub 4/11
Written by:
Sam Beddar, PhD, DABR, FCCPM, FAAPM 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.
Professor and Chief of Clinical Research
Radiation Physics
University of Texas MD Anderson Cancer Center
Houston, Texas 77030 USA
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