Firas Mourtada, Ph.D.
1997, Johns Hopkins University
The University of Texas M. D. Anderson Cancer Center
Department of Radiation Physics
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Firas Mourtada, Ph.D. 1997, Johns Hopkins University The University of Texas M. D. Anderson Cancer Center |
Research Interests:
The research projects currently active are focused on brachytherapy. For example, intracavitary bracthytherapy (ICBT) is an integral part of the treatment regimens for gynecological cancers. ICBT may be administered preoperatively or postoperatively; and is paired with external beam radiotherapy, chemotherapy, or both. Traditionally, ICBT is delivered using low-dose rate (LDR) 137Cs sources. The sources are manually or remotely afterloaded into applicators that are placed inside the uterine canal and vagina during an operative procedure. LDR radiation is delivered continuously for a time period of approximately 48 hours to deliver a total dose of approximately 30Gy to the tumor. The clinical outcome for a given stage disease is largely determined by the applicator placement and source-position pattern which are highly dependent on physician skill and judgement.
Recently, pulsed-dose rate (PDR) ICBT (Nucletron Co., Netherlands) has been proposed to treat human cervical carcinoma providing an alternative approach to LDR. The PDR approach uses a single 192Ir source controlled automatically with a remote afterloader. A dose fraction is delivered in 10 minutes every hour and is “pulsed” over a 48 hours total treatment time to mimic LDR’s biological effectiveness. It is recognized that PDR has the theoretical advantage over LDR for its computer-based dose distribution optimization (PLATO system, Nucletron Co.) to maximize tumor dose while sparing rectum and bladder. This is important since late-complication probability of normal tissue (rectum and bladder) is proportional to dose delivered to these structures. However, the commercial dose engine in PLATO does not accurately account for the attenuation of the shields in the applicators (which can be as high as 30%) thus cannot optimize using the “true” dose distribution inside the patient. This in fact could result in less favorable clinical outcome. We propose to use the Monte Carlo method, which is considered to be the “gold standard” for dose computation accuracy, to optimize PDR dose distribution. This optimization requires CT-based image guidance to accurately model the applicators inside the patient’s anatomy. Our ultimate objective is to optimize PDR by increasing tumor dose while reducing rectal and bladder doses. Our specific aims are to: 1) validate the Monte Carlo (MC) models of the new PDR system using experimental phantoms; 2) optimize the dose distribution of PDR using CT-based patient specific MC models; and 3) compare PDR results to traditional LDR dose distributions for each patient included in this study. The findings will be used to ultimately create guidelines for PDR source loading and to transfer clinical practice from LDR to PDR. The results from this study will be used by our physicians at MDACC to design randomized PDR clinical trials of gynecological cancer.
Depending on the student’s interests, a tutorial in my laboratory would provide experience with brachytherapy source characterization using experimental dosimetry, and/or theoretical dose modeling using the Monte Carlo or Discrete Ordinate methods.
Program Affiliation:
Program in
Medical Physics