The design and evaluation of a 2D dose verification system for intensity modulated radiotherapy

The usage of intensity modulated radiotherapy (IMRT) treatments necessitates a significant amount of patient-specific quality assurance (QA). This research has investigated the precision and accuracy of Kodak EDR2 film measurements for IMRT verifications, the use of comparisons between 2D dose calculations and measurements to improve treatment plan beam models, and the dosimetric impact of delivery errors. New measurement techniques and software were developed and used clinically at M. D. Anderson Cancer Center. The software implemented two new dose comparison parameters, the 2D normalized agreement test (NAT) and the scalar NAT index. A single-film calibration technique using multileaf collimator (MLC) delivery was developed. EDR2 film's optical density response was found to be sensitive to several factors: radiation time, length of time between exposure and processing, and phantom material. Precision of EDR2 film measurements was found to be better than 1%. For IMRT verification, EDR2 film measurements agreed with ion chamber results to 2%/2mm accuracy for single-beam fluence map verifications and to 5%/2mm for transverse plane measurements of complete plan dose distributions. The same system was used to quantitatively optimize the radiation field offset and MLC transmission beam modeling parameters for Varian MLCs. While scalar dose comparison metrics can work well for optimization purposes, the influence of external parameters on the dose discrepancies must be minimized. The ability of 2D verifications to detect delivery errors was tested with simulated data. The dosimetric characteristics of delivery errors were compared to patient-specific clinical IMRT verifications. For the clinical verifications, the NAT index and percent of pixels failing the gamma index were exponentially distributed and dependent upon the measurement phantom but not the treatment site. Delivery errors affecting all beams in the treatment plan were flagged by the NAT index, although delivery errors impacting only one beam could not be differentiated from routine clinical verification discrepancies. Clinical use of this system will flag outliers, allow physicists to examine their causes, and perhaps improve the level of agreement between radiation dose distribution measurements and calculations. The principles used to design and evaluate this system are extensible to future multidimensional dose measurements and comparisons. ^

Progestational agents and preterm birth: An updated review of the literature

The preterm birth rate has been increasing over time in the United States, causing a large social and individual financial burden. Though the cause of preterm birth is now known, risk factors such as a previous preterm birth and a short cervical length have been identified as possible predictors. There are many contributing social and behavioral factors that play a role was well as medical problems that occur before and during pregnancy. Though there have been prevention methods identified, such as prenatal care, tocolytic therapy and cervical cerclage, none of these methods have shown to definitively prevent preterm birth over a long period of time. 17 alpha hydroxyprogesterone has been recognized as a possible prevention method for women at high risk for preterm birth. Three out of the five studies assessed in this review showed a significant reduction in preterm birth with administration of progesterone, both for women with a previous preterm birth and with a short cervical length. Currently there is no standard of care for those at high risk for preterm birth. More large clinical trials need to be conducted to determine if this progesterone for the prevention of preterm birth is effective. ^