A study was conducted to evaluate the radiation transmission through lead equivalent aprons that are used in a radiology department. A large area beam (poor geometry) was employed for the transmission measurements, and backscatter was simulated by placing 7" of Lucite behind each apron. Separate ionization chambers were used to measure the incident and transmitted x-ray beams. Transmission measurements were made at 70 kVp and 100 kVp through aprons and protective shields from eight different vendors that were marked 0.25 mm and 0.5 mm lead equivalent. Transmissions through 0.254 mm and 0.508 mm of pure lead were also measured and were compared with the transmissions through the lead equivalent materials. In addition, the area densities of the aprons were measured to compare radiation transmission with respect to the weights of the aprons. At 70 kVp, the transmission through 0.254 mm of pure lead was 5.4% and the transmissions through the 0.25 mm lead equivalent materials were 4.3% to 10.2% with a mean value of 7.1% and a standard deviation (s.d.) of 1.4%. At 100 kVp, the values were 15% for 0.254 mm pure lead and 12.3% to 20.7% (mean 16.8%, s.d. 2.1%) for the 0.25 mm lead equivalent materials. The transmission through the 0.508 mm pure lead sample was 0.9% at 70 kVp, and the corresponding transmissions through the 0.5 mm lead equivalent materials were 0.6% to 1.6% (mean 1.0%, s.d. 0.2%). At 100 kVp, the transmission through the 0.508 mm lead sample was 5% and those through the 0.5 mm lead equivalent materials were 3.5% to 6.7% (mean 4.9%, s.d. 0.7%). The radiation transmissions at 70 kVp, through two "lead-free" 0.5 mm lead equivalent aprons, were 1.7% and 1.9% and at 100 kVp the transmissions were 6.1% and 6.8%, respectively. This study indicates that there is a need to establish methods for acceptance testing of aprons and a need to establish acceptance limits for the x-ray transmission of aprons at specific kVp values. There is also a need for the establishment of appropriate methods and frequencies of routine quality assurance testing of radiation protection aprons.

Low energy focused x-ray beams could be used to irradiate tumors inside soft tissue within 5 cm of the surface.

Generally minute doses of drugs have been prescribed in biotherapies, homeopathy, immunization and vaccinations for centuries. Now the use of low doses of drugs is on the rise to combat serious diseases such as advanced cancers around the world. This new therapeutic approach to address solid tumors and other advanced diseases is a departure from the conventional use of maximum dose protocol. A small dose of the prescribed drug is frequently administered in a continuous fashion, at regular intervals, either as a standard treatment or as a maintenance therapy for a long time. However, this new treatment method lacks any standard for drug quantization, dose fractionation, repetition frequency and duration of a treatment course for an individual patient. This paper reviews literature about metronomic therapy and discusses hormesis: both phenomena occur in low dose ranges. Better mathematical models, computer simulations, process optimization and clinical trials are warranted to fully exploit the potential of low dose metronomic therapy to cure chronic and complicated diseases. New protocols to standardize metronomic dosimetry will answer the age old questions related to hormesis and homeopathy. It appears that this new low-dose metronomic therapy will have far reaching effects in curing chronic diseases throughout the world.

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ᮀ MTLn3 cells derived from mouse mammary epithelium are known to be highly malignant and are resistant to both radio-and chemo-therapy. We exposed MTLn3 cells to various doses of inorganic Arsenic trioxide (As 2 O 3 ) in combination with ionizing radiation. Cells were treated with a series of As 2 O 3 concentrations ranging from 20 µM to 1.22 nM for 8 hour, 24 hour and 48 hour periods. Post-treated cell proliferation was quantified by measuring mitochondrial activity and DNA analysis. Cells exposed to radiation and As 2 O 3 at concentration greater than 1.25 µM showed apoptosis and radiations alone treated cells were statistically not different from the control. Hormesis was observed for As 2 O 3 concentrations in the range of 0.078 µM to 0.625 µM while the combined chemo and radiation treatments of the cells did not affect the hormetic effect. We have demonstrated that As 2 O 3 (in the presence and absence of ionizing radiation) in specific low concentrations induced apoptosis in the otherwise chemoresistant cancer cells. This low concentrationmediated cell death is immediately followed by a surge in cell survival. Low dosing dosimetry is highly desirable in metronomic therapy however, it has a narrow window since necrosis, hormesis, apoptosis and other dose-dependent biological processes take place in this region. Further quantifiable dosimetry is highly desired for routine clinical practice.