Diana Campos

Determination of absorbed dose in water at the reference point d(r0, theta0) for an 192Ir HDR brachytherapy source using a Fricke system.

A ring-shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a Ir192 high dose rate (HDR) source at 1cm from its center in water, D(r0,θ0). It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the Ir192 radioactive source. A ring cavity around the source with 1.5mm thickness and 5mm height is centered at 1cm from the central axis of the source. This ring cavity is etched in a disk shaped base with 2.65cm diameter and 0.90cm thickness. The cavity has a wall around it 0.25cm thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure D(r0,θ0). Irradiations were performed with a Nucletron microselectron HDR unit loaded with an Ir192 Alpha Omega radioactive source. A Spectronic® 1001 spectrophotometer was used to measure the optical absorbance using a 1mL quartz cuvette with 1.00cm light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the Ir192 Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air-kerma strength, and a published dose-rate constant was used to determine the dose rate at the reference point. The time to deliver 30.00Gy to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the D(r0,θ0) by 2.0%. Applying the corresponding correction factor, the D(r0,θ0) value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43% (k=1). The Fricke device provides a promising method towards calibration of brachytherapy radiation sources in terms of D(r0,θ0) and audit HDR source calibrations.

Enhanced response of the fricke solution doped with hematoporphyrin under X-rays irradiation

The vials filled with Fricke solutions were doped with increasing concentrations of Photogem®, used in photodynamic therapy. These vials were then irradiated with low-energy X-rays with doses ranging from 5 to 20 Gy. The conventional Fricke solution was also irradiated with the same doses. The concentration of ferric ions for the Fricke and doped-Fricke irradiated solutions were measured in a spectrophotometer at 220 to 340 nm. The results showed that there was an enhancement in the response of the doped-Fricke solution, which was proportional to the concentration of the photosensitizer. The use of such procedure for studying the radiosensitizing property of photosensitizers based on the production of free radicals is also discussed.

Study of a spherical phantom for Gamma knife dosimetry

Four 16 cm diameter spherical phantoms were modeled in this study: a homogenous water phantom, and three water phantoms with 1 cm thick shell each made of different materials (PMMA, Plastic Water™ and polystyrene). The PENELOPE Monte Carlo code was utilized to simulate photon beams from the Leksell Gamma Knife (LGK) unit and to determine absorbed dose to water (Dw) from a single 18 mm beam delivered to each phantom. A score spherical volume of 0.007 cm3 was used to simulate the dimensions of the sensitive volume of the Exradin A‐16 ionization chamber, in the center of the phantom. In conclusion, the PMMA shell filled with water required a small correction for the determination of the absorbed dose, while remaining within the statistical uncertainty of the calculations (±0.71). Plastic Water™ and polystyrene shells can be used without correction. There is a potential advantage to measuring the 4 mm helmet output using these spherical water phantoms. PACS numbers: 87.10.Rt, 87.50.cm

The Effect of the Shape and Size of Gold Seeds Irradiated with Ultrasound on the Bio-Heat Transfer in Tissue

The aim of this report is to propose a new methodology to treat prostate cancer with macro-rod-shaped gold seeds irradiated with ultrasound and develop a new computational method for temperature and thermal dose control of hyperthermia therapy induced by the proposed procedure. A computer code representation, based on the bio-heat diffusion equation, was developed to calculate the heat deposition and temperature elevation patterns in a gold rod and in the tissue surrounding it as a result of different therapy durations and ultrasound power simulations. The numerical results computed provide quantitative information on the interaction between high-energy ultrasound, gold seeds and biological tissues and can replicate the pattern observed in experimental studies. The effect of differences in shapes and sizes of gold rod targets irradiated with ultrasound is calculated and the heat enhancement and the bio-heat transfer in tissue are analyzed.

On the need for quality assurance in superficial kilovoltage radiotherapy

External auditing of beam output and energy qualities of four therapeutic X-ray machines were performed in three radiation oncology centres in northeastern Brazil. The output and half-value layers (HVLs) were determined using a parallel-plate ionisation chamber and high-purity aluminium foils, respectively. The obtained values of absorbed dose to water and energy qualities were compared with those obtained by the respective institutions. The impact on the prescribed dose was analysed by determining the half-value depth (D(1/2)). The beam outputs presented percent differences ranging from -13 to +25%. The ratio between the HVL in use by the institution and the measurements obtained in this study ranged from 0.75 to 2.33. Such deviations in HVL result in percent differences in dose at D(1/2) ranging from -52 to +8%. It was concluded that dosimetric quality audit programmes in radiation therapy should be expanded to include dermatological radiation therapy and such audits should include HVL verification.

Nutrition and Orthomolecular Supplementation in Lung Cancer Patients

This article reviews updates and provides some data related to nutritional and orthomolecular supplementation in oncology patients with an emphasis on lung cancer, a commonly diagnosed tumor with significant nutritional disturbances. Cancer and its treatment play a significant role in nutritional imbalance which likely has negative impact on the patient both in terms of quality and quantity of life. Nutritional supplementation may correct these imbalances with significant clinical benefit both physiologically and psychologically. This review will help assist in providing clinically useful data to assess the cancer patient’s nutritional status and to guide nutritional intervention to assist these patients’ recovery.

Preclinical Validation of the Located Hyperthermia Using Gold Macro-Rods and Ultrasound as an Effective Treatment for Solid Tumors

Hyperthermia, the procedure of raising the temperature of a part of or the whole body above normal for a defined period of time, is applied alone or as an adjunctive with various established cancer treatment modalities such as radiotherapy and chemotherapy. In this study used a method for inducing hyperthermia in solid tumors with a combination of gold macro rod (GR) and ultrasound, the feasibility of this technique was described only with computational models and in vitro. The Ehrlich tumor, derived from a mouse adenocarcinoma, has been used to investigate the bio-heat transfer and the effect of gold rods irradiated with ultrasound. The in vivo measurements demonstrated that the technique inhibited more 80% of the tumor growth in both experimental models tested. These results not only confirm the bio heat transfer to tissue as predicted by analytical calculation and in vitro measurements, but are also proved to be a potential alternative to kill cancer cells.

SU-F-E-05: Determination of Breakeven Points of in Vitro Meats and in Vivo Mice Based On Tissue Temperature Enhancement Pattern

PURPOSE To determine the breakeven points in fresh commercial meat and in vivo mice using the tissue temperature enhancement pattern. METHODS A 1 cm length and 0.1 cm diameter gold rod were implanted in fresh chicken breast, beef, fish, in vivo Mus Musculus white mice (medial dorsal region) and insonated with ultrasound. The temperature enhancement of gold rods was measured with a needle type thermistor over a temperature range from 35-50 oC. From these results the breakeven points were determined by plotting the gold rod temperature versus ultrasound exposure time and determining the interception point of two curves fitted by a linear regression of thermal response above and below 43 °C. RESULTS The linear correlation coefficients for all fitted curves lie within 0.97 and 0.99. The breakeven points were found to be the same for all kinds of fresh meat (fish = 42.1 ±1.1, chicken breast = 42.3 ±0.9, beef = 42.6 ±0.8) and in vivo Mus Musculus white mice (43.3 ±0.6). These temperatures agree with the standardized value (e.g. equivalent minutes at 43 °C) for comparison of thermal treatments (Proc. SPIE Int. Soc. Opt. Eng. 2003 June 2; 4954: 37). CONCLUSION The interception of the thermal response curves above and below 43 °C may be used as a fast method and useful dosimetric tool in clinical research.

SU‐F‐E‐04: A Paris System‐Based Implant Approach to Hyperthermia Cancer Tumor with Gold Seeds and Ultrasound

PURPOSE To apply the Paris system-based implant for an uniform bio-heat distribution from implanted gold rods in tissue insonated with ultrasound. METHODS Experiments with single-plane implants using parallel equidistant 1.018 ± 0.015 cm height and 0.136 ± 0.001 cm diameter 24-K gold rods) arranged in triangular and square shapes were performed in Mus Musculus white mice (medial dorsal region). The mice were anesthetized and gold rods were implanted by means of a trocar needle and the implanted region was insonated with a 4-cm diameter transducer oscillating with a nominal frequency of 1 MHz and power of about 75 W. Intramuscular tissue temperature measurements were taken using implantable needle type thermocouples affixed to a portable Fluke thermometer. Superficial tissue temperature profile was also measured with a FLIR infrared camera and thermographic analysis were performed using the ImageJ computer software. In both cases, the central implant planes have been assigned to that approximately bisects all the implanted rods. RESULTS Measured with the needle type thermistor, for the triangular implant, the percentage deviation between the maximum and minimum temperature within the triangular plane was 5%. For a square shape, this percentage deviation was 6%. The thermographic analysis have shown a deviation of 3% and 5% for the triangular and square shapes, respectively. CONCLUSION Based on the temperature measurements with needle type thermistor and thermographic analysis, the Paris system-based implant approach for gold rods implanted in tissue and exposed to ultrasound may greatly improve the bio-heat propagation and sustain a constant temperature profile inside triangular and square patterns formed by gold rods implants. Additionally, the Paris system may minimize ablations areas and treatment length in hyperthermia if used in cancer tumor treatment.

Consistency of vendor-specified activity values for 192Ir brachytherapy sources

A long-term comparison was done between the manufacturer-stated ¹⁹²Ir activity and the measured ¹⁹²Ir activities determined with a well-type ionization chamber. Sources for a Nucletron Micro Selectron high-dose-rate (HDR) unit were used for this purpose. The radioactive sources reference activities were determined using a PTW well-type ionization chamber traceable to the National Institute of Standards and Technology Primary Calibration Laboratory. The measurements were taken in a period of 56 months with 17 different radioactive sources. The manufacturer stated activities were taken from the source calibration certificate provided by the manufacturer. These values were compared with the measured activities. The results have shown that both the percentage deviation of the monthly control measurements with the well-type chamber and the ratio between the measured activities to the manufacturer-stated value lie within ± 2.5%. These results were compared with similar published data and with uncertainty level (3% of the mean and 5% maximum deviation from mean) for brachytherapy sources calibration recommended by the AAPM. It was concluded that a threshold level of ±2.5% can be used as a suitable quality assurance indicator to spot problems in our department. The typical ±5% uncertainty as provided by the manufacturers may be tightened to ±3% to be more in line with published AAPM reports.