Development of a 3D printing process of bolus using BolusCM material for radiotherapy with electrons.

This work presents the optimized parameters of 3D printing for print bolus using BolusCM material. Printing parameters were selected of the homogeneity and absence of air gaps. The dosimetric features of printed bolus were measured with a plane-parallel ionization chamber and EBT3 radiochromic film. Measured features were compared with those estimated with Monte Carlo methods. BolusCM shows good characteristics to be used as bolus material in radiotherapy with electrons, where the printing process allows personalizing the bolus in function of patient characteristics. The material low-cost, the 3D printing and the dosimetric features are few of the advantages of using BolusCM material in radiotherapy with electrons in skin cancer treatment.

Bolus 3D printing for radiotherapy with conventional PLA, ABS and TPU filaments: Theoretical-experimental study.

A theoretical-experimental study of the interaction of electron beams with 3 filaments conventionally used for 3D printing is presented in this paper. Pieces of polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) are studied using Monte Carlo simulation with Geant4 and experimental measurements with plane-parallel ionization chambers and radiochromic films. Using different printing parameters and computed tomography, the presence of air gaps and the uniformity in the bolus density made with the different materials are evaluated. The main parameters in the Percentage Depth Dose (PDDs) are determined, the manufacturing process is standardized and the printing profiles are generated for each of the materials in order to obtain uniform attenuation characteristics in the pieces and improve adaptation to irregular anatomical areas.

Dosimetric analysis of graphitic carbon nitride quantum dots exposed to a gamma radiation for a low-dose applications.

In this study, graphitic carbon nitride quantum dots (g-C3N4QDs) were synthesized using different solvents, characterized, and then exposed to a gamma-ray source (137Cs) at irradiation doses of 0.1, 1.48, 2.05 and 3.25 Gy. The intensities of the emission bands progressively were attenuated as the received dose of gamma radiation increased. The changes were quantified with the help of a non-linear fit model. The material showed promising use as a dosimeter for low-dose radiation applications.

Characterization of a novel material to be used as bolus in radiotherapy with electrons.

Features of new material to be used as bolus in external radiotherapy were determined and their performance were evaluated. The characterization was carried out using Monte Carlo methods with the Geant4 code where the Percentage Depth Dose (PDD) due to electrons was estimated. In the Monte Carlo model the linear accelerator head was included. Calculated results were experimentally validated with measurements made for 6, 9, 12 and 16 MeV electron beams. The key characteristics of the implemented material were identified, guaranteeing a low cost bolus, easy to be customized and to be used in clinical applications. In comparison with commercial materials the new materials are superior from the cost to the effectiveness of their use in clinical treatments.

Optimization by Monte Carlo method of photon fluence from the X-ray beam spectrum in a bimodal tomographic system.

A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camera that contains 8 bars, each one with 67,200 hybrid pixels are modeled in GEANT4 simulation code. Several conical X-ray spectra were simulated, particularly a spectrum with a peak energy of 17.4 keV used in tomography on small animals. Three phantoms located in the tomographic center were added to the simulation to evaluate the image quality and its magnification based on the simulation of different photon fluences and the rotation effect of the tomographic system with an average angular velocity of 360o per minute. The images were recorded and analyzed in 2D through ROOT software toolkit in virtual XPAD3 detector. The quantitative method 20-80% of the maximum intensity of radiation was used for obtain the contouring of the phantoms, this method is used in radiotherapy and radiodiagnosis imaging. For this purpose, the images were taken to DICOM format in order to estimate the optical density of the contours and to evaluate the optimum and minimum photon fluence to be used in the tomographic system in order to reduce the absorbed doses in the individuals. This study allowed to determine the optimal fluence to validate it with realistic fluences used in the tomographic prototype ClearPET /XPAD-CT and to make an intercomparison with the absorbed doses measured with detectors located in the tomographic center.

Doses in sensitive organs during prostate treatment with a 60Co unit.

Using thermoluminiscent dosimeters the absorbed dose in the bladder, rectum and thyroid have been evaluated when 200 cGy was applied to the prostate. The treatment was applied with a (60)Co unit. A water phantom was built and thermoluminiscent dosimeters were located in the position where the prostate, bladder, rectum and thyroid are located. The therapeutic beam was applied in 4 irradiations at 0, 90, 180 and 270° with the prostate at the isocenter. The TLDs readouts were used to evaluate the absorbed dose in each organ. The absorbed doses were used to estimate the effective doses and the probability of developing secondary malignacies in thyroid, rectum and bladder.

Calculation of fluence and absorbed dose in head tissues due to different photon energies.

Calculations of fluence and absorbed dose in head tissues due to different photon energies were carried out using the MCNPX code, to simulate two models of a patient's head: one spherical and another more realistic ellipsoidal. Both head models had concentric shells to describe the scalp skin, the cranium and the brain. The tumor was located at the center of the head and it was a 1 cm-radius sphere. The MCNPX code was run for different energies. Results showed that the fluence decreases as the photons pass through the different head tissues. It can be observed that, although the fluence into the tumor is different for both head models, absorbed dose is the same.

131I activity in urine to the sewer system due to thyroidal treatments.

In nuclear medicine, estimating the radioactivity contained in the urine of patients treated with I and discharged to the environment could prevent the exposure of a population to radioactive effluents and the pollution of the aquatic environment with ionizing radiation. This can be a regulatory requirement (as in Spain) or requested by the sewer authority. Seventy-nine differentiated thyroid cancer cases (undergone as inpatients) and 187 hyperthyroidism cases (undergone as outpatients) were treated in our hospital with I throughout the year 2009. In hyperthyroidism treatments, the effective elimination constant was used to calculate the corresponding discharged activity in the urine, giving an activity level always below 0.7 GBq. In differentiated thyroid cancer treatments, patient's urine was collected in storage tanks during the hospitalization. Measurements of external exposure at 1 m made every day were used to calculate the activity contained in the urine. The tank activity was always below 15 GBq, but always higher than 2 GBq. Obtained results show that effective doses to sewage workers, received from liquid discharges, can only be reduced to less than 10 µSv if storage tanks are installed. Without tanks, 157 µSv can be reached, above the constrain dose used in nuclear installations (100 µSv). Our calculations may be helpful to the regulatory authority to review the clinical radiation waste normative, especially in countries where the discharges are released directly into public sewage plants.

Niveles de dosis en radiología convencional / Radiation doses in conventional radiology

Se ha medido la dosis en la superficie de entrada de ojos, tiroides y gónadas en pacientes sometidos a estudio de radiografía de tele de tórax mediante dosimetría termoluminiscente. Se usaron 5 dosímetros en cada una de las exploraciones; encontrándose los siguientes rangos de dosis: 20 mGy a 350 mGy. En el caso de los pacientes pediátricos se propone incluir la información de las dosis recibidas en su cartilla de vacunación con el fin de hacer un seguimiento de los posibles efectos nocivos en su salud.

Doses have been measured at the entrance surface of eyes, thyroid and gonads in patients undergoing chest x-ray studies, using thermo-luminiscent dosimetry. Five dosimeters were used in each investigation, and doses ranged from 20 mGy to 350 mGy. In the case of pediatric patients, it is proposed that dose information from diagnostic examinations is included in the vaccination chart in order to correlate with findings at follow-up.

Correlation between external exposure and activity in patients undergoing 131I thyroid cancer therapy.

The uptake and clearance of 131I activity for inpatients undergoing cancer therapy were determined from routine external dose survey measurements. A bi-exponential behavior was found, with the two time constants representing the iodine dynamics in the thyroid on one hand and in the rest of the body on the other. The external dose at 1 m from the patient was correlated to the activity in the thyroid remnant and inside the body, the averaged value being 52.8 +/- 11.4 microSv GBq(-1) h(-1). The temporal evolution of activity in the body, the urinary system and the thyroid remnant area were determined taking into account the clearance from thyroid and whole body (effective retention constants averages 0.23 +/- 0.14 d(-1) and 1.46 +/- 0.34 d(-1)) and the uptake in thyroid (3.15 +/- 3.36%). Applications of this study in the public and environmental radiation protection areas are presented.

Neutron KERMA factors of human tissues

A program to calculate the neutron KERMA in human tissues has been developed. The program was developed in Mathcad and contains the neutron kerma factors of those elements that are present in different human tissues. Having the elemental composition of any human tissue the neutron kerma can be easily calculated. The program was tested using the elemental composition of tumor tissues such as sarcoma, melanoma, carcinoma and adenoid cystic. Neutron kerma for adipose and muscle tissue for normal adult was calculated. The results are in agreement with those published in literature. The neutron kerma for water was also calculated because in some dosimetric calculations water is used to describe normal and tumor tissues. From this comparison was found that at larger energies kerma factors are approximately the same, but energies less than 100 eV the differences are large.

Campos neutrónicos producidos por un acelerador lineal para radioterapia / Neutron fields produced by linear accelerator for radiotherapy

Mediante una serie de medidas y cálculos Monte Carlo se han determinado las características dosimétricas y los espectros de los fotoneutrones que se producen en torno a un acelerador lineal para radioterapia de 18 MV. Las medidas se realizaron con dosímetros termoluminiscentes TLD 600 y TLD 700 que se expusieron desnudos y emparedados con Cd, así como dentro de una esfera de parafina y dentro de esferas Bonner.

Measurements and Monte Carlo calculations has been utilized to determine the dosimetric features as well as the neutron spectra of photoneutrons produced around an 18 MV linear accelerator for radiotherapy. Measurementes were carried out with bare and Cd covered thermolumiscent dosimeters, TLD600 and TLD700, as well as inside a paraffine moderator. TLD pairs were also utilized as thermal neutrons inside a Bonner sphere spectrometer.

Monte Carlo simulation estimates of neutron doses to critical organs of a patient undergoing 18 MV x-ray LINAC-based radiotherapy.

Absorbed photoneutron dose to patients undergoing 18 MV x-ray therapy was studied using Monte Carlo simulations based on the MCNPX code. Two separate transport simulations were conducted, one for the photoneutron contribution and another for neutron capture gamma rays. The phantom model used was of a female patient receiving a four-field pelvic box treatment. Photoneutron doses were determinate to be higher for organs and tissues located inside the treatment field, especially those closest to the patient's skin. The maximum organ equivalent dose per x-ray treatment dose achieved within each treatment port was 719 microSv/Gy to the rectum (180 degrees field), 190 microSv/Gy to the intestine wall (0 degrees field), 51 microSv/Gy to the colon wall (90 degrees field), and 45 microSv/Gy to the skin (270 degrees field). The maximum neutron equivalent dose per x-ray treatment dose received by organs outside the treatment field was 65 microSv/Gy to the skin in the antero-posterior field. A mean value of 5 +/- 2 microSv/Gy was obtained for organs distant from the treatment field. Distant organ neutron equivalent doses are all of the same order of magnitude and constitute a good estimate of deep organ neutron equivalent doses. Using the risk assessment method of the ICRP-60 report, the greatest likelihood of fatal secondary cancer for a 70 Gy dose is estimated to be 0.02% for the pelvic postero-anterior field, the rectum being the organ representing the maximum contribution of 0.011%.

Neutron spectra and dosimetric features around an 18 mv linac accelerator.

Using the difference between responses to neutrons of TLD-600 and TLD-700, three experimental devices were constructed and arranged to measure thermal neutron fluences, neutron spectra, and neutron doses inside the treatment room of a radiotherapy 18 MV Linear electron accelerator (Linac). Thermal neutron fluences were measured with TLD-600/TLD-700 pairs arranged in both a bare and a cadmium (Cd) foil covered methacrylate box. Neutron spectra were measured in 26 energy bins by introducing pairs of TLD-600/TLD-700 in air and into the middle of five polyethylene spheres with diameters of 3, 5, 8, 10, and 12 inches. A PC version of the BUNKI code was used to unfold the six measurements in each sphere to obtain the 26 energy bins. Neutron and photon doses were measured by introducing pairs of TLD-600/TLD-700 into the middle of a single 25-cm-diameter paraffin sphere. The three required neutron calibrations were carried out at the Nuclear Technology Laboratory of the Polytechnique University of Madrid (UPM), using an 241Am-Be neutron source with an alpha activity of 111 GBq and a yield of 6.6 x 10(6) neutrons s(-1). Three devices were needed for the necessary calibrations: a BF3 counter for the thermal neutron fluence calibration, a LUDLUM 42-5 Bonner spectrometer with five 0.95 g cm(-3) polyethylene spheres with a LiI(Eu) 4 x 4 mm2 scintillation counter for the neutron spectrometer calibration and a NEMO 9140 remmeter for the paraffin remmeter calibration. The Monte Carlo code MCNP 4C has been used in two ways: to calculate the neutron kerma contribution to two TLDs (type 600 and 700) both in air and inside the paraffin sphere, and to determine the neutron spectra at those Linac room zones where the neutron spectra were measured. Thermal neutron fluences of 2.9 x 10(4) +/- 8.6 x 10(3) cm(-2) s(-1), measured around the Linac head plane, and 2.3 x 10(4) +/- 2.3 x 10(3) cm(-2) s(-1), measured at the patient couch plane, are in agreement with previous independent measurements from other authors. The calculated and measured neutron spectra obtained in the treatment room showed three distinct regions: a peak around 0.1 MeV, a flat epithermal region and a thermal region with values similar to those mentioned above. Patient dose equivalents of 0.5 mSv and 5 mSv from neutrons and photons, respectively, were obtained per treatment Gray.