Simple variance reduction in Monte Carlo calculations of specific absorbed fractions: Russian roulette and splitting at the source organ.

Purpose: To investigate the capabilities of several variance reduction techniques in the calculation of specific absorbed fractions in cases where the source and the target organs are far away and/or the target organs have a small volume.

Methods: The specific absorbed fractions have been calculated by using the Monte Carlo code PENELOPE and by assuming the thyroid gland as the source organ and the testicles, the urinary bladder, the uterus, and the ovaries as the target ones. A mathematical anthropomorphic phantom, similar to the MIRD-type phantoms, has been considered.

Monte Carlo calculation of charge collection efficiencies in ionization chambers.

Collection efficiency is an important quantity in dosimetry with ionization chambers. It can be calculated by solving a hyperbolic system of partial differential equations. This system can be solved only in few, simple, idealized geometries, but for more realistic designs an analytical resolution is no longer possible.

Response of the ArcCHECK® device at 6 MV and 15 MV for VMAT and IMRT quality control.

Purpose: To study the response of the ArcCHECK® device as VMAT and IMRT verification system.

Methods: Various tests analyzing the linearity, the repeatability and the angular dependence of the device response, its dependence with the pulse repetition rate and the leakage losses were performed. The long-term response in dose measurements and the uniformity of the detectors conforming the system were controlled using a statistical process control program.

An on-lattice agent-based Monte Carlo model simulating the growth kinetics of multicellular tumor spheroids.

Purpose: To develop an on-lattice agent-based model describing the growth of multicellular tumor spheroids using simple Monte Carlo tools.

Methods: Cells are situated on the vertices of a cubic grid. Different cell states (proliferative, hypoxic or dead) and cell evolution rules, driven by 10 parameters, and the effects of the culture medium are included.

A radiobiological study of the schemes with a low number of fractions in high-dose-rate brachytherapy as monotherapy for prostate cancer.

Purpose: Schemes with high doses per fraction and small number of fractions are commonly used in high-dose-rate brachytherapy (HDR-BT) for prostate cancer. Our aim was to analyze the differences between published clinical results and the predictions of radiobiological models for absorbed dose required in a single fraction monotherapy HDR-BT.

Material And Methods: Published HDR-BT clinical results for low- and intermediate-risk patients with prostate cancer were revised.

Evaluation of the overdiagnosis in breast screening programmes using a Monte Carlo simulation tool: a study of the influence of the parameters defining the programme configuration.

Objectives: To build up and test a Monte Carlo simulation procedure for the investigation of overdiagnosis in breast screening programmes (BSPs).

Design: A Monte Carlo tool previously developed has been adapted for obtaining the quantities of interest in order to determine the overdiagnosis: the annual and cumulative number of cancers detected by screening, plus interval cancers, for a population following the BSP, and detected clinically for the same population in the absence of screening. Overdiagnosis is obtained by comparing these results in a direct way.

Radiobiological parameters for breast cancer: a Monte Carlo analysis of START trial published results.

Objective:: Trial results are usually given in terms of end point confidence intervals, the data concerning the participating patients being not available. Sometimes, it would be useful or necessary to obtain derived quantities, such as dose-response relationships, from the known information. In this work, we describe a methodology that allows to do that and illustrate it by analyzing the UK standardization of breast radiotherapy (START) trials.

Impact of cardiosynchronous brain pulsations on Monte Carlo calculated doses for synchrotron micro- and minibeam radiation therapy.

Purpose: The purpose of this study was to assess the effects of brain movements induced by heartbeat on dose distributions in synchrotron micro- and minibeam radiation therapy and to develop a model to help guide decisions and planning for future clinical trials.

Methods: The Monte Carlo code PENELOPE was used to simulate the irradiation of a human head phantom with a variety of micro- and minibeam arrays, with beams narrower than 100 μm and above 500 μm, respectively, and with radiation fields of 1 × 2 cm and 2 × 2 cm. The dose in the phantom due to these beams was calculated by superposing the dose profiles obtained for a single beam of 1 μm × 2 cm.

Air density dependence of the soft X-ray PTW 34013 ionization chamber.

Purpose: We studied the dependence on air density of the response of the PTW 34013 ionization chamber, recently upgraded for dosimetry control of low energy X-ray beams.

Methods: Measurements were performed by changing the pressure conditions inside a pressure chamber. The behavior of the measurements against the air density inside this chamber was analyzed.

Monte Carlo dosimetric characterization of the Flexisource Co-60 high-dose-rate brachytherapy source using PENELOPE.

Purpose: Co sources have been commercialized as an alternative to Ir sources for high-dose-rate (HDR) brachytherapy. One of them is the Flexisource Co-60 HDR source manufactured by Elekta. The only available dosimetric characterization of this source is that of Vijande et al.

Air density dependence of the response of the PTW SourceCheck 4pi ionization chamber for I brachytherapy seeds.

Purpose: To analyze the air density dependence of the response of the new SourceCheck 4pi ionization chamber, manufactured by PTW.

Methods: The air density dependence of three different SourceCheck 4pi chambers was studied by measuring I sources. Measurements were taken by varying the pressure from 746.

Computation of the electron beam quality [Formula: see text] factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE.

The quality correction factor [Formula: see text] for electron beams was calculated for three thimble ionization chambers, namely, NE2571, NE2571A and NE2581A. The Monte Carlo code PENELOPE was used to estimate the overall correction factor f of these chambers for electron beams with nominal energies ranging between 6 and 22MeV, corresponding to a Varian Clinac 2100 C/D. A Co beam was used as reference quality Q.

A Monte Carlo analysis of breast screening randomized trials.

Purpose: To analyze breast screening randomized trials with a Monte Carlo simulation tool.

Methods: A simulation tool previously developed to simulate breast screening programmes was adapted for that purpose. The history of women participating in the trials was simulated, including a model for survival after local treatment of invasive cancers.

Monte Carlo systems used for treatment planning and dose verification.

General-purpose radiation transport Monte Carlo codes have been used for estimation of the absorbed dose distribution in external photon and electron beam radiotherapy patients since several decades. Results obtained with these codes are usually more accurate than those provided by treatment planning systems based on non-stochastic methods. Traditionally, absorbed dose computations based on general-purpose Monte Carlo codes have been used only for research, owing to the difficulties associated with setting up a simulation and the long computation time required.

Photon beam quality correction factors for the NE2571A and NE2581A thimble ionization chambers using PENELOPE.

The beam quality correction factor kQ,Q0 and the perturbation factor pQ for photon beams were calculated for the NE2571A and NE2581A ionization chambers, using the Monte Carlo simulation code PENELOPE. Results are compared to those quoted for the NE2571 and NE2581 chambers in previous works. Both kQ,Q0 and pQ obtained for NE2571A and NE2581A chambers agree with those of their predecessors NE2571 and NE2581 ones.

Characterization of the PTW SourceCheck ionization chamber with the Valencia lodgment for (125)I seed verification.

In brachytherapy using (125)I seed implants, a verification of the air kerma strength of the sources used is required. Typically, between 40 and 100 seeds are implanted. Checking all of them is unaffordable, especially when seeds are disposed in sterile cartridges.

Monte Carlo calculation of specific absorbed fractions: variance reduction techniques.

The purpose of the present work is to calculate specific absorbed fractions using variance reduction techniques and assess the effectiveness of these techniques in improving the efficiency (i.e. reducing the statistical uncertainties) of simulation results in cases where the distance between the source and the target organs is large and/or the target organ is small.

Electron beam quality k(Q,Q0) factors for various ionization chambers: a Monte Carlo investigation with PENELOPE.

In this work we calculate the beam quality correction factor k(Q,Q0) for various plane-parallel ionization chambers. A set of Monte Carlo calculations using the code PENELOPE/PENEASY have been carried out to calculate the overall correction factor f(c,Q) for eight electron beams corresponding to a Varian Clinac 2100 C/D, with nominal energies ranging between 6 MeV and 22 MeV, for a (60)Co beam, that has been used as the reference quality Q0 and also for eight monoenergetic electron beams reproducing the quality index R50 of the Clinac beams. Two field sizes, 10 × 10 cm(2) and 20 × 20 cm(2) have been considered.

Dosimetric characterization of the (60)Co BEBIG Co0.A86 high dose rate brachytherapy source using PENELOPE.

(60)Co sources are being used as an alternative to (192)Ir sources in high dose rate brachytherapy treatments. In a recent document from AAPM and ESTRO, a consensus dataset for the (60)Co BEBIG (model Co0.A86) high dose rate source was prepared by using results taken from different publications due to discrepancies observed among them.

A method to relate StarTrack(®) measurements to R50 variations in clinical linacs.

The relation between the data recorded with any device for the daily checking of the behavior of a clinical linac and the reference magnitudes to be monitored may be unknown. An experimental method relating the energy stability of the electron beam measured with StarTrack(®) to the R50 beam quality index is proposed. The bending magnet current is varied producing a change in the exit energy window and, therefore, a modification of the R50 value.

On the shape of the Task Group 43 anisotropy factor for linear brachytherapy sources at short distances.

Purpose: To investigate the peak shown by the American Association of Physicists in Medicine (AAPM) Task Group 43 1D anisotropy function at short distances from the source.

Methods And Materials: The 1D anisotropy function of an ideal nonencapsulated photon linear source is calculated. A simple analytical model developed to evaluate the dose because of photon point-like sources has been applied.

Quality indexes based on water measurements for low and medium energy x-ray beams: a theoretical study with PENELOPE.

Purpose: To study the use of quality indexes based on ratios of absorbed doses in water at two different depths to characterize x-ray beams of low and medium energies.

Methods: A total of 55 x-ray beam spectra were generated with the codes XCOMP5R and SPEKCALC and used as input of a series of Monte Carlo simulations performed with PENELOPE, in which the percentage depth doses in water and the kQ,Q0 factors, defined in the TRS-398 protocol, were determined for each beam. Some of these calculations were performed by simulating the ionization chamber PTW 30010.

Monte Carlo study for designing a dedicated "D"-shaped collimator used in the external beam radiotherapy of retinoblastoma patients.

Purpose: Retinoblastoma is the most common intraocular malignancy in the early childhood. Patients treated with external beam radiotherapy respond very well to the treatment. However, owing to the genotype of children suffering hereditary retinoblastoma, the risk of secondary radio-induced malignancies is high.

Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources.

Purpose: Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction.

A Monte Carlo tool to study the mortality reduction due to breast screening programs.

Purpose: To develop a Monte Carlo tool that permits to study the reduction in breast cancer mortality rate due to breast screening programs.

Methods: Simulations implement woman histories undergoing a screening program, include a model of survival after local treatment of invasive cancers and use distributions of time gained due to screening detection against symptomatic detection and overall sensitivity of the screening obtained previously. Mortalities for the whole woman population and for those women with ages within the range considered in the program have been calculated.