Validation of a Monte Carlo-based dose calculation engine including the 1.5 T magnetic field for independent dose-check in MRgRT.

Purpose: Adaptive MRgRT by 1.5 T MR-linac requires independent verification of the plan-of-the-day by the primary TPS (Monaco) (M). Here we validated a Monte Carlo-based dose-check including the magnetostatic field, SciMoCa (S).

Analysis of tumour dose-response data from animal experiments via two TCP models accounting for tumor hypoxia and resensitization.

To treat animal dose-response data exhibiting inverse dose-response behavior with two tumor control probability (TCP) models accounting for tumor hypoxia and re-oxygenation leading to resensitization of the tumor. One of the tested TCP models uses a modified linear-quadratic (LQ) model of cell survival where both α and β radiosensitivities increase in time during the treatment due to re-oxygenation of the hypoxic tumor sub-population. The other TCP model deals with two types of hypoxia-chronic and acute-and accounts for tumor re-sensitization via oxygenation of the chronically hypoxic and fluctuating oxygenation of the acutely hypoxic sub-populations.

Automated Planning for Prostate Stereotactic Body Radiation Therapy on the 1.5 T MR-Linac.

Purpose: Adaptive stereotactic body radiation therapy (SBRT) for prostate cancer (PC) by the 1.5 T MR-linac currently requires online planning by an expert user. A fully automated and user-independent solution to adaptive planning (mCycle) of PC-SBRT was compared with user's plans for the 1.

The Impact of Different Timing Schedules on Prostate HDR-Mono-Brachytherapy. A TCP Modeling Investigation.

Background: Mechanistic TCP (tumor control probability) models exist that account for possible re-sensitization of an initially hypoxic tumor during treatment. This phenomenon potentially explains the better outcome of a 28-day vs 14-day treatment schedule of HDR (high dose rate) brachytherapy of low- to intermediate-risk prostate cancer as recently reported.

Methods: A TCP model accounting for tumor re-sensitization developed earlier is used to analyze the reported clinical data.

Theoretical investigation of the impact of different timing schemes in hypofractionated radiotherapy.

Purpose: This study compares the effectiveness of three fractionation schemes of equal fraction size, comprising five fractions of SBRT over 5 days, 10 days, or 15 days, respectively.

Method: This comparative study is based on two tumor-control-probability (TCP) models that take into account tumor cell re-sensitization and repopulation during treatment; the Zaider-Minerbo-Stavreva (ZMS) and the Ruggieri-Nahum (RN) models. The ZMS model is further modified to include also re-sensitization according to the β mechanism of the linear-quadratic (LQ) model of cell killing.

Analysis of a cohort of prostate patients treated with HDR mono-brachytherapy.

The aim of this study is to perform volumetric and basic radiobiological analyses using the database on prostate patients treated by HDR brachytherapy in our institution during the period 2011-2016. Real-time ultrasound based technique was used, with Oncentra Prostate planning software. The whole period was divided into two sub-periods, according to the 100% dose per fraction, which was 10.

Adaptive SBRT by 1.5 T MR-linac for prostate cancer: On the accuracy of dose delivery in view of the prolonged session time.

Purpose: Adaptive Stereotactic Body Radiotherapy (SBRT) of prostate cancer (PC) by online 1.5 T MRi-guidance prolongs session-time, due to contouring and planning tasks, thus increasing the risk of prostate motion. Hence, the interest to verify the adequacy of the delivered dose.

Modelling the effect of spread in radiosensitivity parameters and repopulation rate on the probability of tumour control.

Purpose: To investigate the impact of a variable inter-individual spread in the tumour cell radiosensitivity and repopulation rate on the tumour control probability (TCP).

Methods: The radiosensitivity parameters and the repopulation rate are presumed to be log-normally distributed among the population. Corresponding distributions of TCP across the population are built using a Monte-Carlo simulation algorithm.

Investigation of the effect of natural tumor cell death on radiotherapy outcomes.

The aim of the work is to investigate the impact of radiation-independent (natural or spontaneous) tumor cell death on tumor control probability (TCP) during and following fractionated external-beam radiotherapy employing both analytical and numerical methods. The analytical method solves a TCP model accounting for tumor repopulation and non-radiation tumor cell death during fractionated external-beam radiotherapy. The numerical method is based on a Monte Carlo simulation of the processes of radiation-induced cell kill, as well as cell division and natural cell death randomly taking place in the time interval between fractions.

Oral Hygiene Index in Early Childhood Caries, Before and After Topical Fluoride Treatment.

Background: Circular caries occurs in the earliest age of the children (1 - 1.5 year), immediately after the eruption of the deciduous teeth. During this period, children are too young to be able to properly implement oral hygiene.

Optimal dose and fraction number in SBRT of lung tumours: A radiobiological analysis.

The efficacy of Stereotactic Body Radiation Therapy (SBRT) in early-stage non-small cell lung cancer for severely hypofractionated schedules is clinically proven. Tumour control probability (TCP) modelling might further optimize prescription dose and number of treatment fractions (n). To this end, we will discuss the following controversial questions.

Technical Note: Correction for intra-chamber dose gradients in reference dosimetry of flattening-filter-free MV photon beams.

Purpose: To estimate and correct for the volume averaging effect which results from the intra-chamber dose gradients when a Farmer ionization chamber (IC) is used for reference dosimetry in flattening-filter-free (FFF) MV photon beams.

Methods: An intra-chamber dose gradients correction factor (kicdg) to the charge reading of a Farmer IC is estimated by comparison to a small volume IC (∼0.1 cm(3)), in the FFF beams of a TrueBeam™ (Varian, Inc.

Influence of the Ethnic Affiliation, Level of Education and Place of Living on Oral Health at Geriatric Population with Total and Partial Dentures in Republic of Macedonia.

Introduction: Health is the main component of the quality of life, while oral health is component of the general health. The socio-demographic characteristics are one of the important factors for perception of the oral health and the quality of life. The main purpose of this study was to perform an evaluation of the quality of life of geriatric patients (older than 65) with built-in oral prosthetic dentures depending on the ethnic affiliation, level of education and place of living, as socio-demographic characteristics.

Applying radiobiological plan ranking methodology to VMAT prostate SBRT.

The impact of a rectal spacer and an increased near maximum target dose in VMAT prostate SBRT is studied. For a group of 11 patients (35Gy-in-five-fractions VMAT prostate SBRT) a set of 4 plans were generated, namely two VMAT plans, with D2%⩽37.5Gy (Hom) and with D2%⩽40.

Volumetric-modulated arc stereotactic body radiotherapy for prostate cancer: dosimetric impact of an increased near-maximum target dose and of a rectal spacer.

Objective: In volumetric-modulated arc therapy (VMAT) prostate stereotactic body radiotherapy (SBRT), dose coverage of the planning target volume (PTV) becomes challenging when the sparing of rectum, bladder and urethra is strictly pursued. Our current 35-Gy-in-five-fraction plans only assure 33.2 Gy to ≥95% PTV ([Formula: see text] ≥ 95%).

On differences in radiosensitivity estimation: TCP experiments versus survival curves. A theoretical study.

We have compared two methods of estimating the cellular radiosensitivity of a heterogeneous tumour, namely, via cell-survival and via tumour control probability (TCP) pseudo-experiments. It is assumed that there exists intra-tumour variability in radiosensitivity and that the tumour consists predominantly of radiosensitive cells and a small number of radio-resistant cells.Using a multi-component, linear-quadratic (LQ) model of cell kill, a pseudo-experimental cell-survival versus dose curve is derived.

Computed 88% TCP dose for SBRT of NSCLC from tumour hypoxia modelling.

In small NSCLC, 88% local control at three years from SBRT was reported both for schedule (20-22 Gy ×3) (Fakiris et al 2009 Int. J. Radiat.

Applying a hypoxia-incorporating TCP model to experimental data on rat sarcoma.

Purpose: To verify whether a tumor control probability (TCP) model which mechanistically incorporates acute and chronic hypoxia is able to describe animal in vivo dose-response data, exhibiting tumor reoxygenation.

Methods And Materials: The investigated TCP model accounts for tumor repopulation, reoxygenation of chronic hypoxia, and fluctuating oxygenation of acute hypoxia. Using the maximum likelihood method, the model is fitted to Fischer-Moulder data on Wag/Rij rats, inoculated with rat rhabdomyosarcoma BA1112, and irradiated in vivo using different fractionation schemes.

Analytical investigation of the possibility of parameter invariant TCP-based radiation therapy plan ranking.

Purpose: To analytically investigate the possibility of a parameter invariant ranking of radiotherapy (RT) plans based on comparing the tumor control probabilities (TCPs) produced by the competing plans for different values of the radiobiological model parameters determining the radiation response.

Method: Individual TCP models based on the Single hit model of cell kill and on the linear-quadratic (LQ) model of cell damage, with and without repopulation, are considered. The tumor dose distributions in case of heterogeneous dose irradiation are described by a Gaussian distribution function on the basis of which a TCP expression is derived depending only on the mean dose to the tumor and its standard deviation and the TCP model parameters.

Population TCP estimators in case of heterogeneous irradiation: a new discussion of an old problem.

Purpose: To investigate the capacity of two phenomenological expressions to describe the population tumor response in case of a heterogeneous irradiation of the tumor. The generalization of the individual tumor control probability (TCP) models to include the case of a heterogeneous irradiation is a trivial problem. However, an analytical solution that results in a closed form population TCP formula for the heterogeneous case is, unfortunately, a very complex mathematical problem.

Probability dynamics of a repopulating tumor in case of fractionated external radiotherapy.

In this work two analytical methods are developed for computing the probability distribution of the number of surviving cells of a repopulating tumor during a fractionated external radio-treatment. Both methods are developed for the case of pure birth processes. They both allow the description of the tumor dynamics in case of cell radiosensitivity changing in time and for treatment schedules with variable dose per fraction and variable time intervals between fractions.

Confidence limits of the probability of success in animal experiments and clinical studies: a Bayesian approach.

Purpose: To determine from the number of trials, n, and the number of observed successes, k the most probable value, the variance and the confidence limits of the probability of success, p, in animal experiments and clinical studies subject to binomial statistics.

Method: In such experiments the probability of success is an unknown parameter. The Bayesian approach to the problem is advocated, based on constructed distribution of the probability of success.

A theoretical approach to the problem of dose-volume constraint estimation and their impact on the dose-volume histogram selection.

This paper outlines a theoretical approach to the problem of estimating and choosing dose-volume constraints. Following this approach, a method of choosing dose-volume constraints based on biological criteria is proposed. This method is called "reverse normal tissue complication probability (NTCP) mapping into dose-volume space" and may be used as a general guidance to the problem of dose-volume constraint estimation.

Reverse mapping of normal tissue complication probabilities onto dose volume histogram space: the problem of randomness of the dose volume histogram sampling.

A very important issue in contemporary inverse treatment radiotherapy planning is the specification of proper dose-volume constraints limiting the treatment planning algorithm from delivering high doses to the normal tissue surrounding the tumor. Recently we have proposed a method called reverse mapping of normal tissue complication probabilities (NTCP) onto dose-volume histogram (DVH) space, which allows the calculation of appropriate biologically based dose-volume constraints to be used in the inverse treatment planning. The method of reverse mapping requires random sampling from the functional space of all monotonically decreasing functions in the unit square.

Limitations of a TCP model incorporating population heterogeneity.

The variation between individuals in their dose-response characteristics complicates attempts to extract estimates of radiobiological parameters (e.g. alpha, beta, etc) from fits to clinical dose-response data.