Interlaced proton grid therapy – Linear energy transfer and relative biological effectiveness distributions

PurposeInterlaced beams have previously been proposed for delivering proton grid therapy. This study aims to assess dose-averaged LET (LET_d) and RBE-weighted dose (D_RBE) distributions of such beam geometries, and compare them with conventional intensity modulated proton therapy (IMPT).MethodsIMPT plans and four different interlaced proton grid therapy plans were generated for five patient cases (esophagus, lung, liver, prostate, anus). The constant RBE = 1.1 was assumed for optimization. The LET_d was subsequently Monte Carlo calculated for each plan and used as input for two LET-dependent variable RBE models. The fulfilment of clinical goals, along with DVH and spatial distribution evaluations, were then assessed and compared.ResultsAll plans fulfilled the clinical target goals assuming RBE = 1.1. The target coverage was slightly compromised for some grid plans when assuming the variable RBE models. All IMPT plans, and 18 of 20 grid plans, fulfilled all clinical goals for the organs at risk when assuming RBE = 1.1, whereas most plans failed at least one goal when assuming the variable RBE models. Compared with the IMPT plans, the grid plans demonstrated substantially different LET_d distributions due to the fundamentally different beam geometries. However, D_RBE distributions in the target were similar.ConclusionsDespite the unconventional beam geometries of interlaced proton grid plans, with resulting alternating dose and LET_d patterns, the fulfillment of realistic clinical goals seems to be comparable to regular IMPT plans, both assuming RBE = 1.1 and variable RBE models. In addition, the alternating grid patterns do not seem to give rise to unexpected D_RBE hot-spots.     

RBE variation in prostate carcinoma cells in active scanning proton beams: In-vitro measurements in comparison with phenomenological models

PurposeIn-vitro radiobiological studies are essential for modelling the relative biological effectiveness (RBE) in proton therapy. The purpose of this study was to experimentally determine the RBE values in proton beams along the beam path for human prostate carcinoma cells (Du-145). RBE-dose and RBE-LET_d (dose-averaged linear energy transfer) dependencies were investigated and three phenomenological RBE models, i.e. McNamara, Rørvik and Wilkens were benchmarked for this cell line.MethodsCells were placed at multiple positions along the beam path, employing an in-house developed solid phantom. The experimental setup reflected the clinical prostate treatment scenario in terms of field size, depth, and required proton energies (127.2–180.1 MeV) and the physical doses from 0.5 to 6 Gy were delivered. The reference irradiation was performed with 200 kV X-ray beams. Respective (α/β) values were determined using the linear quadratic model and LET_d was derived from the treatment planning system at the exact location of cells.Results and ConclusionIndependent of the cell survival level, all experimental RBE values were consistently higher in the target than the generic clinical RBE value of 1.1; with the lowest RBE value of 1.28 obtained at the beginning of the SOBP. A systematic RBE decrease with increasing dose was observed for the investigated dose range. The RBE values from all three applied models were considerably smaller than the experimental values. A clear increase of experimental RBE values with LET_d parameter suggests that proton LET must be taken into consideration for this low (α/β) tissue.     

Dosimetric verification of a high dose rate brachytherapy treatment planning system in homogeneous and heterogeneous media

ObjectivesTo verify the dosimetric accuracy of treatment plans in high dose rate (HDR) brachytherapy by using Gafchromic EBT2 film and to demonstrate the adequacy of dose calculations of a commercial treatment planning system (TPS) in a heterogeneous medium.MethodsAbsorbed doses at chosen points in anatomically different tissue equivalent phantoms were measured using Gafchromic EBT2 film. In one case, tandem ovoid brachytherapy was performed in a homogeneous cervix phantom, whereas in the other, organ heterogeneities were introduced in a phantom to replicate the upper thorax for esophageal brachytherapy treatment. A commercially available TPS was used to perform treatment planning in each case and the EBT2 films were irradiated with the HDR Ir-192 brachytherapy source.ResultsFilm measurements in the cervix phantom were found to agree with the TPS calculated values within 3% in the clinically relevant volume. In the thorax phantom, the presence of surrounding heterogeneities was not seen to affect the dose distribution in the volume being treated, whereas, a little dose perturbation was observed at the lung surface. Doses to the spinal cord and to the sternum bone were overestimated and underestimated by 14.6% and 16.5% respectively by the TPS relative to the film measurements. At the trachea wall facing the esophagus, a dose reduction of 10% was noticed in the measurements.ConclusionsThe dose calculation accuracy of the TPS was confirmed in homogeneous medium, whereas, it was proved inadequate to produce correct dosimetric results in conditions of tissue heterogeneity.     

Assessment of out-of-field doses in radiotherapy treatments of paediatric patients using Monte Carlo methods and measurements

PurposeTo assess out-of-field doses in radiotherapy treatments of paediatric patients, using Monte Carlo methods to implement a new model of the linear accelerator validated against measurements and developing a voxelized anthropomorphic paediatric phantom.MethodsCT images of a physical anthropomorphic paediatric phantom were acquired and a dosimetric planning using a TPS was obtained. The CT images were used to perform the voxelization of the physical phantom using the ImageJ software and later implemented in MCNP. In order to validate the Monte Carlo model, dose measurements of the 6 MV beam and Linac with 120 MLC were made in a clinical setting, using ionization chambers and a water phantom. Afterwards TLD measurements in the physical anthropomorphic phantom were performed in order to assess the out-of-field doses in the eyes, thyroid, c-spine, heart and lungs.ResultsThe Monte Carlo model was validated for in-field and out-of-field doses with average relative differences below 3%. The average relative differences between TLD measurements and Monte Carlo is 14,3% whilst the average relative differences between TLD and TPS is 55,8%. Moreover, organs up to 22.5 cm from PTV center show TLD and MCNP6 relative differences and TLD and TPS relative differences up to 21.2% and 92.0%, respectively.ConclusionsOur study provides a novel model that could be used in clinical research, namely in dose evaluation outside the treatment fields. This is particularly relevant, especially in pediatric patients, for studying new radiotherapy treatment techniques, since it can be used to estimate the development of secondary tumours.     

The consideration of biological effectiveness of low energy protons using biophysical modeling of the effects induced by exposure of V79 cells

We have applied Monte Carlo track structure simulations to estimate relative biological effectiveness (RBE) of low-energy protons using biophysical modelling of radiation effects induced by exposure of V79 cells growing in mono-layer. The microscopic energy deposition in cell nucleus and sub-nucleus volumes was investigated in order to understand the reasons of enhanced biological effectiveness near Bragg peak. Theoretical estimations of RBE based on frequency/dose average lineal energy and calculated yields of initial DNA breaks were collated with experimental RBE_M data. It was found: (1) dose average lineal energy for whole cell nucleus as a function of proton energy shows a distinct peak at 550 keV; (2) the peak values for subnucleus volumes are large compared with the whole cell nucleus; (3) the yield of complex DNA breaks correlates with experimental RBE_M data.     

FLUKA simulation of target fragmentation in proton therapy

In proton therapy, secondary fragments are created in nuclear interactions of the beam with the target nuclei. The secondary fragments have low kinetic energies and high atomic numbers as compared to primary protons. Fragments have a high LET and deposit all their energy close to the generation point. For their characteristics, secondary fragments can alter the dose distribution and lead to an increase of RBE for the same delivered physical dose. Moreover, the radiobiological impact of target fragmentation is significant mostly in the region before the Bragg peak, where generally healthy tissues are present, and immediately after Bragg peak. Considering the high biological impact of those particles, especially in the case of healthy tissues or organs at risk, the inclusion of target fragmentation processes in the dose calculation of a treatment planning system can be relevant to improve the treatment accuracy and for this reason it is one of the major tasks of the MoVe IT project.In this study, Monte Carlo simulations were employed to fully characterize the mixed radiation field generated by target fragmentation in proton therapy. The dose averaged LET has been evaluated in case of a Spread Out Bragg Peak (SOBP). Starting from LET distribution, RBE has been evaluated with two different phenomenological models. In order to characterize the mixed radiation field, the production cross section has been evaluated by means of the FLUKA code. The future development of present work is to generate a MC database of fragments fluence to be included in TPS.     

A Monte Carlo study on dose distribution evaluation of Flexisource 192Ir brachytherapy source

Aim

The aim of this study is to evaluate the dose distribution of the Flexisource ¹⁹²Ir source.

Background

Dosimetric evaluation of brachytherapy sources is recommended by task group number 43 (TG. 43) of American Association of Physicists in Medicine (AAPM).

Materials and methods

MCNPX code was used to simulate Flexisource ¹⁹²Ir source. Dose rate constant and radial dose function were obtained for water and soft tissue phantoms and compared with previous data on this source. Furthermore, dose rate along the transverse axis was obtained by simulation of the Flexisource and a point source and the obtained data were compared with those from Flexiplan treatment planning system (TPS).

Results

The values of dose rate constant obtained for water and soft tissue phantoms were equal to 1.108 and 1.106, respectively. The values of the radial dose function are listed in the form of tabulated data. The values of dose rate (cGy/s) obtained are shown in the form of tabulated data and figures. The maximum difference between TPS and Monte Carlo (MC) dose rate values was 11% in a water phantom at 6.0 cm from the source.

Conclusion

Based on dosimetric parameter comparisons with values previously published, the accuracy of our simulation of Flexisource ¹⁹²Ir was verified. The results of dose rate constant and radial dose function in water and soft tissue phantoms were the same for Flexisource and point sources. For Flexisource ¹⁹²Ir source, the results of TPS calculations in a water phantom were in agreement with the simulations within the calculation uncertainties. Furthermore, the results from the TPS calculation for Flexisource and MC calculation for a point source were practically equal within the calculation uncertainties.     

The FLUKA Monte Carlo code coupled with an OER model for biologically weighted dose calculations in proton therapy of hypoxic tumors

IntroductionThe increased radioresistance of hypoxic cells compared to well-oxygenated cells is quantified by the oxygen enhancement ratio (OER). In this study we created a FLUKA Monte Carlo based tool for inclusion of both OER and relative biological effectiveness (RBE) in biologically weighted dose (ROWD) calculations in proton therapy and applied this to explore the impact of hypoxia.MethodsThe RBE-weighted dose was adapted for hypoxia by making RBE model parameters dependent on the OER, in addition to the linear energy transfer (LET). The OER depends on the partial oxygen pressure (pO₂) and LET. To demonstrate model performance, calculations were done with spread-out Bragg peaks (SOBP) in water phantoms with pO₂ ranging from strongly hypoxic to normoxic (0.01–30 mmHg) and with a head and neck cancer proton plan optimized with an RBE of 1.1 and pO₂ estimated voxel-by-voxel using [¹⁸F]-EF5 PET. An RBE of 1.1 and the Rørvik RBE model were used for the ROWD calculations.ResultsThe SOBP in water had decreasing ROWD with decreasing pO₂. In the plans accounting for oxygenation, the median target doses were approximately a factor 1.1 lower than the corresponding plans which did not consider the OER. Hypoxia adapted target ROWDs were considerably more heterogeneous than the RBE_1.1-weighted doses.ConclusionWe realized a Monte Carlo based tool for calculating the ROWD. Read-in of patient pO₂ and estimation of ROWD with flexibility in choice of RBE model was achieved, giving a tool that may be useful in future clinical applications of hypoxia-guided particle therapy.     

Experimental benchmarking of RayStation proton dose calculation algorithms inside and outside the target region in heterogeneous phantom geometries

PurposeThe aim of the presented study was to complement existing literature on benchmarking proton dose by comparing dose calculations with experimental measurements in heterogeneous phantom. Points of interest inside and outside the target were considered to quantify the magnitude of calculation uncertainties in current and previous proton therapy practice that might especially have an impact on the dose in organs at risk (OARs).MethodsThe RayStation treatment planning system (RaySearch Laboratories), offering two dose calculation algorithms for pencil beam scanning in proton therapy, i.e., Pencil Beam (PB) and Monte Carlo (MC), was utilized. Treatment plans for a target located behind the interface of the heterogeneous tissues were generated. Dose measurements within and behind the target were performed in a water phantom with embedded slabs of various tissue equivalent materials and 24 PinPoint ionization chambers (PTW). In total 12 test configurations encompassing two different target depths, oblique beam incidence of 30 degrees and range shifter, were considered.ResultsPB and MC calculated doses agreed equally well with the measurements for all test geometries within the target, including the range shifter (mean dose differences ± 3%). Outside the target, the maximum dose difference of 9% (19%) was observed for MC (PB) for the oblique beam incidence and inserted range shifter.ConclusionThe accuracy of MC dose algorithm was superior compared to the PB algorithm, especially outside the target volumes. MC based dose calculation should therefore be preferred in treatment scenarios with heterogeneities, especially to reduce clinically relevant uncertainties for OARs.     

Monte Carlo GEANT4-based application for in vivo RBE study using small animals at LNS-INFN preclinical hadrontherapy facility

Preclinical studies represent an important step towards a deep understanding of the biological response to ionizing radiations. The effectiveness of proton therapy is higher than photons and, for clinical purposes, a fixed value of 1.1 is used for the relative biological effectiveness (RBE) of protons considered 1.1. Recent in vitro studies have reported that the RBE along the spread-out Bragg peak (SOBP) is not constant and, in particular, the RBE value increases on the distal part of SOBP. The present work has been carried-out in the perspective of a preclinical hadrontherapy facility at LNS-INFN and was focused on the experimental preparation of an in vivo study concerning the RBE variation along the SOBP. The main purpose of this work was to determine, using GEANT4-based Monte Carlo simulations, the best configuration for small animal treatments. The developed GEANT4 application simulates the proton-therapy beam line of LNS-INFN (CATANA facility) and allows to import the DICOM-CT images as targets. The RBE will be evaluated using a deterministic radiation damage like myelopathy as end-point. In fact, the dose at which the $50\%$ of animals will show the myelopathy is supposed to be LET-dependent. In this work, we studied different treatment configurations in order to choose the best two that maximize the LET difference reducing as much as possible the dose released to healthy tissue. The results will be useful to plan hadrontherapy treatments for preclinical in vivo studies and, in particular, for the future in vivo RBE studies.     

An assessment of a 3D EPID-based dosimetry system using conventional two- and three-dimensional detectors for VMAT

PurposeTo provide a 3D dosimetric evaluation of a commercial portal dosimetry system using 2D/3D detectors under ideal conditions using VMAT.MethodsA 2D ion chamber array, radiochromic film and gel dosimeter were utilised to provide a dosimetric evaluation of transit phantom and pre-treatment ‘fluence’ EPID back-projected dose distributions for a standard VMAT plan. In-house 2D and 3D gamma methods compared pass statistics relative to each dosimeter and TPS dose distributions.ResultsFluence mode and transit EPID dose distributions back-projected onto phantom geometry produced 2D gamma pass rates in excess of 97% relative to other tested detectors and exported TPS dose planes when a 3%, 3 mm global gamma criterion was applied. Use of a gel dosimeter within a glass vial allowed comparison of measured 3D dose distributions versus EPID 3D dose and TPS calculated distributions. 3D gamma comparisons between modalities at 3%, 3 mm gave pass rates in excess of 92%. Use of fluence mode was indicative of transit results under ideal conditions with slightly reduced dose definition.Conclusions3D EPID back projected dose distributions were validated against detectors in both 2D and 3D. Cross validation of transit dose delivered to a patient is limited due to reasons of practicality and the tests presented are recommended as a guideline for 3D EPID dosimetry commissioning; allowing direct comparison between detector, TPS, fluence and transit modes. The results indicate achievable gamma scores for a complex VMAT plan in a homogenous phantom geometry and contributes to growing experience of 3D EPID dosimetry.     

MOSFET dose measurements for proton SOBP beam

PurposeThe aim of this work was to develop a computational scheme for the correction of the LET dependence on the MOSFET response in water phantom dose measurements for a spread-out Bragg peak (SOBP) proton beam.MethodsThe LET dependence of MOSFET was attributed to the stopping power ratio of SiO₂ to H₂O and to the fractional hole yield in the SiO₂ layer. Using literature values for the stopping powers of the continuous slowing down approximation and measured fractional hole yields vs. electric field and LET, formulas were derived for the computation of a dose-weighted correction factor of a SOBP beam.ResultsDose-weighted correction factors were computed for a clinical 190-MeV proton SOBP beam in a high-density polyethylene phantom. By applying correction factors to the SOBP beam, which consisted of weighted monoenergetic Bragg peaks, the MOSFET outputs were predicted and agreed well with the measured MOSFET responses.ConclusionBy applying LET dependent correction factors to MOSFET data, quality assurance of dose verification based on MOSFET measurements becomes possible for proton therapy.     

A comparison of electronic portal dosimetry verification methods for use in stereotactic radiotherapy

Three methods of transit dosimetry using Electronic Portal Imaging Devices (EPIDs) were investigated for use in routine in-vivo dosimetry for cranial stereotactic radiosurgery and radiotherapy. The approaches examined were (a) A full Monte Carlo (MC) simulation of radiation transport through the linear accelerator and patient; (b) Calculation of the expected fluence by a treatment planning system (TPS); (c) Point doses calculated along the central axis compared to doses calculated using parameters acquired using the EPID. A dosimetric comparison of each of the three methods predicted doses at the imager plane to within ±5% and a gamma comparison for the MC and TPS based approaches showed good agreement for a range of dose and distance to agreement criteria. The MC technique was most time consuming, followed by the TPS calculation with the point dose calculation significantly quicker than the other methods.     

Ultrasound-guided intraoperative electron beam radiation therapy: A phantom study

PurposeTo develop the method for ultrasound (US)-guided intra-operative electron beam radiation therapy (IOERT).MethodsWe first established the simulation, planning, and delivery methods for US-guided IOERT and constructed appropriate hardware (the multi-function applicator, accessories, and US phantom). We tested our US-guided IOERT method using this hardware and the Monte Carlo simulation IOERT treatment planning system (TPS). The IOERT TPS used a compensator to build the conformal dose distribution. Then, we used the TPS to evaluate the effect of setup uncertainty on target coverage by introducing phantom setup error ranging from 0 mm to 10 mm to the plans with and without the compensator.ResultsThe simulation, planning, and delivery methods for US-guided IOERT were introduced and validated on a phantom. A complete technique for US-guided IOERT was established. Target coverage decreased by about 12% and 29% as the phantom setup error increased to 5 mm and 10 mm for the plans with compensator, respectively. Without compensator, the corresponding target coverage decreases were 2% and 13%, respectively.ConclusionIn our study, we developed the multi-function applicator, US Phantom, and TPS for IOERT. The procedures included not only dose distribution planning, but also intraoperative US imaging, which provided the information necessary during surgery to improve IOERT quality assurance. Target coverage was more sensitive to setup errors with compensator compared to no compensator. Further studies are needed to validate the clinical efficacy of this US-guided IOERT method.     

Dose calculation accuracy in proximity of a pacemaker: A multicenter study with threecommercial treatment planning systems

This study compares Treatment Planning System (TPS) out of field dose calculation on a pacemaker (PMK) during external beam radiotherapy treatment. We consider four TPSs (Elekta-Monaco, Oncentra- Masterplan and two Philips-Pinnacle3) commissioned for two linacs (Elekta Sinergy and Varian Clinac) delivering two test beams (a highly modulated one and a square field) and two clinical breast plans. To calculate and measure dose to a PMK we built a Real Water3 phantom with a PMK embedded in it. Measures are performed with thermo-luminescent dosimeters and Mosfet dosimeters. We evaluate differences between TPS calculated values for the dose to the PMK (both point dose and dose-volume histogram parameters) when the PMK is positioned in the first 10 cm outside the radiation fields. TPS calculation accuracy is evaluated comparing such values with measures. Differences in TPS calculations are on average 3.5 cGy Gy^-1 for the modulated beam, and always lower than 2 cGy Gy^-1 for the square beam. TPS dose calculation depends mostly on the TPS algorithm and model rather than the linac commissioned. TPSs considered show different degrees of calculation accuracy. In the first 4 cm to the field edge three out of four TPSs are in good agreement with measurements in the square beam, but only one keeps the agreement in the modulated beam: the others show over and underestimations up to +20% −40%. The same accuracy is found considering a homogeneous phantom. Our results confirm what reported in previous studies and highlight the impact of TPS commissioning.     

Evaluation of the effects of implementing a diode transmission device into the clinical workflow

PurposeThis work investigated effects of implementing the Delta⁴ Discover diode transmission detector into the clinical workflow.MethodsPDD and profile scans were completed with and without the Discover for a number of photon beam energies. Transmission factors were determined for all beam energies and included in Eclipse TPS to account for the attenuation of the Discover. A variety of IMRT plans were delivered to a Delta⁴ Phantom+ with and without the Discover to evaluate the Discover’s effects on IMRT QA. An imaging QA phantom was used to assess the detector’s effects on MV image quality. OSLDs placed on the Phantom+ were used to determine the detector’s effects on superficial dose.ResultsThe largest effect on PDDs after d_max was 0.5%. The largest change in beam profile symmetry and flatness was 0.2% and 0.1%, respectively. An average difference in gamma passing rates (2%/2 mm) of 0.2% was observed between plans that did not include the Discover in the measurement and calculation to plans that did include the Discover in the measurement and calculation. The Discover did not significantly change the MV image quality, and the largest observed increase in the relative superficial dose when the Discover was present was 1%.ConclusionsThe effects the Discover has on the linac beam were found to be minimal. The device can be implemented into the clinic without the need to alter the TPS beam modeling, other than accounting for the device’s attenuation. However, a careful workflow review to implement the Discover should be completed.     

Monte Carlo dose verification of VMAT treatment plans using Elekta Agility 160-leaf MLC

In this study, we verified volumetric modulated arc therapy (VMAT) plans in an Elekta Synergy system with an integrated Agility 160-leaf multileaf collimator (MLC) by comparing them with Monte Carlo (MC)-calculated dose distributions using the AAPM TG-119 structure sets. The head configuration of the linear accelerator with the integrated MLC was simulated with the EGSnrc/BEAMnrc code. Firstly, the dosimetric properties of the MLC were evaluated with the MC technique and film measurements. Next, VMAT plans were created with the Pinnacle³ treatment planning system (TPS) for four regions in the AAPM TG-119 structures. They were then verified by comparing them with MC-calculated dose distributions using dose volume histograms (DVHs) and three-dimensional (3D) gamma analysis. The MC simulations for the Agility MLC dosimetric properties were in acceptable agreement with measurements. TPS-VMAT plans using TG-119 structure sets agreed with MC dose distributions within 2% in the comparison of D₉₅ in planning target volumes (PTVs) evaluated from DVHs. In contrast, higher dose regions such as D₂₀, D₁₀, and D₅ in PTVs for TPS tended to be smaller than MC values. This tendency was particularly noticeable for mock head and neck with complicated structures. In 3D gamma analysis, the passing rates with 3%/3mm criteria in PTVs were ≥99%, except for mock head and neck (89.5%). All passing rates for organs at risk (OARs) were in acceptable agreement of >96%. It is useful to verify dose distributions of PTVs and OARs in TPS-VMAT plans by using MC dose calculations and 3D gamma analysis.     

Accuracy of dose calculation algorithms for static and rotational IMRT of lung cancer: A phantom study

PurposeTo evaluate the dosimetric accuracy of Pencil beam (PB), Anisotropic Analytical Algorithm (AAA) and Collapsed Cone Convolution Superposition (CCCS) in thoracic tumours for various IMRT techniques.MethodsStep-and-shoot Linac IMRT (IMRT), arc volumetric RapidArc (RA) and Helical Tomotherapy (HT) lung treatments for different clinical situations (mediastinum tumour, single metastasis and multiple metastases) were simulated and calculated with PB/AAA, AAA, CCCS, respectively. Delivery quality assurance plans were first verified in homogeneous media (Cheese phantom and ArcCHECK); then several low-density inhomogeneous phantoms were used: the Multiplug ArcCHECK, the commercial ArcCHECK slightly modified with a low density lung–shape insert and a custom-made slab heterogeneous phantom simulating the thorax region. Absolute doses and planar dose maps were checked to assess the agreement between measured and calculated dose distributions.ResultsIn total, data referred to 195 point dose measurements and 189 planar measurements were considered. Average point absolute deviations <3% were found for all the delivery techniques/dose algorithms. In small targets completely embedded in very low density media, deviations up to 7–10% and 4–5% were found for PB and AAA/CCCS respectively. Excellent results were found for planar measurements in ArcCHECK configurations, where ≥95% of points satisfy the 3%/3 mm acceptance criteria for all the algorithms.ConclusionsA satisfactory agreement (<2%) between planned and measured doses was generally found for CCCS and AAA, excepting the very critical situation of a small tumour completely embedded in air. A significant dose overestimation (from few to 5–7%) was confirmed for PB in complex inhomogeneous arrangements.     

Calculation and measurement of doses in the surface layers of a phantom when using Tomotherapy

BackgroundThe calculation and measurement on the surface of the skin presents a significant dosimetric problem because of numerous factors which have an influence on the dose distribution in this region.AimThe overall aim of this study was to check the agreement between doses measured with thermoluminescent detectors (TLD) during tomotherapy photon beam irradiation of the skin area of a solid water cylindrical phantom with doses calculated with Hi-Art treatment planning system (TPS).Material and MethodThe measurements of the dose were made with the use of a solid water cylindrical phantom - Cheese Phantom. Two bolus phantoms were used: 5 mm and 10 mm Six different planning treatments were generated. The doses were measured using TL detectors.ResultsIn the case of a tumor located near the surface of the skin, the mean dose for 0.5 cm bolus was - 1.94 Gy, and for 1 cm bolus - 2.03 Gy. For the tumor located inside the phantom and organ at risk on the same side that TL detectors, for a 0.5 cm bolus, mean dose was 0.658 Gy, and for a 1 cm bolus, 0.62 Gy.ConclusionThe analysis of results showed that the relative percentage difference between measured and planned dose in the field of irradiation was less than 10%, while the largest differences were on the board of the field of radiation and outside of the field of irradiation, where the dose was 0.08 Gy to 1 Gy.     

Distribution of the relative biological effectiveness of fast neutrons according to the depth of the irradiated tissue

A study was made of the dependence of relative biological effectiveness (RBE) and isoeffective dose of fast neutrons (produced by U-120 cyclotron) upon the depth of the exposed tissue. It was shown that the isoeffective dose and RBE vary significantly with the depth of the tissue-equivalent medium. The investigations were carried out with the purpose of improving the radiobiological and dosimetric techniques for the treatment of malignant tumors using a neutron beam from U-120 cyclotron.