Energy and dose dependence of GafChromic EBT3-V3 film across a wide energy range

AimTo determine the energy and dose dependence of GafChromic EBT3-V3 film over an energy range 0.2 mm Al HVL to 6 MV.BackgroundThe decay scheme of a brachytherapy source may be complex and the spectrum of energy can be wide. LiF TLDs are the golden standard recommended for dosimetric measures in brachytherapy, for their energy independence, but TLDs could be not available in some centres. An alternative way to perform dose measurements is to use GafChromic films, but they show energy dependence.Methods and materialsFilms have been irradiated at increasing dose with three different beams: 6 MV beam, TPR20, 10 = (0.684 ± 0.01), HVL = (2.00 ± 0.01)mmAl and HVL = (0.20 ± 0.01)mmAl. Calibration curves were generated using the same dose range (0cGy to 850cGy) for the three energies. Using the 6 MV calibration curve as reference, the film response in terms of net optical density (OD) was evaluated.ResultsThe difference in the calibration curve obtained by irradiating the film with 6 MV and 2 mm Al HVL energy beams is less than 3 %, within the calibration uncertainty, in the dose range 500-850cGy. The OD of EBT3-V3 film is significantly lower at 0.2 mmAl HVL compared to 6 MV, showing differences up to 25 %.ConclusionWithin the range 6 MV-2 mm Al HVL and dose higher than 500cGy, GafChromic EBT3-V3 films are energy independent. In this dose range, films can be calibrated in a simple geometry, using a 6 MV Linac beam, and can be used for brachytherapy sources dose measures. The use of EBT3 films can be extended to reference dosimetry in Ir-192 clinical brachytherapy.     

Evaluation of Gafchromic® EBT3 films characteristics in therapy photon,electron and proton beams

PurposeTo evaluate the uncertainties and characteristics of radiochromic film-based dosimetry system using the EBT3 model Gafchromic^® film in therapy photon, electron and proton beams.Material and methodsEBT3 films were read using an EPSON Expression 10000XL/PRO scanner. They were irradiated in five beams, an Elekta SL25 6 MV and 18 MV photon beam, an IBA 100 MeV 5 × 5 cm² proton beam delivered by pencil-beam scanning, a 60 MeV fixed proton beam and an Elekta SL25 6 MeV electron beam. Reference dosimetry was performed using a FC65-G chamber (Elekta beam), a PPC05 (IBA beam) and both Markus 1916 and PPC40 Roos ion-chambers (60 MeV proton beam). Calibration curves of the radiochromic film dosimetry system were acquired and compared within a dose range of 0.4–10 Gy. An uncertainty budget was estimated on films irradiated by Elekta SL25 by measuring intra-film and inter-film reproducibility and uniformity; scanner uniformity and reproducibility; room light and film reading delay influences.ResultsThe global uncertainty on acquired optical densities was within 0.55% and could be reduced to 0.1% by placing films consistently at the center of the scanner. For all beam types, the calibration curves are within uncertainties of measured dose and optical densities. The total uncertainties on calibration curve due to film reading and fitting were within 1.5% for photon and proton beams. For electrons, the uncertainty was within 2% for dose superior to 0.8 Gy.ConclusionsThe low combined uncertainty observed and low beam and energy-dependence make EBT3 suitable for dosimetry in various applications.     

Wax boluses and accuracy of EBT and RTQA radiochromic film detectors in radiotherapy with the JINR Phasotron proton beam

Aim

To present the results obtained using radiochromic films EBT and RTQA 1010P for the reconstruction the dose distributions for targets irradiated by proton beam and modified by wax boluses.

Background

In Medico-Technical Complex at the Joint Institute for Nuclear Research in Dubna implemented technology of wax boluses.

Materials and methods

Wax boluses are easier to make and they give better dose distributions than boluses made from modeling clay previously used at our center. We irradiated two imaginary targets, one shaped as a cylinder and the other one as two cuboids. The evaluated calibration curve was used for calculation of the dose distributions measured by the EBT and RTQA radiochromic film. In both cases, the measured dose distributions were compared to the dose distributions calculated by the treatment planning system (TPS). We also compared dose distributions using three different conformity indices at a 95% isodose.

Results

Better target coverage and better compliance of measurements (semiconductor detectors and radiochromic films) with calculated doses was obtained for cylindrical target than for cuboidal target. The 95% isodose covered well the tumor for both target shapes, while for cuboidal target larger volume around the target received therapeutic dose, due to the complicated target shape. The use wax boluses provided to be effective tool in modifying proton beam to achieve appropriate shape of isodose distribution.

Conclusion

EBT film yielded the best visual matching. Both EBT and RTQA films confirmed good conformity between calculated and measured doses, thus confirming that wax boluses used to modify the proton beam resulted in good dose distributions.     

Dose to the skin in helical tomotherapy: Results of in vivo measurements with radiochromic films

PurposeThe aim of this study is to report results of measurements of dose to the skin in vivo with radiochromic EBT films in treatments with helical tomotherapy.Methods and materialsIn vivo measurements were performed by applying pieces of radiochromic films to the skin or to the inner side of thermoplastic mask before the treatment. The sites of treatment included scalp, brain, head and neck, cranio-spinal axis and lower limbs. Skin dosimetry was performed in a patient who experienced grade 3–4 acute side effects to the skin shortly after the first treatment sessions. For each patient we measured the setup errors using the daily MVCT acquired for image guidance of the treatment. EBT films were read with a flatbed Epson Expression scanner and images were processed with an in-house written routine.ResultsA total of 96 measurements of dose to the skin performed on 14 patients. The mean difference and standard error of the mean difference between measured and TPS-calculated dose was ?9.2% ± 2.6% for all treatments, ?6.6% ± 2.6% for head and neck treatments. These differences were statistically significant at the 0.05 significance level (t-Student test). Planned dose and dose range in the region of measurements were not correlated with dose discrepancy.ConclusionsRadiochromic EBT films are suitable detectors for surface dose measurements in tomotherapy treatments. Results show that TPS overestimates dose to the skin measured with EBT radiochromic films. In vivo skin measurements with EBT films are a useful tool for quality assurance of tomotherapy treatments, as the treatment planning system may not give accurate dose values at the surface.     

Measurement of percentage dose at the surface for a 6 MV photon beam

AimTo evaluate if a radiochromic film (RF) Gafchromic EBT3 is suitable for surface dose measurements of radiotherapy treatments performed with a 6 MV linear accelerator. Two aspects of RF were analyzed, beam energy dependence and surface dose determination.BackgroundThe measurements done at the surface or near the radiation source are done without charged electronic equilibrium and also have contribution of electron contamination. The detectors used for these measurements should not alter the dose to the target. To counteract these dosimetric problems it is proposed to do the measurements with radiochromic films which are thin detectors and have tissue equivalent properties.Materials and MethodsThe measurements were done using a Novalis linear accelerator (LINAC) with nominal energy of 6 MV. To determine the surface dose, the total scatter factors (TSF) of three different field sizes were measured in a water phantom at 5 cm depth. Energy dependence of EBT3 was studied at three different depths, using a solid water phantom. The surface measurements were done with the RF for the same field sizes of the TSF measurements. The value of the percentage depth dose was calculated normalizing the doses measured in the RF with the LINAC output, at 5 cm depth, and the TSF.ResultsThe radiochromic films showed almost energy independence, the differences between the curves are 1.7% and 1.8% for the 1.5 cm and 10 cm depth, respectively. The percentage depth doses values at the surface measured for the 10 cm × 10 cm, 5 cm × 5 cm and 1 cm × 1 cm were 26.1 ± 1.3%, 21.3 ± 2.4% and 20.2 ± 2.6%, respectively.ConclusionsThe RF-EBT3 seems to be a detector suitable for measurements of the dose at the surface. This suggests that RF-EBT3 films might be good candidates as detectors for in vivo dosimetry.     

Calibration of MTT assay in proton beams using radiochromic films

PurposeThis study provides methodology of calibrating as well as controlling the output for an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay irradiated in a low energy proton beam using EBT3-model GAFCHROMIC^TM film, without correcting for quenching effect.MethodsA calibrated Markus ionization chamber was used to measure the depth dose and beam output for 26.5 MeV protons produced by a CS30 cyclotron. A time-controlled aluminum cylinder was added in front of the horizontal beam-exit serving as a radiation shutter. Following the TRS-398 reference dosimetry protocol for proton beams, the output was calibrated in water at a reference depth of 3 mm. EBT3 film was calibrated for doses up to 8 Gy at the same depth. To verify the dose distribution for each 96-well MTT assay plate, EBT3 film was placed at the reference depth during irradiation and cell doses were scaled by measured percent depth dose (PDD) data.ResultsThe radiochromic film dosimetry system in this study provides dose measurements with an uncertainty better than 3.3% for doses higher than 1 Gy. From a single exposure and utilizing the Gaussian shape of the beam, multiple dose points can be obtained within different wells of the same plate ranging from 6.9 Gy (sigma ∼4%) in the central well, and 2 Gy (sigma ∼8%) for wells positioned closer to the periphery.ConclusionsWe described a methodology for radiochromic film-based dose monitoring system, using low-energy protons, which can be used for the MTT assay in any proton beam, except within Bragg peak region.     

Development of a phantom for dose distribution verification in Stereotactic Radiosurgery

A geometric acrylic phantom was designed and built for dose distribution verification in Stereotactic Radiosurgery. Acrylic objects representing the tumor tissue, (target volume (TV)), and the organ at risk (OAR), the brainstem, were inserted inside this phantom. The TV is represented by two semi-spheres of acrylic with a diameter of 13.0 mm, both having a central cavity for accommodation of a TLD-100 detector and a small radiochromic Gafchromic EBT film. The OAR is represented by the two parts of a 38.0 mm length acrylic cylinder with a diameter 18.0 mm and cavities along the cylinder central axis able to accommodate 5 TLD – 100 detectors and another of EBT film between the two cylinder parts. This experimental setup was submitted to a radiosurgical treatment, after which the TL dosimeters were evaluated and their responses were compared with the planned dose values. The radiochromic EBT films showed the dose distributions. The linear accelerator used was a Varian 2300 C/D, generating a 6 MV photon beam. The investigated phantom system was able to check the accuracy of dose delivery to predetermined points and the dose distribution due to stereotactic radiosurgery treatments and proved to be a good tool for quality control in these situations.     

Radiation dose verification of an X-ray based blood irradiator using EBT3 radiochromic films calibrated using Gamma Knife machine

AimBlood irradiators (BI) initial acceptance testing and routine annual dosimetry checks require radiation dose measurements in order to comply with regulatory requirements.BackgroundTraditionally thermo-luminescence dosimeters (TLD) have been used to measure the dose. The EBT3 film is reported to be a better dosimeter for low energy X-rays than its predecessors EBT2 and EBT. To the best of our knowledge, the use of EBT3 films to perform dosimetry on X-ray based BI has not been reported yet.Materials and methodsWe performed routine radiation dosimetry checks using EBT3 films on a new X-ray based BI and compared the results with TLD dosimetry. Calibration films were irradiated with radiation beam from a Co-60 Gamma Knife (GK) radiosurgery machine and, alternatively, using an Ir-192 high dose rate (HDR) brachytherapy device. The films were calibrated to cover a wide dose range from 1 to 40 Gy. Such a wide dose range has not been reported yet in BI film dosimetry.ResultsWe obtained a relative difference of about 6.6% between doses measured using TLD and those measured using EBT3 films. Both irradiation methods using GK or HDR were found to be adequate for the calibration of the EBT3 Gafchromic films.ConclusionsWe recommend the use of EBT3 films in routine X-ray based BI dosimetry checks. The presented method takes advantage of available radiotherapy equipment that can be efficiently used for EBT3 films calibration. The method is fast, reproducible and saves valuable medical physicist's time.     

Polarized dosimetry method for Gafchromic EBT3

PurposeTo analyze the changes in the polarization state of the flatbed scanner light caused by the EBT3 films and to propose a new method for correcting the lateral effects.Methods and materialsThe polarization changes induced by radiochromic films are analyzed using linear polarizing film. Based on the results, the linear polarizing films are used in the scanning process of the EBT3 films. This method is tested against the conventional EBT3 dosimetry using a series of simple regular beams and 21 cases of IMRT.ResultsThe mean results are statically different from the conventional dosimetry with EBT3. Depending on the transmission axis of the polarizing sheet, the results are better or worse compared to conventional dosimetry EBT3 film. When the transmission axis of the polarizing sheet is parallel to the coating direction, the dosimetry results are better and its variability is smaller. However, when the polarizer transmission axis is perpendicular to the coating direction, results are worse as well as its variability.ConclusionUsing a polarized film with the polarization axis parallel to the coating direction of the radiochromic film, and preferably above it, significantly improves the dosimetry results and is an easy and inexpensive way to correct the lateral artifacts of the conventional EBT3 dosimetry.     

Energy dependence of radiochromic dosimetry films for use in radiotherapy verification

Aim

The purpose of the study was to examine the energy dependence of Gafchromic EBT radiochromic dosimetry films, in order to assess their potential use in intensity-modulated radiotherapy (IMRT) verifications.

Materials and methods

The film samples were irradiated with doses from 0.1 to 12 Gy using photon beams from the energy range 1.25 MeV to 25 MV and the film response was measured using a flat-bed scanner. The samples were scanned and the film responses for different beam energies were compared.

Results

A high uncertainty in readout of the film response was observed for samples irradiated with doses lower than 1 Gy. The relative difference exceeds 20% for doses lower than 1 Gy while for doses over 1 Gy the measured film response differs by less than 5% for the whole examined energy range. The achieved uncertainty of the experimental procedure does not reveal any energy dependence of Gafchromic EBT film response in the investigated energy range.

Conclusions

Gafchromic EBT film does not show any energy dependence in the conditions typical for IMRT but the doses measured for pre-treatment plan verifications should exceed 1 Gy.     

A comparison between radiochromic EBT2 film model and its predecessor EBT film model

The manufacturer has introduced the new EBT2 film model so as to improve its predecessor, the EBT radiochromic film model. According to the manufacturer, some of its main advantages include a higher tolerance to light exposure and it can correct non-uniformity of the active layer thickness using a marker dye. However, the equivalence in uniformity between both models was questioned by some authors, and the asymmetrical configuration of layers of the EBT2 film model produces a new dependence on the film side being scanned (front and back orientation). In this study, the EBT2 radiochromic film model was compared with the EBT model and the new marker dye feature was assessed. We also compared this correction method with a pre-irradiated pixel value correction method. An Epson Expression 10000XL scanner in transmission mode was used to scan the films and the red channel response was analyzed. We confirmed the lower-measured signal dependence on the visible light exposure of the EBT2 film model. Differences in pixel values remained below 0.5% for a minimum of 15 days. In regard to the uniformity, similar results for EBT2 and EBT film models were obtained; in both cases inhomogeneity was found to be less than 1%, in relative pixel value from the mean. However, we found that the signal-to-noise ratio was reduced for low doses by 37% for old EBT2 batch and by 21% for new EBT2 batch compared to signal-to-noise ratio for EBT. The EBT2 film model's pixel value difference for the front and back orientation reached up to 1.0% in the red channel. Our results did not show a clear advantage between to use a pre-irradiated pixel value correction and to use the manufacturer's correction.     

Gafchromic film dosimetry: Four years experience using FilmQA Pro software and Epson flatbed scanners

Purposes: To assess performance of FilmQA Pro software for pre-treatment patient-specific quality assurance (QA), using radiochromic films and two commercial flatbed scanners. To evaluate a novel multichannel approach compared to the classical red channel evaluation.Material and methodsPatient films (mostly EBT2 films, one box of EBT3) were digitalized using successively two flatbed scanners: the A4-size Epson V750 and the A3-size Epson 10000XL. Prior to patient dose verification, basic characteristics of films and scanners were investigated. Patient films were analyzed using FilmQA Pro software, which enables to use the signal from all three colour channels (Red, Green, Blue).ResultsCompared to the red channel evaluation, multichannel evaluation presents better passing rates with regard to local gamma index. As expected, we obtained better results using A3-size scanner compared to A4-size scanner, especially when considering large region of interest. An observation of great interest was made for both scanners: after intensive use, a tilting in the blue transmittance profiles appeared in the lamp direction, making multichannel analysis unsuitable for accurate dose evaluation.     

On the use of EBT3 film for relative dosimetry of kilovoltage X ray beams

EBT3 films were evaluated for relative dosimetry in water, in the energy range of therapeutic kV X ray beams. A film batch was calibrated in air for all nine beam qualities of a clinical unit (XStrahl 200). Monte Carlo (MC) simulations using MCNP v.6 facilitated the calculation of the film absorbed dose (f), and beam quality (k_bq) energy dependences in air. Results were found in agreement with corresponding data in the literature. Film samples from the same batch were irradiated in water along the central beam axis for each beam quality. Experimental percentage depth dose (PDD) results obtained using calibration data in air showed quality and depth dependent differences from corresponding MC simulations. These differences increased beyond film dosimetry uncertainty (<3.3%), reaching up to 8% at increased depth. The observed differences reduced only slightly when spectral variation as a function of measurement point was accounted for, using photon effective energy. PDD measurements and corresponding MC results facilitated the determination of f and k_bq in water. Results showed that the origin of the observed differences between experimental and MC PDD results is the difference between film response in air and water, as a result of radiation field perturbation from the film oriented along the central beam axis. This implies a directional dependence of film response which necessitates that the angular distribution of photons impinging on the film is the same in the calibration and measurement geometries.     

Establishing the impact of temporary tissue expanders on electron and photon beam dose distributions

PurposeThis study investigates the effects of temporary tissue expanders (TTEs) on the dose distributions in breast cancer radiotherapy treatments under a variety of conditions.MethodsUsing EBT2 radiochromic film, both electron and photon beam dose distribution measurements were made for different phantoms, and beam geometries. This was done to establish a more comprehensive understanding of the implant's perturbation effects under a wider variety of conditions.ResultsThe magnetic disk present in a tissue expander causes a dose reduction of approximately 20% in a photon tangent treatment and 56% in electron boost fields immediately downstream of the implant. The effects of the silicon elastomer are also much more apparent in an electron beam than a photon beam.ConclusionsEvidently, each component of the TTE attenuates the radiation beam to different degrees. This study has demonstrated that the accuracy of photon and electron treatments of post-mastectomy patients is influenced by the presence of a tissue expander for various beam orientations. The impact of TTEs on dose distributions establishes the importance of an accurately modelled high-density implant in the treatment planning system for post-mastectomy patients.     

Dosimetric evaluation of Gafchromic EBT2 film for breast intraoperative electron radiotherapy verification

PurposeQuality assurance (QA) is one of the most important issues that should be addressed for intraoperative electron radiotherapy (IOERT), which is not benefiting from image-based treatment planning system. The aim of this study is to evaluate the dosimetric characteristics of Gafchromic EBT2 film for breast IOERT QA procedure.MethodsDue to the fact that some dedicated accelerators are being used for IOERT, dependence of the film response to energy, field size, dose rate and incidence angle of electron beam from the LIAC IOERT accelerator was studied. Then, film response curve to breast IOERT doses was obtained and its accuracy was evaluated and justified through comparison to the results of ionometric dosimetry.ResultsThe results of this study indicated that there are no significant differences between the film responses at different energies of 6, 8, 10 and 12 MeV (P-value = 0.99). Similarly, no field size dependency was found when evaluating the response of the film to different field sizes ranging from 4 to 10 cm (P-value = 0.94). Film response was found to be independent of the dose rate of intraoperative electron beam (P-value = 0.12). Film response variations with changing the beam incidence angle were not significant (P-value > 0.8). Calibration curve at the dose range of 8–24 Gy had an acceptable accuracy. The difference between the results of film dosimetry and ionometric dosimetry was around 5% which was in agreement with the results of dose uncertainty estimation.ConclusionThe EBT2 film was found to be a potentially appropriate tool for breast IOERT verification.     

Application of Gafchromic EBT2 film for intraoperative radiation therapy quality assurance

PurposeIntraoperative radiation therapy (IORT) using electron beam is commonly done by mobile dedicated linacs that have a variable range of electron energies. This paper focuses on the evaluation of the EBT2 film response in the green and red colour channels for IORT quality assurance (QA).MethodsThe calibration of the EBT2 films was done in two ranges; 0–8 Gy for machine QA by red channel and 8–24 Gy for patient-specific QA by green channel analysis. Irradiation of calibration films and relative dosimetries were performed in a water phantom. To evaluate the accuracy of the film response in relative dosimetry, gamma analysis was used to compare the results of the Monte Carlo simulation and ionometric dosimetry. Ten patients with early stage breast cancer were selected for in-vivo dosimetry using the green channel of the EBT2 film.ResultsThe calibration curves were obtained by linear fitting of the green channel and a third-order polynomial function in the red channel (R2 = 0.99). The total dose uncertainty was up to 4.2% and 4.7% for the red and green channels, respectively. There was a good agreement between the relative dosimetries of films by the red channel, Monte Carlo simulations and ionometric values. The mean dose difference of the in-vivo dosimetry by green channel of this film and the expected values was about 1.98% ± 0.75.ConclusionThe results of this study showed that EBT2 film can be considered as an appropriate tool for machine and patient-specific QA in IORT.     

On the re-calibration process in radiochromic film dosimetry

PurposeThe accuracy and precision of the dose estimates obtained with radiochromic film dosimetry are investigated in a clinical environment. The improvement in the accuracy of dose estimates reached with corrective methods is analyzed. Two novel re-calibration algorithms for radiochromic film dosimetry are presented.MethodsTwo different EBT3 lots are evaluated in two different centres. They are calibrated in Varian linacs and read in two different EPSON scaners. Once the lots are calibrated, three films per lot are considered and divided into stripes that are exposed to known doses. Several dosimetry protocols usually employed in radiochromic film dosimetry are used to convert film responses to absorbed doses. These protocols are characterized by different choices of the film responses or different sensitometric curves. Finally, the accuracy and reproducibility of the dose estimates is investigated with and without the corrective methods.Results and ConclusionsThe variabilities that affect radiochromic film dosimetry, such as intra-lot variability, inter-scan variability, post-exposure time and film autodevelopment may give rise to inaccuracies in the dose estimates. However, the implementation of re-calibration methods leads to more accurate dose estimates. All the investigated protocols showed more accurate and reproducible results when the re-calibrated methods were employed. So, the novel re-calibration methods may be applied in order to improve the accuracy and reproducibility of radiochromic film dosimetry.     

Prevention of Transfusion-Associated Graft-versus-Host Disease by Irradiation: Technical Aspect of a New Ferrous Sulphate Dosimetric System

Irradiation of whole blood and blood components before transfusion is currently the only accepted method to prevent Transfusion-Associated Graft-Versus-Host-Disease (TA-GVHD). However, choosing the appropriate technique to determine the dosimetric parameters associated with blood irradiation remains an issue. We propose a dosimetric system based on the standard Fricke Xylenol Gel (FXG) dosimeter and an appropriate phantom. The modified dosimeter was previously calibrated using a ⁶⁰Co teletherapy unit and its validation was accomplished with a ¹³⁷Cs blood irradiator. An ionization chamber, standard FXG, radiochromic film and thermoluminescent dosimeters (TLDs) were used as reference dosimeters to determine the dose response and dose rate of the ⁶⁰Co unit. The dose distributions in a blood irradiator were determined with the modified FXG, the radiochromic film, and measurements by TLD dosimeters. A linear response for absorbed doses up to 54 Gy was obtained with our system. Additionally, the dose rate uncertainties carried out with gel dosimetry were lower than 5% and differences lower than 4% were noted when the absorbed dose responses were compared with ionization chamber, film and TLDs.     

Evaluation of LiF:Mg,Ti (TLD-100) for Intraoperative Electron Radiation Therapy Quality Assurance

Background

Purpose of the present work was to investigate thermoluminescent dosimeters (TLDs) response to intraoperative electron radiation therapy (IOERT) beams. In an IOERT treatment, a large single radiation dose is delivered with a high dose-per-pulse electron beam (2–12 cGy/pulse) during surgery. To verify and to record the delivered dose, in vivo dosimetry is a mandatory procedure for quality assurance. The TLDs feature many advantages such as a small detector size and close tissue equivalence that make them attractive for IOERT as in vivo dosimeters.

Methods

LiF:Mg,Ti dosimeters (TLD-100) were irradiated with different IOERT electron beam energies (5, 7 and 9 MeV) and with a 6 MV conventional photon beam. For each energy, the TLDs were irradiated in the dose range of 0–10 Gy in step of 2Gy. Regression analysis was performed to establish the response variation of thermoluminescent signals with dose and energy.

Results

The TLD-100 dose-response curves were obtained. In the dose range of 0–10 Gy, the calibration curve was confirmed to be linear for the conventional photon beam. In the same dose region, the quadratic model performs better than the linear model when high dose-per-pulse electron beams were used (F test; p<0.05).

Conclusions

This study demonstrates that the TLD dose response, for doses ≤10Gy, has a parabolic behavior in high dose-per-pulse electron beams. TLD-100 can be useful detectors for IOERT patient dosimetry if a proper calibration is provided.     

Electron radiotherapy (IOERT) for applications outside of the breast: Dosimetry and influence of tissue inhomogeneities

PurposeThe purpose of study is to investigate the dosimetry of electron intraoperative radiotherapy (IOERT) of the Intraop Mobetron 2000 mobile LINAC in treatments outside of the breast. After commissioning and external validation of dosimetry, we report in vivo results of measurements for treatments outside the breast in a large patient cohort, and investigate if the presence of inhomogeneities can affect in vivo measurements.Methods and materialsApplicator factors and profile curves were measured with a stereotactic diode. The applicators factors of the 6 cm flat and beveled applicators were also confirmed with radiochromic films, parallel-plate ion chamber and by an external audit performed with ThermoLuminescent Dosimeters (TLDs). The influence of bone on dose was investigated by using radiochromic films attached to an insert equivalent to cortical bone, immersed in the water phantom. In vivo dosimetry was performed on 126 patients treated with IOERT using metal oxide-silicon semiconductor field effect transistors (MOSFETs) placed on the tumor bed.ResultsRelatively small differences were found among different detectors for measurements of applicator factors. In the external audit, the agreement with the TLD was mostly within ±0.2%. The largest increase of dose due to the presence of cortical bone insert was +6.0% with energy 12 MeV and 3 cm applicator. On average, in vivo dose was significantly (+3.1%) larger than prescribed dose.ConclusionIOERT in applications outside the breast results in low discrepancies between in vivo and prescribed doses, which can be also explained with the presence of tissue inhomogeneity.