Photon Beam Research Articles

Dosimetric assessment of the mono and dual-isocentric VMAT technique based on flattening filter-free beams for SBRT with non-contiguous spinal targets.

The study aimed to evaluate the planning characteristics of spinal stereotactic body radiotherapy (SBRT) using mono- and dual-isocentric volumetrically modulated arc therapy (VMAT) techniques. The dosimetric indices were compared between different beam arrangement techniques for spinal SBRT planning, including spinal cord avoidance, planning target volume (PTV) dose coverage, conformity, homogeneity, and gradient index. A total of 8 PTVs were contoured on RANDO phantom computed tomography (CT) images, with 4 PTVs per section of the spine (thoracic and lumbar). VMAT plans for each PTV were generated using 4 different beam arrangement techniques with a 6-MV FFF photon beam, two of which were mono-isocentric (MI) and 2 of which were dual-isocentric (DI). Dose calculations for all plans were performed using the Acuros XB algorithm. The study found that when non-contiguous spinal lesions are widely spaced, it may be more effective to use 4-Arcs DI to generate a better homogeneity index and gradient index, whereas 2-Arcs MI was beneficial for closely spaced lesions. Furthermore, the use of more arcs with a dual isocenter reduced the volume of partial cord receiving 10 Gy (V10Gy), maximum dose to 0.03 cc of partial cord (D0.03cc), and monitor units (MUs). The results showed that DI has a higher plan quality than MI for treating non-contiguous spine SBRT, with better homogeneity and a lower dose to the spinal cord, as well as comparable tumor coverage, delivery accuracy, and adequate tumour coverage. 4-Arcs DI had the sharpest dose falloff and achieved the lowest overall spinal cord doses at the expense of twice the treatment time as 2Arcs-MI. These results could help figure out which VMAT beam arrangements are best for treatingnon-contiguous spinal tumors.

Evaluation of the RadCalc collapsed cone dose calculation algorithm against measured data.

This work describes the experimental validation of the RadCalc (Lifeline software Inc, Tyler) collapsed cone dose calculation algorithm against measured data for a range of scenarios. 6 MV photon beam data were measured in a large water tank on a Varian TrueBeam linear accelerator. These were input into the RadCalc software, in conjunction with head geometry and output calibration information, then used to create a collapsed cone beam model. The model performance was assessed by comparison against measurement, using a selection of homogeneous and inhomogeneous geometries not incorporated into the original beam model. Dose calculations generated using the collapsed cone algorithm are generally in good agreement with measurement. However, the primary collimating of the linac is not accounted for in the RadCalc model and hence dose in the corners of large fields is significantly overestimated. Percentage depth doses were within 0.5% beyond a depth of 2 cm. The dose in the build-up region was underestimated by RadCalc Version 7.1.4.1, with (Distance To Agreement) discrepancies of up to 3 mm which were corrected in Version 7.2.2.0. Beam profiles for homogeneous phantom comparisons were within 2% in the central 80% of the field with out of field dose underestimated by no more than 3%. Dose comparisons in heterogeneous geometries were acceptable and generally within 3.5%. The largest observed differences were found at density interfaces and a result of the RadCalc dose resolution of 2 mm against 1 mm measured. Absolute dose comparisons demonstrated that RadCalc agreed with measurement to within 1.2% under homogeneous media irradiation geometries. For static beam IMRT deliveries agreement was within 2% or 2 mm of measured data, and for complex VMAT deliveries within 3% or 2 mm. The implementation of the (model-based) photon collapsed cone algorithm in RadCalc shows generally good agreement with measured data over a range of simple and complex scenarios considered.

A Simplified Approach for Determination of Inflection Points of Flattening Filter-Free Photon Beam Using In-House Developed Software and Derivation of Reference Levels.

This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented. Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X90%], 75% [X75%], and 60% [X60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs). The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF). A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.

Comparison of double-differential cross-section between nuclear data library and experimental data for photoneutron production

In this study, we compared double differential cross-sections (DDXs) between the experimental data obtained by 16.6 MeV of polarized photons and the DDXs from JENDL2004 and JENDL/PD-2016.1 for 197Au, natPb, natCu, and natTi targets. Using Python-based software, we extracted the DDXs from the nuclear data libraries (NDLs), which were subsequently deduced considering the abundances of each target’s isotopes, the width of the photon beam, and the energy resolution of the neutron detectors. For the Ti target, the experimental DDX data were consistent with that of the NDLs. For Pb, Au, and Cu targets, the experimental DDX data at neutron energies higher than 4 MeV were larger than the DDX values obtained from the NDLs. The inconsistency between the DDXs of the experimental data and those of the NDLs indicates the need to improve the physical models to generate the spectrum of photoneutrons.

Paraffin gauze bolus as tissue compensator in photon irradiation for mycosis fungoides – regarding a case study

Abstract Introduction: Total skin electron beam therapy is a treatment option in patients with mycosis fungoides (MF) affecting a significant amount of the body surface. For patients with involvement of soles and interdigital folds, however, this approach is ineffective, requiring alternatives such as localised radiotherapy (RT). Although electron beams are well suited for superficial lesions, on irregular surfaces it provides inadequate tumour coverage and excess dose variance, requiring photon irradiation with tissue compensation. Methods: We present the case of a patient with extensive cutaneous MF with skin lesions spread over both lower limbs and treated on these affected areas with photon beam RT. Long sheets of paraffin gauze dressings were used to create a 0·5-cm-thick bolus. The patient received a single fraction of 8 Gy. In vivo dosimetry using Gafchromic films was performed. Results: After 3 months, a complete response was achieved. In this case, paraffin gauze bolus proved to be an inexpensive, convenient, effective and flexible method for irregular superficial cancer irradiations. Conclusion: Paraffin gauze bolus is a suitable option for irregular contours.

Collimated gamma beams with high peak flux driven by laser-accelerated electrons

Abstract Laser-accelerated electrons are promising in producing gamma-photon beams of high peak flux for the study of nuclear photonics, obtaining copious positrons and exploring photon–photon interaction in vacuum. We report on the experimental generation of brilliant gamma-ray beams with not only high photon yield but also low divergence, based on picosecond laser-accelerated electrons. The 120 J 1 ps laser pulse drives self-modulated wakefield acceleration in a high-density gas jet and generates tens-of-MeV electrons with 26 nC and divergence as small as $1.51{}^{\circ}$ . These collimated electrons produce gamma-ray photons through bremsstrahlung radiation when transversing a high-Z solid target. We design a high-energy-resolution Compton-scattering spectrometer and find that a total photon number of $2.2\times {10}^9$ is captured within an acceptance angle of $1.1{}^{\circ}$ for photon energies up to $16\;\mathrm{MeV}$ . Comparison between the experimental results and Monte Carlo simulations illustrates that the photon beam inherits the small divergence from electrons, corresponding to a total photon number of $2.2\times {10}^{11}$ and a divergence of $7.73{}^{\circ}$ .

Dosimetric Study of Hybrid Intensity Modulated Radiation Therapy Treatment Plan with Flattened Filter Free Photon Beam for Carcinoma of Breast: Treatment Planning Study

Dosimetric Study of Hybrid Intensity Modulated Radiation Therapy Treatment Plan with Flattened Filter Free Photon Beam for Carcinoma of Breast: Treatment Planning Study

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium.

In Radiotherapy, computation of dose is important since in a small field with heterogeneity, dose is usually computed with discrepancies. The present study was aimed to evaluate the dosimetry of treatment planning algorithms in lung equivalent heterogeneous medium for Volumetric Modulated Arc Therapy (VMAT) with step and shoot Intensity-Modulated Radiation Therapy (ss-IMRT), and dynamic Intensity-Modulated Radiation Therapy (d-IMRT). In this experimental study, Computerized Imaging Reference System (CIRS) phantom was used with an inhomogeneous Racemosa wood cylinder for two types of tumors, namely, Left Lung Central Tumor (LCT) and Left Lung Peripheral Tumor (LPT) in the CIRS left lung cavity. The computed tomography (CT) datasets were employed with the generation of VMAT, d-IMRT and ss-IMRT plans for the LCT and LPT irradiated with 6 MV photon beams. In this study, the accuracy and efficacy of two algorithms: Monte Carlo (MC) and the Pencil Beam (PB), from the Monaco treatment planning system (TPS), were tested by using Gafchromic EBT3 films and CIRS thorax phantom. Regardless of treatment techniques, both algorithms exhibited higher divergence in LPT than LCT. In both LCT and LPT, the highest deviation was near the tumor-lung junction. However, the deviation was higher in the PB algorithm than MC algorithm, with a minimally acceptable variation of -0.8%. The MC algorithm shows more consistency for EBT3 measured dose in lung equivalent heterogeneous medium. However, accurate dose predictions are complicated due to electronic disequilibrium within and at the interface of inhomogeneity. These constraints may cause variations from the anticipated outcomes of the treatments.

Small-field Dosimetry of 6- and 10-MV Flattening Filter-free and Flattening Filter Photon Beams for Therapeutic Use

Small-field Dosimetry of 6- and 10-MV Flattening Filter-free and Flattening Filter Photon Beams for Therapeutic Use

Particle Accelerators and Gamma-therapeutic Devices - an Effective Tool for Cancer Treatment

The review is based on the analysis of the state and the concept of modernization of world radiation oncology. The material contains brief information about the reasons for the use of radiation therapy for the treatment of cancer foci; active sources of particles; achieved results of therapy, etc. The role of accelerator technology, innovative related equipment and nuclear physics methods for the treatment of oncological diseases is described. The main characteristics of linear electron accelerators with the energy Ee = 6 MeV, the parameters of multifunctional installations with Ee = (4 - 25) MeV generating several photon and electron beams and accelerators of protons and carbon ions are given. It is shown that to date, the treatment of malignant foci with beams of protons and carbon ions has surpassed all existing methods in terms of efficiency.

Monitoring Linear Accelerator Output Constancy and Overall Performance Using the PTW Quickcheckwebline

Daily morning quality assurance (QA) for all available beams using conventional phantom measures only output and beam quality. PTW QUICKCHECKwebline (PTW QCw) is a compact movable light-weight dosimetry equipment used for daily QA, capable of measuring flatness, symmetry, beam quality and output constancy of a given beam in a single exposure. The purpose of this study was to analyze and monitor the output constancy of a medical linear accelerator using PTW QCw and assess the overall performance of the PTW QCw. The output parameters of 4, 6 and 15 MV photon beams and 4, 6, 8, 10, 12 and 15 MeV electron beams of the Elekta Synergy linear accelerator in Kathmandu Cancer Center were analyzed. It was found in the study that all the parameters were well within the recommended tolerance limit of ±3%. Some known modifications in the settings of the linear accelerator gantry, couch, and collimator were introduced separately during the exposures, and the percentage variations from the baseline values were noted to check the sensitivity of the PTW QCw using 6 MV photon beam. The PTW QCw was able to detect the deviations introduced to the external irradiation conditions for both photon and electron beams under daily testing conditions. The results from this study suggest that daily dosimetric consistency measurements using the PTW QCw helps to monitor the overall performance of the linear accelerator.

Measuring and Determining the Output Factor of 6 and 10 MV WFF Photon Beams in Small Square and Rectangular Fields using Semiflex TM 31010 and Pintpoint TM 31014 Ionization Chamber

Research has been carried out on Measuring and Determining the Output Factors of 6 and 10 MV WFF photon beams in Small Square and Rectangular fields using Semiflex TM 31010 and PintPoint TM 31014 Ionization Chamber. This study aims to determine the value of the small field output factor. Measurements were carried out in a water phantom at a depth of 10 cm with a 100 cm SSD technique. The area of ​​the irradiation field used is (2 × 2; 3 × 3; 4 × 4; 2.5 × 1.6; 3.6 × 2.5; 4.5 × 2; and 5 × 3.2) cm2. Field output factor calculations were performed using the IAEA TRS. 483 dosimetry protocol. The results of measurements and calculations obtained for the two detectors used show that a decrease in the value of the output factor occurs when the field size is getting smaller. The output factor value in a small rectangular field looks smaller when compared to the output factor value in a small square field.

Performance characteristics of a parallel plate dosimeter based on PVA/MWCNT-OH nanocomposite for photon beam radiation

A new homemade Polyvinyl Alcohol/Multi-Walled Carbon Nanotube Hydroxyl (PVA/MWCNT-OH) nanocomposite dosimeter was developed for photon beam radiation in this research. A parallel plate dosimeter with 0.40 cm3 sensitive volume was fabricated with PVA/MWCNT-OH nanocomposite which equipped with necessary connector so that its response against irradiation can be recorded by a standard electrometer. The dosimetric characteristics of the Homemade Nano-Composite (HNC) dosimeter were studied in Secondary Standard Dosimetery Laboratory (SSDL) with Picker V9 Co-60 irradiator. The sensitivity of the HNC dosimeter was about three times higher than reference standard dosimeters (0.35 cm3 Ross parallel plate ion chamber). Other performance tests such as leakage current, linearity response based on radiation dose, saturation response, polarity effect, directional dependence, field size and energy dependence were performed. All results obtained were in good agreement with IEC 60,731 standard. Therefore, the HNC dosimeter is suitable for routine dosimetric procedures in photon beam radiation.

Development and benchmarking of the first fast Monte Carlo engine for helium ion beam dose calculation: MonteRay.

Monte Carlo (MC) simulations are considered the gold-standard for accuracy in radiotherapy dose calculation; however, general purpose MC engines are computationally demanding and require long runtimes. For this reason, several groups have recently developed fast MC systems dedicated mainly to photon and proton external beam therapy, affording both speed and accuracy. To support research and clinical activities at the Heidelberg Ion-beam Therapy Center (HIT) with actively scanned helium ion beams, this work presents MonteRay, the first fast MC dose calculation engine for helium ion therapy. MonteRay is a CPU MC dose calculation engine written in C++, capable of simulating therapeutic proton and helium ion beams. In this work, development steps taken to include helium ion beams in MonteRay are presented. A detailed description of the newly implemented physics models for helium ions, for example, for multiple coulomb scattering and inelastic nuclear interactions, is provided. MonteRay dose computations of helium ion beams are evaluated using a comprehensive validation dataset, including measurements of spread-out Bragg peaks (SOBPs) with varying penetration depths/field sizes, measurements with an anthropomorphic phantom and FLUKA simulations of a patient plan. Improvement in computational speed is demonstrated in comparison against reference FLUKA simulations. Dosimetric comparisons between MonteRay and measurements demonstrated good agreement. Comparing SOBPs at 5, 12.5, and 20cm depth, mean absolute percent dose differences were 0.7%, 0.7%, and 1.4%, respectively. Comparison against measurements behind an anthropomorphic head phantom revealed mean absolute dose differences of about 1.2% (FLUKA: 1.5%) with per voxel errors ranging from -4.5% to 4.1% (FLUKA: -6% to 3%). Computed global 3%/3mm 3D-gamma passing rates of ∼99% were achieved, exceeding those previously reported for an analytical dose engine. Comparisons against FLUKA simulations for a patient plan revealed local 2%/2mm 3D-gamma passing rates of 98%. Compared to FLUKA in voxelized geometries, MonteRay saw run-time reductions ranging from 20× to 60×, depending on the beam's energy. MonteRay, the first fast MC engine dedicated to helium ion therapy, has been successfully developed with a focus on both speed and accuracy. Validations against dosimetric measurements in homogeneous and heterogeneous scenarios and FLUKA MC calculations have proven the validity of the physical models implemented. Timing comparisons have shown significant speedups between 20 and 60 when compared to FLUKA, making MonteRay viable for clinical routine. MonteRay will support research and clinical practice at HIT, for example, TPS development, validation and treatment design for upcoming clinical trials for raster-scanned helium ion therapy.

Calorimeter measurements of absolute dose in aluminum, a surrogate of bone, to validate dose-to-medium in Acuros XB

Objective. While the accuracy of dose calculations in water with Acuros XB is well established, experimental validation of dose in bone is limited. Acuros XB reports both dose-to-medium and dose-to-water, and these values differ in bone, but there are no reports of measurements of validation in bone. This work compares Acuros XB calculations to measurements of absolute dose in aluminum (medium similar to bone). The validity of using selected relative dosimeters in aluminum is also investigated. Approach. A calorimeter with an aluminum core embedded in an aluminum phantom was selected as bone surrogate for the measurement of absolute dose. Matching the medium of the core to the medium of the phantom allowed eliminating the calculation of the conversion between media. The dose was measured at the fixed depth of 3.3 cm in aluminum (∼9 g·cm−2) with 6X, 10X, 6FFF and 10FFF photon beams from a TrueBeam Varian linac. In addition, experimental cross-calibration between water and aluminum was performed for an IBA CC13 ionization chamber, a PTW microDiamond and EBT3 Gafchromic film. Main results. Calculations with Acuros XB dose-to-medium in aluminum differed from the calorimetry data by −2.8% to −3.5%, depending on the beam. Use of dose-to-water would have resulted in about 39% discrepancy. The cross calibration coefficient between water and aluminum yielded values of about 0.87 for the CC13 chamber, 0.91 for the microDiamond, and 0.88 for the film, and independent of the beam within about ±1%. Significance. It was demonstrated the value of the dose-to-medium in aluminum (surrogate of bone) computed with Acuros XB is close to the value of the absolute dose measured with a calorimeter, and there is a significant discrepancy when dose-to-water is used instead. The use of an ionization chamber, a microDiamond and Gafchromic film in aluminum required a considerable correction from calibration in water.

New physics searches with an optical dump at LUXE

We propose a novel way to search for feebly interacting massive particles, exploiting two properties of systems involving collisions between high energy electrons and intense laser pulses. The first property is that the electron-laser collision results in a large flux of hard photons, as the laser behaves effectively as a thick medium. The second property is that the emitted photons free-stream inside the laser and thus for them the laser behaves effectively as a very thin medium. Combining these two features implies that the electron-intense-laser collision is an apparatus, which can efficiently convert $\mathcal{O}(10\text{ }\text{ }\mathrm{GeV})$ electrons to a large flux of hard, collinear photons. The photons are directed onto a solid dump in which feebly interacting massive particles may be produced. With the much smaller backgrounds induced by the photon beam compared to those expected in electron- or proton-beam dump experiments and combined with a relatively shorter dump used here, the sensitivity to short lifetimes is unparalleled. We denote this novel apparatus as ``optical dump'' or NPOD (new physics search with optical dump). The proposed LUXE experiment at the European XFEL has all the basic required ingredients to realize this experimental concept for the first time. Moreover, the NPOD extension of LUXE is essentially parasitic to the main experiment and thus, practically it does not have any bearing on its main program. We discuss how the NPOD concept can be realized in practice by adding a detector after the last physical dump of the experiment to reconstruct the two-photon decay of a new spin-0 particle. We show that even with a relatively short dump, the search can still be background-free. Remarkably, even with a few days of data taking with a 40 TW laser corresponding to its initial run, LUXE-NPOD will be able to probe an uncharted territory of models with pseudoscalars and scalars. Furthermore, with a 350 TW laser of the main run, LUXE-NPOD will have a unique reach for these models. In particular it can probe natural scalar theories for masses above 100 MeV. We note that the new NPOD concept may be ported to other existing or future facilities worldwide, including, e.g., future lepton colliders.

Carbon Radiotheraphy For Head and Neck Cancer: Dosimetric Comparison with Photon Plans

Radiation therapy is one of the most widely used treatment methods for tumors. The therapeutic use of carbon ions is more advantageous than other radiotherapy techniquies especially photon-based irradiation due to its physical properties and radiobiological effects, and therefore it has received more attention. One of the most important reasons for that carbon ion beams are more effective than photon beams while minimizing the dose in the normal tissues around the target, it offers an improved dose distribution that leads to sufficient dose concentration in tumors. In addition, the carbon beam reaches its maximum at the end of its range, which increases with depth, and due to this feature, it provides a higher biological efficiency. In radiotherapy studies, Monte Carlo simulation is widely used to determine the dose distributions and to obtain the correct properties of the beams. With MC simulation, it helps to understand the relative biological efficiency as well as the spatial model of energy storages. In this study, a geometry with critical organs (skull, brain, nasopharynx and thyroid) based on a MIRD phantom was modeled with the Monte Carlo simulation tool GATE (vGATE 9.0). In this experiment, the tumor was irradiated with different carbon beam energies and photon beams. The aim is to calculate the energy accumulations in the region and surrounding organs with the MC method, and as a result, to show the dosimetric advantages of carbon radiotherapy over photon radiotherapy.

On the sensitivity of PROMs during breast radiotherapy

PurposeTo investigate the sensitivity of patient-reported outcome measures (PROMs) to detect treatment-related side effects in patients with breast cancer undergoing external beam photon radiotherapy. MethodsAs part of daily clinical care, an in-house developed PROM tool was used to assess side effects in patients during a) whole-breast irradiation (WBI) to 40 Gy, b) WBI with a sequential boost of 10 Gy, and c) partial-breast irradiation (PBI) to 40 Gy. Results414 patients participated in this prospective study between October 2020 and January 2022, with 128 patients (31 %) receiving WBI, 241 (58 %) receiving WBI followed by a sequential boost, and 50 patients (12 %) receiving PBI. Significant differences in the reported toxicities (itching, radiation skin reaction, skin darkening, and tenderness and swelling) were reported between the WBI cohorts with and without boost (p < 0.001, p < 0.001, p < 0.001, and p = 0.002, respectively). The comparison of PBI with WBI (no-boost) yielded significant differences for radiation skin reaction (p < 0.001). ConclusionThe results highlight the high sensitivity of PROMs to detect treatment-related side effects in patients with breast cancer. Thus, PROMs may be a valuable tool for quality control and may support evidence-based learning from real-world data originating from daily routine care.

Two-Color Operation of a Soft X-ray FEL with Alternation of Undulator Tunes

FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable, which allows for testing and using advanced lasing concepts. In particular, we developed a two-color operation mode based on the alternatingly tuned undulator segments (every other segment is tuned to the second wavelength). This scheme is advantageous in comparison with a subsequent generation of two colors in two consecutive sections of the undulator line. First, source positions of the two FEL beams are close to each other which makes it easier to focus them on a sample. Second, the amplification is more efficient in this configuration since the segments with respectively “wrong” wavelength still act as bunchers. We studied operation of this scheme in the regime of small and large separation of tunes (up to a factor of two). We developed new methods for online intensity measurements of the two colors simultaneously that require a combination of two detectors. We also demonstrated our capabilities to measure spectral and temporal properties of two pulses with different wavelengths.

Dose sensitivity of MAGIC-f polymer gel using different MRI sequences

This study aims to evaluate the dose sensitivity of MAGIC-f gel irradiated by high-energy photon beams, comparing quantification using different MRI sequences. Irradiation was performed using 6 MV photons with 600 cGy/min dose rate, field size of 20x20 cm², and 94 cm source-to-surface distance. Two gel batches were produced on different days and placed in vials. In the first batch, doses of 0, 2, 4, 6, 8, 10, 20, and 40 Gy were planned. The second batch was irradiated with doses of 0, 2, 4, 6, 10, 12, 14, and 16 Gy. MR images were acquired with Spin Echo (SE, TR=3 s) and Multi Spin Echo (MSE, TR = 3s or 10s, turbo factor 24) sequences. The dose is assessed via changes in the transverse relaxation time in the irradiated gel. In MSE, dose sensitivity in the first batch was 0.27 (TR=3 s) and 0.28 Gy-1s-1 (TR=10 s) and in the second batch, 0.31 and 0.31 Gy-1s-1 (TR = 3 s and TR = 10 s, respectively). In the SE sequence, dose sensitivity was 0.42 for the first batch and 0.43 Gy-1s-1 for the second batch. Linearity of dose-response was only obtained for doses below 10 Gy. Comparing the dose sensitivity extracted from MSE and SE sequences using TR= 3s, differences around 30% were found. Thus, although MSE-MRI offers a faster protocol of imaging acquisition it is less precise for quantification of relaxation times, as TE is not a well-defined quantity. The performance of the gel as a dosimeter is consequently sequence dependent.