MV Photon Beams Research Articles

Protocol determination for OSL in vivo measurements of absorbed dose in the oral mucosa in oral cancer patients: A pilot study

Radiation-induced oral mucositis (RIOM) is one of the major oral complications caused by radiotherapy (RT), and can lead a negative impact on patients’ quality of life. Considering that there is no specific radiation therapy dose constraint for oral mucosa, the need to study the correlation between absorbed dose and effect in this area is crucial. This pilot study aims to report in vivo OSL dosimetry protocol to investigate the dose distribution in the oral mucosa in patients with oral cancer using Intraoral customised Stent (IOS). For measurements, aluminium oxide nanoDot dosimeters and a microStar ii OSL reader from Landauer Inc. were used. The OSL dosimetry system was calibrated with a 6 MV photon beam using an Elekta Synergy linear accelerator and solid water phantoms following the recommendations of the AAPM TG 191 protocol. The dose distribution in the oral mucosa using seven OSL dosimeters fixed on the intraoral stent was evaluated and compared with the dose distribution available from the RT planning for the patient. Our experimental results showed the expected linearity response of the nanoDot dosimeters from 20 to 200 cGy. The repeatability of readings was better than 1.0% in all commissioning measurements. The uncertainty budget of the commissioning analysis resulted in an overall type An uncertainty of ∼3.4% at the 1-sigma level for dose calculation, compatible with the TG 191 protocol. The dose distribution in the oral mucosa was assessed and dose deviations up to 35% can be found in high dose gradient regions of the treatment planning. This type of deviation may impact on the development and progression of RIOM, as analysed in this protocol. It is feasible to establish this procedure in vivo dosimetry for a patient undergoing RT using a multidisciplinary approach. Additionally, intraoral customised stents can decrease radiation doses in the oral mucosa, and the understanding of the dose distribution in the oral mucosa may help to minimise damages from radiation.

Doses delivered to small and large breasts and adjacent organs in left breast cancer patients utilizing 3D and IM radiotherapy

BackgroundRadiotherapy is still the most facilitated modality for treatment of malignant tumors, including breast cancer, with or without chemotherapy and after surgery or when surgery is impossible. AimThe present article concerns a number of parameters used in radiation therapy techniques, involving the minimum, maximum, mean dose, volume covered with 95% of dose, and global maximum dose delivered to planning target volume (PTV), and the organs at risk, including left lung, heart, thyroid gland, spinal cord, humerus, super clavicle lymph node, and the right breast using the constraints of Radiation Therapy Oncology Group (RTOG). Patients and MethodsTwenty patients with breast tumors, females only, were enrolled in the study. A LINAC with a 6 MV photon beam was used to deliver the prescribed dose. The whole breast irradiation was applied to each patient using two planning techniques: 3D conformal and intensity modulated radiotherapy, and the planning was constructed within 95%–107% of the prescribed dose to the planning target volume as recommended by the RTOG. ResultsThe results showed a significant difference (at the level of P < 0.05) between the two planning techniques based on the doses received by PTV and the OARs. The results were discussed. ConclusionWe concluded that inverse intensity modulation radiation therapy (IMRT) for breast cancer does not improve late toxicity or oncologic outcomes. So, inverse IMRT is not yet the norm, and health insurance usually doesn't pay for treatment unless it's absolutely necessary, like to stop a heart attack. .

Enhanced Cherenkov imaging for real-time beam visualization by applying a novel carbon quantum dot sheeting in radiotherapy.

Cherenkov imaging can be used to visualize the placement of the beam directly on the patient's surface tissue and evaluate the accuracy of treatment planning. However, Cherenkov emission intensity is lower than ambient light. At present, time gating is the only way to realize Cherenkov imaging with ambient light. This study proposes preparing a novel carbon quantum dot (cQD) sheeting to adjust the wavelength of Cherenkov emission to obtain the optimal wavelength meeting the sensitive detection region of the camera, meanwhile the total optical signal is also increased. By combining a specific filter, this approach might help in using lower-cost camera systems without intensifier-coupled to accomplish in vivo monitoring of the surface beam profile on patients with ambient light. The cQD sheetings were prepared by spin coating and UV curing with different concentrations. All experiments were performed on the Varian VitalBeam system and optical emission was captured using an electron multiplying charge-coupled device (EMCCD) camera. To quantify the optical characteristics and certify the improvement of light intensity as well as signal-to-noise ratio (SNR) of cQD sheeting, the first part of the study was carried out on solid water with 6 and 10 MV photon beams. The second part was carried out on an anthropomorphic phantom to explore the applicability of sheeting when using different radiotherapy materials and the imaging effect of sheeting with the impact of ambient light sources. Additionally, thanks to the narrow emission spectrum of the cQD, a band-pass filter was tested to reduce the effect from environmental lights. The experimental results show that the optical intensity collected with sheeting has an excellent linear relationship (R2 >0.99) with the dose for 6 and 10 MV photons. The full-width half maximum (FWHM) in x and y axis matched with the measured EBT film image, with accuracy in the range of ±1.2and ±2.7mmstandard deviation, respectively. CQD sheeting can significantly improve the light intensity and SNR of optical images. Using 0.1mg/ml sheeting as an example, the signal intensity is increased by 209%, and the SNR is increased by 147.71% at 6 MV photons. The imaging on the anthropomorphic phantom verified that cQD sheeting could be applied to different radiotherapy materials. The average optical intensity increased by about 69.25%, 63.72%, and 61.78%, respectively, after adding cQD sheeting to bolus, mask sample and the combination of bolus and mask. Corresponding SNR is improved by about 62.78%, 56.77%, and 68.80%, respectively. Through the sheeting, optical images with SNR>5 can be obtained in the presence of ambient light and it can be improved through combining with a band-pass filter. When red ambient lights are on, the SNR is increased by about 98.85% after adding a specific filter. Through a combination of cQD sheeting and corresponding filter, light intensity and SNR of optical images can be increased significantly, and it shed new light on the promotion of the clinical application of optical imaging to visualize the beam in radiotherapy.

A prospective randomized comparison of simultaneous integrated boost with sequential boost intensity-modulated radiotherapy in locally advanced head and neck cancer.

A comparison of simultaneous integrated boost (SIB) with sequential boost (SEQ) using intensity-modulated radiotherapy along with concurrent cisplatin in locally advanced head and neck cancer (HNC) was made with regard to their survival outcomes and toxicity profile. A total of 34 patients were enrolled between October 2016 and March 2019. They were randomized into two arms, SIB and SEQB. All patients were treated with 6 MV photon beam on Linear Accelerator with weekly concurrent cisplatin at 35 mg/m2. Overall survival (OS) and disease-free survival (DFS) were the primary end points and acute and late toxicities were the secondary end points. The median follow-up period was 40.6 and 37.3 months for SIB and SEQB, respectively. At the end of 5 years, the median OS was 40.6 and 37.3 months (P = 0.947) and the median DFS was 35.1 and 37.3 months in the SIB and SEQB arms, respectively (P = 0.991). Complete response at 3 months was 64.7% and 76.5% and partial response was 23.5% and 17.6%, whereas progressive disease was 11.8% and 5.9% in SIB and SEQB arms, respectively. Acute dermatitis, mucositis, dysphagia, and salivary gland toxicities were higher in the SIB arm compared to the SEQB arm. SIB and SEQ arms were comparable in terms of OS and DFS. However, the acute toxicities were higher in the SIB arm, although the difference was not significant, compared to the SEQB arm.

Characterization of a commercial EPID-based in-vivo dosimetry and its feasibility and implementation for treatment verification in Malaysia

Abstract Introduction: In vivo dosimetry verification is currently a necessity in radiotherapy centres in Europe countries as one of the tools for patient-specific QA, and now its demand is currently rising in developed countries, such as Malaysia. The aim of this study is to characterize commercial EPID-based dosimetry and its implementation for radiotherapy treatment verification in Malaysia. Materials and Methods: In this work, the sensitivity and performance of a commercially available in vivo dosimetry system, EPIgray® (DOSIsoft, Cachan, France), were qualitatively evaluated prior to its use at our centre. EPIgray response to dose linearity, field size, off-axis, position, and angle dependency tests were performed against TPS calculated dose for 6 MV and 10 MV photon beams. Relative deviations of the total dose were evaluated at isocentre and different depths in the water. EPIgray measured dose was validated by using IMRT and VMAT prostate plan. All calculation points were at the beam isocentre and at points suggested by TG-119 with accepted tolerance of ±10% dose threshold. Results: EPIgray reported good agreement for linearity, field size, off-axis, and position dependency with TPS dose, being within 5% tolerance for both energy ranges. The average deviation was less than ±2% and ±7% in 6 MV and 10 MV photon beams, respectively, for the angle dependency test. A clinical evaluation performed for the IMRT prostate plan gave average agreement within ±3% at the plan isocentre for both energies. While for the VMAT plan, 95% and 100% of all points created lie below ±5% for 6 MV and 10 MV photon beam energy, respectively. Conclusion: In summary, based on the results of preliminary characterization, EPID-based dosimetry is believed as an important tool and beneficial to be implemented for IMRT/VMAT plans verification in Malaysia, especially for in vivo verification, alongside existing pre-treatment verification.

Time-resolved radiation dosimetry using a cerium and terbium Co-doped YAG crystal scintillator

Time-resolved radiation dosimetry is an important factor in ensuring dose delivery during radiotherapy is within the prescribed doses for treatment. One method for time-resolved radiation dosimetry is by radioluminescence (RL) measurement technique using doped-silica optical fibre scintillators. The benefits of RL measurement technique include the capability to measure in real-time, high spatial resolution, and greater adaptability. Additionally, time-resolved dosimetry can be achieved by employing suitable scintillators with short rise and decay time. Silica optical fibre scintillators when doped with suitable dopants, provides the temporal resolution required for pulse-by-pulse dosimetry. Yttrium Aluminium Garnet (YAG) crystal optical fiber doped with Cerium and Terbium are discussed as a possible scintillator for time-resolved radiation dosimetry. The Cerium and Terbium co-doped YAG crystal scintillator samples are irradiated under a 6 MV photon beam from a Elekta Synergy® LINAC. The irradiation doses ranged from 100 cGy/min to 600 cGy/min. The measurements were made using an RL system with a gating time of 1μs. Linear RL response to dose of the irradiated scintillator samples was shown with minimal detectable memory, no afterglow or plateau effects. A rise time of 189.3 ns and a decay time of 260 ns were recorded, indicating promising potential for time-resolved radiation dosimetry.

Evaluating the influence of 6MV and 10MV photon beams on cervical cancer volumetric-modulated arc therapy plans

Cervical cancer is a common gynecological cancer among women worldwide. To determine the effects of 6MV and 10MV volumetric-modulated arc therapy (VMAT) photon beams on the target volume (TV) planning and critical organs in cases of cervical cancer. Fifty patients with carcinoma of the cervix who underwent radiotherapy were selected. The transverse diameter (T) of the cross section of the upper edge of the sacroiliac joint on computerized tomography (CT) images of the patients was measured, and the mean value was calculated as 34cm. All patients were divided into two groups: Group A (T < 34cm) and Group B (T > 34cm). The VMAT plans were generated using 6MV and 10MV plans separately. The prescription dose was 47.5Gy, and the daily dose was 1.9Gy. In Group A, the planning target volume (PTV) dose assessment parameters of 6MV and 10MV plans and their homogeneity and conformity indices were not statistically significantly different. A significant difference was observed between the 6MV and 10MV plans for the PTV dose assessment parameters and the homogeneity index of the plans for Group B. The monitor units (MUs) of the 10MV plans were lower than in the 6MV plans in both Groups A and B, and the difference was statistically significant. The assessment parameter V40 Gy of both the rectum and bladder in the 6MV plans was smaller than the corresponding parameter in the 10MV plans in Group A; in Group B, the assessment parameter V50 Gy of the rectum in the 10MV plans was smaller than in the 6MV plans. When T < 34cm, 6MV energy is more suitable for the external irradiation of cervical cancer. When T > 34cm, 10MV energy is more suitable for cervical cancer radiotherapy. Therefore, 10MV should be considered for patients with a large abdominal size.

Evaluation of Bismuth Oxide Nanoparticles (BiONPs) as a Safe Radiobiological Enhancer for Breast Cancer Radiotherapy

Cancer incidence has been increasing over the years and it is the second leading cause of death globally [1]. The therapeutic strategies in killing the cancerous tissue while keeping the normal healthy tissue uninterrupted can be further improved by introducing nanoparticles (NPs) as radiosensitizers in radiotherapy. In pre-clinical research, a few nanoparticle elements had shown the potential to be radiosensitizers, such as gold, superparamagnetic iron oxide, platinum, and bismuth nanoparticles. Bismuth oxide nanoparticles (BiONPs) have been investigated as a potential radiosensitizer in radiotherapy due to their least toxic and biocompatibility properties. In addition, due to the presence of metallic nanoparticles in cells and their environment, more DNA damage will be introduced and thus enhance the radiation treatment efficacy.&#x0D; &#x0D; This research project was conducted to evaluate the potential of BiONPs to increase the radiation treatment in MCF-7 breast cancer cells and their side effects on the non-targeted breast cancer cells. BiONPs were synthesized through the hydrothermal method, as established in the previous study [2]. The treated and control cells in flasks were irradiated with radiation doses between 0 to 12 Gy at a constant dose rate of 300 cGy/minutes in the beam field size of 10 cm x 10 cm for a 6 MV photon beam, delivered with linear accelerator Primus model (Siemen Healthcare, USA). The irradiated cell-conditioned medium (ICCM) was collected from the targeted cells and transferred into the non-targeted cells. The cell viability assay was employed to evaluate the effect of BiONPs on directly irradiated and non-irradiated cells.&#x0D; &#x0D; In our prior work, the BiONPs had shown to boost radiosensitisation effects in treated cells compared to control cells, with a sensitisation enhancement ratio (SER) of 1.38 [3], as shown in Figure 1. The increased radiosensitisation effects might be attributed to the characteristics of BiONPs with a high effective atomic number (Z=83), which promotes radiation interaction, mainly radiation absorption and scattering. Meanwhile, the present study demonstrated that the non-irradiated MCF-7 cells could maintain their cell viability for more than 80% after 48 h incubation with ICCM treated with BiONPs at 2, 6, and 12 Gy. Furthermore, a comparable trend in cell viability was observed in non-irradiated MCF-7 cells for treated and control groups (p&lt;0.05), as illustrated in Figure 2. This finding indicated that BiONPs are not harmful and do not contribute to side effects in non-targeted cells.&#x0D; The present works have provided evidence that using BiONPs as radiosensitizers in radiotherapy is safe and does not significantly introduce side effects in the non-targeted cells. These data proved the impacts of BiONPs as a potential tool for a safe radiobiological enhancer that will benefit future radiation therapy strategies in cancer management.

Hybrid pencil beam model based on photon characteristic line algorithm for lung radiotherapy in small fields

Abstract Hybrid pencil beam model (HPBM) based on photon characteristic line algorithm has been presented to get accurate three-dimensional (3D) dose distribution for lung radiotherapy in small fields. In the model, we introduced a scattering factor to accurately describe the transport behavior of scattered photons and secondary electrons, combined with the equivalent depth correction and the weighted density correction. The pencil beam kernels of heterogeneous lung phantoms were redefined by the scattering factor and depth dose for a reference field by photon characteristic line algorithm. Subsequently, the 3D dose distribution in lung phantoms with density of 0.1, 0.26, and 0.4 g/cm3, was calculated by the Finite-size pencil beam algorithm in five regular fields and an irregular field for 6 MV photon beam. The dose distributions obtained by the HPBM are in agreement with those obtained by the MC simulations, with a relative error of less than 3% in most of the cases. However, there are apparent discrepancies at media interfaces and lung anterior portion. Moreover, at media interfaces, relative dose errors of the two methods decrease with the increase in field size and lung density. The depth range in which relative errors is greater than 3% increases with the increase in field size at lung anterior portion. In these examples, maximum relative errors are between 5 and 29%. Nevertheless, it is shown that the HPBM based on photon characteristic line algorithm has potential research values in lung dose calculation under conditions of small fields.

Therapeutic effects of in-vivo radiodynamic therapy (RDT) for lung cancer treatment: a combination of 15MV photons and 5-aminolevulinic acid (5-ALA)

Objective. Radiodynamic therapy (RDT) uses high-energy photon beams instead of visible/near-infrared light to treat deep-seated tumors that photodynamic therapy cannot achieve due to the low penetration depth of laser beams. The purpose of this study is to investigate the therapeutic effect of RDT with 15 MV photon beams combined with 5-aminolevulinic acid (5-ALA) using a mouse model. Approach. A subcutaneous C57BL/6 mouse model of KP1 small-cell lung cancer cell line was used. The tumors (N = 120) were randomized into four groups to observe individual and synergistic effects of 5-ALA and radiation treatment: control (untreated, N = 42), radiation treatment (RT) only (N = 20), 5-ALA only (N = 20), and RDT (N = 38). For the RT only and RDT groups, 4 Gy in a single fraction was delivered to the tumors using 15 MV photons. For the 5-ALA only and RDT groups, 5-ALA was injected at a dose of 100 mg kg−1 by tail-vein 4 h prior to RT. The tumor response was assessed by monitoring tumor growth using 1.5 T MR, maximum standardized uptake value (SUVmax) and total lesion glycolysis (TLG) using [18F]FDG PET/CT, and animal survival. Main results. RDT achieved a statistically significant delay in tumor growth by 52.1%, 48.1%, and 57.9% 7 days post-treatment compared to 5-ALA only, RT only, and control group (P < 0.001), respectively. There were no significant differences in tumor growth between 5-ALA only and RT only groups. An additional 38.5%–40.9% decrease in tumor growth was observed, showing a synergistic effect with RDT. Furthermore, RDT significantly decreased [18F]FDG uptakes in SUVmax and TLG 7 days post-treatment by 47.4% and 66.5% (P < 0.001), respectively. RDT mice survived the longest of all treatment groups. Significance. RDT with 15 MV photons and 5-ALA resulted in greater tumor control compared to the control and other treatment groups. A significant synergistic effect was also observed with RDT. These preliminary results demonstrate an effective cancer treatment modality.

Validation of Monte Carlo multithreading TOpas 3.6 software in order to simulate the 6 MV Elekta Synergy MLCi2 platform linac.

Monte Carlo simulation is generally appreciated as an extraordinary technique to investigate particle physics processes and interactions in nuclear medicine and Radiation Therapy. The present task validates a new methodology of Monte Carlo simulation based on the Multithreading technique to reduce CPU time to simulate a 6 MV photon beam provided by the Elekta Synergy MLCi2 platform medical linear accelerator treatment head utilizing TOpas version 3.6 Monte Carlo software and the Slurm Marwan cluster. The simulation includes the linear accelerator (LINAC) major components. Calculations are performed for the photon beam with several treatment field sizes varying from 3 × 3 to 10 × 10 cm2 at a 100 cm of distance from the source to the surface of the IBA dosimetry water box. The simulation was wholly approved by comparison with experimental distributions. To evaluate simulation accuracy, gamma index formalism for (2%/2mm) and (3%/2mm) criteria, Distance To Agreement DTA, and the estimator standard error ɛ and ɛ max are used. Good agreement between simulations and measurements was observed for depth doses and lateral dose profiles, respectively. The gamma index comparisons also highlighted this agreement; more than 97% of the points for all simulations satisfy the quality assurance criteria of (2%/2mm). Regarding calculation performance, the event processing speed is faster using Gate-[mp] compared to TOpas-[mt] mode when running the identical simulation code for both. Consequently, according to the achieved results, the proposed methodology shows the first validation of TOpas in radiotherapy linacs simulations and a reduction in calculation time, capping simulation accuracy as much as possible. For this reason, this software is recommended to be serviceable for Treatment Planning Systems (TPS) purposes.

Geant4 Code Based Simulation of 6 MV Photon Beam for Analysis of Dose Distribution

Geant4 Code Based Simulation of 6 MV Photon Beam for Analysis of Dose Distribution

Dosimetric Benefits with a Lower Energy Photon Beam in Stereotactic Radiosurgery

<h3>Purpose/Objective(s)</h3> Stereotactic radiosurgery (SRS) relies on very small field sizes on the order of a few millimeters to ablate lesions and spare normal structures. Currently a 6 MV photon beam is most often utilized beam energy although there has been an interest in developing lower energy photon beams for stereotactic radiosurgery due to their sharper dose fall off. This study aims to find if there is a dosimetric benefit of using a lower energy photon beam over 6 MV photons for SRS. <h3>Materials/Methods</h3> A 2.5 MV is developed for imaging purpose and is available from a linear accelerator. Monte Carlo simulations were used to simulate both 2.5 MV and 6 MV beams and calculate dose distribution. The details of the incident beams including cone accessory were simulated, with calculated doses benchmarked against measurements. The dose comparison between using 6 MV and 2.5 MV beams were based on a realistic treatment plan for thalamotomy treatment. <h3>Results</h3> For the same target dose coverage, the dose fall off is significantly faster with 2.5 MV beams. Based on calculated 3D dose distributions for a realistic patient treatment plan using 21 arcs with 4 mm cone beams delivered 15000 cGy to the target, the DVH analysis showed the maximum doses to brainstem, chiasm, and optic nerves were 691 cGy (435 cGy), 266 cGy (135 cGy) and 103 cGy (38 cGy) for 6 MV (2.5 MV) beams respectively. The mean organ doses are 136 cGy (64 cGy), 155 cGy (66 cGy) and 51 cGy (19 cGy) to brain stem, Chiasm and optic nerves for 6 MV (2.5 MV) beams respectively. <h3>Conclusion</h3> The dose reductions to organs at risk (OARs) with 2.5 MV beams are very significant ranging from 37% maximum dose to brain stem to 50% mean dose to chiasm, optical nerves and eyes. The sharper dose fall-off with 2.5 MV beam reduced unintended doses to OARs while providing the same target dose coverage. A dosimetric advantage of using 2.5 MV has been observed for delivery of an extremely high dose with very small circular field in SRS.

Validating TG119 VMAT Commissioning on a Volumetric Phantom

<h3>Purpose/Objective(s)</h3> The present work adapts AAPM TG119 on a volumetric detector array and evaluates its feasibility for VMAT commissioning for two different Treatment Planning Systems (TPS). <h3>Materials/Methods</h3> TG119 describes a group of test plans for standard structure sets following prescription and dose constraints objectives. These plans were calculated and evaluated using both Elekta Monaco V5.0 (Montecarlo) and Varian Eclipse v15.6 (AAA algorithm) TPS. TG119 structure sets were inserted on virtual CT images for volumetric Quality Assurance (QA) phantom. A set of plans calculated on both TPS were delivered on a 6MV photon beam on an Elekta Synergy Linac. A set of plans was generated only on Eclipse for a Varian Halcyon Linac with 6MV Flattening Filter Free beam. Generated plans were delivered, dose distribution was concurrently measured with Ion Chamber (IC) point doses using a cavity plug holder inserted on the QA phantom. Dose constraints and goals comparison between TPS was executed. Gamma analysis was performed for 3%3mm and 3%2mm global gamma index and Confidence Limits (CL) according to the TG119 definition of Normal quantile were calculated. Measured and planned point doses on relevant positions were compared. <h3>Results</h3> TG119 goals were mostly satisfied except for some critical situations: PTV D99 goal on head & neck plan calculated on Eclipse TPS and Superior Target D10 goal on Multitarget Plan for Monaco TPS calculation. Gamma Analysis for 3%3mm range of passing rate was 96.8% to 100% while CLs range between 4.1% and 4.7% for a Normal quantile for Monaco TPS. For Eclipse TPS range of passing rate achieved was among 97.2% and 99.9%, CLs range was between 3.2% and 3.1%. For Eclipse plans delivered on Halcyon, the passing rate range was among 98.6% and 99.8%, CLs between 1.6% and 1.7%. 3%2mm global gamma index analysis shows a range of passing rate of 93.5% and 100% for Monaco TPS while CLs range between 4.8% and 8.3%. For Elekta plans on Eclipse TPS range of passing rate was 95.6% and 98.8%, CLs range was between 5.1% and 4.5%. The gamma passing rate range for Halcyon plans was between 94.5% and 99.3 and CLs between 3.4% and 6.0%. IC measurements for Synergy Linac showed an average dose difference of 0.84% between measured and calculated plans on Monaco, range among -3.15% and 7.01%, the greatest differences were found on C-Shape plan for high gradient regions measurements. For Eclipse TPS, the average dose difference was 1.28%, range between -1.04% and 10.26%, the highest difference was found in high gradient region C-Shape plan. For Halcyon plans, IC measurements showed an average dose difference of 0.74%, ranging between -0.27% and 3.38%. <h3>Conclusion</h3> CLs agreed with TG119 reference values even when stricter requirements were used. New criteria are more appropriate for modern treatments, but TG119 methodology remains a valid procedure for VMAT. The methodology described for commissioning VMAT technique on a volumetric QA phantom shows to be robust and consistent for various TPS and lilacs.

Evaluating Therapeutic Effects of In Vivo 15MV Radiodynamic Therapy (RDT) with 5-Aminolevulinic Acid (5-ALA) Using 1.5T MRI and [18F]FDG PET/CT

<h3>Purpose/Objective(s)</h3> A combination of photosensitizer and high-energy photon beam is required to perform radiodynamic therapy (RDT) for tumor treatment. High-energy photon beams activate the photosensitizer, leading to cellular toxicity by producing extra reactive oxygen species to kill malignant cells. The purpose of this study was to investigate the therapeutic effect of RDT with 15 MV photon beams combined with 5-aminolevulinic acid (5-ALA) using a mouse model. <h3>Materials/Methods</h3> All animal studies were approved by our Institutional Animal Care and Use Committee. A subcutaneous murine KP1 small-cell lung cancer model using C57BL/6 mice was used. The tumors (n=126) were randomly assigned into four groups, including control (untreated), radiation treatment (RT) only, 5-ALA only, and RDT to observe individual and synergistic effects of 5-ALA and radiation treatment. Treatment was performed when the tumor reached 5-8 mm in diameter. A single fraction of 4 Gy was delivered to the tumors using 15 MV photons on a clinical linear accelerator for RT only and RDT groups. 5-ALA was injected at 100 mg/kg by tail-vein 4 hours prior to RT for 5-ALA only and RDT groups. Tumor volumes were measured using a 1.5 T MR scanner on the day of treatment and weekly post-treatment. Tumor growth for each tumor was quantified as the ratio of tumor volume one- and two-week post-treatment to the tumor volume on the treatment day. SUV_max and total lesion glycolysis (TLG) were measured using [¹⁸F]FDG PET/CT for control and RDT groups. A 10 min static scan was acquired an hour after an injection of 80 µCi [¹⁸F]FDG. SUV_max was calculated as the maximum measured activity concentration divided by the injected whole bodyweight activity concentration. TLG was quantified as a product of SUV_mean and the metabolic tumor volume. <h3>Results</h3> The tumor growth in the RDT group was delayed by 48.3±11.3%, 46.3±9.2%, and 54.6±12.7% at one-week post-treatment compared to 5-ALA only, RT only, and the control group (P<0.001), respectively. There were no significant differences in tumor growth between 5-ALA only, RT only, and the control group. Moreover, about a 40% additional decrease in tumor growth was observed, showing a synergistic effect of RDT. SUV_max and TLG showed 47.4±8.8% and 66.5±5.3% decrease at one-week post-treatment, respectively. Also, a higher number of distant metastases were observed using [¹⁸F]FDG PET/CT in the control group than in the RDT group. <h3>Conclusion</h3> Assessment of radiodynamic therapy combined with 5-ALA administration and 15 MV high-energy radiation treatment showed improved treatment outcomes compared to the control, RT only, and 5-ALA only groups. Tumor growth delay and tumor activity suppression were significantly improved. Moreover, a synergistic effect of 5-ALA and 15 MV photon beams was observed. The preliminary (hypothesis-generating) results advocate a further investigation into larger sample sizes.

Surface Dose and Skin Toxicity in Low-Magnetic Field MR-Linac

<h3>Purpose/Objective(s)</h3> Radiation induced skin toxicity is a common side effect that results in poor patient satisfaction and unplanned treatment breaks thus prolonging the overall treatment time with poor outcome. It is hypothesized that treatments on low-field MR-Linac will not produce higher surface dose which is investigated in this study. <h3>Materials/Methods</h3> Skin dose has always been an area of active clinical interest that is dependent on many parameters including beam energy, field size, material thickness and atomic number in the beam, material distance from surface, source to surface distance, beam angle (obliquity factor), concomitant chemotherapy etc. Along with these parameters, magnetic field is also a critical parameter that affect surface dose. With the development of the MRL system focus has shifted towards Lawrence force giving rise to electron return effect along with other treatment parameters affecting the skin dose. A Linac equipped with 6MV FFF photons with 90 cm source to axis distance is used. A Markus parallel plate ionization chamber is used in a solid water phantom with proper correction factor to investigate surface and buildup dose with six different gantry angles 15⁰ apart gantry (equivalent of standard Linac 0⁰, 15⁰, 30⁰, 45⁰, 60⁰, and 75⁰) for field sizes of 1.66 × 1.66 cm² (small), 9.96 × 9.9 cm² (reference) and 24.1 × 24.1 cm² (maximum). Measurements were made with increasing buildup thickness in steps of 1 mm to 20 mm of solid water in 0.35 T magnetic field. <h3>Results</h3> In traditional linear accelerators surface dose is 30-40% for a 6MV photon beam, without any modifier. This value increases significantly with beam angle. In MR-Linac, surface dose is relatively low, 12.6%, 14.9% and 16.7% for small, reference and maximum fields at zero-degree gantry angle, respectively. These values are 12% to 2% higher (at 0⁰ and 75⁰ respectively) for maximum field size compared to the reference field size. For lower field sizes minimum variation of 10% was observed at 75° for reference field size. The surface dose increases with increasing radiation field size but magnitude is still lower as the case with traditional lilacs. Table 1 shows the surface dose with field size and gantry angles. <h3>Conclusion</h3> Surface dose in low-field magnetic environment is relatively lower than traditional accelerators. It is concluded that low-field MR-Linac system may not add any additional skin toxicity compared to conventional Linac. However, the effect may be different for high-field MR-Linac system, and appropriate skin evaluation needs to be performed to differentiate between radiation induced toxicity specially for the oblique beams versus RF-thermal effect.

Influence of readout conditions on the thermoluminescence properties of mobile phone display glass for retrospective dosimetry

The glass of mobile phone displays is one of the most popular materials used in retrospective dosimetry, but despite many studies, information on repeatability depending on the measurement mode and location of the collected sample on the screen is limited. In this study, two thermoluminescence readout modes (three-step plateau heating and linear heating) were investigated to compare their accuracy. Glass samples from the widespread iPhone 6 and Samsung Galaxy J530 screens were irradiated using a 137Cs gamma ray source and a 6 MV photon beam to assess their dosimetric properties (repeatability, uniformity, sensitivity, linearity, fading) in the range of low and high doses. It has been found that the three-step plateau heating mode is more accurate and faster for measurements than linear heating mode, which is advantageous considering a readout shorter time in a possible emergency situation. Additionally, the results for aliquots taken from two different locations of the more sensitive glass (iPhone 6) did not differ significantly.

RapidPlan models for prostate radiotherapy treatment planning with 10-MV photon beams

Abstract Introduction: The RapidPlan is a radiotherapy planning tool that uses a dataset of approved plans to predict the dose distribution and automatically generates the dose–volume constraints for optimisation of the new plan. This study compares three strategies of model building for the treatment of prostate cancer with the 10-MV photon beam. Methods: Three models for prostate treatment were compared: Model 6X, Model10X and Model6Xrefined. Model6X is already used in our department and was trained on treatment plans based on the 6-MV photon beam. Model10X was trained on treatment plans based on the 10-MV photon beam and manually optimised by an experienced medical physicist. Finally, Model6Xrefined was trained on plans automatically created by the Model6X, but using the 10-MV photon beam. The three models were used to generate 25 new plans with the 10-MV photon beam. Results: Model10X generated plans with 2 Gy lower mean dose to bladder-PTV and rectum-PTV volumes and 8% lower V15Gy at bladder and rectum volumes, although the number of monitor units increased by 170 on average. Conclusions: The model trained on manually optimised plans generated plans with higher normal tissue sparing. However, model building is a time-consuming process, so a cost–benefit balance should be performed.

Assessment of Surface and Build-up Doses for a 6 MV Photon Beam using Parallel Plate Chamber, EBT3 Gafchromic Films, and PRIMO Monte Carlo Simulation Code.

Background: Accurate assessment of surface and build-up doses has a key role in radiotherapy, especially for the superficial lesions with uncertainties involved while performing measurements in the build-up region.Objective: This study aimed to assess surface and build-up doses for 6 MV photon beam from linear accelerator using parallel plate ionization chamber, EBT3 Gafchromic films, and PRIMO Monte Carlo (MC) simulation code.Material and Methods: In this experimental study, parallel plate chamber (PPC05) and EBT3 Gafchromic films were used to measure doses in a build-up region for 6 MV beam from the linear accelerator for different field sizes at various depths ranging from 0 to 2 cm from the surface with 100 cm source to surface distance (SSD) in a solid water phantom. Measured results were compared with Monte Carlo simulated results using PENELOPE-based PRIMO simulation code for the same setup conditions. Effect of gantry angle incidence and SSD were also analyzed for depth doses at the surface and build-up regions using PPC05 ion chamber and EBT3 Gafchromic films.Results: Doses measured at the surface were 14.78%, 19.87%, 25.83%, and 31.54% for field sizes of 5×5, 10×10, 15×15, and 20×20 cm2, respectively for a 6 MV photon beam with a parallel plate chamber and 14.20%, 19.14%, 25.149%, and 30.90%, respectively for EBT3 Gafchromic films. Both measurement sets were in good agreement with corresponding simulated results from the PRIMO MC simulation code; doses increase with the increase in field sizes.Conclusion: Good agreement was observed between the measured depth doses using parallel plate ionization chamber, EBT3 Gafchromic films, and the simulated depth doses using PRIMO Monte Carlo simulation code.

Evaluation and Comparison of Dosimetric Characteristics of Semiflex®3D and Microdiamond in Relative Dosimetry under 6 and 15 MV Photon Beams in Small Fields

Background: In modern radiotherapy techniques, the frequently small and non-uniformed fields can increase treatment efficiency due to their highly conformal dose distribution. Particular features including lack of Lateral Charge Particle Equilibrium (LCPE) lead to detectors with high resolution since any error in obtained dosimetric data could cause patient mistreatments.Objective: This study aims to evaluate and compare two small detectors (Semiflex®3D and microdiamond) dosimetric characteristics in small field relative dosimetry.Material and Methods: In this experimental study, the dosimetric properties of Semiflex®3D and microdiamond were assessed under 6 and 15 MV photon beams. The linearity and stability of the detector’s response and dose rate were measured. Square-field sizes ranging from 0.6×0.6 - 5×5 cm2 were used for obtaining percentage depth dose curves (PDDs) and in-plane profiles. The angular and temperature dependence of both detectors’ responses were also studied.Results: The detector response shows good stability, no deviation from linearity, and low dose rate dependence (≤1.6%). PDDs and in-plan profiles of both detectors are in good agreement and no significant difference was observed except for the high dose gradient regions (P-value≤0.017). Both detectors demonstrated low angular dependence (<0.3%) with temperature dependence lower than 1% for both detectors.Conclusion: The results indicate both investigated detectors were well performed in small field relative dosimetry and for measuring penumbra, it is better to use microdiamond detector.