Depth Of Maximum Dose Research Articles

Energy response of CaSO4:Dy thermoluminescence detector to medical linear accelerator photon beams.

The study aims to evaluate the energy response of the thermoluminescent dosemeter (TLD) CaSO4:Dy from high energy photon beams produced from medical linear accelerator. The test was performed on the polymethyl methacrylate phantom surface and at the depth of dose maximum with a source-to-surface distance of 100cm and the radiation field size of 12×12cm. The results were compared with the TLD response exposed to 60Co standard source. The results show that the TLD response to the linac's photon differs >30% compared to the TLD response to 60Co exposure when measured at the phantom surface, while at the depth of maximum dose the response is similar (< ±10%), indicating that the TLD response is no longer dependent on the energy. This implies that the current dose reading evaluation based on 60Co calibration curve should be corrected to obtain more accurate dose report of the radiation workers.

Exploring the impact of filament density on the responsiveness of 3D-Printed bolus materials for high-energy photon radiotherapy

Background3D-printed boluses in radiation therapy receive consideration for their ability to enhance treatment precision and patient comfort. Yet, thorough validation of 3D-printed boluses using various validation procedures and statistical analysis is missing. This study aims to determine the effectiveness of using 3D-printed boluses in radiation therapy. MethodThe CT Hounsfield Unit (HU) profiles of the 3D-printed materials were compared to those of the commercial bolus using the Eclipse Treatment Planning System (TPS) unit. Furthermore, absolute dose measurements were carried out to assess the efficacy of the 3D-printed samples by using concordance correlation coefficient to assess the agreement between 3D materials and the commercial bolus. ResultsThe average HU profiles of 3D-printed materials were: −144.53 (ABS), −124.40 (ASA), 9.55 (PLA-P), −140.79 (Polycarbonate), −68.58 (PLA-S), and −113.159 (PET-G), respectively. PDD scans showed that air gaps between the bolus and surface shifted the maximum dose depth. Whereas dosimetry has shown that ASA and Polycarbonate are different in attenuation from other tested filaments. This limitation could affect their performance in specific applications within radiation therapy. The final analysis, using the TPS-generated datasets to assess the area under the dose curve in the build-up zone of each 3D-bolus, excluded ABS. ConclusionsThe results from PDD scans and dose assessments offer compelling proof that 3D-printed boluses are effective for delivering surface dosage and are like commercially available boluses. Moreover, specific materials showed a statistically significant improvement in delivering the dose. The results highlight the capability of 3D-printed boluses to enhance the effectiveness of radiation therapy.

Comprehensive analysis of peripheral dose in electron beam therapy with a Varian TrueBeam Linac

ObjectiveTo investigate the characteristics of peripheral doses outside electron-beam applicators in Varian TrueBeam linacs. MethodPeripheral doses outside the electron applicator were measured for 6-, 9- and 12-MeV beams at the maximum dose depth (Dmax) for each energy source and at a source-to-surface distance of 100 cm. Measurements were performed using EBT3 films in solid water phantoms. The impact of field size on the penumbra width and peripheral doses was studied using various cutouts, including 3 cm × 3 cm, 6 cm × 6 cm, and 10 cm × 10 cm in a 10 cm × 10 cm applicator with the gantry and collimator at 0°. The influence of the applicator size was investigated using a circular cutout of 5 cm in diameter for various applicator sizes, including 6 cm × 6 cm, 10 cm × 10 cm, 15 cm × 15 cm, 20 × 20 cm, and 25 cm × 25 cm, at Dmax for each energy, while keeping the gantry and collimator angle at 0°. The measured dose profiles were compared with the Eclipse treatment planning system (TPS) predicted dose profiles. The effect of varying gantry angles (0°, 90°, and 270°) for a 3 cm × 3 cm cutout in a 10 cm × 10 cm applicator for each energy source and varying collimator angles (0°, 90°, and 270°) for a 10 cm × 10 cm field were investigated to determine their effects on the penumbra widths and peripheral doses. ResultsBoth the penumbra width and peripheral dose values increased with energy across different field sizes, gantry angles, collimator angles, and applicator sizes. Root Mean Square Deviation (RMSD) analysis indicated minimal differences between the measured profiles and TPS data. Peripheral doses remained below 5% of the maximum dose approximately 10–15 mm away from the field edges, suggesting the potential for implementing additional shielding where required. ConclusionsThis study highlights the importance of considering peripheral doses in electron radiotherapy. It is important to note the impact on healthy tissues beyond the treatment area to ensure patient safety and prevent the long-term side effects of treatment. These findings emphasize the necessity of implementing appropriate measures to minimize peripheral doses.

Cerenkov free micro-dosimetry in small-field radiation therapy technique

Objective. Optical fiber-based scintillating dosimetry is a recent promising technique owing to the miniature size dosimeter and quality measurement in modern radiation therapy treatment. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov effect and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement in radiation therapy treatment protocol by investigating several dosimetric characteristics. Approach. A micro-dosimetry technique was proposed with the performance evaluation of a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head based on IR-emitting micro-clusters with a sensitive volume of 1.5 × 10−6 mm3. The proposed system was evaluated under the 6 MV LINAC beam used in patient treatment. Overall measurements were performed using IBATM water tank phantoms by following TRS-398 protocol for radiotherapy. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm2 to 10 × 10 cm2 under LINAC. In addition, several dosimetric parameters such as percentage depth dose (PDD), high lateral resolution beam profiling, dose linearity, dose rate linearity, repeatability, reproducibility, and field output factor were investigated to realize the performance of the novel detector. Main results. This study highlighted a complete removal of the Cerenkov effect using a point-like miniature detector, especially for small field radiation therapy treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼0.18%) for the dose rate of 20–1000 cGy s−1. An entire linear response (R 2 = 1) was obtained for the dose delivered within the range of 4–1000 cGy, using a selected field size of 1 × 1 cm2. Perfect repeatability (max 0.06% variation from average) with day-to-day reproducibility (0.10% average variation) was observed. PDD profiles obtained in the water tank present almost identical behavior to the reference dosimeter with a build-up maximum depth dose at 1.5 cm. The small field of 0.5 × 0.5 cm2 profiles have been characterized with a high lateral resolution of 100 µm. Significance. Unlike recent plastic scintillation detector systems, the proposed micro-dosimetry system in this study requires no Cerenkov corrections and showed efficient performance for several dosimetric parameters. Therefore, it is expected that considering the detector correction factors, the IR-ISD system can be a suitable dose measurement tool, such as in small-field dose measurements, high and low gradient dose verification, and, by extension, in microbeam radiation and FLASH radiation therapy.

Planar dose calculation of electron therapy

Purpose. The aim of this study is to determine the planar dose distribution of irregularly-shaped electron beams at their maximum dose depth (z max) using the modied lateral build-up ratio (LBR) and curve-fitting methods. Methods. Circular and irregular cutouts were created using Cerrobend alloy for a 14 × 14 cm2 applicator. Percentage depth dose (PDD) at the standard source-surface-distance (SSD = 100 cm) and point dose at different SSD were measured for each cutout. Orthogonal profiles of the cutouts were measured at z max. Data were collected for 6, 9, 12, and 15 MeV electron beam energies on a VERSA HDTM LINAC using the IBA Blue Phantom2 3D water phantom system. The planar dose distributions of the cutouts were also measured at z max in solid water using EDR2 films. Results. The measured PDD curves were normalized to a normalization depth (d 0) of 1 mm. The lateral-buildup-ratio (LBR), lateral spread parameter (σ R (z)), and effective SSD (SSD eff ) for each cutout were calculated using the PDD of the open applicator as the reference field. The modified LBR method was then employed to calculate the planar dose distribution of the irregular cutouts within the field at least 5 mm from the edge. A simple curve-fitting model was developed based on the profile shapes of the circular cutouts around the field edge. This model was used to calculate the planar dose distribution of the irregular cutouts in the region from 3 mm outside to 5 mm inside the field edge. Finally, the calculated planar dose distribution was compared with the film measurement. Conclusions. The planar dose distribution of electron therapy for irregular cutouts at z max was calculated using the improved LBR method and a simple curve-fitting model. The calculated profiles were within 3% of the measured values. The gamma passing rate with a 3%/3 mm and 10% dose threshold was more than 96%.

Evaluating the performance of thermoplastic 3D bolus used in radiation therapy

A 3D-printed bolus is being developed to deliver accurate doses to superficial cancers. In this study, flexible thermoplastic filaments, specifically PLA, TPU, PETG, and HIPS, were fabricated into boluses and then compared to commercial bolus for the variation of the dose elevation region of photon beams. The experimental results indicate that the maximum dose depth is similar, and the consistent trend of the percentage depth dose confirms the potential usage as a build-up bolus.

Beam quality and the mystery behind the lower percentage depth dose in grid radiation therapy

Grid therapy recently has been picking momentum due to favorable outcomes in bulky tumors. This is being termed as Spatially Fractionated Radiation Therapy (SFRT) and lattice therapy. SFRT can be performed with specially designed blocks made with brass or cerrobend with repeated holes or using multi-leaf collimators where dosimetry is uncertain. The dosimetric challenge in grid therapy is the mystery behind the lower percentage depth dose (PDD) in grid fields. The knowledge about the beam quality, indexed by TPR20/10 (Tissue Phantom Ratio), is also necessary for absolute dosimetry of grid fields. Since the grid may change the quality of the primary photons, a new kq,q0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbf{k}}_{\\mathbf{q},{\\mathbf{q}}_{0}}$$\\end{document} should be evaluated for absolute dosimetry of grid fields. A Monte Carlo (MC) approach is provided to resolving the dosimetric issues. Using 6 MV beam from a linear accelerator, MC simulation was performed using MCNPX code. Additionally, a commercial grid therapy device was used to simulate the grid fields. Beam parameters were validated with MC model for output factor, depth of maximum dose, PDDs, dose profiles, and TPR20/10. The electron and photon spectra were also compared between open and grid fields. The dmax is the same for open and grid fields. The PDD with grid is lower (~ 10%) than the open field. The difference in TPR20/10 of open and grid fields is observable (~ 5%). Accordingly, TPR20/10 is still a good index for the beam quality in grid fields and consequently choose the correct kq,q0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbf{k}}_{\\mathbf{q},{\\mathbf{q}}_{0}}$$\\end{document} in measurements. The output factors for grid fields are 0.2 lower compared to open fields. The lower depth dose with grid therapy is due to lower depth fluence with scatter radiation but it does not impact the dosimetry as the calibration parameters are insensitive to the effective beam energies. Thus, standard dosimetry in open beam based on international protocol could be used.

Reconfiguring a Plane-Parallel Transmission Ionization Chamber to Extend the Operating Range into the Ultra-High Dose-per-pulse Regime.

This study aims to investigate the feasibility of enhancing the charge collection efficiency (CCE) of a transmission chamber by reconfiguring its design and operation. The goal was to extend the range of dose-per-pulse (DPP) values with no or minimal recombination effects up to the ultra-high dose rate (UHDR) regime. The response of two transmission chambers, with electrode distance of 1 mm and 0.6 mm, respectively, was investigated as a function of applied voltage. The chambers were mounted one-by-one in the electron applicator of a 10 MeV FLASH-modified clinical linear accelerator. The chamber signals were measured as a function of nominal DPP, which was determined at the depth of dose maximum using EBT-XD film in solid water and ranged from 0.6 mGy per pulse to 0.9 Gy per pulse, for both the standard voltage of 320 V and the highest possible safe voltage of 1,200 V. The CCE was calculated and fitted with an empirical logistic function that incorporated the electrode distance and the chamber voltage. The CCE decreased with increased DPP. The CCE at the highest achievable DPP was 24% (36%) at 320 V and 51% (82%) at 1,200 V, for chambers with 1 mm (0.6 mm) electrode distance. For the combination of 1,200 V- and 0.6-mm electrode distance, the CCE was ∼100% for average dose rate up to 70 Gy/s at the depth of dose maximum in the phantom at a source-to-surface distance of 100 cm. Our findings indicate that minor modifications to a plane-parallel transmission chamber can substantially enhance the CCE and extending the chamber's operating range to the UHDR regime. This supports the potential of using transmission chamber-based monitoring solutions for UHDR beams, which could facilitate the delivery of UHDR treatments using an approach similar to conventional clinical delivery.

Dosimetric characterization of foam padding with posterior fields in palliative radiation therapy

Patients undergoing external beam radiation therapy for the palliative treatment of painful bony metastases may have difficulty maintaining a still position on a rigid uncovered couch top, both during CT simulation as well as during patient setup, image guidance, and treatment on the linear accelerator. For these patients, a thin foam pad or mattress is sometimes used to mitigate patient discomfort. It was desired to quantify the effect of the padding in cases in which the patient is to be treated supine with posterior beams when the majority of the beam weighting traverses both the couch and the pad. Ion chamber measurements in-phantom were acquired with 6 MV, 10 MV, and 15 MV photon beams. At depths of maximum dose, the pad resulted in a difference of signal collected ≤1%. At the phantom surface, the pad resulted in an increase in signal ranging from 1% to 6.5% for the measured beams. CT data of the pad, both with and without applied pressure, indicated that the pad had average HU values close to air.

Comparison of the accuracy of Monte Carlo and Ray Tracing dose calculation algorithms for multiple target brain treatments on CyberKnife.

Single plan multiple brain targets (MBT) stereotactic radiosurgery dose difference between Monte Carlo (MC) and Ray Tracing (RT) algorithms has not been studied. A retrospective study and dose measurements were performed to access factors influencing dose differences. Fifty-three RT treatment plans with a total of 209 brain metastases were extracted from Precision Treatment Planning System (TPS). These plans were generated using fixed cones and were delivered using the CyberKnife M6 system. The same treatment plans were recalculated using MC algorithm and keeping the beam parameters unchanged. MC calculated plan parameters were extracted and dose differences were normalised to MC calculated dose. Correlations were investigated. RT and MC calculated off-centre-ratio (OCR) and tissue-phantom-ratio (TPRs) were exported from the TPS and compared with measured. Plans with 5 gross tumour volumes (GTVs) were created on a phantom and dose measured using a CC04 ionisation chamber and microdiamond detector for comparison with calculated doses. Calculated and measured TPR agreed within ± 1% beyond depth of maximum dose. The OCR showed differences up to 4.3% in the penumbra and out-of-field (OOF) regions. Largest RT and MC calculated GTV mean dose difference was -5.7%. An increase in the number of GTVs and reduction in the geometric separation of metastases were associated with increased differences between RT and MC calculated doses. In conclusion, calculated dose disagreement in MBT depends on the number of GTVs per plan, number of GTVs within a certain separation distance and plan complexity. MC dose calculation is recommended for complex CyberKnife SRS of MBT.

Technical note: Point-by-point ion-recombination correction for accurate dose profile measurement in high dose-per-pulse irradiation field.

Although flattening filter free (FFF) beams are commonly used in clinical treatment, the accuracy of dose measurements in FFF beams has been questioned. Higher dose per pulse (DPP) such as FFF beams from a linear accelerator may cause problems in dose profile measurements using an ionization chamber due to the change of the charge collection efficiency. Ionization chambers are commonly used for percent depth dose (PDD) measurements. Changes of DPP due to chamber movement during PDD measurement can vary the ion collection efficiency of ionization chambers. In the case of FF beams, the DPP fluctuation is negligible, but in the case of the FFF beams, the DPP is 2.5 ∼ 4 times larger than that of the FF beam, and the change in ion collection efficiency is larger than that of the FF beam. PDD profile normalized by maximum dose depth, 10 cm depth for example, may therefore be affected by the ion collection efficiency. In this study, we investigate the characteristics of the ion collection efficiency change depending on the DPP of each ionization chamber in the FFF beam. We furthermore propose a method to obtain the chamber- independent PDD by applying a DPP-dependent ion recombination correction. Prior to investigating the relationship between DPP and charge collection efficiency, Jaffe-plots were generated with different DPP settings to investigate the linearity between the applied voltage and collected charge. The absolute dose measurement using eight ionization chambers under the irradiation settings of 0.148, 0.087, and 0.008 cGy/pulse were performed. Applied voltages for the Jaffe-plots were 100, 125, 150, 200, 250, and 300V. The ion recombination correction factor Pion was calculated by the two-voltage analysis (TVA) method at the applied voltages of 300 and 100V. The DPP dependency of the charge collection efficiency for each ionization chamber were evaluated from the DPP- Pion plot. PDD profiles for the 10 MV FFF beam were measured using Farmer type chambers (TN30013, FC65-P, and FC65-G) and mini-type chambers (TN31010, TN31021, CC13, CC04, and FC23-C). The PDD profiles were corrected with ion recombination correction at negative and positive polar applied voltages of 100 and 300V. From the DPP-Pion relation for each ionization chamber with DPP ranging from 0.008 cGy/pulse to 0.148 cGy/pulse, all Farmer and mini-type chambers satisfied the requirements described in AAPM TG-51 addendum. However, Pion for the CC13 was most affected by DPP among tested chambers. The maximum deviation among PDDs using eight ionization chambers for 10 MV FFF was about 1%, but the deviation was suppressed to about 0.5% by applying ion recombination correction at each depth. In this study, the deviation of PDD profile among the ionization chambers was reduced by the ion recombination coefficient including the DPP dependency, especially for high DPP beams such as FFF beams. The present method is particularly effective for CC13, where the ion collection efficiency is highly DPP dependent.

Dosimetric characteristics of 6MV flattening filter free and flattened beams among beam-matched linacs: a three-institutional study

BackgroundBeam matching is a concept in radiotherapy applied to clinics where more than one linac is employed to harmonise beam characteristics across linacs for allowing patients interchange without replanning. In view of this, the current study analyzes and compares dosimetric characteristics of 6MV flattening filter free and flattened beams of three beam-matched linear accelerators (linacs) from three different clinics with the aim to evaluate the matching under tight criteria for gamma analysis.MethodsThree Elekta linacs from three different clinics were included. The linacs have the same collimator assembly, Elekta Agility. Beam data were collected during commissioning process using PTW dosimetry systems. Dose profiles and percentage depth doses (PDD) were analyzed using 1D gamma analysis (1 mm/1%) as well as the following parameters: depth of maximum dose, PDD10, flatness, unflattnes, symmetry, penumbra, output factors. Additionally, five stereotactic treatment plans were optimized in one clinic and calculated by all three planning systems (Monaco) for a dosimetric comparison.ResultsGamma analysis of dose profiles and PDDs showed clinically acceptable results of 96.3% passing rate for profiles and 100% passing rate for PDDs. All dosimetric parameters were in good agreement with the reference data. Furthermore, dosimetric comparisons between stereotactic treatment plans showed a maximum standard deviation of 0.48 Gy for the maximum dose to PTV, and a maximum standard deviation of 0.1 Gy for the dose to the organs at risk.ConclusionsAll three linacs showed a strong agreement between parameters and passed the gamma analysis using 1% DD/1mm DTA criteria. This study confirmed the matching between linacs, offering the possibility to interchange patients with no replanning.

Assessment of out-of-field radiation doses for high dose per pulse intraoperative electron beam radiotherapy using TLD-100

PurposeThis research aims to assess the out-of-field surface doses for different combinations of electron energy, applicator size, and distance from the applicator wall of high dose-per-pulse IntraOperative electron Radiation Therapy (IOeRT) using thermoluminescent dosimeters (TLDs). Materials and methodsThe out-of-field doses for various combinations of IOeRT electron beam energy/applicator size were measured using ionometric dosimetry. The calibrated LiF:Mg,Ti dosimeters (TLD-100) were used to make the measurements. TLD results were benchmarked using an Advanced Markus chamber and a polymethyl methacrylate slab phantom. TLDs were read out using a HARSHAW (type 4000) manual TLD reader. ResultsThe TLDs received out-of-field absorbed doses ranging from 0.033 to 0.545 mGy/MU depending on the applicator size, electron energy, and distance from the applicator's outer wall. The mean discrepancies between TLDs and Advanced Markus ion chamber measured data were about 1.82% in the PMMA slab phantom at a depth of maximum dose for each electron energy. ConclusionThe skin surface dose can be significant during IOeRT. The maximum out-of-field doses have occurred at high electron beam energy and closer distances around the applicator wall. TLD can measure the skin's dose level according to its good agreement with the reference Advanced Markus dosimeter. The TLD-100 can be used as a reliable dosimeter for intraoperative radiation dosimetry.

Treatment planning with a 2.5MV photon beam for radiation therapy.

The shallow depth of maximum dose and higher dose fall-off gradient of a 2.5MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5MV beam has an energy bridging the gap between kilo-voltage (kV) and mega-voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles. We have commissioned and utilized a MATLAB-based, open-source treatment planning software (TPS), matRad, for intensity-modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose. Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5MV beam deposited 6%-19% less integral doses to the nasal cavity, orbit, and GBM cases than 6MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%-14.9%, 2.2%-8.1%, and 2.5%-19.0% lower for the 2.5MV beam in the nasal cavity, orbit, and GBM plans. This study demonstrates that the 2.5MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single-energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low- and middle-income countries, and investigations on dose enhancement from high-Z nanoparticles.

Two Novel Irradiation Methods for Angiosarcoma of Total Scalp Irradiation

<h3>Purpose/Objective(s)</h3> Due to large, irregular and superficial spread of the complex target, conventional radiotherapy via photon and electron beams matching technique for angiosarcoma of total scalp irradiation (TSI) presents major technical and dosimetric challenges. To increase superficial target coverage, reduce normal brain dose, and eliminate the difficulty of patient set up and fields matching, we propose two novel irradiation methods: fully-automated non-coplanar HyperArc VMAT and co-planar Halcyon delivery platform utilizing a 3D-printed 1 cm scalp bolus. <h3>Materials/Methods</h3> The technical and dosimetric performance of the proposed two novel methods was simulated using nine previously treated TSI patients in our institution. HyperArc plans utilized 6MV-FFF beam (800 MU/min) on SBRT-dedicated Linac with fully-automated HyperArc module and 1 cm 3D-printed scalp bolus for dose build up to the superficial target to deliver a prescription dose of 70 Gy in 35 fractions. For comparison, these plans were re-planned via 4 full-arcs on recently installed fast rotating co-planar Halcyon Linac equipped with 6MV-FFF (800 MU/min) with lower mean energy of 1.3 MeV and nominal depth of maximum dose at 1.3 cm. Identical isocenter location and similar planning parameters and objectives, were used on both Linac platforms. Plan quality, including BED10 and treatment delivery accuracy and efficacy, was compared. <h3>Results</h3> Both platforms generated highly conformal, homogenous TSI plans and showed statistically insignificant differences on target coverage, mean target dose, conformity, and dose homogeneity. The average BED10 of the mean target dose was 92.0 ± 1.4 Gy (HyperArc) vs 93.4 ± 0.9 Gy (Halcyon) (p = 0.06). HyperArc provided mean brain dose and V60Gy of 8.1 ± 1.5 Gy and 0.8 ± 0.9 cc respectively, compared to 8.5 ± 1.4 Gy (p > 0.05) and 1.4 ± 0.7 cc (p = 0.04), on Halcyon. For both platforms, significantly lower maximal dose of < 5 Gy was observed in organs at risk (OARs), including spinal cord, brainstem, optic pathway, hippocampi, eyes and lenses, and cochlea (p > 0.05 for all OARs). Halcyon plan complexity slightly decreased as seen in the average decreases of total monitor units, modulation factor and beam-on time by 119, 0.6, and 0.6 min respectively, and the estimated overall treatment time was reduced by an average of 2.4 min. Treatment time for both platforms was less than 15 minutes. Portal dosimetry quality assurance results of HyperArc and the corresponding Halcyon plans were 99.8% and 100%, demonstrating comparable treatment delivery accuracy. <h3>Conclusion</h3> We demonstrated that both Halcyon and HyperArc platforms can deliver an accurate and efficient treatment of greater than 90 Gy BED10 to large, complex and superficial angiosarcoma of the scalp and face with significantly lower mean brain dose of less than 10 Gy. Clinical use of these platforms is underway in our center and highly recommended to other centers, including community centers, expanding the use of Halcyon Linac to underserved patient cohort.

Effect of Diode-Based Transmission Detector Measurement on Dose Perturbation during Delivery of 6MV Photon

<h3>Purpose/Objective(s)</h3> Delivery dose quality assurance (QA) during treatment planning execution is the most direct and effective way to ensure that the prescribed dose is delivered accurately and the patient is irradiated safely. The purpose of this article is to evaluate the stability and sensitivity of the diode-based transmission detector (TD) installed on the beam path during radiotherapy, and analyze the effect of TD on the photon beam fluence and dose distribution. <h3>Materials/Methods</h3> The beam fluence with and without TD was measured for 6MV on a linear accelerator. The point doses at different depths (0.0cm∼15.0cm), different dose values (100MU∼500MU), different dose rates (100MU/min∼600MU/min) and different irradiation fields (3cm × 3cm∼20cm × 20cm) were measured by cylindrical three-dimensional water tank, and the transmission factors (TF) were calculated and analyzed. The percentage depth dose (PDD) and beam profile under different parameters were collected to analyze the effect of TD on ray quality and dose distribution. The effect of different irradiation fields on the γ passing rate was evaluated by a planar dosimeter. <h3>Results</h3> The diode-based TD has the high stability of 0.1% (1SD) and excellent position monitoring performance (≤0.2mm). The TF varies with the depth, dose, dose rate and irradiation fields. When the depth is 0cm, the TF has maximum value of 99.55%. For the depth of 0cm∼5cm, the TF increases with the increase of dose and dose rate (<i>R</i>=0.91, 0.75). For the depth of 5cm, the TF is least affected by dose and dose rate (1SD: 0.01%, 0.07%), and decreased with the increase of irradiation fields, 98.94% for 3cm × 3cm. When the depth is >5cm, it decreases with the dose increasing (<i>R</i>=−0.88∼−0.26), and increases with the dose rate increasing (<i>R</i>=0.78). The average TF under all the above conditions is 98.46%, that is, beam attenuation is 1.54%. The movement of the position of maximum dose depth is 0.124cm for 5cm × 5cm and 0.250cm for 3cm × 3cm to the surface of the water (0cm), otherwise ≤0.003cm. TD increases dose in build-up region, 1.49% for fields of 20cm × 20cm. TD effects ray quality (≤0.0028), beam symmetry and flatness (≤0.68%). The γ passing rate does not change under the commonly used indexes of 3%/3mm and 2%/2mm. <h3>Conclusion</h3> The diode-based TD has high stability and excellent monitoring performance. Although it has little effect on ray quality, beam symmetry, flatness and γ passing rate, it will cause beam attenuation and increase surface dose.

Dose Field Shaping and Biological Effectiveness of the Effect of Pulsed Electron Accelerator Novac-11 on Mammalian Cells

The development of technologies for using the Novac-11 pulsed electron accelerator in radiation therapy of animals with spontaneous neoplasms requires dosimetric and radiobiological studies. The studies were performed on cultured Chinese hamster V-79 fibroblasts after irradiation with 10 MeV electrons in a dose range up to 12 Gy and 60Co γ-radiation. Chemical dosimeters FBX and Fricke were used as additional test-systems. The depth dose curves were measured and the maximum dose depth of the electron beam was determined in tissue-equivalent phantoms. Cell survival and the data of chemical dosimetric systems showed that the effects of electron irradiation did not differ from that of 60Co γ-radiation. It was concluded that the use of Novac-11 in the therapy of animals with spontaneous neoplasms is advisable.

The magnetic field dependent displacement effect and its correction in reference and relative dosimetry

Objective. This study investigates the perturbation correction factors of air-filled ionization chambers regarding their depth and magnetic field dependence. Focus has been placed on the displacement or gradient correction factor Additionally, the shift of the effective point of measurement that can be applied to account for the gradient effect has been compared between the cases with and without magnetic field. Approach. The perturbation correction factors have been simulated by stepwise modifications of the models of three ionization chambers (Farmer 30013, Semiflex 3D 31021 and PinPoint 3D 31022, all from PTW Freiburg). A 10 cm × 10 cm 6 MV photon beam perpendicular to the chamber’s axis was used. A 1.5 T magnetic field was aligned parallel to the chamber’s axis. The correction factors were determined between 0.4 and 20 cm depth. The shift of from the chamber’s reference point was determined by minimizing the variation of the ratio between dose-to-water and the dose-to-air along the depth. Main Results. The perturbation correction factors with and without magnetic field are depth dependent in the build-up region but can be considered as constant beyond the depth of dose maximum. Additionally, the correction factors are modified by the magnetic field. at the reference depth is found to be larger in 1.5 T magnetic field than in the magnetic field free case, where an increase of up to 1% is observed for the largest chamber (Farmer 30013). The magnitude of for all chambers decreases by 40% in a 1.5 T magnetic field with the sign of remains negative. Significance. In reference dosimetry, the change of in a magnetic field can be corrected by applying the magnetic field correction factor when the chamber is positioned with its at the depth of measurement. However, due to the depth dependence of the perturbation factors, it is more convenient to apply the -shift during chamber positioning in relative dosimetry.

Small beam dosimetry by using Al2O3 optically stimulated luminescent (OSL) dosimeters at high energy photons and electrons

The study focused on the measurements of depth dose for small beam in the high energy photons and electrons. The percentage depth dose (PDD) was measured in 6 and 10 MV photons and 9 and 12 MeV electrons at 3 × 3 cm field sizes by using the Al2O3 optically stimulated luminescent (OSL) dosimeters. The PDD in OSL dosimeters were compared to those in ionization chamber and Gafchromic EBT3 film dosimeter. The results showed that the PDD in OSL dosimeters in lower photon and electron energies were in good agreement within 4% to ionization chamber and film. The PDD in 10 MV photons however showed gradual increase of deviation up to 10% beyond the depth of maximum dose (dmax). The surface doses in OSL dosimeters were significantly higher compared to those in ionization chamber and film dosimeter. The overall results suggested the suitability of OSL dosimeters to be used as indirect dosimetry works in high energy photons and electrons.

Dosimetric validation of Acuros® XB algorithm for RapidArc™ treatment technique: A post software upgrade analysis.

To validate the Acuros® XB (AXB) algorithm in Eclipse treatment planning system (TPS) for RapidArc™ (RA) technique following the software upgrades. A Clinac-iX (2300CD) linear accelerator and Eclipse TPS (Varian Medical System, Inc., Palo Alto, USA) was used for commissioning of AXB algorithm using a 6 megavolts photon beam. Percentage depth dose (PDD) and profiles for field size 2 cm × 2 cm, 4 cm × 4 cm, 6 cm × 6 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm to 40 cm × 40 cm were taken. AXB calculated PDDs and profiles were evaluated against the measured and analytical anisotropic algorithm (AAA)-calculated PDDs and profiles. Test sites recommended by American Association of Physicists in Medicine task group (AAPM TG)-119 recommendation were used for RA planning and delivery verification using AXB algorithm. AXB shows excellent agreement with measurements and AAA calculated data. The CLs were consistent with the baseline values published by TG-119. AXB algorithm has the potential to perform photon dose calculation with comparable fast calculation speed without negotiating the accuracy. AAPM TG-119 was successfully implemented to access the proper configuration of AXB algorithm following the TPS upgrade.