Source-skin Distance Research Articles

Automated robotic-assisted patient positioning method and dosimetric impact analysis for boron neutron capture therapy

Boron Neutron Capture Therapy (BNCT) represents a revolutionary approach in targeted radiation treatment for cancer. While the therapy’s potential in precise targeting is well-recognized, a critical bottleneck remains in the accurate positioning of patients for treatment delivery. This study proposes a novel automated robotic-assisted patient positioning system specifically engineered for BNCT applications. The system utilizes high-precision industrial robotics and is fully integrated with NeuMANTA, a proprietary treatment planning system designed for BNCT. Through a systematic workflow, the robotic arm algorithmically calculates and executes the patient’s positioning based on the treatment plan, thus enhancing the accuracy and efficacy of the treatment. We validate the positioning system using an anthropomorphic phantom and evaluate the dosimetric impact of positional deviations. The results indicate that the system achieves high accuracy, with a maximum observational deviation of 3 mm in Source-to-Skin Distance (SSD) and 2 mm along the surface. Dosimetric analysis reveals that the resulting dose changes are less than 1% in surface orientation deviations and less than 5% in SSD orientation deviations. The study concludes that the robotic patient positioning system substantially advances in BNCT treatment delivery. This work not only sets a new benchmark for patient positioning in BNCT, but also provides a comprehensive framework for integrating advanced robotics into radiotherapy, paving the way for more precise and effective cancer treatments.

The effect of geometrical parameters of skin brachytherapy patch source on depth dose distribution using Monte Carlo simulation

Brachytherapy of superficial skin tumors using beta-emitting sources is a method that has been investigated by some researchers in both simulation and experimental studies with promising results. In the current study, the effect of geometrical parameters of some relevant radionuclides including Y-90, Re-188, P-32, and Ho-166 on the depth dose distribution in skin tissue has been investigated through Monte Carlo simulation.MCNPX Monte Carlo code was employed to model the above-mentioned patch sources in cylindrical format and then the effect of patch geometrical parameters including the source-to-skin distance (SSD), patch thickness, and patch diameter on depth dose distribution was assessed through modeling and calculation of the dose inside a cubic phantom mimicking the skin tissue.The obtained results demonstrated that increasing the SSD, patch thickness, and patch diameter (with the same activity) will reduce the depth dose distribution. Changing the SSD has a more significant effect on the dose gradient within the depth than other geometrical parameters. It was also observed that the effect of patch diameter on the skin-delivered dose gets less sensible as the patch size goes beyond the range of beta radiation inside tissue.Finally, it can be concluded that the patch source geometrical parameters can affect the depth dose distribution inside the skin tissue. This fact may be of concern regarding the delivery of a high radiation dose in a single treatment session. Therefore, variations of patch source geometrical parameters should be considered during the skin dose calculation plan.

In Vivo Lens Dosimetry in a Case of En Face Electron Adjuvant Radiotherapy for Cutaneous Nasal Bridge Basal Cell Carcinoma: A Case Report

"Radiation therapy represents one of the main treatment modalities for basal cell carcinoma (BCC), the most common type of skin cancer. The proximity of organs at risk (OARs) increases the risk of side effects. Treatment planning system (TPS) estimates the absorbed dose, but the real value can be determined only by in vivo dosimetry. We measured the absorbed dose at the lenses’ level in a case who received electron irradiation for a resected BCC with positive microscopic margins, located at the bridge of the nose. The thermoluminescent eye lens dosimeters (TLD) were placed under the lead protections. We compared the measured dose with the values estimated by TPS. The treatment involved delivering 50 Gy in 25 fractions. A Monaco 5.11 Treatment Planning System (TPS) was used to plan treatment with a 9 MeV electron field and a 10x10 cm applicator at a 100 cm Source-to-Skin Distance (SSD). Customized lead layers and circular lead blocks were used for protection. The TPS estimated maximum doses of 5.87 Gy for the left lens, and 2.70 Gy for the right lens, respectively. After measuring the doses for the first three fractions by TLD, we calculated that maximum dose for the left lens would get to 0.55 Gy, and to 0.30 Gy for the right lens. In this case report we show that irradiation for a BCC localised at the bridge of the nose is possible with proper shielding and can be safely delivered, without exposing the patient to long- term side effects"

Improved organ sparing using auto-planned Stanford volumetric modulated arc therapy for total body irradiation technique.

To evaluate dosimetric differences between auto-planned volumetric modulated arc therapy (VMAT) total body irradiation (TBI) technique and two-dimensional radiotherapy using anterior-posterial/posterio-anterial beams (2D AP/PA) TBI technique. Ten pediatric patients treated with VMAT-TBI on Varian c-arm linac were included in this study. VMAT-TBI plans were generated using our in-house developed and publicly shared auto-planning scripts. For each VMAT-TBI plan, a 2D AP/PA plan was created replicating the institution's clinical setup with the patient positioned at extended source to skin distance (SSD) with a compensator to account for differences in patient thickness, 50% transmission daily lung blocks, and electron chest wall boosts prescribed to 50% of the photon prescription. Clinically relevant metrics were analyzed and compared between the VMAT and 2D plans. All VMAT-TBI plans achieved planned target volume (PTV) D90%≥100% of prescription. VMAT-TBI PTV D90% significantly increased (7.1%±2.9%, p<.001) compared to the 2D technique, whereas no differences were observed in global Dmax (p<.2) and PTV V110% (p<.4). Compared to the 2D plans, significant decreases in the Dmean to the lungs (-25.6%±11.5%, p<.001) and lungs-1cm (-34.1%±10.1%, p<.001) were observed with the VMAT plans. The VMAT technique also enabled decrease of dose to other organs: kidneys Dmean (-32.5%±5.0%, p<.001) and lenses Dmax (-5.3%±8.1%, p=.03); and in addition, for 2Gy prescription: testes/ovaries Dmean (-41.5%±11.5%, p<.001), brain Dmean (-22.6%±5.4%, p=.002), and thyroid Dmean (-18.2%±16.0%, p=.03). Superior lung sparing with improved target coverage and similar global Dmax were observed with the VMAT plans as compared to 2D plans. In addition, VMAT-TBI plans provided greater dose reductions in gonads, kidneys, brain, thyroid, and lenses.

Accuracy of In-Field and Out-Field Doses Calculated by Analytical Anisotropic and Pencil Beam Convolution Algorithms: A Dosimetric Study

Out-of-field doses may affect the formation of secondary cancers, especially in radiosensitive organs, in patients treated with radiotherapy. The aim of this study is to investigate the in-field dose and out-of-field dose accuracy of Eclipse's analytic anisotropic algorithm (AAA) and pencil beam convolution (PBC) algorithms using TLDs. A tissue equivalent phantom containing a total of 21 measurement points at a depth of 5 cm from the anterior and posterior was created. Using Eclipse AAA and PBC algorithms in TPS, 100 MU for AP/PA fields and 95 cm source-skin distance (SSD) were planned. In-field measurement points including isocenter were 3, 5, 7 and 11 points for 3x3, 5x5, 7x7 and 10x10 cm2, respectively. Measuring points outside the field edge were 38, 36, 34 and 30 points for 3x3, 5x5, 7x7 and 10x10 cm2, respectively. In-field point dose values calculated by TPS for different fields were compared with TLD doses measured at the same location. The difference between in-field dose estimation and TLD measurements of both algorithms was generally below 1%. The difference between TPS and TLD was found to be 4.41% for the 10x10 cm2 irradiation field, due to the field edge at a distance of 5 cm from the isocenter. As the field size decreased, the out-of-field dose calculation performance of the AAA and PBC algorithms was adversely affected. For the 10x10 cm2 irradiation field, the TLD measurements and the out-of-field point dose difference of the PBC algorithm were found to be 39.40%. This difference was at most 12.06% for the AAA algorithm. The Eclipse TPS is good at calculating the in-field dose but underestimates the off-field dose. In out-of-field dose calculation, the AAA algorithm gives more accurate results than the PBC algorithm. Additionally, the smaller the field size, the worse the outfield dose accuracy. The use of in vivo dosimeters is recommended in order to estimate the out-of-field dose with great accuracy in radiotherapy.

Investigating the robustness of the AlignRT InBore™ co-calibration process and determining the overall tracking errors

ObjectiveTo determine the overall tracking errors inherent to the co-calibration procedure of AlignRT InBore™’s (Vision RT Ltd., London, UK) ceiling-mounted and ring-mounted cameras. MethodsExtrinsic calibration errors related to the mismatch between ceiling and InBore cameras’ isocentres and treatment isocentre were determined using MV images and the SRS package and compared to traditional plate-based error. Next, using a realistic anthropomorphic female phantom, intrinsic calibration errors were determined while varying source-skin distance (80 to 100 cm), breast board inclination (0° to 12.5°), room lighting conditions (0 to 258 lx), skin colour (dark, white and natural skin colour), and pod occlusion. ResultsMV images of the cube proved plate-based calibration to suffer from large errors especially in the vertical direction (up to 2 mm). Intrinsic calibration errors were considerably lower. Indeed, RTD values of ceiling and InBore cameras showed little variability with isocentre depth (within 1.0 mm/0.4°), surface orientation and breast board inclination (within 0.7 mm/0.3°), changing lighting conditions (within 0.1 mm/0.2°), skin colour/tone (within 0.3 mm/0.3°) and camera pod occlusion (within 0.3 mm/0.2°). ConclusionThe use of MV-images proved critical to maintain co-calibrating errors of ceiling and InBore cameras to Halcyon’s treatment isocentre below 1 mm.

The Effects of Vitamin A and Magnesium Sulfate on the Expression of Nox4 Following Irradiation in Bone Marrow Cells

Purpose: Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase is one of the probable sources of Reactive Oxygen Species generated by ionizing radiation. This study aimed to determine the expressions of Nox4 and radioprotective effects of magnesium sulfate and vitamin A following whole-body 2 Gy X-ray irradiation.&#x0D; Materials and Methods: In this research, 6-7 weeks old Naval Medical Research Institute (NMRI) male mice were kept in a standard cage with an appropriate temperature and 12 on 12 off light cycle. Three concentrations of vitamin A and magnesium sulfate were intraperitoneally injected into mice 2 hours before irradiation. The dose rate was 50 cGy/min at Source Skin Distance (SSD) = 100 cm and a field size of 10 × 10cm2. The mice were anesthetized and sacrificed by cervical dislocation 24 hours after irradiation. Then, the expression of Nox4 was assessed by Real-Time Polymerase Chain Reaction (PCR).&#x0D; Results: There were significant differences between the mean of gene expression in groups treated with vitamin A and magnesium sulfate compared to only radiation group (P &lt; 0.05).&#x0D; Conclusion: Based on the results of this study, it is likely that vitamin A and magnesium sulfate neutralize the harmful effects of free radicals due to their antioxidant properties.

A novel method to selectively elicit cold sensations without touch

BackgroundThermal and tactile stimuli are transduced by different receptor classes. However, mechano- and thermo-sensitive afferents interact at spinal and supraspinal levels. Yet, most studies on responses to cooling stimuli are confounded by mechanical contact, making these interactions difficult to isolate. Methods for precise control of non-mechanical thermal stimulations remain challenging, particularly in the cold range. New methodWe developed a non-tactile, focal, temperature-controlled, multi-purpose cooling stimulator. This method controls the exposure of a target skin region to a dry-ice source. Using a thermal camera to monitor skin temperature, and adjusting the source-skin distance accordingly, we could deliver non-tactile cooling stimuli with customisable profiles, for studying different aspects of cold sensation. ResultsTo validate our method, we measured absolute and relative thresholds for cold sensation without mechanical contact in 13 human volunteer participants, using the method of limits. We found that the absolute cold detection threshold was 32.71 oC ± 0.88 oC. This corresponded to a threshold relative to each participant’s baseline skin temperature of − 1.08 oC ± 0.37 oC. Comparisons with existing methodOur method allows cooling stimulation without the confound of mechanical contact, in a controllable and focal manner. ConclusionsWe report a non-contact cooling stimulator and accompanying control system. We used this to measure cold thresholds in the absence of confounding touch. Our method enables more targeted studies of both cold sensory pathways, and of cold-touch interactions.

Characterization of GafChromic EBT2 film dose measurements using a tissue-equivalent water phantom for a Theratron® Equinox Cobalt-60 teletherapy machine.

In vivo dosimetry is a quality assurance tool that provides post-treatment measurement of the absorbed dose as delivered to the patient. This dosimetry compares the prescribed and measured dose delivered to the target volume. In this study, a tissue-equivalent water phantom provided the simulation of the human environment. The skin and entrance doses were measured using GafChromic EBT2 film for a Theratron® Equinox Cobalt-60 teletherapy machine. We examined the behaviors of unencapsulated films and custom-made film encapsulation. Films were cut to 1 cm × 1 cm, calibrated, and used to assess skin dose depositions and entrance dose. We examined the response of the film for variations in field size, source to skin distance (SSD), gantry angle and wedge angle. The estimated uncertainty in EBT2 film for absorbed dose measurement in phantom was ±1.72%. Comparison of the measurements of the two film configurations for the various irradiation parameters were field size (p = 0.0193, α = 0.05, n = 11), gantry angle (p = 0.0018, α = 0.05, n = 24), SSD (p = 0.1802, α = 0.05, n = 11) and wedge angle (p = 0.6834, α = 0.05, n = 4). For a prescribed dose of 200 cGy and at reference conditions (open field 10 cm x 10 cm, SSD = 100 cm, and gantry angle = 0º), the measured skin dose using the encapsulation material was 70% while that measured with the unencapsulated film was 24%. At reference irradiation conditions, the measured skin dose using the unencapsulated film was higher for open field configurations (24%) than wedged field configurations (19%). Estimation of the entrance dose using the unencapsulated film was within 3% of the prescribed dose. GafChromic EBT2 film measurements were significantly affected at larger field sizes and gantry angles. Furthermore, we determined a high accuracy in entrance dose estimations using the film.

Mitigating effects of methanolic leaf extract of Duranta erecta against X-ray induced oxidative stress in Wistar albino rats

Carcinogenic effects and other harmful effects associated with low dose-rate and low dose radiation have recently been reported. Therefore, it is important to identify effective and safe radioprotectors or radiation mitigators that can counter the effects of ionizing radiation damage. Therefore, the aim of the study was to evaluate the mitigating potential of methanolic leaves extract of Duranta erecta (DE) against acute whole-body X-ray irradiation-induced oxidative stress in Wistar albino rats. Rats in groups B, C and D, were exposed to double X-rays radiation at a source to skin distance (SSD) of 70 cm to deliver a total radiation dose of 18.4mGy at the rate of 9.2mGy/exposure using 100kVp and 30mAs exposure factors and quality factor of the X-ray machine (P) of 15. Rats in group A (control) were neither irradiated nor administered with DE extract. In contrast, group B rats were irradiated but not treated. DE extract at doses of 500 and 1000 mg/kg body weight was administered to groups C and D rats for 15 consecutive days. On post-irradiation days 1, 7, 14 and 21, the antioxidant status of the rats was evaluated and compared with control. Parameters assessed were catalase (CAT), superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA). Mean serum levels of GSH, SOD, CAT and MDA in the irradiated and treated groups did not vary significantly (P &gt; 0.05) from the un-irradiated control group. In conclusion, methanolic extract of DE mitigated against radiation-induced decline in serum GSH, SOD, CAT, and radiation-induced MDA elevation. Results obtained indicated that methanolic extract of DE can be used potentially as a natural radiation mitigating agent.

Lactoferrin improves hepatic pyroptosis in mice after irradiation

ObjectiveTo investigate the effects of lactoferrin (Lf) on hepatic pyroptosis (an inflammatory form of programmed cell death) in mice exposed to radiation. MethodsA total of thirty-six BALB/c male mice were randomly divided into four groups, namely the control group, 5 ​Gy group, 5 ​Gy ​+ ​2 ​mg Lf group, and 5 ​Gy ​+ ​4 ​mg Lf group. The mice were administered whole-body ionizing radiation using a PRIMUS accelerator, with a single dose of 5 ​Gy and an absorbed dose rate of 2.0 ​Gy/min at a source-skin distance of 100 ​cm. Lf solution was intraperitoneally injected into the mice 2 ​h before and per day after radiation. The mice were sacrificed 1, 3, and 9 ​d after radiation, and their livers were used for histopathologic examination, immunohistochemistry analysis, and Western blot analysis for absent in melanoma 2 (AIM2) inflammasome pathway. ResultsHistopathologic examination showed the disorder of the hepatocellular structure and the accumulation of inflammatory cells after radiation. Lf intervention inhibited hepatocellular proliferation and decreased the infiltration of inflammatory cells. Immunohistochemistry analysis indicated that AIM2 overexpression was significantly attenuated by 4 ​mg of Lf (t ​= ​3.065, P ​< ​0.05) 3 ​d after radiation and by 2 ​mg and 4 ​mg of Lf (t ​= ​4.032, t ​= ​2.786, P ​< ​0.05) 9 ​d after radiation. Western blot analysis showed that Lf downregulated the hepatic overexpression of AIM2, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), IL-1β, and IL-18. 2 ​mg of Lf significantly downregulated the abovementioned protein expression 3 ​d (t ​= ​7.934, 4.092, 5.193, 2.916, P ​< ​0.05) and 9 ​d after radiation (t ​= ​5.016, 3.882, 9.528, P ​< ​0.05 for AIM2, ASC, IL-1β). ConclusionsLf intervention suppressed the hepatic pyroptosis in mice exposed to ionizing radiation by downregulating the protein expression of AIM2 inflammasome.

Study of Analysis the Sensitivity of the Computational Environment for Radiological Research Field Size Based on Two Dimensional Dose Distribution for Water Phantom Cases

Purpose This study analysed the sensitivity of the field size from variations in the target volume dimensions, depth, and position. The variations in the target volume analysis were used to determine the width of the field size. Thus, the quality control of the radiation beam can be obtained. Materials and Methods The computed tomography (CT) image of the IBA Dose 1 type of water phantom consists of 350 slices. Variations in the dimension of the target volume were modelled in 10×10×10 cm3, 10×12×10 cm3 , 10.2×10×10.2 cm3, and 15×15×15 cm3. Beam parameters use one beam of irradiation on the central axis 0°, 6 MV energy, 100 cm source-skin distance (SSD), beamlet delta x, and y set to 0.1 cm. Dose distribution in the form of the XZ isodose curve and dose profile was used to observe the field size. Results In this study, the isodose curve was successfully displayed in the XZ isodose curve. The field size’s sensitivity has been successfully reviewed from variations of the target volume, depth, and position. The target X and Z direction analysis is used in determining the width and length of the field size. Conclusion The analysis related to the field size sensitivity study was obtained from a relatively valid calculation. The field size was evaluated with variations in depth of 1.5 cm, 5 cm, 10 cm, and variations in positions of 10 cm, 12 cm, 14 cm, 18 cm, and 20 cm. This study will be used as a reference to validate the distribution of computational environment for radiotherapy research (CERR) dose in the future. Thus, the accuracy of the dose calculation can be obtained.

Investigation of effect of filter on the stand-up technique for total skin irradiation by Monte Carlo simulation.

PurposeThe aim of this study was to investigate dosimetric effects of scattering filter on the stand‐up technique for total skin irradiation (TSI) with a single electron field by Monte Carlo (MC) simulation.MethodsMC simulations were performed with BEAMnrc and DOSXYZnrc packages under EGSnrc environment. Scattering filter of a metal disc was mounted in the accessory slot. The filter materials (Cu, Fe, Au, Zn, Ag) were investigated, with thickness ranging from 0.05 to 0.55 mm, depending on material. The extended source to skin distance (SSD) ranging from 250 to 350 cm was studied. The following dosimetric quantities were evaluated: percent depth dose (PDD), profiles and output factor at depth of maximum, and composite dose distribution on a 30‐cm diameter cylindrical phantom. They were compared with the standard dual beam technique used at our clinic. The effects on different patient sizes were also studied.ResultsNo filter produced acceptable profile flatness (±10% within the central 160 cm) at 250 cm SSD. At 300 cm SSD, Au (0.1 mm), Ag (0.25 mm), Cu (0.5 mm) produced acceptable flatness while Zn (0.45 mm) required 325 cm SSD. For these four configurations, the dmax was 0.90–0.99 cm, similar to dual beam (0.97 cm); R50 was 1.85–1.91 cm, compared with dual beam of 2.06 cm; the output factor ranged from 0.025 to 0.029, lower than the dual beam (0.080). With the composite fields for four configurations, the dmax was 0.10 cm, compared with dual beam (0.16 cm). The surface dose was 97%, similar to dual beam (96%). B‐factor was 3.3–3.4, compared with dual beam of 3.1. The maximum X‐ray contamination was 3%, higher than dual beam (1%).ConclusionsThe investigation suggests the TSI stand‐up technique can be implemented using a single electron beam if a customized filter is used. More dosimetric measurements are needed to validate the MC results and clinical implementation.

Validation of the dosimetry of total skin irradiation techniques by Monte Carlo simulation.

PurposeTo validate the dose measurements for two total skin irradiation techniques with Monte Carlo simulation, providing more information on dose distributions, and guidance on further technique optimization.MethodsTwo total skin irradiation techniques (stand‐up and lay‐down) with different setup were simulated and validated. The Monte Carlo simulation was primarily performed within the EGSnrc environment. Parameters of jaws, MLCs, and a customized copper (Cu) filter were first tuned to match the profiles and output measured at source‐to‐skin distance (SSD) of 100 cm where the secondary source is defined. The secondary source was rotated to simulate gantry rotation. VirtuaLinac, a cloud‐based Monte Carlo package, was used for Linac head simulation as a secondary validation. The following quantities were compared with measurements: for each field/direction at the treatment SSDs, the percent depth dose (PDD), the profiles at the depth of maximum, and the absolute dosimetric output; the composite dose distribution on cylindrical phantoms of 20 to 40 cm diameters.ResultsCu filter broadened the FWHM of the electron beam by 44% and degraded the mean energy by 0.7 MeV. At SSD = 100 cm, MC calculated PDDs agreed with measured data within 2%/2 mm (except for the surface voxel) and lateral profiles agreed within 3%. At the treatment SSD, profiles and output factors of individual field matched within 4%; dmax and R80 of the simulated PDDs also matched with measurement within 2 mm. When all fields were combined on the cylindrical phantom, the dmax shifted toward the surface. For lay‐down technique, the maximum x‐ray contamination at the central axis was (MC: 2.2; Measurement: 2.1)% and reduced to 0.2% at 40 cm off the central axis.ConclusionsThe Monte Carlo results in general agree well with the measurement, which provides support in our commissioning procedure, as well as the full three‐dimensional dose distribution of the patient phantom.

Electron contamination for 6 MV photon beams from an Elekta linac: Monte Carlo simulation

In external beam radiotherapy, the photons from a linear accelerator (linac) machine undergo multiple interactions, not only in the patient but also in the linac head and the air column between the linac head and the patient. Electrons are released from these interactions and contaminate the beams. The current study evaluates electron contamination for 6 MV photon beams from an Elekta linac using Monte Carlo simulation. The linac head was simulated by the BEAMnrc code and the absorbed dose in a phantom was calculated using the DOSXYZnrc code. The parameters of the initial electron beams on the target, such as mean energy and radial intensity distribution, were determined by matching the calculated dose distributions with the measured dose (at 10 x 10 cm2 field size and 90 cm source-skin distance). The central axis depth-dose curves of electron contamination were calculated for various field sizes from 5 x 5 cm2 to 40 x 40 cm2. We investigated the components that generated the electron contamination for a field size of 10 x 10 cm2. The optimal initial electron beam energy was 6.3 MeV with a full-width half maximum (FWHM) of the radial intensity distribution of 1.0 mm. These parameters were found to be in good agreement with the measured data. Electron contamination increased as the field size increased. At a depth of 1.0 mm and field sizes of 5 x 5, 10 x 10, 20 x 20, 30 x 30, and 40 x 40 cm2, the doses from electron contamination were 3.71, 5.19, 14.39, 18.97 and 20.89 %, respectively. Electron contamination decreased with increased depth. At a depth of 15 mm, the electron contamination was about 1 %. It was mainly generated in the air column between the linac head and the phantom (3.65 %), the mirror (0.99 %), and the flattening filter (0.59 %) (for the depth of 1.0 mm and the field size of 10 x 10 cm2).

Comparison of calculated and measured basic dosimetric parameters for total body irradiation with 6- and 18-MV photon beams

AbstractPurpose:Total body irradiation (TBI) is an external beam radiation therapy in which large field size and extended source skin distances (SSDs) are applied to deliver a therapeutic dose to the whole body. As measurements in such situations are not common and have more uncertainties in comparison to standard dosimetry situations, it is more precise if calculated beam data can be used instead of measurements taken under TBI situations. The purpose of this study is to compare calculated beam data [percentage depth dose (PDD) and dose rate] with those obtained from simulated treatment measurements.Materials and methods:PDD and dose rates were measured for the 6- and 18-MV photon beams under TBI and standard conditions using 9,000 cm3 water phantom and ion chambers (Markus and Farmer). The results were then compared with the calculated PDD and dose rate data. The beam flatness was also measured under TBI and standard conditions for both 6- and 18-MV photon beams, and the results were then compared.Results:A comparison of the measurement and calculated beam data shows that the difference between calculated and measured PDD values is −6·97 and −4·14% for the 6- and 18-MV photon beams, respectively. The ratio of calculated to measured dose rate was 1·09 and 1·02 for the 6- and 18-MV photon beams, respectively. The beam flatness under TBI conditions was 4·59% for 6-MV and 5·37% for 18-MV photon beam, whereas under standard conditions, these values were 1·50 and 1·98% for 6- and 18-MV radiation beams, respectively.Findings:According to the results, due to a high error level in dose rate and PDD calculations, these parameters must be directly measured under TBI conditions; however, regarding the obtained results, direct measurement is not necessary for the 18-MV photon beam.

Relative dosimetry measurements in kilovoltage X-rays with OSLDs

Dosimetry for kilovoltage X-ray units requires a careful choice of equipment due a typically high energy dependence of standard detectors. The use of optically stimulated luminescence detectors (OSLDs) for in-vivo dosimetry and the measurement of relative output factors is investigated in this study. Supralinearity and the suitability of OSLDs for relative dose measurements are determined for the Landauer nanoDot OSLD system (Landauer, Inc., Greenwood, IL). OSLDs were found to exhibit supralinearity for therapeutic doses in kV X-rays, with the effect more pronounced in lower energy beams. Relative lead cutout factors measured with OSLDs were well within 5% of published values. OSLD measurements of applicator factors at the surface of a water phantom showed a systematic offset (> + 5%) to derived values and values measured with a PTW 23342 soft X-ray ionisation chamber (PTW, Freiburg, Germany), due to the change in source-to-skin distance (SSD) between the applicators used in this study. OSLDs are suitable for relative dosimetry in kilovoltage beams between 80 and 120 kVp when the SSD similar to the calibration/reference conditions.

A novel approach to Verify air gap and SSD for proton radiotherapy using surface imaging

PurposeTo develop a novel approach to accurately verify patient set up in proton radiotherapy, especially for the verification of the nozzle – body surface air gap and source-to-skin distance (SSD), the consistency and accuracy of which is extremely important in proton treatment.MethodsPatient body surfaces can be captured and monitored with the optical surface imaging system during radiation treatment for improved intrafraction accuracy. An in-house software package was developed to reconstruct the patient body surface in the treatment position from the optical surface imaging reference capture and to calculate the corresponding nozzle – body surface air gap and SSD. To validate this method, a mannequin was scanned on a CT simulator and proton plans were generated for a Mevion S250 Proton machine with 20 gantry/couch angle combinations, as well as two different snout sizes, in the Varian Eclipse Treatment Planning Systems (TPS). The surface generated in the TPS from the CT scan was imported into the optical imaging system as an RT Structure for the purpose of validating and establishing a benchmark for ground truth comparison. The optical imaging surface reference capture was acquired at the treatment setup position after orthogonal kV imaging to confirm the positioning. The air gaps and SSDs calculated with the developed method from the surface captured at the treatment setup position (VRT surface) and the CT based surface imported from the TPS were compared to those calculated in TPS. The same approach was also applied to 14 clinical treatment fields for 10 patients to further validate the methodology.ResultsThe air gaps and SSDs calculated from our program agreed well with the corresponding values derived from the TPS. For the phantom results, using the CT surface, the absolute differences in the air gap were 0.45 mm ± 0.33 mm for the small snout, and 0.51 mm ± 0.49 mm for the large snout, and the absolute differences in SSD were 0.68 mm ± 0.42 mm regardless of snout size. Using the VRT surface, the absolute differences in air gap were 1.17 mm ± 1.17 mm and 2.1 mm ± 3.09 mm for the small and large snouts, respectively, and the absolute differences in SSD were 0.81 mm ± 0.45 mm. Similarly, for patient data, using the CT surface, the absolute differences in air gap were 0.42 mm ± 0.49 mm, and the absolute differences in SSD were 1.92 mm ± 1.4 mm. Using the VRT surface, the absolute differences in the air gap were 2.35 mm ± 2.3 mm, and the absolute differences in SSD were 2.7 mm ± 2.17 mm.ConclusionThese results showed the feasibility and robustness of using an optical surface imaging approach to conveniently determine the air gap and SSD in proton treatment, providing an accurate and efficient way to confirm the target depth at treatment.

Investigation of Effect of Filter on the Total Skin Irradiation Using Monte Carlo Simulation

The standard total skin irradiation (TSI) procedure for patients with Mycosis fungoides at our clinic is the Stanford technique where dual overlapping electron beams are directed at patient standing at an extended source to skin distance (SSD) of 300 cm. Patients rotate along the cranial-caudal axis in 6 positions to get full coverage to skin. Recently we developed and implemented a technique of laying down position for frail patients. One key requirement for this technique is the use of customized Cu filter to broaden the beam. The purpose of this study is to investigate the effect of the filter designs on the standard standing technique with a single beam. The filter is placed at the interface mount of the linac. The material studied include Cu, Fe, Au, Zn, and Ag. These materials were chosen based on their availability and stability. The thickness ranges from 0.05 mm to 0.55 mm, depending on the material. The extended SSD ranges from 250 cm to 350 cm. Our recent MC simulation study using the EGSnrc system on the laydown technique with 0.25 mm Cu filter has produced results that agree well with the commissioning measurement. For each material, we varies the thickness and SSD, to study the following quantities: percent depth dose (PDD), profile at dmax, and output at dmax, and compared them with the standard dual beam setup at 300 cm SSD that has been used in the clinic. Higher atomic number material and/or thicker filter has higher scattering power to broaden beam, but also attenuates beam more with lower output. No material can produce acceptable profile flatness (±10% within the central 160 cm region) at the SSD of 250 cm, suitable for a small linac room. At 300 SSD, Au (0.1 mm), Ag (0.25 mm) and Cu (0.45 mm) are acceptable. Zn (0.45 mm) requires SSD of 325 cm to meet the requirement. For all 4 configurations, the dmax is 0.87 - 0.99 cm, similar to dual beam with no filter at 0.97 cm. The R50 is 1.85 – 1.91 cm, compared to 2.06 cm for dual open beams. The output ranges from 0.025 – 0.029, slightly lower than the open beams at 0.040. The Monte Carlo simulation is a very useful tool to investigate the effect of the different filters and provides valuable suggestion in the technique optimizations. The result suggests that the standard standing position TSI technique can be implemented using a single beam instead of dual overlapping beam if the customized filters are used. Actual manufacturing and measurement will be performed to validate these simulation results.

Vulvar Cancer: Dosimetric Comparison of Advanced 3D Conformal Radiation Therapy Technique with Anteroposterior and Posteroanterior Irradiation Techniques

Introduction: The commonly used technique of radiation therapy for vulvar cancer consists of anteroposterior (AP) and posteroanterior (PA) fields. This is the first study that reports the dosimetric comparison between the AP-PA techniques and the new 3D advanced conformal technique (3D-ACT) based on the multiplicity of treatment fields in patients with squamous cell cancer of the vulva in the postoperative setting. Material and Methods: This comparative planning study was conducted on15 patients with vulvar carcinoma treated with adjuvant radiation therapy at the National Institute of Oncology in Rabat, Morocco. Three treatment plans were performed, corresponding to three techniques, namely photons with source-skin distance inguinal supplement, modified segmental boost technique and 3D advanced conformal technique. For each plan, the dose-volume histogram was used to generate planning target volumes (total and inguinal PTV) and organs at risk (bladder, rectum, bowel and femoral heads) parameters. Results: The 95% isodose volume was significantly reduced with the advanced conformal technique (p <0.0001) without compromising the total PTV coverage (P= 0.94). This technique resulted in the best conformity and homogeneity index. The 3D-ACT decreased significantly the PTVs Dmax and Dmean (p <0.0001), and offered better homogeneity for inguinal PTV (i.e., 1.07±0.01, p <0.0001).The 3D-ACT decreased the rectum absorbed dose, V40 (volume receiving ≥40Gy), V45, and Dmaxto50.21±27.21, 22.81±10.22, and 46.56±1.11, respectively. With regard to femoral heads, the 3D-ACT decreased the Dmax and V45 in comparison to the other two techniques. Conclusion: The 3D-ACT seems to be an alternative to the AP-PA irradiation techniques in postoperative setting when IMRT is unavailable.