Beam Radiation Research Articles

Monte Carlo investigation of electron fluence perturbation in MRI-guided radiotherapy beams using six commercial radiation detectors

With the integration of treatments with MRI-linacs to the clinical workflow, the understanding and characterization of detector response in reference dosimetry in magnetic fields are required. The external magnetic field perturbs the electron fluence. The degree of perturbation depends on the irradiation conditions and on the detector type. The purpose of this study is to evaluate the magnetic field impact on the electron fluence spectra in several detectors to provide a deeper understanding of detector response in these conditions. Monte Carlo calculations of the electron fluence are performed in six detectors (solid-state: PTW60012 and PTW60019, ionization chambers: PTW30013, PTW31010, PTW31021, and PTW31022) in water and irradiated by a 7 MV FFF photon beam with a small and a reference field, at 0 and 1.5 T. Three chamber axis orientations are investigated: parallel or perpendicular (either the Lorentz force pointing towards the stem or the tip) to the magnetic field and always perpendicular to the photon beam. One orientation for the solid-state detector is studied: parallel to the photon beam and perpendicular to the magnetic field. Additionally, electron fluence spectra are calculated in modified detector geometries to identify the underlying physical mechanisms behind the fluence perturbations. The total electron fluence in the Farmer chamber varies up to 1.24% and 5.12% at 1.5 T, in the parallel and perpendicular orientation, respectively. The interplay between the gyration radius and the Farmer chamber cavity length significantly affects the electron fluence in the perpendicular orientation. For the small-cavity chambers, the maximal variation in total electron fluence is 0.19% in the parallel orientation for the reference field. Significant small-field effects occur in these chambers; the magnetic field reduces the total electron fluence (with respect to the no field case) between 9.86% and 14.50%, depending on the orientation. The magnetic field strongly impacted the solid-state detectors in both field sizes, probably due to the high-Z components and cavity density. The maximal reductions of total electron fluence are 15.06 ± 0.09% (silicon) and 16.00 ± 0.07% (microDiamond). This work provides insights into detector response in magnetic fields by illustrating the interplay between several factors causing dosimetric perturbation effects: (1) chamber and magnetic field orientation, (2) cavity size and shape, (3) extracameral components, (4) air gaps and their asymmetry, (5) electron energy. Low-energy electron trajectories are more susceptible to change in magnetic fields, and are associated with detector response perturbation. Detectors with higher density and high-Z extracameral components exhibit more significant perturbations in the presence of a magnetic field, regardless of field size.

Microdosimetric characterization of a clinical proton therapy beam: comparison between simulated lineal energy distributions in spherical water targets and experimental measurements with a silicon detector

Objective. Treatment planning based on computer simulations was proposed to account for the increased relative biological effectiveness (RBE) of proton radiotherapy beams near to the edges of the irradiated volume. Since silicon detectors could be used to validate the results of these simulations, it is important to explore the limitations of this comparison. Approach. Microdosimetric measurements with a MicroPlus Bridge V2 silicon detector (thickness = 10 μm) were performed along the Bragg peak of a clinical proton beam. The lineal energy distributions, the dose-mean values, and the RBE calculated with a biological weighting function were compared with PHITS simulations (microdosimetric target = 1 μm water sphere), and published clonogenic survival in vitro RBE data for the V79 cell line. The effect of the silicon-to-water conversion was also investigated by comparing three different methodologies (conversion based on a single value, novel bin-to-bin conversions based on SRIM and PSTAR). Main results. Mainly due to differences in the microdosimetric targets, the experimental dose-mean lineal energy and RBE values at the distal edge were respectively up to 53% and 28% lower than the simulated ones. Furthermore, the methodology chosen for the silicon-to-water conversion was proven to affect the dose-mean lineal energy and the RBE10 up to 32% and 11% respectively. The best methodology to compensate for this underestimation was the bin-to-bin silicon-to-water conversion based on PSTAR. Significance. This work represents the first comparison between PHITS-simulated lineal energy distributions in water targets and corresponding experimental spectra measured with silicon detectors. Furthermore, the effect of the silicon-to-water conversion on the RBE was explored for the first time. The proposed methodology based on the PSTAR bin-to-bin conversion appears to provide superior results with respect to commonly used single scaling factors and is recommended for future studies.

Multi-level multi-leaf collimators: Optimization of layer thicknesses and a feasibility study.

The function of multi-leaf collimators (MLC) is to modulate and shape the intensity of a radiotherapy beam by either blocking or unblocking beamlets. A variation on this functionality is tested in this work wherein the MLC is split into layers, with each layer attenuating the beam by a different amount. In this design, full blocking of a beamlet occurs only if all layers are blocked. This work suggests that such a device, a multi-layer MLC (MLMLC), can deliver dose distributions like a single layer MLC can deliver while requiring less time and monitor units (MU) METHODS: Optimal fluences were made for prostate plans using the Eclipse v13.6. An algorithm was developed to create step-and-shoot MLMLC patterns to match these optimal fluences when using up to six layers of MLC. Twelve MLMLC plans were made in total. These patterns were imported back into Eclipse as equivalent tungsten compensators and doses were calculated. Dose-volume histogram (DVH) values, total monitor units (MU), and total time to deliver were compared between arc-style MLMLC plans and nine-field step and shoot IMRT plans created completely in Eclipse using a single layer MLC. When using three or more layers, specified DVH values between the two sets agreed to within 5% while requiring roughly half as much time to deliver and about 20% fewer MU. Demonstrated that having multi-layer MLC can deliver dose distributions like a single layer MLC with less time and monitor units.

A MOSFET-Based Method for Measuring Peak Kilovoltage (kVp) in Diagnostic X-Ray Beams

Peak kilovoltage (kVp) is an X-ray tube parameter that can influence the radiograph image quality and therefore, if the kVp is different from the nominal value, it can provide an unnecessary radiation dose to the patient if the examination has to be repeated. Therefore, some radiation protection institutions and health organizations (ICRP, IAEA) make recommendations to monitor kVp in medical diagnostic X-ray equipment in clinics and hospitals. There are some methods for measuring kVp in diagnostic X-ray beams, and the most common is the well-known two-sensor method, which uses two filters to attenuate the radiation beam, and it is based on the measurement of each identical sensor. The purpose of this article is to present a method for non-invasive measurement of kVp in medical diagnostic X-ray beams using the MOSFET device. Actually, MOSFET is well known as a detector for ionizing radiation dosimetry mainly in radiotherapy beams. Recently, MOSFET has also been used as dosimeter in diagnostic X-ray beams. In this work it will be shown a kVp measurement technique with MOSFET, which does not use the attenuation factor of the radiation filters, but instead takes advantage of the effect of the device package itself, known as the buildup cap effect. The results show that even with damage to the device exposed to radiation, MOSFET can be used as sensor for kVp measurement.

A treatment planning comparison of photon stereotactic ablative radiotherapy and proton beam therapy for the re-irradiation of pelvic cancer recurrence.

BackgroundPatients who experience a pelvic cancer recurrence in or near a region that received initial radiotherapy, typically have few options for treatment. Organs at risk (OAR) have often reached their dose constraint limits leaving minimal dose remaining for standard re-irradiation (reRT). However, photon based stereotactic ablative radiotherapy (SABR) has been utilised for reRT with promising initial results although meeting OAR constraints can be challenging. Proton beam therapy (PBT) could offer an advantage.Materials and methodsSABR plans used for treatment for ten pelvic reRT patients were dosimetrically compared to PBT plans retrospectively planned using the same CT and contour data. PBT plans were created to match the CTV dose coverage of SABR treatment plans with V100% ≥95%. An ‘as low as reasonably achievable’ approach was taken to OAR tolerances with consideration of OAR dose from the initial radiation (using equivalent dose in 2 Gy fractions).ResultsDosimetric comparison of relevant OAR statistics showed a decrease in OAR dose using PBT over SABR in all patients, with equivalent target coverage. The largest statistically significant reduction was seen for the colon D0.5 cm3 with a median reduction from 13.1 Gy to 5.9 Gy. There were statistically significant dose reductions in the median dose to small bowel, sacral plexus and cauda equina.ConclusionPBT has the potential for significant dose reductions for OARs in the pelvic reRT setting compared to SABR. However, it remains unclear if the magnitude of these OAR dose reductions will translate into clinical benefit.

Flattening Filter-Free Volumetric-Modulated Arc Radiotherapy for Left-Sided Whole-Breast, Partial-Breast, and Postmastectomy Irradiations.

Purpose:Unflattened photon beams exhibit many benefits over traditional flattened beams for radiotherapy (RT), but comprehensive evaluations of dosimetric results and beam-on time using flattening filter-free (FFF) beams for all types of breast irradiations are still lacking. The purpose of this study was to investigate if FFF RT can maintain equal or better dose coverage than standard flattened-beam RT while reducing doses to organs at risk (OARs) and beam-on time for various types of breast cancer irradiations.Methods and Materials:FFF volumetric-modulated arc therapy (FFF-VMAT) and standard VMAT (STD-VMAT) treatment plans were created for 15 whole-breast irradiation (WBI) patients with 50 Gy/25 fractions, 13 partial-breast irradiation (PBI) patients with 38.5 Gy/10 fractions, and 9 postmastectomy irradiation (PMI) patients with 50 Gy/25 fractions. Planning target volume (PTV) coverage and dose to OARs were evaluated.Results:Both techniques produced clinically acceptable plans for all three types of irradiations. For WBI, FFF-VMAT plans exhibited similar PTV and OARs evaluation metrics as STD-VMAT. For PBI, FFF-VMAT plans showed significantly lower mean and maximum doses for ipsilateral and contralateral lungs, contralateral breast, and heart. For PMI, FFF-VMAT plans showed significantly lower mean dose and V5 for contralateral breast but significantly higher Dmean, Dmax, and V20 for ipsilateral lung and significantly higher Dmean, V22.5, and V30 for heart. FFF-VMAT techniques significantly reduced beam-on time than STD-VMAT for all cases.Conclusion:This work has shown that FFF beams are most beneficial for small-field irradiation such as PBI, and breast cancer patients could potentially benefit from the shortened beam-on time.

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties.

This paper presents guidelines for the calibration of radiation beams that were issued by the International Atomic Energy Agency (IAEA TRS 398), the American Association of Physicists in Medicine (AAPM TG 51) and the German task group (DIN 6800-2). These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standard laboratory’s reference quality beam, where the previous protocols were based on air kerma standards. This study aims to determine uncertainties in dosimetry for electron beam radiotherapy using internationally established high-energy radiotherapy beam calibration standards. Methods: Dw was determined in 6-, 12- and 18 MeV electron energies under reference conditions using three cylindrical and two plane-parallel ion chambers in concert with the IAEA TRS 398, AAPM TG 51 and DIN 6800-2 absorbed dose protocols. From mean measured Dw values, the ratio TRS 398/TG 51 was found to vary between 0.988 and 1.004, while for the counterpart TRS 398/DIN 6800-2 and TG 51/DIN 6800-2, the variation ranges were 0.991–1.003 and 0.997–1.005, respectively. For the cylindrical chambers, the relative combined uncertainty (k = 1) in absorbed dose measurements was 1.44%, while for the plane-parallel chambers, it ranged from 1.53 to 1.88%. Conclusions: A high degree of consistency was demonstrated among the three protocols. It is suggested that in the use of the presently determined dose conversion factors across the three protocols, dose intercomparisons can be facilitated between radiotherapy centres.

RT-4 Treatment outcome of proton beam therapy for glioblastoma

Introduction: Proton beam therapy enables high dose irradiation for tumors while reducing the dose to surrounding normal tissue due to the sharp energy peak called the Bragg peak. We retrospectively analyzed the efficacy of the high dose radiotherapeutic strategy using proton beam for glioblastoma (GBM) in our institution. Methods: Twenty-nine patients with newly diagnosed GBM who underwent high dose proton beam therapy concomitant with temozolomide were investigated. All patients received hyperfractionated concomitant radiotherapy consisting of X-ray radiotherapy (50.4Gy in 28 fractions) and proton beam therapy (46.2Gy [RBE] in 28 fractions). The survival outcome and adverse events were analyzed. Results: The median overall survival time and progression free survival time for all 29 patients were 31.0 months (95%CI, 25.9–36.1) and 11.0 months (95%CI, 7.8–14.2), respectively. No significant survival difference according to the MGMT methylation status was shown. Failure patterns after proton beam therapy included 17 cases of local recurrence, 3 cases of distant recurrence, and 5 cases of dissemination. Although there was no significant difference in time to recurrence according to the failure pattern, there was a tendency of longer survival in the local recurrence group. Regarding adverse events, radiation necrosis was observed in 8 cases (including 2 asymptomatic cases). The median time to onset of necrosis after radiation was 18.2 months (95%CI, 10.3–26.2). There were 5 cases of long survivor over 5 years out of 29 cases (17.2%). Of these, 4 cases developed radiation necrosis. Conclusions: Our results indicate that high dose proton beam therapy of 96.6Gy (RBE) prolonged survival in selected GBM patients. Particularly in long survivors, special attention and effective treatment to radiation necrosis is a remaining problem.

COMPARISON OF TOXICITY PROFILES AMONG HEAD & NECK CANCER PATIENTS UNDERGOING 3D CRT, IMRT & IGRT MODES OF RADIOTHERAPY

Introduction: Radiotherapy is the one of the main modes of treating oral cancer and in recent days radiation delivery and beam shaping is evolving with novel methods. Some of the methods of radiation delivery include Three dimensional conformal radiotherapy(3D CRT), Intensity Modulated Radiotherapy ( IMRT), Image Guided Radiotherapy ( IGRT), stereotactic body radiotherapy and proton beam therapy to name a few. However these techniques are always associated with some pitfalls such as mucositis, skin reactions, dysphagia and xerostomia which occur in both acute and chronic manner. Hence there is a continuous necessity to optimize dose distribution to reduce the toxicities and have a positive impact on the quality of life of the patient. Aim: To assess and compare the toxicity proles occurring due to radiotherapy in head and neck cancer patients undergoing 3D CRT, IMRT and IGRTmodes. Materials and Methods: A total of 60 patients with a Kornofsky Performance Scale (KPS) more than 70 were included in the study. Of the 60 patients included in the study 20 were in the 3D CRT group, 20 were in the IMRT group and 20 were in the IGRT group. The patients were assessed for grade of mucositis and skin reactions in an acute and chronic manner. Results: The results showed that 3D CRT group demonstrated signicantly more acute and chronic toxicities in relation to mucositis and skin reactions when compared to IMRT and IGRT. However on comparing the toxicities between IMRT and IGRT groups there were insignicant differences. Conclusion: In our study, IMRT and IGRT were associated with a signicantly lower incidence of toxicity in relation to mucositis and skin reactions and hence they are more tissue sparing and improves the quality of life of the patient.

Reference dosimetry audits for radiotherapy beams in Italy

Reference dosimetry audits for radiotherapy beams in Italy

An examination of nationwide trends in accelerated partial breast irradiation – The replacement of breast brachytherapy with intraoperative radiotherapy and external beam radiation

PurposeTo examine recent modality utilization trends in accelerated partial breast irradiation (APBI) in the National Cancer Database (NCDB) based on the American Society for Radiation Oncology (ASTRO) guidelines. Materials and MethodsA total of 58,194 patients treated with APBI were identified. Patients were segregated by APBI modality (brachytherapy, external beam radiotherapy [EBRT], and intraoperative radiotherapy ([IORT]). These patients were then further classified by suitability to receive APBI based on ASTRO guidelines. Temporal trends in utilization were evaluated using linear regression. Logistic regression was applied to study factors contributing to APBI modality choice and treatment within the ASTRO suitability groups. ResultsPatients treated with brachytherapy, EBRT, and IORT comprised 70.5%, 17.5%, and 12.0% of patients treated with APBI. From 2008 to 2017, total APBI cases remained relatively stable (−54.1 cases/year, p = 0.161) while brachytherapy cases decreased by 258.7 cases/year (p < 0.001). EBRT and IORT increased by 51.5 cases/year (p = 0.019) and 153.1 cases/year (p < 0.001), respectively. 40.0% of patients treated with APBI were classified as “suitable”, which increased from 2010 to 2017 from 35.3% to 45.3% (slope = 1.51%/year, r2 = 0.61, p = 0.022). In comparison, 36.0% (36.1% in 2010 to 33.1% in 2017) of patients were classified as “cautionary” (slope = −0.33%/year, r2 = 0.63, p = 0.019) and 23.9% (28.6% in 2010 to 21.6% in 2017) of patients were classified as “unsuitable” (slope = −1.18%/year, r2 = 0.67, p = 0.012). ConclusionsWhile overall APBI utilization has remained stable since 2008, this has been accompanied by a decline in brachytherapy and a rise in IORT. The causes of these trends should be the topic of future research.

On Efficacy of Microwave Ablation in the Thermal Treatment of an Early-Stage Hepatocellular Carcinoma.

Simple SummaryHepatocellular carcinoma accounts for around 75% of all liver cancers, and represents the fourth most common cause of cancer-related deaths worldwide. Microwave ablation is a worldwide-diffused treatment of hepatocellular carcinoma. According to the literature, the success rate for completely eliminating small liver tumors in patients treated with microwave ablation is greater than 85%. Microwave ablation is also highly recommended for COVID-19 patients with liver tumors as a fast treatment with a short recovery time. The involvement of the temperature dependence of the heat capacity, the thermal conductivity, and blood perfusion, is pivotal for establishing the correct ablation process and preserving the healthy tissue. The obtained simulation results clearly show that precisely localized heating distributions and heating efficiency can be achieved by using a multislot antenna probe. Deeper knowledge in this area would aid in the prediction and planning of patient-individual procedures.Microwave ablation at 2.45 GHz is gaining popularity as an alternative therapy to hepatic resection with a higher overall survival rate than external beam radiation therapy and proton beam therapy. It also offers better long-term recurrence-free overall survival when compared with radiofrequency ablation. To improve the design and optimization of microwave ablation procedures, numerical models can provide crucial information. A three-dimensional model of the antenna and targeted tissue without homogeneity assumptions are the most realistic representation of the physical problem. Due to complexity and computational resources consumption, most of the existing numerical studies are based on using two-dimensional axisymmetric models to emulate actual three-dimensional cancers and surrounding tissue, which is often far from reality. The main goal of this study is to develop a fully three-dimensional model of a multislot microwave antenna immersed into liver tissue affected by early-stage hepatocellular carcinoma. The geometry of the tumor is taken from the 3D-IRCADb-01 liver tumors database. Simulations were performed involving the temperature dependence of the blood perfusion, dielectric and thermal properties of both healthy and tumoral liver tissues. The water content changes during the ablation process are also included. The optimal values of the input power and the ablation time are determined to ensure complete treatment of the tumor with minimal damage to the healthy tissue. It was found that a multislot antenna is designed to create predictable, large, spherical zones of the ablation that are not influenced by varying tissue environments. The obtained results may be useful for determining optimal conditions necessary for microwave ablation to be as effective as possible for treating early-stage hepatocellular carcinoma, with minimized invasiveness and collateral damages.

Feasibility of 18-MV grid therapy from radiation protection aspects: unwanted dose and fatal cancer risk caused by photoneutrons and scattered photons

PurposePhotoneutron production is a common concern when using 18-MV photon beams in radiation therapy. In Spatially Fractionated Grid Radiation Therapy (SFGRT), the grid block in the collimation system modifies the neutron production, photon scattering, and electron contamination in and out of the radiation field. Such an effect was studied with grids made of different high-Z materials by Monte Carlo simulations. The results were also used to evaluate the lifetime risk of fatal cancers. MethodsMCNPX® code (2.7.0 extensions) was employed to simulate an 18-MV LINAC (Varian 2100 C/D). Three types of grid made of brass, cerrobend, and lead were used to study the neutron and electron fluence. Output factors for each grid with different field sizes were calculated. A revised female MIRD phantom with an 8-cm spherical tumor inside the liver was used to estimate the dose to the tumor and the critical organs. A 20-Gy SFGRT plan with Anterior Posterior (AP) - Posterior Anterior (PA) grid beams was compared with a Conventional Fractionated Radiation Therapy (CFRT) plan which delivered 40-Gy to the tumor by AP-PA open beams. Neutron equivalent dose, photon equivalent dose, as well as lifetime risks of fatal cancer were calculated in the organs at risk. ResultsThe grid blocks reduced the fluence of contaminant electrons inside the treatment field by more than 50%. The neutron fluences per electron-history in SFGRT plans with brass, cerrobend and lead were on average 55%, 31% and 31% less than that of the CFRT plan, respectively. However, when converting to fluences per delivered dose (Gy), the cerrobend and lead grid may incur higher neutron dose for 20 × 20 cm2 field size and above. The changes in neutron mean energy, as well as the correlated radiation weighting factors, were insignificant. The total risk due to the photoneutrons in the SFGRT plans was 87% or lower than that in the CFRT plans. In both SFGRT and CFRT plans, the contribution of the primary and scattered photons to the fatal cancer risk was 2 times or more than the photoneutrons. The total risks from photons in SFGRT with brass, cerrobend, and lead blocks were 1.733, 1.374, and 1.260%, respectively, which were less than 30% of the total photon-risk in CFRT (5.827%). ConclusionIn the brass, cerrobend, and lead grids, the attenuation of photoneutrons outweighs its photoneutron production in 18-MV SFGRT. The total cancer risks from photons and photoneutrons in the SFGRT plans were 30% or less of the risks in the CFRT plans (5.911%). Using 18 MV photon beams with brass, cerrobend, and lead grid blocks is still a feasible option for SFGRT.

Dosimetric evaluation of different planning techniques based on flattening filter-free beams for central and peripheral lung stereotactic body radiotherapy

This study aimed to dosimetrically compare and evaluate the flattening filter-free (FFF) photon beam-based three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) for lung stereotactic body radiotherapy (SBRT). RANDO phantom computed tomography (CT) images were used for treatment planning. Gross tumor volumes (GTVs) were delineated in the central and peripheral lung locations. Planning target volumes (PTVs) was determined by adding a 5 mm margin to the GTV. 3DCRT, IMRT, and VMAT plans were generated using a 6-MV FFF photon beam. Dose calculations for all plans were performed using the anisotropic analytical algorithm (AAA) and Acuros XB algorithms. The accuracy of the algorithms was validated using the dose measured in a CIRS thorax phantom. The conformity index (CI), high dose volume (HDV), low dose location (D2cm), and homogeneity index (HI) improved with FFF-VMAT compared to FFF-IMRT and FFF-3DCRT, while low dose volume (R50%) and gradient index (GI) showed improvement with FFF-3DCRT. Compared with FFF-3DCRT, a drastic decrease in the mean treatment time (TT) value was observed with FFF-VMAT for different lung sites between 57.09% and 60.39%, while with FFF-IMRT it increased between 10.78% and 17.49%. The dose calculation with Acuros XB was found to be superior to that of AAA. Based on the comparison of dosimetric indices in this study, FFF-VMAT provides a superior treatment plan to FFF-IMRT and FFF-3DCRT in the treatment of peripheral and central lung PTVs. This study suggests that Acuros XB is a more accurate algorithm than AAA in the lung region.

Preliminary Study of a Large Energy Acceptance FFA Beam Delivery System for Particle Therapy

The availability and use of ion beams for radiotherapy has grown significantly, led by technological developments to exploit the dosimetric advantages offered by charged particles. The benefits of particle therapy (PT) are well identified however its utilisation is still limited by high facility costs and technological challenges. A possibility to address both of these can be considered by improvements to the beam delivery system (BDS). Existing beamlines and gantries transport beams with a momentum range of ±1% and consequently, adjustments in depth or beam energy require all the magnetic fields to be changed. The speed to switch energies is a limiting constraint of the BDS and a determinant of the overall treatment time. A novel concept using fixed field alternating gradient (FFA) optics enables a large energy acceptance (LEA) as beams of varying energies can traverse the beamline at multiple physical positions given the same magnetic field. This presents the potential to provide faster, higher quality treatments at lower costs, with the capability to deliver advanced PT techniques such as multi-ion therapy. We explore the applicability and benefits of a LEA BDS.

Retrospective analysis of characteristics associated with higher-value radiotherapy episodes of care for bone metastases in Medicare fee-for-service beneficiaries

ObjectivesThe Centers for Medicare & Medicaid Services’ newly enacted Radiation Oncology Model (‘RO Model’) was designed to test the cost-saving potential of prospective episode-based payments for radiation treatment for 17...

Improving Clinical dosimetric Accuracy of cancer treatment using a special quality of Electron and Photon Beam

In external beam radiation therapy, electron and photon beams have extraordinary characteristics in the treatment of cancer. The electron and photon beam characteristic are essential to study before calibration of machine. This study focused on the dosimetric characteristics of different energies of electron beams for different field size. The basic objective of this work is, to calculate dosimetric parameters and characteristics of electron beam, specially depth dose characteristics along central axis. In this work, 6 MeV, 9 MeV, 12 MeV, 15 MeV and 18 MeV of electron beam and 6 MV and 15 MV of photon beam with different field size is used. Characteristics of depth dose of electron and photon beam in water have analyzed to provide better quality of radiation therapy treatment planning. The different beam characteristics are due to different interactions that occurs between electron beams giving them a definite range whereas photon beams are attenuated leading to dose deposition and much larger range with no definite end. Depth dose characteristics of electron and photon beams do not show same characteristics as interaction of beam with matter depends on the quality of beam. Attenuation and penetration factors change with changing dosimetric parameters. Complete analysis of dosimetric characteristics of electron and photon beam help to choose more accurate beam for the treatment of cancer. This work will help to increase accuracy in treatment of cancer with radiotherapy.

Relevance of Combined Electron and Photon Beams in Radiotherapy of Head and Neck Cancers in the Era of Intensity-Modulated Radiotherapy

Introduction External beam radiotherapy (EBRT) for head and neck (H&amp;N) cancers continues to be delivered using varied technologies, ranging from the old two-dimensional conventional radiotherapy (2DRT) techniques to the modern three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc therapy (VMAT) in different centers in India. Due to limitations of spinal cord tolerance, electron and photon beams are combined in 2DRT and 3DCRT techniques for treating nodal volume of the H&amp;N cases. However, many centers having modern technology practice IMRT/VMAT in place of electron beams. The purpose of this study is to analyze the role of combined electron and photon beams in radiotherapy of H&amp;N cancers and its relevance in the modern era of IMRT/VMAT.Materials and Methods Data were collected through a survey conducted on cancer centers in India where radiotherapy is being given by 2DRT, 3DCRT, and IMR/VMAT for the treatment of head and neck cancers.Results The mean percentage of H&amp;N (H&amp;N) cases among all cases were 39.2% (standard deviation [SD]: 14.22), out of which 16.63% (SD: 20.83) were treated with a combination of photon and electron beams and 49.73% (SD: 37.41) were treated with IMRT/VMAT. The average percentage of H&amp;N cases of government institutes was 38.39% (SD: 14.11) and that of private institutes was 40.14% (SD: 14.11). Patients treated with photon and electron combination and IMRT/VMAT were 22.19% (SD: 11.24) and 24.05% (SD: 23.99), respectively, in government institutes, and 10.29% (SD: 11.24) and 79.09% (SD: 26.75) in private institutes.Conclusion As per this study, we conclude that despite the availability of IMRT/VMAT, a combination of electron and photon beams is still relevant in India. Since a large proportion of the patients are still treated with the electron and photon combination, it is imperative that further studies on field–junction dosimetry should be conducted to ensure accurate dose delivery.

Real-Time Respiratory Tumor Motion Prediction Based on a Temporal Convolutional Neural Network: Prediction Model Development Study.

BackgroundThe dynamic tracking of tumors with radiation beams in radiation therapy requires the prediction of real-time target locations prior to beam delivery, as treatment involving radiation beams and gating tracking results in time latency.ObjectiveIn this study, a deep learning model that was based on a temporal convolutional neural network was developed to predict internal target locations by using multiple external markers.MethodsRespiratory signals from 69 treatment fractions of 21 patients with cancer who were treated with the CyberKnife Synchrony device (Accuray Incorporated) were used to train and test the model. The reported model’s performance was evaluated by comparing the model to a long short-term memory model in terms of the root mean square errors (RMSEs) of real and predicted respiratory signals. The effect of the number of external markers was also investigated.ResultsThe average RMSEs of predicted (ahead time=400 ms) respiratory motion in the superior-inferior, anterior-posterior, and left-right directions and in 3D space were 0.49 mm, 0.28 mm, 0.25 mm, and 0.67 mm, respectively.ConclusionsThe experiment results demonstrated that the temporal convolutional neural network–based respiratory prediction model could predict respiratory signals with submillimeter accuracy.

Dosimetric Uncertainties Resulting From Interfractional Anatomic Variations for Patients Receiving Pancreas Stereotactic Body Radiation Therapy and Cone Beam Computed Tomography Image Guidance

PurposeTo estimate the effects of interfractional anatomic changes on dose to organs at risk (OARs) and tumors, as measured with cone beam computed tomography (CBCT) image guidance for pancreatic stereotactic body radiation therapy. Methods and MaterialsWe evaluated 11 patients with pancreatic cancer whom were treated with stereotactic body radiation therapy (33-40 Gy in 5 fractions) using daily CT-on-rails (CTOR) image guidance immediately before treatment with breath-hold motion management. CBCT alignment was simulated in the treatment planning software by aligning the original planning CT to each fractional CTOR image set via fiducial markers. CTOR data sets were used to calculate fractional doses after alignment by applying the rigid shift of the planning CT and CTOR image sets to the planning treatment isocenter and recalculating the fractional dose. Accumulated dose to the gross tumor volume (GTV), tumor vessel interface, duodenum, small bowel, and stomach were calculated by summing the 5 fractional absolute dose-volume histograms into a single dose-volume histogram for comparison with the original planned dose. ResultsFour patients had a GTV D100% of at least 1.5 Gy less than the fractional planned value in several fractions; 4 patients had fractional underestimation of duodenum dose by 1.0 Gy per fraction. The D1.0 cm3 <35 Gy constraint was violated for at least 1 OAR in 3 patients, with either the duodenum (n = 2) or small bowel (n = 1) D1.0 cm3 being higher on the accumulated dose distribution (P = .01). D100% was significantly lower according to accumulated dose GTV (P = .01) and tumor vessel interface (P = .02), with 4 and 2 patients having accumulated D100% ≥4 Gy lower than the planned value for the GTV and tumor vessel interface, respectively. ConclusionsFor some patients, CBCT image guidance based on fiducial alignment may cause large dosimetric uncertainties for OARs and target structures, according to accumulated dose.