Megavoltage Research Articles

Dosimetric Evaluation of the Treatment Plan on Indigenous Heterogeneous Phantoms using Analytical Anisotropic Algorithm and Acuros-XB Algorithm for Different Photon Energies.

Background: Modern radiotherapy techniques are using advanced algorithms; however, phantoms used for quality assurance have homogeneous density; accordingly, the development of heterogeneous phantom mimicking human body sites is imperative to examine variation between planned and delivered doses.Objective: This study aimed to analyze the accuracy of planned dose by different algorithms using indigenously developed heterogeneous thoracic phantom (HT).Material and Methods: In this experimental study, computed tomography (CT) of HT was done, and the density of different parts was measured. The plan was generated on CT images of HCP with 6 and 15 Megavoltage (MV) photon beams using different treatment techniques, including three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT). Plans were delivered by the linear accelerator, and the dose was measured using the ion chamber (IC) placed in HT; planned and measured doses were compared.Results: Density patterns for different parts of the fabricated phantom, including rib, spine, scapula, lung, chest wall, and heart were 1.849, 1.976, 1.983, 0.173, 0.855, and 0.833 g/cc, respectively. Variation between planned and IC estimated doses with the tolerance (±5%) for all photon energies using different techniques. Acuros-XB (AXB) showed a slightly higher variation between computed and IC estimated doses using HCP compared to the analytical anisotropic algorithm (AAA).Conclusion: The indigenous heterogeneous phantom can accurately simulate the dosimetric scenario for different algorithms (AXB or AAA) and be also utilized for routine patient-specific QA.

A study on radiation interactions, dose enhancement, and hydrolysis with metallic nanoparticles irradiated by 6 megavoltage X-rays: Geant4 Monte Carlo simulation

Nanoparticles (NPs) have been suggested to increase cancer radiotherapy efficiency. However, a fulfillment of knowledge on mechanisms of radiation dose enhancement by NPs is needed. The aim of present study was to evaluate the enhancement of radiation effects by metal NPs at physical and chemical levels. Geant4-DNA Monte Carlo simulation was used for assessment of radiation interaction processes, radiation dose effect and the produced hydrolysis byproducts following 6 MV X-rays. According to the results NPs of this study may be divided in three categories: low dose enhancers (TiO2NP, Fe3O4NP, GeNP), medium dose enhancers (BiNP, AgNP) and high dose enhancers (GNP, PtNP). It found that mass density of NPs may be the most effective feature on DER. Higher radiation enhancement efficiencies by GNP, PtNP may be produced due to the induced high energetic photoelectrons and Compton electrons and also the produced free radicals.

Abstract 1630: Development of a clinically relevant in vitro model of chemo-radioresistant cervical cancer cells for insights into treatment resistance

Abstract Resistance to therapeutic treatment is a common phenomenon that contributes to relapse in several cancers including cervical that is the fourth most common cancer in women across the world. Acquired resistance to chemotherapy, radiotherapy or their combination contributes to a majority of relapse cases which suggests the need to develop models that can be used for preliminary screening of drugs or decipher the associated signaling mechanisms contributing to this resistance. Various chemo-resistant, as well as radio-resistant models, have been established as in vitro models. In cervical cancer treatment, often, radiation therapy is accompanied by the addition of radio-sensitizers such as cisplatin that increase its treatment efficiency. Hence, a combined chemo-radio-resistant in vitro model seems more relevant clinically in cervical cancer. Therefore, we designed our study to establish a cellular model that is resistant to a combined treatment of chemotherapy and radiotherapy. A chemo-radio resistant cervical cancer cell line (HeLa) was developed in vitro by a fractionated exposure of a combination of cisplatin and megavoltage X-rays. Briefly, HeLa cells were sensitized with cisplatin (0.1µM increase at every fraction) prior to radiation exposure (2Gy). The cells were treated once in 5 days and eventually after 25 fractions, delivered in 20 weeks, the cells were made resistant up to a total dose of 2.5µM cisplatin + 50Gy. These cells were further characterized and compared with radioresistant HeLa cells as well as parental cells. For this purpose, proliferation assay, clonogenic survival assay, cell cycle analysis and apoptosis assay were performed. The resistivity was confirmed by comet assay and Gamma-H2AX staining. Interestingly, an increase in cell proliferation and clonogenic survival rates was observed in chemo-radio-resistant cells. FACS analysis revealed that the proportion of cells in G2/M phase increased and apoptotic rates declined in chemo-radio-resistant cells. Further, changes in comet tails, olive moment and Gamma-H2AX foci formation in chemo-radio-resistant groups confirmed resistivity. These cells were also analyzed for their metastatic properties and results suggest that induced chemo-radio-resistant cells are more tumorigenic as compared to only radioresistant cells as well as the parental ones. In conclusion, the establishment of a chemo-radio-resistant cell line may serve as a model to study signalling mechanisms, drug screening and develop novel drugs. Further studies are underway to induce the chemo-radio resistance in other cell lines by a similar method. Citation Format: Sanchita Khurana, Surbhi Singla, Reena Sharma, Bhavana Rai, Shalmoli Bhattacharyya. Development of a clinically relevant in vitro model of chemo-radioresistant cervical cancer cells for insights into treatment resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1630.

Design optimization of an electron-to-photon conversion target for ultra-high dose rate x-ray (FLASH) experiments at TRIUMF

Objective. To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF. Approach. An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum–aluminum (Ta–Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5–1.5 mm), beam energies (E e− = 8, 10 MeV) and electron (Gaussian) beam sizes ( = 2–10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress–strain conditions and fatigue life of the target assembly. Main results. Dose-rates of up to 128 Gy s−1 at the phantom surface, or 85 Gy s−1 at 1 cm depth, were obtained for a 1 × 1 cm2 field size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam (E e− = 10 MeV, 2 = 5 mm, P = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s−1, albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime. Significance. Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s−1.

Time-resolved plastic scintillator dosimetry in MR linear accelerators without image distortion

One of the newest developments within radiotherapy is the integration of Magnetic Resonance (MR) scanners and Megavoltage X-rays from linear accelerators into the new MR-Linacs. Some MR-Linacs are able to perform gated treatments based on continuously acquired 2D MR images taken during dose delivery, which has the potential to reduce margins required for tumor coverage. We have developed a dosimetry system that can provide time-resolved, dose-per-pulse, dosimetry without distorting the MR images in order to characterize this technology. The system is based on a plastic BCF-60 scintillation detector (PSD) coupled to an optical PMMA fiber cable. The detector was placed in a plastic tube filled with water and inserted into the piston of a dynamic MRI compatible phantom to be treated on a ViewRay MRIdian 0.35 T MR-Linac. The piston performed a sinusoidal movement to simulate a breathing cycle of either 4 or 8 s. We demonstrate that the detector system is able to provide real-time dose-per-pulse measurements without causing distortions in the MR images. The time-resolved dosimetry system revealed systematic dose rate transients during gated treatments that lasted about 1 s in every gating sequence where the beam turned on and off. Detection of such effects require real time dosimetry which does not interfere with the MRI based gating.

Local dose rate effects in implantable cardioverter–defibrillators with flattening filter free and flattened photon radiation

PurposeIn the beam penumbra of stereotactic body radiotherapy volumes, dose rate effects in implantable cardioverter–defibrillators (ICDs) may be the predominant cause for failures in the absence of neutron-generating photon energies. We investigate such dose rate effects in ICDs and provide evidence for safe use of lung tumor stereotactic radioablation with flattening filter free (FFF) and flattened 6 Megavolt (MV) beams in ICD-bearing patients.MethodsSixty-two ICDs were subjected to scatter radiation in 1.0, 2.5, and 7.0 cm distance to 100 Gy within a 5 × 5 cm2 radiation field. Radiation was applied with 6 MV FFF beams (constant dose rate of 1400 cGy/min) and flattened (FLAT) 6 MV beams (430 cGy/min). Local dose rates (LDR) at the position of all ICDs were measured. All ICDs were monitored continuously.ResultsWith 6 MV FFF beams, ICD errors occurred at distances of 1.0 cm (LDR 46.8 cGy/min; maximum ICD dose 3.4 Gy) and 2.5 cm (LDR 15.6 cGy/min; 1.1 Gy). With 6 MV FLAT beams, ICD errors occurred only at 1 cm distance (LDR 16.8 cGy/min; 3.9 Gy). No errors occurred at an LDR below 7 cGy/min, translating to a safe distance of 2.5 cm (1.5 Gy) in flattened and 7 cm (0.4 Gy) in 6 MV FFF beams.ConclusionA LDR in ICDs larger than 7 cGy/min may cause ICD malfunction. At identical LDR, differences between 6 MV FFF and 6 MV FLAT beams do not yield different rates of malfunction. The dominant reason for ICD failures could be the LDR and not the total dose to the ICD. For most stereotactic treatments, it is recommended to generate a planning risk volume around the ICD in which LDR larger than 7 cGy/min are avoided.

Radiosensitization Effect of Gold Nanoparticles on Plasmid DNA Damage Induced by Therapeutic MV X-rays.

Gold nanoparticles (AuNPs) can be used with megavolt (MV) X-rays to exert radiosensitization effects, as demonstrated in cell survival assays and mouse experiments. However, the detailed mechanisms are not clear; besides physical dose enhancement, several chemical and biological processes have been proposed. Reducing the AuNP concentration while achieving sufficient enhancement is necessary for the clinical application of AuNPs. Here, we used positively charged (+) AuNPs to determine the radiosensitization effects of AuNPs combined with MV X-rays on DNA damage in vitro. We examined the effect of low concentrations of AuNPs on DNA damage and reactive oxygen species (ROS) generation. DNA damage was promoted by 1.4 nm +AuNP with dose enhancement factors of 1.4 ± 0.2 for single-strand breaks and 1.2 ± 0.1 for double-strand breaks. +AuNPs combined with MV X-rays induced radiosensitization at the DNA level, indicating that the effects were physical and/or chemical. Although −AuNPs induced similar ROS levels, they did not cause considerable DNA damage. Thus, dose enhancement by low concentrations of +AuNPs may have occurred with the increase in the local +AuNP concentration around DNA or via DNA binding. +AuNPs showed stronger radiosensitization effects than −AuNPs. Combining +AuNPs with MV X-rays in radiation therapy may improve clinical outcomes.

Investigation of image quality of MV and kV CBCT with low-Z beams and high DQE detector.

To investigate cone beam computed tomography (CBCT) image quality using novel combinations of kilovoltage (kV) and megavoltage (MV) beams and detectormaterials. MV and kV CBCT imaging was simulated using the Fastcat hybrid Monte Carlo application. CBCT imaging with various beam energies was investigated: 2.5 and 6 MV photon beams generated with carbon, aluminum, and tungsten targets and a 120 kVp x-ray tube beam based off of a Varian Truebeam on-board imager (OBI). Cadmium tungstate (CWO), gadolinium oxysulfide (GOS), and cesium iodide (CsI) detectors with identical pixel pitch of 0.784 mm were evaluated. Modulation transfer functions (MTF) for all detector/beam combinations were calculated. MV and kV CBCT images for each detector/beam combination of a contrast phantom containing inserts with rib and spongiosa bone, lung, and adipose tissues were simulated with an imaging dose of 7 mGy. Contrast to noise ratio (CNR) of all inserts were compared for all detector/beam combinations. CBCT images of an anthropomorphic head phantom with silver amalgam fillings were also generated. The CWO/120 kVp beam combination resulted in the highest MTF at low frequencies and the CsI detector showed the highest MTF for all other beams and at high frequencies. The CWO/120 kVp beam combination showed the highest CNR for all tissues. The unoptimized CWO/2.5 MV carbon target beam showed the highest CNR of the MV beam/detector combinations with CNR 4% and 17% worse than the optimized Truebeam CsI 120 kVp setup with a bowtie filter and antiscatter grid. Additionally, the CWO 2.5 MV setup showed qualitative reduction of metal artifacts surrounding silver amalgam fillings in an anthropomorphic headphantom. This finding makes a compelling case that further optimization of this CWO carbon target setup could produce CBCT images with similar CNR to current OBI CBCT for equivalent dose with added resilience to metalartifacts.

Cerenkov radiation-activated probes for deep cancer theranostics: a review.

Cerenkov radiation (CR) from radionuclides and megavoltage X-ray radiation can act as an in situ light source for deep cancer theranostics, overcoming the limitations of external light sources. Despite the blue-weighted emission and low quantum yield of CR, activatable probes-mediated CR can enhance the in-vivo diagnostic signals by Cerenkov resonance energy transfer and also can produce therapeutic effects by reactive species generation/drug release, greatly promoting the biomedical applications of CR. In this review, we describe the principles and sources of CR, construction of CR-activated probes and their application to tumor optical imaging and therapy. Finally, future prospects for the design and biomedical application of CR-activated probes are discussed.

The markerless lung target tracking AAPM Grand Challenge (MATCH) results.

Lung stereotactic ablative body radiotherapy (SABR) is a radiation therapy success story with level 1 evidence demonstrating its efficacy. To provide real-time respiratory motion management for lung SABR, several commercial and preclinical markerless lung target tracking (MLTT) approaches have been developed. However, these approaches have yet to be benchmarked using a common measurement methodology. This knowledge gap motivated the MArkerless lung target Tracking CHallenge (MATCH). The aim was to localize lung targets accurately and precisely in a retrospective in silico study and a prospective experimental study. MATCH was an American Association of Physicists in Medicine sponsored Grand Challenge. Common materials for the in silico and experimental studies were the experiment setup including an anthropomorphic thorax phantom with two targets within the lungs, and a lung SABR planning protocol. The phantom was moved rigidly with patient-measured lung target motion traces, which also acted as ground truth motion. In the retrospective in silico study a volumetric modulated arc therapy treatment was simulated and a dataset consisting of treatment planning data and intra-treatment kilovoltage (kV) and megavoltage (MV) images for four blinded lung motion traces was provided to the participants. The participants used their MLTT approach to localize the moving target based on the dataset. In the experimental study, the participants received the phantom experiment setup and five patient-measured lung motion traces. The participants used their MLTT approach to localize the moving target during an experimental SABR phantom treatment. The challenge was open to any participant, and participants could complete either one or both parts of the challenge. For both the in silico and experimental studies the MLTT results were analyzed and ranked using the prospectively defined metric of the percentage of the tracked target position being within 2mm of the ground truth. A total of 30 institutions registered and 15 result submissions were received, four for the in silico study and 11 for the experimental study. The participating MLTT approaches were: Accuray CyberKnife (2), Accuray Radixact (2), BrainLab Vero, C-RAD, and preclinical MLTT (5) on a conventional linear accelerator (Varian TrueBeam). For the in silico study the percentage of the 3D tracking error within 2mm ranged from 50% to 92%. For the experimental study, the percentage of the 3D tracking error within 2mm ranged from 39% to 96%. A common methodology for measuring the accuracy of MLTT approaches has been developed and used to benchmark preclinical and commercial approaches retrospectively and prospectively. Several MLTT approaches were able to track the target with sub-millimeter accuracy and precision. The study outcome paves the way for broader clinical implementation of MLTT. MATCH is live, with datasets and analysis software being available online at https://www.aapm.org/GrandChallenge/MATCH/ to support future research.

Impact of the dose quantity used in MV photon optimization on dose distribution, robustness, and complexity

Convolution/superposition algorithms used in megavoltage (MV) photon radiotherapy model radiation transport in water, yielding dose to water-in-water (Dw,w ). Advanced algorithms constitute a step forward, but their dose distributions in terms of dose to medium-in-medium (Dm,m ) or dose to water-in-medium (Dw,m ) can be problematic when used in plan optimization due to their different dose responses to some atomic composition heterogeneities. Failure to take this into account can lead to undesired overcorrections and thus to unnoticed suboptimal and unrobust plans. Dose to reference-like medium (Dref,m* ) was recently introduced to overcome these limitations while ensuring accurate transport. This work evaluates and compares the performance of these four dose quantities in planning target volume (PTV)-based optimization. We considered three cases with heterogeneities inside the PTV: virtual phantom with water surrounded by bone; head and neck; and lung. These cases were planned with volumetric modulated arc therapy (VMAT) technique, optimizing with the same setup and objectives for each dose quantity. We used different algorithms of the Varian Eclipse treatment planning system (TPS): Acuros XB (AXB) for Dm,m and Dw,m , and Analytical Anisotropic Algorithm (AAA) for Dw,w . Dref,m* was obtained from Dm,m distributions using an in-house software considering water as the reference medium (Dw,m* ). The optimization process consisted of: (1) common first optimization, (2) dose distribution computed for each quantity, (3) re-optimization, and (4) final calculation for each dose quantity. The dose distribution, robustness to patient setup errors, and complexity of the plans were analyzed and compared. The quantities showed similar dose distributions after the optimization but differed in terms of plan robustness. The cases with soft tissue and high-density heterogeneities followed the same pattern. For AXB Dm,m , cold regions appeared in the heterogeneities after the first optimization. They were compensated in the second optimization through local fluence increases, but any positional mismatch impacted robustness, with clinical target volume (CTV) variations from the nominal scenario around +3% for bone and up to +7% for metal. For AXB Dw,m the pattern was inverse (hot regions compensated by fluence decreases) and more pronounced, with CTV dose variations around -7% for bone and up to -17% for metal. Neither AXB Dw,m* nor AAA Dw,w presented these dose inhomogeneities, which resulted in more robust plans. However, Dw,w differed markedly from the other quantities in the lung case because of its lower radiation transport accuracy. AXB Dm,m was the most complex of the four dose quantities and AXB Dw,m* the least complex, though we observed no major differences in this regard. The dose quantity used in MV photon optimization can affect plan robustness. Dw,w distributions from convolution/superposition algorithms are robust but may not provide sufficient radiation transport accuracy in some cases. Dm,m and Dw,m from advanced algorithms can compromise robustness because their different responses to some composition heterogeneities introduce additional fluence compensations. Dref,m* offers advantages in plan optimization and evaluation, producing accurate and robust plans without increasing complexity. Dref,m* can be easily implemented as a built-in feature of the TPS and can facilitate and simplify the treatment planning process when using advanced algorithms. Final reporting can be kept in Dm,m or Dw,m for clinical correlations.

Clinical Assessment of a Novel Ring Gantry Linear Accelerator-Mounted Helical Fan-Beam kVCT System

PurposeTo assess clinically relevant image quality metrics (IQMs) of helical fan beam kilovoltage (kV) fan beam computed tomography (CT). Methods and MaterialskVCT IQMs were evaluated on an Accuray Radixact unit equipped with helical fan beam kVCT to assess the capabilities of this newly available modality. kVCT IQMs were evaluated and compared to a kVCT simulator and linear accelerator-based cone beam CTs (CBCT) using a commercial CBCT image quality phantom. kVCTs were acquired on the Accuray Radixact for all combinations of kVp and mAs in fine mode using a 440-mm field of view (FOV). Evaluated IQMs were spatial resolution, overall uniformity, subject contrast, contrast-to-noise ratio (CNR), and effective slice thickness. Imaging dose was assessed for planar kV imaging. ResultsOn this kVCT system spatial resolution and contrast were consistent across all settings with 0.28 ± 0.03 lp/mm and 9.8% ± 0.7% (both 95% confidence interval). CNR strongly depended on selected mode (views per rotation) and body size (mA per view) and ranged between 7.9 and 34.9. Overall uniformity was greater than 97% for all settings. Large FOV was not found to substantially affect the IQMs whereas small FOV affected IQMs due to its effect on pitch. Technique-matched CT simulator scans were comparable for uniformity and contrast, while spatial resolution was higher (0.43 ± 0.06 lp/mm), and CNR was between 4% (140 kVp) and 51% (100 kVp) lower. For kV-CBCT, spatial resolutions ranging from 0.37 to 0.44 lp/mm were achieved with comparable contrast, CNR, and uniformity to kVCT. All kVCT scans exhibit imaging artifacts due to helical acquisition. Clinical acquisitions of megavoltage (MV) CT, kV-CBCT, and kVCT on the same patient showed improved and comparable image quality of kVCT compared to MVCT and kV-CBCT, respectively. ConclusionsHelical fan beam kVCT allows for daily image guidance for localization and setup verification with comparable performance to existing kV-CBCT systems. Scan parameters must be selected carefully to maximize image quality for the desired tasks. Due to the large effective slice thicknesses for all parameter combinations, kVCT scans should not be used for simulation or planning of stereotactic procedures. Finally, improved image quality over MVCT has the potential to greatly improve manual and automated adaptive monitoring and planning.

Tattoo-Free Set-ups for Breast Cancer Patients Receiving Regional Nodal Irradiation: Evaluation of Accuracy and Time Efficiency

Purpose/Objective(s)Permanent skin-based tattoos have been considered in treatment planning an essential aspect of ensuring patient positioning accuracy for radiation delivery in breast cancer patients. Despite this benefit, tattoos may also be a reminder of cancer treatment long past the treatment itself, causing unnecessary emotional distress. With the advent of advanced imaging techniques, routine tattoo placement may no longer be necessary. We performed a retrospective study evaluating a tattoo-free method of set-up for breast cancer patients receiving RNI.Materials/MethodsFollowing a transition in our institution's clinical practice toward a tattoo-free set-up in May 2020, we compared a cohort of breast cancer patients, in which tattoos were referenced for daily alignment (“tattoo group”) and a second cohort in which tattoos were placed but not referenced for daily alignment (“no tattoo group”). The number of patients in the two groups were matched by tumor laterality (right versus left) and breath-hold utilization. Patients in both cohorts were positioned using surface-guided imaging with periodic megavoltage (MV) x-ray imaging to confirm patient positioning. The physical shifts obtained from MV imaging, after surface-imaging, and the duration of daily patient treatment were compared between the two cohorts using the Mann-Whitney U-test.ResultsThere were 14 patients in each cohort; 8 left-sided breath-hold patients and 6 right-sided non-breath-hold patients, for a total of 61 recorded duration times and shifts for the tattoo group and 59 recorded duration times and shifts for the no-tattoo group. The average physical 3-dimensional shifts for the no-tattoo group was smaller compared to the tattoo group, mean 4.4 mm versus 5.7 mm (P < 0.01) and patient time in treatment room was also decreased for the no-tattoo group: mean 19.7 min versus 21.3 min (P = 0.03).ConclusionBased on our preliminary results for a cohort of women receiving RNI for breast cancer treatment at our institution, omitting radiation tattoos while utilizing daily surface imaging led to improved patient setup accuracy and decreased patient time on the treatment machine. Utilizing daily surface imaging obviates the requirement for skin-based tattoos in this patient population, improves efficiency of machine utilization, and provides the means for a tattoo-free set-up to become standard practice. Permanent skin-based tattoos have been considered in treatment planning an essential aspect of ensuring patient positioning accuracy for radiation delivery in breast cancer patients. Despite this benefit, tattoos may also be a reminder of cancer treatment long past the treatment itself, causing unnecessary emotional distress. With the advent of advanced imaging techniques, routine tattoo placement may no longer be necessary. We performed a retrospective study evaluating a tattoo-free method of set-up for breast cancer patients receiving RNI. Following a transition in our institution's clinical practice toward a tattoo-free set-up in May 2020, we compared a cohort of breast cancer patients, in which tattoos were referenced for daily alignment (“tattoo group”) and a second cohort in which tattoos were placed but not referenced for daily alignment (“no tattoo group”). The number of patients in the two groups were matched by tumor laterality (right versus left) and breath-hold utilization. Patients in both cohorts were positioned using surface-guided imaging with periodic megavoltage (MV) x-ray imaging to confirm patient positioning. The physical shifts obtained from MV imaging, after surface-imaging, and the duration of daily patient treatment were compared between the two cohorts using the Mann-Whitney U-test. There were 14 patients in each cohort; 8 left-sided breath-hold patients and 6 right-sided non-breath-hold patients, for a total of 61 recorded duration times and shifts for the tattoo group and 59 recorded duration times and shifts for the no-tattoo group. The average physical 3-dimensional shifts for the no-tattoo group was smaller compared to the tattoo group, mean 4.4 mm versus 5.7 mm (P < 0.01) and patient time in treatment room was also decreased for the no-tattoo group: mean 19.7 min versus 21.3 min (P = 0.03). Based on our preliminary results for a cohort of women receiving RNI for breast cancer treatment at our institution, omitting radiation tattoos while utilizing daily surface imaging led to improved patient setup accuracy and decreased patient time on the treatment machine. Utilizing daily surface imaging obviates the requirement for skin-based tattoos in this patient population, improves efficiency of machine utilization, and provides the means for a tattoo-free set-up to become standard practice.

Dosimetric Parameters Associated With Pathologic Response in Patients Undergoing Preoperative Spatially Fractionated Radiotherapy (GRID) for Soft Tissue Sarcoma

<h3>Purpose/Objective(s)</h3> Spatially fractionated radiotherapy, or GRID radiotherapy, is a technique utilizing multiple beamlets of high dose radiotherapy in a heterogeneous grid pattern to treat tumor non-uniformly with megavoltage X-rays while maintaining normal tissue tolerance. We sought to characterize associations between GRID dosimetric parameters and pathologic response in patients undergoing preoperative GRID radiotherapy for high grade soft tissue sarcoma. <h3>Materials/Methods</h3> We analyzed 26 patients with high grade soft tissue sarcomas undergoing GRID radiotherapy. Dosimetric parameters included mean dose to GTV, maximum dose to 0.01 cc, maximum dose to 0.03 cc, D5, D10, D20, D50, D90, D100, V5, V10, V20, V50, V90, V100, total area under the curve, maximum tumor length, maximum tumor width, tumor volume, equivalent uniform dose to GTV, minimum surface to tumor distance, maximum surface to tumor distance, maximum tumor depth, maximum dose outside GTV, maximum dose to skin, number of beamlets, peak to valley ratio, and peak to peak distance. <h3>Results</h3> The dosimetric parameters most closely associated with pathologic response were maximum dose to 0.01 cc and maximum dose to 0.03 cc (Spearman coefficient of 0.685, <i>P</i>-value of 0.01). Mean dose to GTV, V90, and V100 showed weak associations that weaker associations that were not significant (Spearman coefficient of 0.442, 0.510, and 0.504 with <i>P</i>-values of 0.08, 0.09, 0.09). <h3>Conclusion</h3> This study showed an association between the dosimetric parameters maximum dose to 0.01 cc and maximum dose to 0.03 cc and pathologic response in patients undergoing preoperative GRID radiotherapy for high grade soft tissue sarcoma.

A review on theranostic applications of iodine nanoparticles: Recent findings and perspectives

Application of nanoparticles have in the core of researchers attention for both imaging and therapy of cancers. This review article aimed to prepare an outline on recent applications of iodine nanoparticles (INPs) as theranostic agents in both diagnosis and therapies. Among various strategies are used in treatment of cancers, radiotherapy with radiopharmaceutical agents especially radioisotope of iodine displays satisfactory results for numerous types of cancers. In recent years, new investigations were done in order to develop the novel structure of INPs. These nanoprobes could act as efficient theranostic purposes. Iodine nanoparticles may be applied in nuclear medicine imaging and may be effective with mega voltage (MV) photons in cancer therapy, but this remains to be tested with different cancer cells. By using INPs, effective steps can be taken in the future in both diagnosis and treatment of cancers. This review emphasized the recent research findings on the application of INPs in medical imaging and therapeutic of cancers. The current challenges and the perspectives for their future applications were also represented and discussed.

Effect of contrast medium on treatment modalities planned with different photon beam energies: a planning study.

Routinely, patient's planning scans are acquired after administration of iodinized contrast media but they will be treated in the absence of that. Similarly, high energy photons have a better penetrating power, while low energy photons will result in tighter dose distribution and negligible neutron contamination. The aim of the study was to investigate a suitable photon beam energy in the presence of intravenous contrast medium. An indigenously made original-contrast (OC) phantom was mentioned as virtual-contrast (VC) and virtual-without-contrast (VWC) phantom were generated by assigning the Hounsfield Units (HU) to different structures. Intensity-modulated (IMRT) and volumetric-modulated-arc (VMAT) plans were generated as per criteria of the TG-119 protocol. It was observed that the maximum dose to the spinal cord was better with 6 mega-voltage (MV) in IMRT. The coverage of Prostate PTV (PR PTV) was similar with all the photon energies and was comparable with TG-119, except for original-contrast (OC) phantom using the VMAT technique. Homogeneity-index (HI) was comparatively better for VMAT plans. The contrast CT images lower the dose to targets. IMRT or VMAT plans, generated on such CT images will be delivered with higher doses than evaluated. However, the overdose remains non-significant.

EPR dosimetric studies on strontium sulfate rods for possible use in radiotherapy

Radiation-induced radicals in the crystals of strontium sulfate (SS) as rod dosimeters were studied using an electron paramagnetic resonance (EPR) spectrometer. Dosimetric studies were performed in the dose range of 0.5 to 25 Gy for the dosimeters to investigate their potential applications in radiotherapy (60Co γ-rays and high megavoltage X-ray with 6 and 15 MV). Additionally, the response of these dosimeters was compared to the response of alanine pellet dosimeters at the three-beam qualities. Irradiation of SS dosimeters produces five EPR signals, and their intensity increases linearly with increasing absorbed doses from 0.5 to 25 Gy. A peak of a splitting g-factor (g) = 2.01039 was selected for the present evaluations as it has a higher intensity. The change in response of SS rod dosimeters after irradiation does not exceed ±2% over six months, exhibiting good stability. The response of SS dosimeters increases with increasing the incident beam energy from 60Co gamma rays to 16 MV X-ray beam. For alanine dosimeters, a non-significant change is observed under these beam qualities. The response of SS dosimeter at 6 and 15 MV relative to a60Co beam quality increases by about 3.8% and 14.1%, respectively.Moreover, the response of the SS dosimeters increases 2.24% with increasing the dose rate from 100 to 400 cGy/min, while for the alanine dosimeters, the increase in response is less than 0.49%. Environmental factors (relative humidity levels of 0–76% and temperature degrees of 15–30 °C) have a slight impact on the response of SS rods during irradiation. The overall uncertainty of dose monitoring was reported to be ±4.02% (2σ, 95% confidence levels).

Nontoxic electron collimators.

PurposeThe goal of this work was to develop and test nontoxic electron collimation technologies for clinical use.MethodsTwo novel technologies were investigated: tungsten‐silicone composite and 3D printed electron cutouts. Transmission, dose uniformity, and profiles were measured for the tungsten‐silicone. Surface dose, relative dose output, and field size were measured for the 3D printed cutouts and compared with the standard cerrobend cutouts in current clinical use. Quality assurance tests including mass measurements, Megavoltage (MV) imaging, and drop testing were developed for the 3D printed cutouts as a guide to safe clinical implementation.ResultsDose profiles of the flexible tungsten‐silicone skin shields had an 80–20 penumbra values of 2–3 mm compared to 7–8 mm for cerrobend. In MV transmission image measurements of the tungsten‐silicone, 80% of the pixels had a transmission value within 2% of the mean. An ∼90% reduction in electron intensity was measured for 6 MeV and a 6.4 mm thickness of tungsten‐silicone and 12.7 mm thickness for 16 MeV. The maximum difference in 3D printed cutout versus cerrobend output, surface dose, and full width at half‐maximum (FWHM) was 1.7%, 1.2%, and 1.5%, respectively, for the 10 cm × 10 cm cutouts.ConclusionsBoth flexible tungsten‐silicone and 3D printed cutouts were found to be feasible for clinical use. The flexible tungsten‐silicone was of adequate density, flexibility, and uniformity to serve as skin shields for electron therapy. The 3D printed cutouts were dosimetrically equivalent to standard cerrobend cutouts and were robust enough for handling in the clinical environment.

Dosimetry of a novel converging X-ray source for kilovoltage radiotherapy.

The objective of this work was to evaluate phantom dosimetry of a novel kilovoltage (kV) X-ray source, which employs a stationary tungsten anode and a linearly swept scanning electron beam. The source utilizes converging X-ray collimation along with orthogonal mechanical rotation to distribute surface flux over large area. In this study, this was investigated as a potential solution to fast-falloff limitations expected with kV radiotherapy. This was done with the aim of future clinical development of a lower cost radiotherapy alternative to megavoltage (MV) linac systems. Radiochromic film was employed for dosimetry on the kV X-ray source of the linear-converging radiotherapy system (LCRS). The source utilizes charge particle optics to magnetically deflect and focus an electron beam along a stationary, reflection tungsten target in an ultra-high-vacuum stainless-steel chamber. Resulting X-rays were collimated into converging beamlets that span a large planar angle and converge at the system isocenter. In this study, radiochromic film dosimetry was done at 140 and 145 kVp for a designated planning treatment volume (PTV) of 4 cm diameter. An acrylic phantom was employed for dose distribution measurements of stationary and rotational delivery. Film dosimetry was evaluated in planes parallel to the source X-ray window at various depths, as well as in the plane of gantry rotation. At 140 and 145 kVp and using a collimated 4 cm square field at depth, lesion-to-skin dose ratio was shown to improve with additional beams from different relative source positions, where the different beams are focused at the same isocenter and do not overlap at the phantom surface. It was only possible to achieve a 1:1 Dmax -to-surface ratio with four delivery beams, but the ratio improved to 4:1 with 12 beams, focused at the same isocenter depth of 7.8cm in an acrylic phantom. For the tests conducted, the following Dmax -to-surface ratios were obtained: 0.4:1 lesion-to-skin ratio for stationary delivery from one entry beam, 0.71:1 lesion-to-skin ratio was obtained for two beams, 1.07:1 ratio for four beams, and 4:1 for 12 beams. Dose-depth profiles were evaluated for stationary and rotational dosimetry. Additionally, rotational dosimetry was measured for a case more analogous to a clinical scenario, where the isocenter was located at an off-center simulated lesion. The results demonstrate potential dose-depth improvements with kV arc therapy by distributing the surface flux with a wide converging beam along with perpendicular mechanical source rotation of the LCRS. The system delivered tolerable dose to a large surface area when a threshold of multiple, separated beams was reached. The radiochromic film data support the feasibility of the construct of the LCRS kV radiotherapy system design.

FastCAT: Fast cone beam CT (CBCT) simulation.

To develop fastCAT, a fast cone-beam computed tomography (CBCT) simulator. fastCAT uses pre-calculated Monte Carlo (MC) CBCT phantom-specific scatter and detector response functions to reduce simulation time for megavoltage (MV) and kilovoltage (kV) CBCT imaging. Pre-calculated x-ray beam energy spectra, detector optical spread functions and energy deposition, and phantom scatter kernels are combined with GPU raytracing to produce CBCT volumes. MV x-ray beam spectra are simulated with EGSnrc for 2.5- and 6MeV electron beams incident on a variety of target materials and kV x-ray beam spectra are calculated analytically for an x-ray tube with a tungsten anode. Detectors were modeled in Geant4 extended by Topas and included optical transport in the scintillators. Two MV detectors were modeled-a standard Varian AS1200 GOS detector and a novel CWO high detective quantum efficiency detector. A kV CsI detector was also modeled. Energy-dependent scatter kernels were created in Topas for two 16cm diameter phantoms: A Catphan 515 contrast phantom and an anthropomorphic head phantom. The Catphan phantom contained inserts of 1-5mm in diameter of six different tissue types: brain, deflated lung, compact and cortical bone, adipose, and B-100. fastCAT simulations retain high fidelity to measurements and MC simulations: MTF curves were within 3.5% and 1.2% of measured values for the CWO and GOS detectors, respectively. HU values and CNR in a fastCAT Catphan 515 simulation were seen to be within 95% confidence intervals of an equivalent MC simulation for all of the tissues with root mean squared errors less than 16 HU and 1.6 in HU values and CNR comparisons, respectively. The anthropomorphic head phantom CWO detector CBCT image resulted in much higher tissue contrast and lower noise compared to the GOS detector CBCT image. A fastCAT simulation of the Catphan 515 module with an image size of 1024 1024 10 voxels took 61s on a GPU while the equivalent Topas MC was estimated to take more than 0.3CPU years. We present an open source fast CBCT simulation with high fidelity to MC simulations. The fastCAT python package can be found at https://github.com/jerichooconnell/fastCAT.git.