AAPM protocol for 40-300 kV x-ray beam dosimetry in radiotherapy and radiobiology

Design and validation of a minibeam treatment delivery system for use with a radiation therapy research platform

Minibeam radiation therapy (MBRT) is a promising treatment technique in the early stages of clinical use. In this work, two hexagonal minibeam collimators were designed, fabricated, and validated using film measurements and Monte Carlo simulations. Film and Monte Carlo results demonstrated strong agreement, with the greatest agreement near the beam central axis. One of the previously validated MBRT collimators was then modified to allow for dose calculations on a mouse cone beam computed tomography (CBCT) dataset, and a MBRT dose distribution was preserved in the animal dataset. This validated system can be used in future cell and small animal studies to further explore MBRT in a preclinical setting.

Co-exposure to inhaled tungsten particles and low-dose gamma rays: neurotoxicological outcome in rats

Throughout their lives, individuals are exposed to various pollutants, potentially including co-exposure to radiological and chemical stressors. Yet, existing literature about these combinations is scarce. We selected tungsten and ionizing radiations. Tungsten is an emerging contaminant present as aerosolized particles in several scenarios, potentially concurrently with low-dose irradiation, causing a co-exposure. The cerebral toxicity of this co-exposure was studied after 24 h and 28 days in the frontal cortex and olfactory bulb of male Sprague-Dawley rats exposed to gamma irradiation (50 mGy) and/or inhalation of tungsten particles aerosol (80 mg.m-3). Co-exposure triggered significant effects more frequently than single stressors. Observed effects were associated with oxidative status changes, notably via NRF2 nuclear translocation, and modulation of pro-inflammatory cytokines (IL1β, TNFα). A reduction in cortical microglial density suggested a cellular migration toward the olfactory bulb and could contribute to the occurrence of a neuronal suffering phenotype. The effects persisted at 28 days and were brain structure specific. Biodistribution of tungsten showed that both local and systemic effects might be involved. Our results suggest interaction between our stressors, causing cerebral toxicity, and prove the importance of multi-stressor studies to improve risks evaluation in toxicology and radiation protection, as single stressors might wrongly be deemed safe.

Combinational Radiotherapies Improve Brain Cancer Treatment at High Dose Rates In Vitro

BACKGROUND/OBJECTIVES

Brain cancer remains difficult to treat, with survival statistics stagnant for decades. The resistance of glioblastoma brain tumours can greatly challenge the effectiveness of conventional cancer radiotherapy. However, high dose rate radiotherapy has unique effects that allow for normal tissue sparing whilst maintaining tumour control. The addition of targeted radiosensitisers, such as the chemotherapeutic drug methotrexate (MTX) or the high-Z halogenated pyrimidine drug iododeoxyuridine (IUdR), can improve radiotherapy outcomes. Combining these radiosensitiser agents with ultra-high dose rate (UHDR) synchrotron X-rays can bear synergistic effects to enhance the efficacy of these multi-modal UHDR therapies, providing a means to overcome the radioresistance of brain cancer.

METHODS

Here, we use controlled in vitro assays following treatment, including a clonogenic assay to determine long-term cell survival and γH2AX immunofluorescent confocal microscopy to quantify double-strand DNA breaks (DSBs).

RESULTS

We find significant enhancement for highly synergistic combinations of IUdR+MTX with synchrotron X-rays. Cell survival results demonstrate 5.4 times increased 9L gliosarcoma cell killing when these agents are combined with UHDR synchrotron X-rays compared with conventional X-rays alone at the same 5 Gy dose. The underlying mechanisms are unveiled using γH2AX imaging and reveal significant increases in DSBs and dying cells following exposure to UHDR radiation.

CONCLUSIONS

Our results demonstrate that highly synergistic combination treatments using UHDR synchrotron radiation can yield significantly improved brain cancer killing compared with conventional radiotherapy. We anticipate that these additive, multi-modal combination therapies will provide options for more targeted and effective use of radiotherapies for the future treatment of brain cancer.

A 3D Co-Culture Scaffold Approach to Assess Spatially Fractionated Radiotherapy Bystander and Abscopal Immune Effects on Clonogenic Survival

Spatially fractionated radiotherapy (SFRT) offers a promising approach for debulking large tumors by delivering high-dose radiation to a fraction of the tumor volume. However, the complex tumor microenvironment necessitates models beyond traditional 2D cultures and resource-intensive animal studies for SFRT investigations. Three-dimensional (3D) scaffold-based models with an adequate cross-sectional area have emerged as uniquely suited platforms to bridge this gap, by providing a more realistic platform for GRID-based SFRT research. In this study, we employed a 3D co-culture scaffold model to dissect the contributions of the radiation-induced bystander effect, abscopal effect, and immune system response on clonogenic survival following GRID irradiation. MDA-MB-231 breast cancer cells were seeded on commercial 3D scaffolds and irradiated at a 20 Gy peak dose using lead grids with three- and six-hole patterns, exposing ~12.8% and 25.7% of the scaffold area, respectively. An assessment of reproductive cell survival revealed a significant bystander effect, as the survival was notably lower than predicted based solely on the directly irradiated fraction. Evidence of an abscopal effect was observed by culturing non-irradiated cells in media exposed to GRID irradiation. Furthermore, a co-culture with allogeneic peripheral blood mononuclear cells (PBMCs) modulated clonogenic survival, with an additive effect observed when combined with SFRT. These findings underscore the presence of a bystander effect in GRID radiotherapy and indicate an abscopal immune component, particularly with the three-hole GRID configuration. This study established the utility of in vitro 3D co-culture scaffolds as an effective model system for elucidating complex SFRT-mediated biological responses.

Gafchromic Films as a Complementary In-field Dosimetric Tool to Monitor Low Photon Radiation Doses (≤50 mSv)

ABSTRACT

This study elucidated the radiation response characteristics of a Gafchromic radiochromic film subjected to low photon doses of ≤50 mSv, which corresponds to the annual whole body effective dose limit for radiation workers in Canada. Radiochromic films are investigated for possible use as a complementary tool for the Canadian Armed Forces that can be worn in addition to their existing personal dosimetry to quickly assess personal radiation dose received from radiological hazards without reliance on electronics. The films were exposed to varying photon energies emanating from x-ray generators and radioisotopes, specifically cesium-137, cobalt-60, and americium-241. The resultant radiation-induced film darkening was quantitatively assessed employing three analytical methodologies: net optical density analysis, UV/Visible spectroscopic analysis, and Fourier Transform Infrared spectroscopic analysis. Ideally, a film dosimeter necessitates a pronounced chromatic alteration and the capability to accurately quantify doses ≤50 mSv where net optical density analysis was identified as the optimal modality for interpreting the film darkening into a dose approximation. This new approach established a lower detection threshold of 7.6 mSv for the films when exposed to cesium-137 radiation. Notably, the film exhibited a linear dose response relationship in terms of net optical density; however, a photon energy-dependent variability was observed within the 0-100 mSv dose range. In conclusion, these Gafchromic radiochromic films present a promising candidate for military dosimetry applications. They offer a real-time, visual dose response that can be discerned by military personnel or analyzed using mobile spectroscopic instrumentation. Moreover, these films demonstrate proficiency in the accurate quantification of photon doses ≤50 mSv. Future investigations will evaluate the film's performance under heterogeneous and indeterminate radiation environments, as well as the impact of environmental conditions on the film's performance.

Evaluation of a Commercially Available Radiochromic Film for Use as a Complementary Dosimeter for Rapid In-field Low Photon Equivalent Radiation Dose (≤50 mSv) Monitoring

ABSTRACT

This work investigates the low photon radiation dose (≤50 mSv) response of commercially available radiochromic films as a potential field dosimeter that could be used by the Canadian Armed Forces to complement their existing personal radiation dosimeters. The films were exposed to various photon energies from x-ray devices and radioisotopes (cesium-137, cobalt-60, and americium-241), and their radiation signal was read using three methods: net optical density, UV/visible spectroscopy, and Fourier transform infrared spectroscopy. A complimentary film dosimeter for field usage should, for military use, display a visual color change and detect doses ≤50 mSv. Given the film's radiochromic properties, it was determined that the net optical density method was the most optimal read-out method, which ascertained a minimum detection dose limit of 4.5 mSv under exposure to a clinical orthovoltage operated at 100 kVp. The film presented an overall linear relationship between net optical density and radiation dose; however, they also portrayed a photon energy-dependent response between 0-100 mSv. Overall, the radiochromic films presented a real-time visual dose signal that could be interpreted rapidly in a mobile laboratory and possessed the ability to detect photon doses ≤50 mSv below the vendor's recommended limits, making it a suitable option as a complementary, disposable, military dosimetric tool. Future work includes the investigation of the film's response under multi- and unknown source environments and environmental-dependent factors such as UV/sunlight exposure and extreme temperatures.

A survey of dosimetry quality assurance practice at UK small animal radiation research platform (SARRP) facilities

Introduction: Improvements in preclinical radiation research have been made to better mimic the equipment and techniques implemented in the clinic. The development of dedicated small animal radiation units facilitates such advances by combining treatment planning, image guidance and conformal delivery. One area significantly behind its clinical equivalent are standardised dosimetry quality assurance (QA) protocols, hampering the translatability of results into the development of clinical interventions.Approach: The aim of the study described herein was to summarise the current QA procedures implemented at several institutions on Small Animal Radiation Research Platforms (SARRPs), the system used by the six institutions surveyed, and to determine the barriers to implementing a standard dosimetry protocol. Participants at UK research institutions were invited to complete a questionnaire to ascertain their current preclinical QA practice.Main results: All participants involved undertake regular dose output measurements and most perform image guidance QA measurements. Consistency in QA procedures differed when more complex plan verification or end-to-end testing was discussed.Significance: This survey demonstrates that, although improvements are being made in the awareness of the importance of regular dosimetry tests, there is still a way to go to standardise the procedures with regards to more complex verifications. Incorporating robust QA procedures and strict dose constraints would ensure the reliability and ethical integrity of experiments involving small animals. This approach not only protects the welfare of the animals but also enhances the quality and reproducibility of the preclinical results.

On energy dependency, spectral properties, and orientation dependency of EBT3, EBT-XD, MD-V3, and HD-V2 radiochromic films

Objective. Radiochromic films (RCFs) are indispensable dosimeters for two-dimensional and small field dosimetry. Different models of RCFs with associated dynamic ranges are commercially available to support various dosimetry needs. Here, we study energy dependency, absorption spectra, and orientation dependency of EBT3, EBT-XD, MD-V3, and HD-V2 RCFs.Approach. RCF pieces were irradiated at various dose levels, depending on their dynamic range, using a 6 MV photon beam and a 220 kVp x-ray beam. Films were scanned using a flatbed scanner to obtain the optical density at red, green, and blue color channels. A visible spectrometer was used to measure the absorption spectra of the films. A subset of RCF pieces were scanned at various orientation to investigate the orientation dependency.Main results. In all four models an under-response to the kV beam was observed compared to the MV beam. A noticeable dose-dependent shift in the peak absorption spectrum was noted in MD-V3 and HD-V2 films. An orientation dependency was noted in all models which can be modeled by assuming a polarization axis in the films.Significance. The presented work provides valuable information on the characteristics of different models of RCF.

Initial characterization of a novel dual-robot orthovoltage radiotherapy system

Purpose:Adequate access to radiotherapy is a critical global concern affecting low-resource settings such as low- and middle-income countries and rural regions. We propose to reduce this disparity by developing a novel low-cost radiotherapy device that treats using non-coplanar techniques and a 225 kVp x-ray tube.Methods:This novel device has been preliminarily characterized spectrally, via spectrometer measurements, dosimetrically, via percent depth dose curves and 2D profiles, and geometrically, via a coplanar star-shot. Dosimetric and geometric evaluations were then combined by performing a proof of workflow of the KOALA system. Monte Carlo simulations were run in TOPAS to validate dosimetric measurements and the proof of workflow measurement.Results:Spectral results showed excellent agreement between measured and modelled spectra. Dose errors of  < 2% were achieved for PDD curves. Full width at half maximum values for the 2D profiles were, on average, 0.95 mm higher in simulation compared to film. A star-shot test demonstrated the high geometrical accuracy of the system with a 0.3 mm diameter wobble circle. Finally, a mean absolute percent error of 5  ±  5% (1σ) was measured for the proof of workflow test.Conclusions:This initial characterization showcased the strengths and weaknesses of the KOALA system, with excellent isocenter precision and depth dose accuracy while lacking dosimetric accuracy in the 2D profiles. Further improvements on the source-to-collimator distance and treatment couch material can be made to improve the accuracy of a Monte Carlo model of the KOALA system.

Assessing the Organ Dose in Diagnostic Imaging with Digital Tomosynthesis System Using TLD100H Dosimeters

BACKGROUND

Digital tomosynthesis (DTS) is an advanced imaging modality that enhances diagnostic accuracy by offering three-dimensional visualization from two-dimensional projections, which is particularly beneficial in breast and lung imaging. However, this increased imaging capability raises concerns about patient exposure to ionizing radiation.

METHODS

This study explores the energy and angular dependence of thermoluminescent dosimeters (TLDs), specifically TLD100H, to improve the accuracy of organ dose assessment during DTS. Using a comprehensive experimental approach, organ doses were measured in both DTS and traditional RX modes.

RESULTS

The results showed lung doses of approximately 3.21 mGy for the left lung and 3.32 mGy for the right lung during DTS, aligning with the existing literature. In contrast, the RX mode yielded significantly lower lung doses of 0.33 mGy. The heart dose during DTS was measured at 2.81 mGy, corroborating findings from similar studies.

CONCLUSIONS

These results reinforce the reliability of TLD100H dosimetry in assessing radiation exposure and highlight the need for optimizing imaging protocols to minimize doses. Overall, this study contributes to the ongoing dialogue on enhancing patient safety in diagnostic imaging and advocates for collaboration among medical physicists, radiologists, and technologists to establish best practices.

Cone beam CT (CBCT) in radiotherapy: Assessment of doses using a pragmatic setup in an international setting

INTRODUCTION

The imaging modality kV CBCT on linear accelerators (linacs) is utilised to verify positioning and anatomy in cancer patients undergoing radiotherapy treatment. There is a need for optimisation of radiological protection in kV CBCT imaging protocols to avoid unnecessarily high exposures to normal tissues surrounding the target.

METHODS

A network of ICRP mentees from 23 countries were surveyed for available dosimetry equipment. Standardised measurements on CBCT linac imaging systems were conducted using a cone beam dose index (CBDI) devised as a straightforward measurement for wide beam doses. Measurements were made with (a) 100 mm ionisation chambers or (b) 0.6 cc Farmer ionisation chambers and cylindrical CT PMMA phantoms, and (c) an alternative setup of Farmer chambers and cubical phantoms comprised of slabs of water equivalent material readily available in radiotherapy centres. The measurements were compared with Monte Carlo (MC) simulations.

RESULTS

The survey showed limited availability for the reference setup using 100 mm chambers and CT phantoms. Correction factors were derived to convert normalised CBDI from alternative setups to the reference setup and are on average within 2% of MC simulations.

CONCLUSION

The slab phantom in combination with a Farmer chamber provides an alternative to quantify CBCT radiation dose indices from linac-based image-guided radiotherapy using materials accessible in most centres worldwide. A method is presented to use correction factors for Varian Truebeam linacs if traditional 100 mm chambers and cylindrical CT phantoms are not available. This will enable most radiotherapy centres across the world to engage in meaningful imaging dose measurement and optimisation.

A review of kilovoltage radiotherapy treatment in the United Kingdom: quality control, radiation dosimetry, treatment equipment, and workload

OBJECTIVES

To survey kilovoltage (kV) radiotherapy in the United Kingdom, updating a 2016 study, focussing on radiotherapy physics, including equipment quality control (QC) and radiation dosimetry, with information on installed equipment and clinical activity.

METHODS

All UK radiotherapy physics departments (n = 68) were invited to complete a comprehensive survey. An analysis of the installed equipment base, patient numbers, clinical activity, QC testing, and radiation dosimetry processes were undertaken.

RESULTS

91% of centres (n = 62) responded to the survey. kV radiotherapy was available in 70% of UK radiotherapy departments, with a wide variation in workload; 7-436 patients/centre annually. There has been an increase in centres using treatment calculation software rather than manual methods, up from 36% in 2016 to 50% currently. Only 50% of centres use an independent calculation check method. There was an increase in the use of the addendum to the UK dosimetry code of practice, enabling medium energy calibration in-air rather than at depth in phantom, citing "clinical relevance." Appropriate levels of QC testing were being conducted at UK centres, with Institute of Physics and Engineering in Medicine (IPEM) Report 81 cited as a primary source of guidance. Good consensus for the frequency and tolerance values used for QC was seen across UK centres.

CONCLUSIONS

A comprehensive review of consensus practice for QC and dosimetry in kV radiotherapy across the United Kingdom is presented, with supporting information on equipment installation and clinical use.

ADVANCES IN KNOWLEDGE

Updated data are presented on kV radiotherapy treatment in the United Kingdom, with focus on physics aspects of QC and dosimetry.

Real-time dose measurement in minibeam radiotherapy using radioluminescence imaging

PURPOSE

Minibeam radiotherapy (MBRT) uses small parallel beams of radiation to create a highly modulated dose pattern. The aim of this study is to develop an optical radioluminescence imaging (RLI) approach to perform real-time dose measurement for MBRT.

METHODS

MBRT was delivered using an image-guided small animal irradiator equipped with a custom collimator. Five slabs of plastic scintillators with a thicknesses of 0.5, 1, 2, 3 and 10 mm were placed on top of a mouse phantom, to localize and measure the delivered dose. A thin radioluminescence film (Gd2O2S:Tb) was used to obtain the mini beam dose profile that was compared against GafChromic (GC) films measurements. The RLI signal was detected with a CMOS camera placed at 90 deg with respect to the beam axis. Monte Carlo (MC) simulations were also performed using TOPAS for comparison with the experimental results.

RESULTS

The measured peak to valley dose ratio (PVDR) obtained with RLI was 16.7 in line with GC films measurements. The differences between peak and valley dimension were less that 3% with respect to GC measurements. Using RLI performed with the scintillator slabs, it was possible to localize and measure in real-time MBRT delivery on the mouse phantom.

CONCLUSIONS

We proposed a novel method for MBRT dose localization and measurement in real-time based on RLI. The results we obtained are in good agreement with GC film measurements.

Evidence of Alveolar Macrophage Metabolic Shift Following Stereotactic Body Radiation Therapy -Induced Lung Fibrosis in Mice

PURPOSE

Radiation-induced pneumopathy is the main dose-limiting factor in cases of chest radiation therapy. Macrophage infiltration is frequently observed in irradiated lung tissues and may participate in lung damage development. Radiation-induced lung fibrosis can be reproduced in rodent models using whole thorax irradiation but suffers from limits concerning the role played by unexposed lung volumes in damage development.

METHODS AND MATERIALS

Here, we used an accurate stereotactic body radiation therapy preclinical model irradiating 4% of the mouse lung. Tissue damage development and macrophage populations were followed by histology, flow cytometry, and single-cell RNA sequencing. Wild-type and CCR2 KO mice, in which monocyte recruitment is abrogated, were exposed to single doses of radiation, inducing progressive (60 Gy) or rapid (80 Gy) lung fibrosis.

RESULTS

Numerous clusters of macrophages were observed around the injured area, during progressive as well as rapid fibrosis. The results indicate that probably CCR2-independent recruitment and/or in situ proliferation may be responsible for macrophage invasion. Alveolar macrophages experience a metabolic shift from fatty acid metabolism to cholesterol biosynthesis, directing them through a possible profibrotic phenotype. Depicted data revealed that the origin and phenotype of macrophages present in the injured area may differ from what has been previously described in preclinical models exposing large lung volumes, representing a potentially interesting trail in the deciphering of radiation-induced lung damage processes.

CONCLUSIONS

Our study brings new possible clues to the understanding of macrophage implications in radiation-induced lung damage, representing an interesting area for exploration in future studies.

Deleting Trim33 in Myeloid Cells Improves the Efficiency of Radiotherapy through an IFNβ-Dependent Antitumor Immune Response

Radiotherapy (RT) triggers an immune response that contributes to antitumor effects. Induction of IFNβ is a key event in this immunogenicity of RT. We have previously shown that TRIM33, a chromatin reader, restrains IFNβ expression in Toll-like receptor-activated myeloid cells. In this study, we explored whether deleting Trim33 in myeloid cells might improve the radio-induced immune response and subsequent efficiency of RT. We first established that Trim33-/- bone marrow-derived macrophages showed increased expression of IFNβ in response to direct irradiation, or to treatment with irradiated cancer cells, further supporting our hypothesis. We then tested the efficiency of a single-dose RT in three subcutaneous tumor models and one orthotopic tumor model. In all models, myeloid deletion of Trim33 led to a significantly improved response after RT, leading to a complete and durable response in most of the treated mice bearing orthotopic oral tumors. This effect required the involvement of the type I IFN pathway and the presence of CD8+ T lymphocytes but not NK cells. In addition, cured mice were capable of rejecting a secondary tumor challenge, demonstrating an in situ vaccination effect. We conclude that deleting Trim33 in myeloid cells improves RT efficiency, through a mechanism involving the type I IFN pathway and the immune response. Our work suggests that myeloid Trim33 is a host factor affecting the tumor response to RT, thus representing a new potential therapeutic target for modifying RT responses.

Fractionated low-dose radiotherapy primes the tumor microenvironment for immunotherapy in a murine mesothelioma model

Combination immune checkpoint inhibitors (nivolumab and ipilimumab) are currently a first-line treatment for mesothelioma; however, not all patients respond. The efficacy of treatment is influenced by the tumor microenvironment. Murine mesothelioma tumors were irritated with various radiotherapy doses. Radiotherapy induced vasculature changes were monitored by power Doppler and photoacoustic ultrasound and analyzed via mixed-effects models. Tissue staining was used to investigate the immune cell infiltrate of tumors. The optimal radiotherapy schedule was combined with immune checkpoint inhibitors, and the survival of mice was analyzed. Using low-dose, low-fraction radiotherapy allowed favorable modification of the murine mesothelioma tumor microenvironment. Irradiating tumors with 2 Gy × 5 fractions significantly improved blood flow and reduced hypoxia, consequently increasing the presence of CD8+ and regulatory T cells in the tumor. Understanding the transient nature of these changes is crucial for optimizing the timing of therapeutic delivery. The combination of radiotherapy with dual immunotherapy (anti-PD-1 plus anti-CTLA-4) proved highly curative when administered concurrently. A diminishing rate of cures was noted with an increasing delay between radiotherapy and subsequent immunotherapy. Concurrent low-dose, low-fraction radiotherapy emerges as a translatable approach for improving the efficacy of immune checkpoint inhibitors in patients.

High-throughput, low-cost FLASH: irradiation of Drosophila melanogaster with low-energy X-rays using time structures spanning conventional and ultrahigh dose rates

FLASH radiotherapy is an emerging technique in radiation oncology that may improve clinical outcomes by reducing normal tissue toxicities. The physical radiation characteristics needed to induce the radiobiological benefits of FLASH are still an active area of investigation. To determine the dose rate, range of doses and delivery time structure necessary to trigger the FLASH effect, Drosophila melanogaster were exposed to ultrahigh dose rate (UHDR) or conventional radiotherapy dose rate (CONV) 120-kVp X-rays. A conventional X-ray tube outfitted with a shutter system was used to deliver 17- to 44-Gy doses to third-instar D. melanogaster larvae at both UHDR (210 Gy/s) and CONV (0.2-0.4 Gy/s) dose rates. The larvae were then tracked through development to adulthood and scored for eclosion and lifespan. Larvae exposed to UHDR eclosed at higher rates and had longer median survival as adults compared to those treated with CONV at the same doses. Eclosion rates at 24 Gy were 68% higher for the UHDR group (P < 0.05). Median survival from 22 Gy was >22 days for UHDR and 17 days for CONV (P < 0.01). Two normal tissue-sparing effects were observed for D. melanogaster irradiated with UHDR 120-kVp X-rays. The effects appeared only at intermediate doses and may be useful in establishing the dose range over which the benefits of FLASH can be obtained. This work also demonstrates the usefulness of a high-throughput fruit fly model and a low-cost X-ray tube system for radiobiological FLASH research.

Assessing the deviation from the inverse square law for orthovoltage beams with closed-ended applicators Part II: 30 cm FSD applicators

Dose falls-off faster than the inverse square law (ISL) for orthovoltage beams with closed-ended applicators. This work investigates the discrepancy for 30 cm FSD applicators. When using the ISL alone, the maximum dosimetric error would be 3% and 5% at 10 mm and 20 mm from the applicator, respectively, and increases with larger distances. The effective source position was found to be 22.5 cm and reduces the dosimetric error to less than 1.6% for distances less than 20 mm.

Targeting proliferating cell nuclear antigen enhances ionizing radiation-induced cytotoxicity in prostate cancer cells

BACKGROUND

Proliferating cell nuclear antigen (PCNA) is essential for DNA replication and repair, cell growth, and survival. PCNA also enhances androgen receptor (AR) signaling in prostate cancer (PC) cells. We identified a PCNA interaction protein (PIP) box at the N-terminal domain of AR and developed a small peptide PCNA inhibitor R9-AR-PIP containing AR PIP-box. We also identified a series of small molecule PCNA inhibitors (PCNA-Is) that bind directly to PCNA and interrupt PCNA functions. The present study investigated the effects of the PCNA inhibitors on the sensitivity of PC cells to X-ray radiation.

METHODS

The effects of targeting PCNA on radio sensitivity of PC cells were investigated in four lines of castration-resistant PC (CRPC) cells with different AR expression statuses. The cells were treated with the PCNA inhibitors and X-ray radiation alone or in combination. The effects of the treatment on expression of AR target genes, DNA damage response, DNA damage, homologous recombination repair (HRR), and cytotoxicity were evaluated.

RESULTS

We found that the androgen response element (ARE) occupancy of the DNA damage response gene PARP1 by AR is significantly attenuated by PCNA-I1S or R9-AR-PIP combined with X-ray radiation, while X-ray radiation alone does not enhance the ARE occupancy. PCNA-I1S or R9-AR-PIP alone significantly inhibits occupancy of the AR-occupied regions (AROR) in PRKDC and XRCC2 genes. R9-AR-PIP and PCNA-I1S inhibit expression of AR-Vs target gene cyclin A2 and show the additive effects with radiation in AR-positive CRPC cells. Targeting PCNA by PCNA-I1S and R9-AR-PIP downregulates expression of DNA damage response genes EXO1, Rad54L, Rad51, and/or PARP1 and shows the additive effects with radiation as compared with their respective controls in AR-positive CRPC LNCaP-AI, 22Rv1, and R1-D567 cells, but not in AR-negative PC-3 cells. R9-AR-PIP and PCNA-I1S elevate the levels of phospho-DNA-PKcs(S2056) and γH2AX, indicating DNA damage in response to radiation in AR-positive cells. The HRR is significantly attenuated by PCNA inhibitors PCNA-I1S, R9-AR-PIP, and T2AA in all four CRPC cells examined, and inhibited by Enzalutamide (Enz) only in 22RV1 cells. The cytotoxicity induced by X-ray radiation in androgen-dependent LNCaP cells is enhanced by Enz and a lower concentration of R9-AR-PIP in the colony formation assay. R9-AR-PIP at higher concentration reduces the colony formation and has an additive effect with X-ray radiation in all AR expressing cells, regardless of AR-FL and AR-Vs, but does not significantly alter the colony formation in AR-negative PC-3 cells. PCNA-I1S attenuates colony formation and has an additive effect with ionizing radiation in all four CRPC cells, regardless of AR expression status.

CONCLUSION

These data provide a strong rationale for the therapy studies using PCNA-I1S or R9-AR-PIP in combination with X-ray radiation against CRPC tumors in preclinical models.

Characterization of a new low-dose and low-energy Gafchromic film LD-V1

PURPOSE

To characterize the dose-response, energy dependence, postexposure changes, orientation dependence, and spatial capabilities of LD-V1, a new low-dose Gafchromic film for low-energy x-ray dosimetry.

METHODS

A single sheet of LD-V1 Gafchromic film was cut into 15 × 20 mm2 rectangles with a notch to track orientation. Eight different doses between 5 and 320 mGy were delivered by an MXR-160/22 x-ray tube using x-ray beams of 90, 100, and 120 kVp filtered with 3 mm of Al and 2 mm of Ti. The 120 kVp films were scanned at 1, 1.5, 2, 3, 12, 24, 48, 72, and 168 h postexposure in portrait orientation and additionally scanned in landscape orientation at 24 h. The 90 and 100 kVp films were scanned at 24 h postexposure in portrait orientation. Lastly, a 20 × 200 mm2 strip of film was irradiated using a thin-slit imaging collimator and scanned 24 h postexposure to test the film performance in an x-ray imaging application.

RESULTS

Of the three color channels, the red channel was found to produce a dose-response curve with a large range of net optical density (netOD) values across the considered dose range. A prominent energy dependence was discovered, resulting in dose discrepancies on the scale of 17 mGy between 90 and 120 kVp for a dose of 80 mGy. The measured postexposure changes suggest that the calibration irradiation-to-scan time should be longer than 12 h with a ± 4 h scanning time window for dose errors of <0.5%. An average dose difference of 3.4% was found between the two scanning orientations. Lastly, noise of 4% was measured in the thin slit collimator film for a dose of 30 mGy.

CONCLUSIONS

We have characterized the LD-V1 film for low-energy, low-dose x-ray dosimetry. Energy, scan-time, and orientation dependencies should be considered when using this film.

Minibeam Radiation Therapy Treatment (MBRT): Commissioning and First Clinical Implementation

PURPOSE

Minibeam radiation therapy (MBRT) is characterized by the delivery of submillimeter-wide regions of high "peak" and low "valley" doses throughout a tumor. Preclinical studies have long shown the promise of this technique, and we report here the first clinical implementation of MBRT.

METHODS AND MATERIALS

A clinical orthovoltage unit was commissioned for MBRT patient treatments using 3-, 4-, 5-, 8-, and 10-cm diameter cones. The 180 kVp output was spatially separated into minibeams using a tungsten collimator with 0.5 mm wide slits spaced 1.1 mm on center. Percentage depth dose (PDD) measurements were obtained using film dosimetry and plastic water for both peak and valley doses. PDDs were measured on the central axis for offsets of 0, 0.5, and 1 cm. The peak-to-valley ratio was calculated at each depth for all cones and offsets. To mitigate the effects of patient motion on delivered dose, patient-specific 3-dimensional-printed collimator holders were created. These conformed to the unique anatomy of each patient and affixed the tungsten collimator directly to the body. Two patients were treated with MBRT; both received 2 fractions.

RESULTS

Peak PDDs decreased gradually with depth. Valley PDDs initially increased slightly with depth, then decreased gradually beyond 2 cm. The peak-to-valley ratios were highest at the surface for smaller cone sizes and offsets. In vivo film dosimetry confirmed a distinct delineation of peak and valley doses in both patients treated with MBRT with no dose blurring. Both patients experienced prompt improvement in symptoms and tumor response.

CONCLUSIONS

We report commissioning results, treatment processes, and the first 2 patients treated with MBRT using a clinical orthovoltage unit. While demonstrating the feasibility of this approach is a crucial first step toward wider translation, clinical trials are needed to further establish safety and efficacy.

Response characterization of radiochromic OC-1 films in photon, electron, and proton beams

BACKGROUND

Radiochromic film (RCF) dosimeters with their high spatial resolution and tissue equivalent properties are conveniently used for two-dimensional and small-field dosimetry. OC-1 is a new model of RCF dosimeter that was commercially introduced recently. Due to its novelty there is a need to characterize its response in various radiation beam types.

PURPOSE

To study the response of OC-1 RCFs to megavoltage clinical x-ray, electron, and proton beams, as well as kilovoltage x-ray beams used in a small animal research irradiator.

MATERIALS AND METHODS

OC-1 RCFs were cut into ∼4 × 4 cm2 pieces. RCF samples were irradiated at various dose levels in the range 0.5-120 Gy using different modalities; a small animal radiation research platform (SARRP) (220 kVp), a medical linear accelerator (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF photon beams, as well as 6 and 20 MeV electron beams), and a gantry-mounted proton therapy synchrocyclotron. In order to study any dependency on the fractionation scheme, same dose was delivered at several fractions to a set of films. Different dose rates in the range 200-600 MU/min were delivered to a set of films to investigate any dose rate dependency. The films were scanned pre-irradiation and at 48 h post-irradiation using a flatbed scanner. The net optical density (OD) was measured for red, green, and blue color channel for each film. The orientation dependency was studied by scanning the films at eight different orientations. In order to study the temporal evolution of the response of the films, film samples were irradiated at 10 and 50 Gy using 6 MV photon beams and were scanned upon irradiation at certain time intervals up to 3 months. The spectral response of the films were studied over the visible range using a spectrometer.

RESULTS

For megavoltage photon, electron, and plateau region of the proton beams, we did not observe a significant dependency on the beam quality, dose rate, and fractionation scheme. At the kV beam, an unusual over-response was observed in the films' net OD. An orientation dependency in the response of the films with a sinusoidal trend was observed. The response of the films increased with time following a double or triple exponential trend. The spectral absorption peaks were blue-shifted with dose.

CONCLUSION

OC-1 RCFs were found to be reliable dosimeters with no significant energy dependency in MV range for photon and electron beams including the FFF beams. They over-respond when irradiated by kV x-ray beams compared to MV x-ray beams. Caution must be exercised to maintain the orientation of the films when scanning. Due to the temporal growth in the net OD of the films, same post-irradiation time interval must be used for scanning the calibration and test films.

Technical note: Determination of C Q $C_{Q}$ for a miniature x-ray source using a soft x-ray ionization chamber calibrated in NIST reference beam qualities

BACKGROUND

TheC Q $C_Q$ formalism proposed by Watson et al. allows users of the INTRABEAM (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy system to accurately determine the absorbed dose to water, in the absence of a primary dosimetry standard. However, all publishedC Q $C_Q$ values are for PTW 34013 ionization chambers calibrated in a TW30 reference beam, traceable to PTB (Germany). For North American users, it would be advantageous to haveC Q $C_Q$ data for chambers calibrated in a kV reference beam maintained by the National Institute of Standards and Technology (NIST).

PURPOSE

In this work, we determineC Q $C_Q$ for a PTW 34013 chamber calibrated in three NIST-traceable reference beams: M30, L40, and L50.

METHODS

Using available photon spectra data for M30, L40, and L50 reference beam qualities, Monte Carlo simulations using EGSnrc were performed to calculate the ratio of the absorbed dose to the PTW 34013 chamber air cavity to air-kerma (D gas / K a $D_{\textrm {gas}}/K_a$ ) for these beams. From this ratio,C Q $C_Q$ as a function of depth in water was determined. The effect of the use of a buildup foil was also investigated. An uncertainty analysis considering both the Type A and Type B uncertainties in the calculation ofC Q $C_Q$ was performed.

RESULTS

The largest difference inC Q $C_Q$ was found between L50 and TW30, with a relative decrease of 1.4% (no buildup) to 1.6% (buildup). For M30 and L40, the differences were minimal compared with measurement uncertainties.

CONCLUSIONS

We reportC Q $C_Q$ values for three NIST-traceable kV reference beams. This study reinforces the feasibility of adapting the Watson et al. methodology using different kV reference beams, facilitating the use of INTRABEAM in North America and ensuring the continuity and accuracy of dosimetry standards in intraoperative radiation therapy.

Non-homogenous intratumor ionizing radiation doses synergize with PD1 and CXCR2 blockade

The efficacy and side effects of radiotherapy (RT) depend on parameters like dose and the volume of irradiated tissue. RT induces modulations of the tumor immune microenvironment (TIME) that are dependent on the dose. Low dose RT (LDRT, i.e., single doses of 0.5-2 Gy) has been shown to promote immune infiltration into the tumor. Here we hypothesize that partial tumor irradiation combining the immunostimulatory/non-lethal properties of LDRT with cell killing/shrinkage properties of high dose RT (HDRT) within the same tumor mass could enhance anti-tumor responses when combined with immunomodulators. In models of colorectal and breast cancer in immunocompetent female mice, partial irradiation (PI) with millimetric precision to deliver LDRT (2 Gy) and HDRT (16 Gy) within the same tumor induces substantial tumor control when combined with anti-PD1. Using flow cytometry, cytokine profiling and single-cell RNA sequencing, we identify a crosstalk between the TIME of the differentially irradiated tumor volumes. PI reshapes tumor-infiltrating CD8+ T cells into more cytotoxic and interferon-activated phenotypes but also increases the infiltration of pro-tumor neutrophils driven by CXCR2. The combination of the CXCR2 antagonist SB225002 with PD1 blockade and PI improves tumor control and mouse survival. Our results suggest a strategy to reduce RT toxicity and improve the therapeutic index of RT and immune checkpoint combinations.

Relative biological effectiveness of clinically relevant photon energies for the survival of human colorectal, cervical, and prostate cancer cell lines

Objective.Relative biological effectiveness (RBE) differs between radiation qualities. However, an RBE of 1.0 has been established for photons regardless of the wide range of photon energies used clinically, the lack of reproducibility in radiobiological studies, and outdated reference energies used in the experimental literature. Moreover, due to intrinsic radiosensitivity, different cancer types have different responses to radiation. This study aimed to characterize the RBE of clinically relevant high and low photon energiesin vitrofor three human cancer cell lines: HCT116 (colon), HeLa (cervix), and PC3 (prostate).Approach.Experiments were conducted following dosimetry protocols provided by the American Association of Physicists in Medicine. Cells were irradiated with 6 MV x-rays, an192Ir brachytherapy source, 225 kVp and 50 kVp x-rays. Cell survival post-irradiation was assessed using the clonogenic assay. Survival fractions were fitted using the linear quadratic model, and survival curves were generated for RBE calculations.Main results.Cell killing was more efficient with decreasing photon energy. Using 225 kVp x-rays as the reference, the HCT116 RBESF0.1for 6 MV x-rays,192Ir, and 50 kVp x-rays were 0.89 ± 0.03, 0.95 ± 0.03, and 1.24 ± 0.04; the HeLa RBESF0.1were 0.95 ± 0.04, 0.97 ± 0.05, and 1.09 ± 0.03, and the PC3 RBESF0.1were 0.84 ± 0.01, 0.84 ± 0.01, and 1.13 ± 0.02, respectively. HeLa and PC3 cells had varying radiosensitivity when irradiated with 225 and 50 kVp x-rays.Significance.This difference supports the notion that RBE may not be 1.0 for all photons through experimental investigations that employed precise dosimetry. It highlights that different cancer types may not have identical responses to the same irradiation quality. Additionally, the RBE of clinically relevant photons was updated to the reference energy of 225 kVp x-rays.

Control of Aromatic Disinfection Byproducts in Potable Reuse Water by the UV222/H2O2 vs UV254/H2O2 Advanced Oxidation Processes

Research has demonstrated the difficulty associated with degrading the conventional 1-2 carbon aliphatic halogenated byproducts of disinfectant reactions with organic matter [disinfection byproducts (DBPs)] within advanced oxidation process (AOP) units in potable reuse trains, but the efficacy of AOP units for treating the emerging classes of halogenated aromatic DBPs is unclear. We herein demonstrate more effective removal of 28 halogenated aromatic DBPs in the UV/H2O2 AOP at 222 nm (UV222) than in the conventional UV/H2O2 AOP at 254 nm. Direct photolysis of 28 halogenated aromatic DBPs was greatly enhanced at 222 nm with fluence-based photodecay rate constants of 4.31 × 10-4-1.53 × 10-2 cm2 mJ-1, which was mainly attributed to the higher molar absorption coefficients of halogenated aromatic DBPs at 222 nm than 254 nm. Generally, quantum yields of halogenated aromatic DBPs at both 222 and 254 nm followed the order of halophenols > halohydroxybenzaldehydes > halonitrophenols. All 28 halogenated aromatic DBPs exhibit high reactivity toward HO• with second-order rate constants ranging from 2.18 × 109 to 1.15 × 1010 M-1 s-1 determined by X-ray radiolysis. The UV fluence required to achieve 90% loss of halogenated aromatic DBPs in the UV222/H2O2 AOP was 75-95% lower than that in the UV254/H2O2 AOP, and 90% removal of most tested halogenated aromatic DBPs can be achieved in the UV222/H2O2 AOP within the UV fluence levels commonly applied in potable reuse (700-1000 mJ cm-2).

Evaluation of the measurement accuracy and uncertainty of a solid-state detector under diagnostic x-ray beam conditions

OBJECTIVE

An accurate measurement of x-ray beams is expected to reduce the uncertainties associated with estimating radiation risk to patients in clinical settings. To perform assessment tasks based on the readings of a solid-state detector (SSD) using semiconductor technology, the characteristics of the detector should be elucidated. In this study, we evaluated the measurement accuracy of a new SSD under diagnostic x-ray beam conditions in terms of air kerma, tube voltage, and half-value layer (HVL). The performance of the SSD was then compared with those of reference instruments.

METHODS

The tube voltage was varied within the range of 50-120 kV in steps of 10 kV and the thickness and materials of additional filters were concurrently changed (several combinations were tested). In addition, the dose rate and energy dependence of the SSD were also investigated. These effects were analyzed based on statistical significance tests. Furthermore, the expanded uncertainties in the series of measurements were meticulously calculated.

RESULTS

The results showed average relative differences of -3.26 ± 1.33%, 0.44 ± 1.01%, and -2.60 ± 3.31% for air kerma, tube voltage, and HVL, respectively. Furthermore, air kerma did not exhibit any dependence on dose rate and energy, in contrast to tube voltage and HVL measurements.

CONCLUSION

The measurement values of the SSD fall within the acceptable range of uncertainty, highlighting its measurement accuracy and reliability. Furthermore, based on the characteristics elucidated by this study, valuable insights are provided concerning the assurance of appropriate measurement values in clinical settings.

Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

The purpose of this work was to determine percentage depth dose (PDD) curves for kilovoltage x-rays from the WOmed-T105 unit, with open-ended steel applicators and beam qualities ranging from 0.5 to 4.2 mm Al. Measurements were made with parallel plate chambers in a water phantom, with extrapolation based on a fifth order polynomial used to estimate the surface dose. Measurements were also made with parallel plate chambers in a plastic water phantom, with thin plastic sheets used to obtain detailed measurements at shallow depths (less than 1 mm). Monte Carlo simulations were performed using the EGSnrc package, with two different sources as input: a SpekPy simulation of the x-ray beam and a full simulation of the x-ray tube, treatment head and applicators. Results showed that all four methods (two measurements and two simulations) agreed within the measurement uncertainty at depths greater than 2 mm. At shallow depths, significant differences were noted. At depths less than 0.1 mm, the full Monte Carlo simulation and the solid water measurements showed a sharp spike in surface dose which is attributed to electron contamination, which was not seen in the SpekPy Monte Carlo simulation or the extrapolated water measurements. At depths between 0.1 mm and 2 mm, beyond the range of contaminant electrons, the extrapolated water measurements underestimate the dose by up to 13% compared to the full Monte Carlo simulation and the solid water measurements, attributed to fluorescent photons generated in the applicators. This work demonstrates that for open-ended applicators, measurement of depth doses in water with extrapolation of surface dose has the potential to significantly underestimate the dose at shallow depths between the surface and 2 mm, even after eliminating electron contamination from the beam.

kV reference dosimetry in Australia and New Zealand: Survey results and trends

PURPOSE

To assess the number of radiotherapy kilovoltage (kV) units in service, their clinical utilization, and methodology and equipment used for absorbed dose determination across Australia and New Zealand.

METHODS

A survey was sent to 61 Australian and New Zealand radiotherapy providers in the second half of 2023.

RESULTS

Fifty-seven responses were received, with 43 departments having kV units and providing beam quality data for 185 therapeutic kV beams 20-300 kVp. Percentage depth dose curves were compared between five clinical beams with 100 kVp and 2.13-6.28 mm Aluminum half value layers (HVLs), demonstrating large differences that can occur between beams with the same kVp. Eighteen departments provided clinical utilization data for their kV units, with a total of 4458 treatment courses and their corresponding kVp reported. All departments complied with national and international recommendations with respect to the equipment used for reference dosimetry of kV beams; 77% of ionization chambers used for absorbed dose determination were of Farmer-type, with the remaining 23% being plane parallel soft x-ray chambers. Methods of derivation of air-kerma calibration factors varied, with 73% of respondents using a draft document disseminated by the Australian Primary Standards laboratory, 23% using HVL alone, and 6% using other methods.

CONCLUSIONS

The results of this survey provide a snapshot of kilovoltage radiation therapy use and the number of kV units across Australia and New Zealand. This data can be used as a point of reference for future investigations into clinical utilization and reference dosimetry methods across Australia and New Zealand or for comparisons with other countries, facilitating standardization of reference dosimetry practice for kilovoltage units.

Dosimetric evaluation of a novel modular cell irradiation platform for multi-modality in vitro studies including high dose rate brachytherapy

PURPOSE

High dose-rate (HDR) brachytherapy is integral for the treatment of numerous cancers. Preclinical studies involving HDR brachytherapy are limited. We aimed to describe a novel platform allowing multi-modality studies with clinical HDR brachytherapy and external beam irradiators, establish baseline dosimetry standard of a preclinical orthovoltage irradiator, to determine accurate dosimetric methods.

METHODS

A dosimetric assessment of a commercial preclinical irradiator was performed establishing the baseline dosimetry goals for clinical irradiators. A 3D printed platform was then constructed with 14 brachytherapy channels at 1cm spacing to accommodate a standard tissue culture plate at a source-to-cell distance (SCD) of 1 cm or 0.4 cm. 4-Gy CT-based treatment plans were created in clinical treatment planning software and delivered to 96-well tissue culture plates using an Ir192 source or a clinical linear accelerator. Standard calculation models for HDR brachytherapy and external beam were compared to corresponding deterministic model-based dose calculation algorithms (MBDCAs). Agreement between predicted and measured dose was assessed with 2D-gamma passing rates to determine the best planning methodology.

RESULTS

Mean (±standard deviation) and median dose measured across the plate for the preclinical irradiator was 423.7 ± 8.5 cGy and 430.0 cGy. Mean percentage differences between standard and MBDCA dose calculations were 9.4% (HDR, 1 cm SCD), 0.43% (HDR, 0.4 cm SCD), and 2.4% (EBRT). Predicted and measured dose agreement was highest for MBDCAs for all modalities.

CONCLUSION

A 3D-printed tissue culture platform can be used for multi-modality irradiation studies with great accuracy. This tool will facilitate preclinical studies to reveal biologic differences between clinically relevant radiation modalities.

A simple calibration routine for small inorganic scintillation detectors for in vivo dosimetry during brachytherapy

BACKGROUND

In vivo dosimetry (IVD) is rarely performed in brachytherapy (BT), allowing potential dose misadministration to go unnoticed. This study presents a clinical routine-calibration method of detectors for IVD in high (HDR) and pulsed dose rate (PDR) Ir-192 BT.

PURPOSE

To evaluate the dosimetric precision and feasibility of an in-clinic calibration routine of detectors for IVD in afterloading BT.

METHODS

Calibrations were performed in a PMMA phantom with two needles inserted 20 mm apart. The source was loaded in one of the needles at 15 dwells for 10 s. The detector was placed in the other needle, and its signal was recorded. The mean signal at each dwell position was fitted to the expected dose rate with the calibration factor and the detector's longitudinal position being free parameters. The method was tested with an inorganic scintillation detector using one Ir-192 FlexiSource HDR and two Ir-192 GammaMedPlus PDR sources and followed by validation measurements in water.

RESULTS

The standard measurement uncertainty (k = 1) of the calibration factor in absolute terms (Gy/s) was 3.2/3.4% for the HDR/PDR source. The uncertainty was dominated by source strength uncertainty, and the precision of the method was <1%. The mean ± 1SD of the difference in measured and expected dose rate during validation was 1.5 ± 4.7% (HDR) and 0.0 ± 4.1% (PDR) with a positional uncertainty in the setup of 0.33/0.23 mm (HDR/PDR) (k = 1).

CONCLUSION

A precise and feasible in-clinic calibration method for IVD and source strength consistency tests in BT was presented.

Dosimetry: Was and Is an Absolute Requirement for Quality Radiation Research

This review aims to trace the evolution of dosimetry, highlight its significance in the advancement of radiation research, and identify the current trends and methodologies in the field. Key historical milestones, starting with the first publications in the journal in 1954, will be synthesized before addressing contemporary practices in radiation medicine and radiobiological investigation. Finally, possibilities for future opportunities in dosimetry will be offered. The overarching goal is to emphasize the indispensability of accurate and reproducible dosimetry in enhancing the quality of radiation research and practical applications of ionizing radiation.

Preclinical photon minibeam radiotherapy using a custom collimator: Dosimetry characterization and preliminary in-vivo results on a glioma model

PURPOSE

The purpose of this study is to investigate the dosimetric characteristics of a collimator for minibeam radiotherapy (MBRT) with film dosimetry and Monte Carlo (MC) simulations. The outcome of MBRT with respect to conventional RT using a glioma preclinical model was also evaluated.

METHODS

A multi-slit collimator was designed to be used with commercial small animal irradiator. The collimator was built by aligning 0.6 mm wide and 5 mm thick parallel lead leaves at 0.4 mm intervals. Dosimetry characteristics were evaluated by Gafchromic (CG) films and TOPAS Monte Carlo (MC) code. An in vivo experiment was performed using a glioma preclinical model by injecting two million GL261cells subcutaneously and treating with 25 Gy, single fraction, with MBRT and conventional RT. Survival curves and acute radiation damage were measured to compare both treatments.

RESULTS

A satisfactory agreement between experimental results and MC simulations were obtained, the measured FWHM and distance between the peaks were respectively 0.431 and 1.098 mm. In vivo results show that MBRT can provide local tumor control for three weeks after RT treatment and a similar survival fraction of open beam radiotherapy. No severe acute effects were seen for the MBRT group.

CONCLUSIONS

We developed a minibeam collimator and presented its dosimetric features. Satisfactory agreement between MC and GC films was found with differences consistent with uncertainties due to fabrication and set-up errors. The survival curves of MBRT and open field RT are similar while atoxicity is dramatically lower with MBRT, preliminarily confirming the expected effect.

Investigations on the beam quality correction factor for ionization chambers in high-energy brachytherapy dosimetry

Objective. To enhance the investigations on MC calculated beam quality correction factors of thimble ionization chambers from high-energy brachytherapy sources and to develop reliable reference conditions in source and detector setups in water.Approach. The response of five different ionization chambers from PTW-Freiburg and Standard Imaging was investigated for irradiation by a high dose rate Ir-192 Flexisource in water. For a setup in a Beamscan water phantom, Monte Carlo simulations were performed to calculate correction factors for the chamber readings. After exact positioning of source and detector the absorbed dose rate at the TG-43 reference point at one centimeter nominal distance from the source was measured using these factors and compared to the specification of the calibration certificate. The Monte Carlo calculations were performed using the restricted cema formalism to gain further insight into the chamber response. Calculations were performed for the sensitive volume of the chambers, determined by the methods currently used in investigations of dosimetry in magnetic fields.Main results. Measured dose rates and values from the calibration certificate agreed within the combined uncertainty (k= 2) for all chambers except for one case in which the full air cavity was simulated. The chambers showed a distinct directional dependence. With the restricted cema formalism calculations it was possible to examine volume averaging and energy dependence of the perturbation factors contributing to the beam quality correction factor also differential in energy.Significance. This work determined beam quality correction factors to measure the absorbed dose rate from a brachytherapy source in terms of absorbed dose to water for a variety of ionization chambers. For the accurate dosimetry of brachytherapy sources with ionization chambers it is advisable to use correction factors based on the sensitive volume of the chambers and to take account for the directional dependence of chamber response.

A high-throughput focused collimator for OAR-sparing preclinical proton FLASH studies: commissioning and validation

Objective. To fabricate and validate a novel focused collimator designed to spare normal tissue in a murine hemithoracic irradiation model using 250 MeV protons delivered at ultra-high dose rates (UHDRs) for preclinical FLASH radiation therapy (FLASH-RT) studies.Approach. A brass collimator was developed to shape 250 MeV UHDR protons from our Varian ProBeam. Six 13 mm apertures, of equivalent size to kV x-ray fields historically used to perform hemithorax irradiations, were precisely machined to match beam divergence, allowing concurrent hemithoracic irradiation of six mice while sparing the contralateral lung and abdominal organs. The collimated field profiles were characterized by film dosimetry, and a radiation survey of neutron activation was performed to ensure the safety of staff positioning animals.Main results. The brass collimator produced 1.2 mm penumbrae radiation fields comparable to kV x-rays used in preclinical studies. The penumbrae in the six apertures are similar, with full-width half-maxima of 13.3 mm and 13.5 mm for the central and peripheral apertures, respectively. The collimator delivered a similar dose at an average rate of 52 Gy s-1for all apertures. While neutron activation produces a high (0.2 mSv h-1) initial ambient equivalent dose rate, a parallel work-flow in which imaging and setup are performed without the collimator ensures safety to staff.Significance. Scanned protons have the greatest potential for future translation of FLASH-RT in clinical treatments due to their ability to treat deep-seated tumors with high conformality. However, the Gaussian distribution of dose in proton spots produces wider lateral penumbrae compared to other modalities. This presents a challenge in small animal pre-clinical studies, where millimeter-scale penumbrae are required to precisely target the intended volume. Offering high-throughput irradiation of mice with sharp penumbrae, our novel collimator-based platform serves as an important benchmark for enabling large-scale, cost-effective radiobiological studies of the FLASH effect in murine models.

Commissioning and Assessment of Radiation Field and Dose Inhomogeneity for a Dual X-ray Tube Cabinet Irradiator: To Ensure Accurate Dosimetry in Radiation Biology Experiments

Purpose

Standardization of x-ray cabinet irradiator dose, geometry, and calibration reporting is an ongoing process. Multi-tube designs have been introduced into the preclinical market and give a theoretical benefit but have not been widely assessed for use in preclinical irradiation conditions. The aim of this study was to report our experience commissioning a dual x-ray source cabinet irradiator (CIXD, Xstrahl Limited, United Kingdom) and assess the dose distribution for various experimental conditions.

Methods and Materials

Half-value layer (HVL) measurement, profile measurements, and output calibration were performed using a calibrated ion chamber. Constancy measurements were performed twice daily over 2 weeks to assess output fluctuations. Film measurements were completed using solid water to assess percent depth dose and homogeneity within the field and within variable thicknesses of solid water and phosphate-buffered saline solution. Film measurements were repeated for various arrangements of petri dishes filled with phosphate-buffered saline or water and in a 3D-printed mouse phantom.

Results

The x-ray tubes had a measured in-air output of 1.27 Gy/min. The HVL was 1.7 mm Cu. The upper and lower tubes both exhibited the heel effect, but when operated simultaneously, the effect was reduced. Ion chamber measurements revealed a 15% dose inhomogeneity within the tray area (18 × 18 cm2). Film measurements in the petri dishes indicated minor nonuniformities in the arrangements of the experimental apparatus. Measurements from the mouse phantom with film agreed with ion chamber measurements for various phantom placements and orientations.

Conclusions

X-ray cell culture and animal irradiation with dual tube cabinet irradiation is efficient and robust when using established dosimetric tools to confirm output and homogeneity. The conditions assumed for calibrations are often not maintained during experiments. We have confirmed that inhomogeneities are present for single-tube use; however, they are reduced with simultaneous tube use. Additional dosimetric monitoring should be performed for each unique irradiation setup.

A study of polarity effect for various ionization chambers in kilovoltage x-ray beams

BACKGROUND

Ionization chambers play an essential role in dosimetry measurements for kilovoltage (kV) x-ray beams. Despite their widespread use, there is limited data on the absolute values for the polarity correction factors across a range of commonly employed ionization chambers.

PURPOSE

This study aimed to investigate the polarity effects for five different ionization chambers in kV x-ray beams.

METHODS

Two plane-parallel chambers being the Advanced Markus and Roos and three cylindrical chambers; 3D PinPoint, Semiflex and Farmer chamber (PTW, Freiburg, Germany), were employed to measure the polarity correction factors. The kV x-ray beams were produced from an Xstrahl 300 unit (Xstrahl Ltd., UK). All measurements were acquired at 2 cm depth in a PTW-MP1 water tank for beams between 60 kVp (HVL 1.29 mm Al) and 300 kVp (HVL 3.08 mm Cu), and field sizes of 2-10 cm diameter for 30 cm focus-source distance (FSD) and 4 × 4 cm2 - 20 × 20 cm2 for 50 cm FSD. The ionization chambers were connected to a PTW-UNIDOS electrometer, and the polarity effect was determined using the AAPM TG-61 code of practice methodology.

RESULTS

The study revealed significant polarity effects in ionization chambers, especially in those with smaller volumes. For the plane-parallel chambers, the Advanced Markus chamber exhibited a maximum polarity effect of 2.5%, whereas the Roos chamber showed 0.3% at 150 KVp with the 10 cm circular diameter open-ended applicator. Among the cylindrical chambers at the same beam energy and applicator, the Pinpoint chamber exhibited a 3% polarity effect, followed by Semiflex with 1.7%, and Farmer with 0.4%. However, as the beam energy increased to 300 kVp, the polarity effect significantly increased reaching 8.5% for the Advanced Markus chamber and 13.5% for the PinPoint chamber at a 20 × 20 cm2 field size. Notably, the magnitude of the polarity effect increased with both the field size and beam energy, and was significantly influenced by the size of the chamber's sensitive volume.

CONCLUSIONS

The findings demonstrate that ionization chambers can exhibit substantial polarity effects in kV x-ray beams, particularly for those chambers with smaller volumes. Therefore, it is important to account for polarity corrections when conducting relative dose measurements in kV x-ray beams to enhance the dosimetry accuracy and improve patient dose calculations.

Radiation-induced gastrointestinal and cutaneous injuries: understanding models, pathologies, assessments, and clinically accepted practices

PURPOSE

A U. S. and European joint effort fostering the development of medical countermeasures (MCMs) operable in case of radiological or nuclear emergencies.

METHODS

Based on the joint engagement between the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN), a Statement of Intent to Collaborate was signed in 2014 and a series of working group meeting were established. In December 2022, the NIAID and IRSN hosted a five-day, U.S./European meeting titled 'Radiation-Induced Cutaneous and Gastrointestinal Injuries: Advances in Understanding Pathologies, Assessment, and Clinically Accepted Practices' in Paris, France. The goals of the meeting were to bring together U.S. and European investigators to explore new research avenues for the medical management of skin and gastrointestinal injuries, including specific diagnostics for each organ system, animal models, and promising medical countermeasures (MCMs) to mitigate radiation damage. There was also an emphasis on exploring additional areas of medicine and response to understand best practices from other emergency scenarios, which could be leveraged to improve radiation preparedness, and the importance of accurate dosimetry in preclinical work.

RESULTS

Subsequent to the workshop, seven collaborative projects, funded by both organizations, were established on topics ranging from MCMs and predictive biomarkers, and using physical methods to assess cutaneous radiation injuries, to mechanistic studies to understand radiation-induced damage in multiple organ systems. The importance of accurate dosimetry in preclinical works was highlighted and two recently published U.S./European commentaries that focus on the need for dosimetry standardization in the reported literature had their origins in this meeting. This commentary summarizes the workshop and open discussions among academic investigators, industry researchers, and U.S. and IRSN program representatives.

CONCLUSIONS

Given the substantive progress made due to these interactions, both groups plan to expand out these meetings by incorporating high-level investigators from across the globe, while endeavoring to maintain the informal setting that was conducive to in-depth scientific discussion and enhanced the state of the science in radiation research.

Dosimetric validation of SmART-RAD Monte Carlo modelling for x-ray cabinet radiobiology irradiators

Objective. Accuracy and reproducibility in the measurement of radiation dose and associated reporting are critically important for the validity of basic and preclinical radiobiological studies performed with kilovolt x-ray radiation cabinets. This is essential to enable results of radiobiological studies to be repeated, as well as enable valid comparisons between laboratories. In addition, the commonly used single point dose value hides the 3D dose heterogeneity across the irradiated sample. This is particularly true for preclinical rodent models, and is generally difficult to measure directly. Radiation transport simulations integrated in an easy to use application could help researchers improve quality of dosimetry and reporting.Approach. This paper describes the use and dosimetric validation of a newly-developed Monte Carlo (MC) tool, SmART-RAD, to simulate the x-ray field in a range of standard commercial x-ray cabinet irradiators used for preclinical irradiations. Comparisons are made between simulated and experimentally determined dose distributions for a range of configurations to assess the potential use of this tool in determining dose distributions through samples, based on more readily available air-kerma calibration point measurements.Main results. Simulations gave very good dosimetric agreement with measured depth dose distributions in phantoms containing both water and bone equivalent materials. Good spatial and dosimetric agreement between simulated and measured dose distributions was obtained when using beam-shaping shielding.Significance. The MC simulations provided by SmART-RAD provide a useful tool to go from a limited number of dosimetry measurements to detailed 3D dose distributions through a non-homogeneous irradiated sample. This is particularly important when trying to determine the dose distribution in more complex geometries. The use of such a tool can improve reproducibility and dosimetry reporting in preclinical radiobiological research.

Clonogenic assay and computational modeling using real cell images to study physical enhancement and cellular sensitization induced by metal nanoparticles under MV and kV X-ray irradiation

This study was initiated due to the physically unexplainable tumor controls resulting from metal nanoparticle (MNP) experiments even under MV X-ray irradiation. A more accurate explanation of the mechanism of radiosensitization induced by MNP is warranted, considering both its physical dose enhancement and biological sensitization, as related research is lacking. Thus, we aimed to examine the intricate dynamics involved in MNP-induced radiosensitization. We conducted specifically designed clonogenic assays for the A549 lung cancer cell line with MNP irradiated by 6 MV and 300 kVp X-rays. Two types of MNP were employed: one based on iron oxide, promoting ferroptosis, and the other on gold nanoparticles known for inducing a significant dose enhancement, particularly at low-energy X-rays. We introduced the lethality enhancement factor (LEF) as the fraction in the cell killing attributed to biological sensitization. Subsequently, Monte Carlo simulations were conducted to evaluate the radial dose profiles for each MNP, corresponding to the physical enhancement. Finally, the local effect model was applied to the clonogenic assay results on real cell images. The LEF and the dose enhancement in the cytoplasm were incorporated to increase the accuracy in the average lethal events and, consequently, in the survival fraction. The results reveal an increased cell killing for both of the MNP under MV and kV X-ray irradiation. In both types of MNP, the LEF reveals a biological sensitization evident. The sensitizer enhancement ratio, derived from the calculations, exhibited only 3% and 1% relative differences compared to the conventional linear-quadratic model for gold and ferroptosis inducer nanoparticles, respectively. These findings indicate that MNPs sensitize cells via radiation through mechanisms akin to ferroptosis inducers, not exclusively relying on a physical dose enhancement. Their own contributions to survival fractions were successfully integrated into computational modeling.

Integrated High-Throughput Screening and Large-Scale Isobolographic Analysis to Accelerate the Discovery of Radiosensitizers With Greater Selectivity for Cancer Cells

PURPOSE

High-throughput screening (HTS) platforms have been widely used to identify candidate anticancer drugs and drug-drug combinations; however, HTS-based identification of new drug-ionizing radiation (IR) combinations has rarely been reported. Herein, we developed an integrated approach including cell-based HTS and computational large-scale isobolographic analysis to accelerate the identification of radiosensitizing compounds acting strongly and more specifically on cancer cells.

METHODS AND MATERIALS

In a 384-well plate format, 160 compounds likely to interfere with the cell response to radiation were screened on human glioblastoma (U251-MG) and cervix carcinoma (ME-180) cell lines, as well as on normal fibroblasts (CCD-19Lu). After drug exposure, cells were irradiated or not and short-term cell survival was assessed by high-throughput cell microscopy. Computational large-scale dose-response and isobolographic approach were used to identify promising synergistic drugs radiosensitizing cancer cells rather than normal cells. Synergy of a promising compound was confirmed on ME-180 cells by an independent 96-well assay protocol, and finally, by the gold-standard colony forming assay.

RESULTS

We retained 4 compounds synergistic at 2 isoeffects in U251-MG and ME-180 cell lines and 11 compounds synergistically effective in only one cancer cell line. Among these 15 promising radiosensitizers, 5 compounds showed limited toxicity combined or not with IR on normal fibroblasts.

CONCLUSIONS

Overall, this study demonstrated that HTS chemoradiation screening together with large-scale computational analysis is an efficient tool to identify synergistic drug-IR combinations, with concomitant assessment of unwanted toxicity on normal fibroblasts. It sparks expectations to accelerate the discovery of highly desired agents improving the therapeutic index of radiation therapy.

SOX2 and OCT4 mediate radiation and drug resistance in pancreatic tumor organoids

Pancreatic cancer has a five-year survival rate of only 10%, mostly due to late diagnosis and limited treatment options. In patients with unresectable disease, either FOLFIRINOX, a combination of 5-fluorouracil (5-FU), oxaliplatin and irinotecan, or gemcitabine plus nab-paclitaxel combined with radiation are frontline standard regimens. However, chemo-radiation therapy has shown limited success because patients develop resistance to chemotherapy and/or radiation. In this study, we evaluated the role of pancreatic cancer stem cells (CSC) using OCT4 and SOX2, CSC markers in mouse pancreatic tumor organoids. We treated pancreatic tumor organoids with 4 or 8 Gy of radiation, 10 μM of 5-FU (5-Fluorouracil), and 100 μM 3-Bromopyruvate (3BP), a promising anti-cancer drug, as a single treatment modalities, and in combination with RT. Our results showed significant upregulation of, OCT4, and SOX2 expression in pancreatic tumor organoids treated with 4 and 8 Gy of radiation, and downregulation following 5-FU treatment. The expression of CSC markers with increasing treatment dose exhibited elevated upregulation levels to radiation and downregulation to 5-FU chemotherapy drug. Conversely, when tumor organoids were treated with a combination of 5-FU and radiation, there was a significant inhibition in SOX2 and OCT4 expression, indicating CSC self-renewal inhibition. Noticeably, we also observed that human pancreatic tumor tissues exhibited heterogeneous and aberrant OCT4 and SOX2 expression as compared to normal pancreas, indicating their potential role in pancreatic cancer growth and therapy resistance. In addition, the combination of 5-FU and radiation treatment exhibited significant inhibition of the β-catenin pathway in pancreatic tumor organoids, resulting in sensitization to treatment and organoid death. In conclusion, our study emphasizes the crucial role of CSCs in therapeutic resistance in PC treatment. We recommend using tumor organoids as a model system to explore the impact of CSCs in PC and identify new therapeutic targets.

The assessment of the clinical impact of using a single set of radiotherapy planning data for two kilovoltage therapy units

Kilovoltage therapy units are used for superficial radiotherapy treatment delivery. Peer reviewed studies for MV linear accelerators describe tolerances to dosimetrically match multiple linear accelerators enabling patient treatment on any matched machine. There is an absence of literature on using a single planning data set for multiple kilovoltage units which have limited ability for beam adjustment. This study reviewed kilovoltage dosimetry and treatment planning scenarios to evaluate the feasibility of using ACPSEM annual QA tolerances to determine whether two units (of the same make and model) were dosimetrically matched. The dosimetric characteristics, such as measured half value layer (HVL), percentage depth dose (PDD), applicator factor and output variation with stand-off distance for each kV unit were compared to assess the agreement. Independent planning data based on the measured HVL for each beam energy from each kV unit was prepared. Monitor unit (MU) calculations were performed using both sets of planning data for approximately 200 clinical scenarios and compared with an overall agreement between units of < 2%. Additionally, a dosimetry measurement comparison was completed at each site for a subset of nine scenarios. All machine characterisation measurements were within the ACPSEM Annual QA tolerances, and dosimetric testing was within 2.5%. This work demonstrates that using a single set of planning data for two kilovoltage units is feasible, resulting in a clinical impact within published uncertainty.

An Optimized Method for Evaluating the Potential Gd-Nanoparticle Dose Enhancement Produced by Electronic Brachytherapy

This work reports an optimized method to experimentally quantify the Gd-nanoparticle dose enhancement generated by electronic brachytherapy. The dose enhancement was evaluated considering energy beams of 50 kVp and 70 kVp, determining the Gd-nanoparticle concentration ranges that would optimize the process for each energy. The evaluation was performed using delaminated radiochromic films and a Poly(methyl methacrylate) (PMMA) phantom covered on one side by a thin 2.5 μm Mylar filter acting as an interface between the region with Gd suspension and the radiosensitive film substrate. The results for the 70 kVp beam quality showed dose increments of 6±6%, 22±7%, and 9±7% at different concentrations of 10, 20, and 30 mg/mL, respectively, verifying the competitive mechanisms of enhancement and attenuation. For the 50 kVp beam quality, no increase in dose was recorded for the concentrations studied, indicating that the major contribution to enhancement is from the K-edge interaction. In order to separate the contributions of attenuation and enhancement to the total dose, measurements were replicated with a 12 μm Mylar filter, obtaining a dose enhancement attributable to the K-edge of 29±7% and 34±7% at 20 and 30 mg/mL, respectively, evidencing a significant additional dose proportional to the Gd concentration.

Dosimetric characterization of a rotating anode x-ray tube for FLASH radiotherapy research

PURPOSE

Most current research toward ultra-high dose rate (FLASH) radiation is conducted with advanced proton and electron accelerators, which are of limited accessibility to basic laboratory research. An economical alternative to charged particle accelerators is to employ high-capacity rotating anode x-ray tubes to produce kilovoltage x-rays at FLASH dose rates at short source-to-surface distances (SSD). This work describes a comprehensive dosimetric evaluation of a rotating anode x-ray tube for potential application in laboratory FLASH study.

METHODS AND MATERIALS

A commercially available high-capacity fluoroscopy x-ray tube with 75 kW input power was implemented as a potential FLASH irradiator. Radiochromic EBT3 film and thermoluminescent dosimeters (TLDs) were used to investigate the effects of SSD and field size on dose rates and depth-dose characteristics in kV-compatible solid water phantoms. Custom 3D printed accessories were developed to enable reproducible phantom setup at very short SSD. Open and collimated radiation fields were assessed.

RESULTS

Despite the lower x-ray energy and short SSD used, FLASH dose rates above 40 Gy/s were achieved for targets up to 10-mm depth in solid water. Maximum surface dose rates of 96 Gy/s were measured in the open field at 47 mm SSD. A non-uniform high-to-low dose gradient was observed in the planar dose distribution, characteristic of anode heel effects. With added collimation, beams up to 10-mm diameter with reasonable uniformity can be produced. Typical 80%-20% penumbra in the collimated x-ray FLASH beams were less than 1 mm at 5-mm depth in phantom. Ramp-up times at the maximum input current were less than 1 ms.

CONCLUSION

Our dosimetric characterization demonstrates that rotating anode x-ray tube technology is capable of producing radiation beams in support of preclinical FLASH radiobiology research.

Peripheral blood lymphocytes differ in DNA damage response after exposure to X-rays with different physical properties

Introduction: In radiology, low X-ray energies (<140 keV) are used to obtain an optimal image while in radiotherapy, higher X-ray energies (MeV) are used to eradicate tumor tissue. In radiation research, both these X-ray energies being used to extrapolate in vitro research to clinical practice. However, the energy deposition of X-rays depends on their energy spectrum, which might lead to changes in biological response. Therefore, this study compared the DNA damage response (DDR) in peripheral blood lymphocytes (PBLs) exposed to X-rays with varying beam quality, mean photon energy (MPE) and dose rate.Methods: The DDR was evaluated in peripheral blood lymphocytes (PBLs) by the ɣ-H2AX foci assay, the cytokinesis-block micronucleus assay and an SYTOX-based cell death assay, combined with specific cell death inhibitors. Cell cultures were irradiated with a 220 kV X-ray research cabinet (SARRP, X-Strahl) or a 6 MV X-ray linear accelerator (Elekta Synergy). Three main physical parameters were investigated: beam quality (V), MPE (eV) and dose rate (Gy/min). Additional copper (Cu) filtration caused variation in the MPE (78 keV, 94 keV, 118 keV) at SARRP; dose rates were varied by adjusting tube current for 220 kV X-rays (0.33-3 Gy/min) or water-phantom depth in the 6 MV set-up (3-6 Gy/min).Results: The induction of chromosomal damage and initial (30 min) DNA double-stranded breaks (DSBs) were significantly higher for 220 kV X-rays compared to 6 MV X-rays, while cell death induction was similar. Specific cell death inhibitors for apoptosis, necroptosis and ferroptosis were not capable of blocking cell death after irradiation using low or high-energy X-rays. Additional Cu filtration increased the MPE, which significantly decreased the amount of chromosomal damage and DSBs. Within the tested ranges no specific effects of dose rate variation were observed.Conclusion: The DDR in PBLs is influenced by the beam quality and MPE. This study reinforces the need for consideration and inclusion of all physical parameters in radiation-related studies.

Underestimation of Occupational Radiation Exposure During Endovascular Abdominal Aortic Aneurysm Repair

ABSTRACT

During interventional procedures of endovascular abdominal aortic aneurysm repair (EVAR), the dosimeter was conventionally placed on chest facing toward the surgical table, instead of the main source of scatter radiation. Purpose of this study is to evaluate the underestimation of occupational radiation exposure. Phantom experiments were performed in a hybrid operating room equipped with an interventional angiography system. Electric personal dosimeters were placed at the level of eyes, chest, abdomen, and gonad of three positions, representing the principal operator (PO), assistant operator (AO), and sterile nurse (SN). Personal dose equivalent was measured with two different orientations of radiation detection, facing the table and facing the phantom, respectively. In addition to fluoroscopy, the dose produced by digital subtraction angiography was also measured to estimate the radiation exposure of routine EVAR. In this study, staff doses of 26 EVAR cases were also collected in our hospital to correlate the estimated dose. Our results show that the facing-phantom dose normalized by dose area product of patient is significantly higher than the facing-table dose when the latter is regularly seen in clinical practice. This underestimation could be even worse at a more distant position (e.g., AO and SN) as the incident angle of scatter radiation is larger. Besides, the estimated dose is highly correlated with the on-site measured dose (R 2 ~ 0.8) at chest and gonad of the PO.

Comparison of absorbed doses and organ doses measured with thermoluminescent dosimeters and Gafchromic film for cone beam computed tomography examination of the posterior mandibular region in a head phantom

OBJECTIVES

We aimed to map the correlation between thermoluminescent dosimeters (TLDs) and Gafchromic film for measuring absorbed doses and to compare minimum, maximum, and mean absorbed doses over larger regions of interest and at various craniofacial organs and tissues during cone beam computed tomography (CBCT) exposure of the mandibular third molar region.

STUDY DESIGN

We positioned TLDs at 75 measurement points in a head phantom. Gafchromic film was cut to the same shape as the 5 levels of the phantom and was placed on top of the TLDs. Both dosimetry methods thus included the surface of each level simultaneously. CBCT scans were made using a 5 × 5 cm field of view and a rotation angle of 200°. Measurements included absorbed dose distributions, doses at all 75 points, and minimum, maximum, and mean doses within organs and tissues.

RESULTS

The correlation of point-dose measurements at all TLD sites with doses measured on film was strong (R2 = 0.9687), with greatest correlation at lower doses (<2 mGy). Large deviations between TLD and film measurements of minimum and maximum doses and absorbed doses to the organs occurred at all 5 levels. TLD positioning failed to cover several organ sites; for these, only absorbed dose measurements from the film were available.

CONCLUSIONS

TLDs were unable to sample dose distributions and gradients accurately. The characteristics of Gafchromic LD-V1 film make it a favorable alternative in dental CBCT dosimetry.

Toward a Transportable Cell Culture Platform for Evaluating Radiotherapy Dose Modifying Factors

The current tools for validating dose delivery and optimizing new radiotherapy technologies in radiation therapy do not account for important dose modifying factors (DMFs), such as variations in cellular repair capability, tumor oxygenation, ultra-high dose rates and the type of ionizing radiation used. These factors play a crucial role in tumor control and normal tissue complications. To address this need, we explored the feasibility of developing a transportable cell culture platform (TCCP) to assess the relative biological effectiveness (RBE) of ionizing radiation. We measured cell recovery, clonogenic viability and metabolic viability of MDA-MB-231 cells over several days at room temperature in a range of concentrations of fetal bovine serum (FBS) in medium-supplemented gelatin, under both normoxic and hypoxic oxygen environments. Additionally, we measured the clonogenic viability of the cells to characterize how the duration of the TCCP at room temperature affected their radiosensitivity at doses up to 16 Gy. We found that (78±2)% of MDA-MB-231 cells were successfully recovered after being kept at room temperature for three days in 50% FBS in medium-supplemented gelatin at hypoxia (0.4±0.1)% pO2, while metabolic and clonogenic viabilities as measured by ATP luminescence and colony formation were found to be (58±5)% and (57±4)%, respectively. Additionally, irradiating a TCCP under normoxic and hypoxic conditions yielded a clonogenic oxygen enhancement ratio (OER) of 1.4±0.6 and a metabolic OER of 1.9±0.4. Our results demonstrate that the TCCP can be used to assess the RBE of a DMF and provides a feasible platform for assessing DMFs in radiation therapy applications.

SSRMP Recommendations No 9: Reference dosimetry in low and medium energy x-ray beams

The SSRMP recommendations on reference dosimetry in kilovolt beams as used in radiation therapy were revised to establish current practice in Switzerland. The recommendations specify the dosimetry formalism, reference class dosimeter systems and conditions used for the calibration of low and medium energy x-ray beams. Practical guidance is provided on the determination of the beam quality specifier and all corrections required for converting instrument readings to absorbed dose to water. Guidance is also provided on the determination of relative dose under non-reference conditions and on the cross calibration of instruments. The effect of lack of electron equilibrium and influence of contaminant electrons when using thin window plane parallel chambers at x-ray tube potentials higher than 50kV is elaborated in an appendix. In Switzerland the calibration of the reference system used for dosimetry is regulated by law. METAS and IRA are the authorities providing this calibration service to the radiotherapy departments. The last appendix of these recommendations summarise this calibration chain.