Improvements In Dosimetry Research Articles

Adaptive radiotherapy for muscle invasive bladder cancer: a retrospective audit of two bladder filling protocols

BackgroundRadical radiotherapy for muscle-invasive bladder cancer (MIBC) is challenging due to large variations in bladder shape, size and volume during treatment, with drinking protocols often employed to mitigate geometric uncertainties. Utilising adaptive radiotherapy together with CBCT imaging to select a treatment plan that best fits the bladder target and reduce normal tissue irradiation is an attractive option to compensate for anatomical changes. The aim of this retrospective study was to compare a bladder empty (BE) protocol to a bladder filling (BF) protocol with regards to variations in target volumes, plan of the day (PoD) selection and plan dosimetry throughout treatment.MethodsForty patients were included in the study; twenty were treated with a BE protocol and twenty with a BF protocol to a total prescribed dose of 55 Gy in 20 fractions. Small, medium and large bladder plans were generated using three different CTV to PTV margins. Bladder (CTV) volumes were delineated on planning CTs and online pre-treatment CBCTs. Differences in CTV volumes throughout treatment, plan selection, PTV volumes and resulting dose metrics were compared for both protocols.ResultsMean bladder volume differed significantly on both the planning CTs and online pre-treatment CBCTs between the protocols (p < 0.05). Significant differences in bladder volumes were observed between the planning CT and pre-treatment CBCTs for BF (p < 0.05) but not for BE (p = 0.11). Both protocols saw a significant decrease in bladder volume between first and final treatment fractions (p < 0.05). Medium plans were preferentially selected for BE whilst when using the BF protocol the small plan was chosen most frequently. With no significant change to PTV coverage between the protocols, the volume of body receiving 25.0–45.8 Gy was found to be significantly smaller for BE patients (p < 0.05).ConclusionsThis work provides evidence in favour of a BE protocol compared to a BF protocol for radical radiotherapy for MIBC. The smaller treatment volumes observed in the BE protocol led to reduced OAR and total body doses and were also observed to be more consistent throughout the treatment course. These results highlight improvements in dosimetry for patients who undergo a BE protocol for MIBC.

One-year clinical outcomes of MR-guided stereotactic body radiation therapy with rectal spacer for patients with localized prostate cancer

Background and purposeThis prospective study aimed to investigate adaptive magnetic resonance (MR)-guided stereotactic body radiation therapy (MRgSBRT) with rectal spacer for localized prostate cancer (PC) and report 1-year clinical outcomes.Materials and methodsThirty-four consecutive patients with low- to high-risk localized PC that underwent 5-fraction adaptive MRgSBRT with rectal spacer were enrolled. The dosimetric comparison was performed on a risk- and age-matched cohort treated with MRgSBRT but without a spacer at a similar timepoint. Clinician-reported outcomes were based on Common Terminology Criteria for Adverse Events. Patient-reported outcomes were based on the Expanded Prostate Cancer Index Composite (EPIC) questionnaire at baseline, acute (1–3 months), subacute (4–12 months), and late (> 12 months) phases.ResultsThe median follow-up was 390 days (range 28–823) and the median age was 70 years (range 58–82). One patient experienced rectal bleeding soon after spacer insertion that subsided before MRgSBRT. The median distance between the midline of the prostate midgland and the rectum after spacer insertion measured 7.8 mm (range 2.6–15.3), and the median length of the spacer was 45.9 mm (range 16.8–62.9) based on T2-weighted MR imaging. The use of spacer resulted in significant improvements in target coverage (V100% > 95% = 98.6% [range 93.4–99.8] for spacer vs. 97.8% [range 69.6–99.7] for non-spacer) and rectal sparing (V95% < 3 cc = 0.7 cc [range 0–4.6] for spacer vs. 4.9 cc [range 0–12.5] for non-spacer). Nine patients (26.5%) experienced grade 1 gastrointestinal toxicities, and no grade ≥ 2 toxicities were observed. During the 1-year follow-up period, EPIC scores for the bowel domain remained stable and were the highest among all other domains.ConclusionsMRgSBRT with rectal spacer for localized PC showed exceptional tolerability with minimal gastrointestinal toxicities and satisfactory patient-reported outcomes. Improvements in dosimetry, rectal sparing, and target coverage were achieved with a rectal spacer. Randomized trials are warranted for further validation.

Autologous Stem Cell Transplantation with Intensity Modulated Total Body Irradiation Conditioning for Systemic Sclerosis

Based on the seminal SCOT trial, autologous stem cell transplantation (HSCT) using myeloablative total body irradiation (TBI) and anti-thymocyte globulin (ATG) as a conditioning regimen has become a standard treatment option for certain patients with systemic sclerosis (SSc). In patients with SSc, normal organs are more radiosensitive and prone to compromised function, and therefore lungs and kidneys require dose reduction. With traditional techniques, TBI requires heavy and thick physical blocks, which can be cumbersome and have poor reproducibility. We hypothesized that intensity modulated radiation therapy (IMRT) TBI compared to standard anteroposterior (AP)/posteroanterior (PA) TBI would facilitate improvements in dosimetry and reproducibility (due to not requiring physical blocks) without compromising outcomes. Herein, we report a single-institution retrospective analysis of patients with SSc treated with an IMRT TBI. Patients with SSc who underwent HSCT with TBI between 2017 and 2022 were eligible. All patients underwent conditioning with equine ATG, cyclophosphamide 120 mg/kg, and IMRT TBI administered twice-daily to a total dose of 800 cGy in 200 cGy fractions. A minimum of 80% of the PTV was to receive prescription dose. Mean lung and kidney dose were to be less than 200 cGy. Patients were then replanned using an AP/PA technique for dosimetric comparison. The primary endpoint was planning target volume (PTV), lung, and kidney dosimetry. Secondary endpoints included event-free survival (EFS), overall survival (OS), disease-modifying antirheumatic drug-free survival (DMARD-FS), treatment related mortality (TRM), and toxicity. A total of 14 patients were eligible for our analysis. On dosimetric analysis, the mean dose to the PTV was significantly higher on the IMRT compared to the AP/PA plans (809.4 cGy versus 728.5 cGy, p<0.001). The mean dose to the lungs (239.5 cGy versus 443.9 cGy, p<0.001) and kidneys (204.9 cGy versus 281.2 cGy, p<0.001) was significantly lower. Median follow-up was 34.6 months (1.0-51.7 months). There was one case of TRM secondary to respiratory failure. The 24-month OS, EFS, and DMARD-FS estimates were 92.9%, 74.3%, and 70.0%, respectively. Three patients experienced adverse events, which included respiratory failure (n = 1), renal failure (n = 1), and death (n = 1). No patients experienced clinically significant pneumonitis or nephritis that were deemed to be a likely consequence of TBI. Five patients subsequently initiated DMARDs, but three did so due to worsening skin symptoms without other major organ dysfunction. Use of IMRT TBI as part of the conditioning regimen for HSCT for SSc yields improved dosimetry relative to a standard AP/PA technique, with efficacy and toxicity outcomes comparable with published data. This technique should be considered for patients undergoing HSCT for SSc and warrants inclusion in prospective trials for SSc that involve TBI.

QUANTIFICATION OF ABSORBED DOSE IN 90Y SELECTIVE INTERNAL RADIATION THERAPY FOR HEPATOCELLULAR CARCINOMA TREATMENT: A REVIEW

Selective internal radiation therapy (SIRT) has emerged as a viable strategy for the treatment of incurable hepatic cancers. Although SIRT is a well-known therapy, continuous improvement in personalised dosimetry is required to improve the treatment planning and delivery of therapy. The ability to precisely foresee, plan, and administer the ideal dose to the tumour and non-tumoral tissues, including a final validation of the dose distribution, is the primary principle of radiation. The main way for safely personalised therapy for a maximum response while respecting normal tissue tolerances is to know the true absorbed dose to tissue compartments. Recent clinical studies highlighted the significance of personalised dosimetry to make it safer and more effective. Quantification of the absorbed dose distribution is of utmost importance in SIRT 90Y to optimise the hepatocellular carcinoma (HCC) treatment. The aim of this article was to review various dosimetric approaches in quantifying the absorbed dose of tumours and healthy liver tissue in 90Y SIRT. This article also compares the capabilities of organ-level dosimetry, voxel-level dosimetry and Monte Carlo simulation in assessing the absorbed dose in organs especially liver. The quantification of absorbed dose influences 90Y SIRT tumour dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. Personalised dosimetry for the tumour and healthy liver parenchyma after 90Y SIRT is recommended for patient-tailored therapy with enhanced therapeutic outcomes and for the safe administration of additional treatment cycles.

Prompt gamma ray detection and imaging for boron neutron capture therapy using CdTe detector and novel detector shield - Monte Carlo study.

For boron neutron capture therapy (BNCT), the improvements in patient dosimetry will require information about the spatial variation of 10 B concentration in the tumor and critical organs. A non-invasive approach, based on the detection of prompt gamma (PG) rays from the BNC reaction, may be well-suited to obtain such information. The detectability of the BNC PG rays has been shown experimentally utilizing energy-resolving cadmium telluride (CdTe) detectors. However, the feasibility of this approach under the clinically relevant conditions of BNCT is currently unknown. The present work aimed to investigate the aforementioned feasibility by performing Monte Carlo (MC) simulations under the phantom irradiation geometry relevant to accelerator-based BNCT (a-BNCT). Especially, this investigation focused on demonstrating the enhanced detection of the BNC PG rays using a novel neutron shield for CdTe detectors. Upon demonstrating the efficacy of the proposed detector shield, the BNC PG ray-based quantitative imaging of clinically relevant concentrations of 10 B was also demonstrated. The Geant4 MC simulation toolkit was used to model the phantom irradiation by an epithermal neutron beam as well as the detection of the BNC PG rays from the phantom by CdTe detectors with and without the proposed gadolinium (Gd)-based detector shield. It was also used to model the BNC PG ray-based quantitative imaging of 10 B concentrations under a-BNCT scenarios. Each model included a 20cm-diameter/24cm-height cylindrical PMMA phantom containing 10 B inserts at various concentrations. Arrays of CdTe crystals of 5×5×1 mm3 each (up to 120 in the case of a ring detector) were modeled for acquiring the BNC PG ray signals and quantitative imaging. According to the MC simulations, thermalized neutrons from the phantom were found to reach the CdTe detector and captured by Cd and Te, resulting in the gamma ray background noise that directly interfered with the BNC PG ray signal. The proposed Gd-based detector shield was found to be highly effective in shielding thermal neutrons from the phantom, thereby reducing the unwanted gamma ray background noise. Owing to this shield, the detection of as low as seven parts-per-million (ppm) of 10 B within the phantom of clinically relevant size was possible using 20 billion incident neutron histories. Furthermore, quantitative imaging of 10 B distributed at low concentration (down to 50ppm) within the phantom was demonstrated using computed tomography (CT) simulations with 16 billion incident neutron histories per angular projection. The 10 B detection limit (7.5ppm) was also estimated using the reconstructed CT image. Both 10 B detection limits determined from this investigation are deemed clinically relevant for BNCT. The proposed Gd-based detector shield played an essential role for achieving the currently reported 10 B detection limits. Overall, the present MC simulation work demonstrated highly sensitive BNC PG ray detection and imaging under a-BNCT scenarios using CdTe detectors coupled with a novel detector shield.

Image-guidance triggered adaptive radiation therapy in head and neck squamous cell carcinoma: single-institution experience and implications for clinical practice

PurposeTo report frequency and timing of adaptive radiotherapy (ART) and assess patient, disease, and treatment-related characteristics potentially triggering the need for such adaptive replanning in head and neck squamous cell carcinoma (HNSCC). MethodsMedical records of HNSCC patients treated with definitive intensity modulated radiation therapy (IMRT) with or without concurrent systemic chemotherapy were reviewed retrospectively to identify patients undergoing image-guidance triggered adaptive replanning. Clinico-demographic characteristics of patients undergoing ART were compared with patients treated without adaptation using the chi-square test. ResultsTwo hundred patients with squamous cell cancers of the oropharynx, larynx, or hypopharynx treated with definitive IMRT between 2014 to 2019 comprised the study cohort. Twenty-seven (13.5%) patients underwent adaptive replanning during treatment at a median of 17 fractions (inter-quartile range 14-24 fractions). There were no significant differences in the baseline patient (age, gender), disease (site of primary, staging/grouping), and treatment-related characteristics (dose-fractionation, chemotherapy usage) in patients undergoing ART compared to those treated without adaptation. Weight loss during IMRT emerged as a significant factor predicting the need for ART; patients having ≥10% weight loss from baseline were more likely to undergo treatment adaptation compared to patients with <10% weight loss (p = 0.0002). There was variable impact of ART on dose-volume statistics of organs-at-risk such parotid glands and spinal cord. ConclusionImage-guidance triggered ART for HNSCC is not associated with significant improvement in OAR dosimetry. However, weight loss during definitive IMRT can be a potentially useful trigger for identifying patients who are most likely to benefit from such adaptive replanning

A Realistic Multiregion Mouse Kidney Dosimetry Model to Support the Preclinical Evaluation of Potential Nephrotoxicity of Radiopharmaceutical Therapy.

Suborgan absorbed dose estimates in mouse kidneys are crucial to support preclinical nephrotoxicity analyses of α- and β-particle-emitting radioligands exhibiting a heterogeneous activity distribution in the kidneys. This is, however, limited by the scarcity of reference dose factors (S values) available in the literature for specific mouse kidney tissues. Methods: A computational multiregion model of a mouse kidney based on high-resolution MRI data from a healthy mouse kidney was developed. The model was used to calculate S values for 5 kidney tissues (cortex, outer and inner stripes of outer medulla, inner medulla, and papilla and pelvis) for a wide range of β- or α-emitting radionuclides (45 in total) of interest for radiopharmaceutical therapy, using Monte Carlo calculations. Additionally, regional S values were applied for a 131I-labeled single-domain antibody fragment with predominant retention in the outer stripe of the renal outer medulla. Results: The heterogeneous activity distribution in kidneys of considered α- and low- to medium-energy β-emitters considerably affected the absorbed dose estimation in specific suborgan regions. The suborgan tissue doses resulting from the nonuniform distribution of the 131I-labeled antibody fragment largely deviated (from -40% to 57%) from the mean kidney dose resulting from an assumed uniform activity distribution throughout the whole kidney. The absorbed dose in the renal outer stripe was about 2.0 times higher than in the cortex and in the inner stripe and about 2.6 times higher than in inner tissues. Conclusion: The use of kidney regional S values allows a more realistic estimation of the absorbed dose in different renal tissues from therapeutic radioligands with a heterogeneous uptake in the kidneys. This constitutes an improvement from the simplistic (less accurate) renal dose estimates assuming a uniform distribution of activity throughout kidney tissues. Such improvement in dosimetry is expected to support preclinical studies essential for a better understanding of nephrotoxicity in humans. The dosimetric database has added value in the development of new molecular vectors for radiopharmaceutical therapy.

Feasibility study of computational occupational dosimetry: evaluating a proof-of-concept in an endovascular and interventional cardiology setting

Individual monitoring of radiation workers is essential to ensure compliance with legal dose limits and to ensure that doses are As Low As Reasonably Achievable. However, large uncertainties still exist in personal dosimetry and there are issues with compliance and incorrect wearing of dosimeters. The objective of the PODIUM (Personal Online Dosimetry Using Computational Methods) project was to improve personal dosimetry by an innovative approach: the development of an online dosimetry application based on computer simulations without the use of physical dosimeters. Occupational doses were calculated based on the use of camera tracking devices, flexible individualised phantoms and data from the radiation source. When combined with fast Monte Carlo simulation codes, the aim was to perform personal dosimetry in real-time. A key component of the PODIUM project was to assess and validate the methodology in interventional radiology workplaces where improvements in dosimetry are needed. This paper describes the feasibility of implementing the PODIUM approach in a clinical setting. Validation was carried out using dosimeters worn by Vascular Surgeons and Interventional Cardiologists during patient procedures at a hospital in Ireland. Our preliminary results from this feasibility study show acceptable differences of the order of 40% between calculated and measured staff doses, in terms of the personal dose equivalent quantity Hp(10), however there is a greater deviation for more complex cases and improvements are needed. The challenges of using the system in busy interventional rooms have informed the future needs and applicability of PODIUM. The availability of an online personal dosimetry application has the potential to overcome problems that arise from the use of current dosimeters. In addition, it should increase awareness of radiation protection among staff. Some limitations remain and a second phase of development would be required to bring the PODIUM method into operation in a hospital setting. However, an early prototype system has been tested in a clinical setting and the results from this two-year proof-of-concept PODIUM project are very promising for future development.

Three Quarters of a Century of Research on RF Exposure Assessment and Dosimetry-What Have We Learned?

This commentary, by three authors with an aggregate experience of more than a century in technology and health and safety studies concerning radiofrequency (RF) energy, asks what has been learned over the past 75 years of research on radiofrequency and health, focusing on technologies for exposure assessment and dosimetry. Research programs on health and safety of RF exposure began in the 1950s, initially motivated by occupational health concerns for military personnel, and later to address public concerns about exposures to RF energy from environmental sources and near-field exposures from RF transmitting devices such as mobile phones that are used near the body. While this research largely focused on the biological effects of RF energy, it also led to important improvements in exposure assessment and dosimetry. This work in the aggregate has made RF energy one of the best studied potential technological hazards and represents a productive response by large numbers of scientists and engineers, working in many countries and supported by diverse funding agencies, to the ever rapidly evolving uses of the electromagnetic spectrum. This review comments on present needs of the field, which include raising the quality of dosimetry in many RF bioeffects studies and developing improved exposure/dosimetric techniques for the higher microwave frequencies to be used by forthcoming communications technologies. At present, however, the major uncertainties in dosimetric modeling/exposure assessment are likely to be related to the inherent variability in real-world exposures, rather than imprecision in measurement technologies.

Varian ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time.

The Varian Ethos system allows for online adaptive treatments through the utilization of artificial intelligence (AI) and deformable image registration which automates large parts of the anatomical contouring and plan optimization process. In this study, treatments of intact prostate and prostate bed, with and without nodes, were simulated for 182 online adaptive fractions, and then a further 184 clinical fractions were delivered on the Ethos system. Frequency and magnitude of contour edits were recorded, as well as a range of plan quality metrics. From the fractions analyzed, 11% of AI generated contours, known as influencer contours, required no change, and 81% required minor edits in any given fraction. The frequency of target and noninfluencer organs at risk (OAR) contour editing varied substantially between different targets and noninfluencer OARs, although across all targets 72% of cases required no edits. The adaptive plan was the preference in 95% of fractions. The adaptive plan met more goals than the scheduled plan in 78% of fractions, while in 15% of fractions the number of goals met was the same. The online adaptive recontouring and replanning process was carried out in 19 min on average. Significant improvements in dosimetry are possible with the Ethos online adaptive system in prostate radiotherapy.

Radioembolization Dosimetry with Total-Body 90Y PET.

Transarterial radioembolization (TARE) is a locoregional radiopharmaceutical therapy based on the delivery of radioactive 90Y microspheres to liver tumors. The importance of personalized dosimetry to make TARE safer and more effective has been demonstrated in recent clinical studies, stressing the need for quantification of the dose-response relationship to ultimately optimize the administered activity before treatment and image it after treatment. 90Y dosimetric studies are challenging because of the lack of accurate and precise methods but are best realized with PET combined with Monte Carlo simulations and other image modalities to calculate a segmental dose distribution. The aim of this study was to assess the suitability of imaging 90Y PET patients with the total-body PET/CT uEXPLORER and to investigate possible improvements in TARE 90Y PET-based dosimetry. The uEXPLORER is the first commercially available ultra-high-resolution (171 cps/kBq) total-body digital PET/CT device with a 194-cm axial PET field of view that enables the whole body to be scanned at a single bed position. Methods: Two PET/CT scanners were evaluated in this study: the Biograph mCT and the total-body uEXPLORER. Images of a National Electrical Manufacturers Association (NEMA) image-quality phantom and 2 patients were reconstructed using our standard clinical oncology protocol. A late portal phase contrast-enhanced CT scan was used to contour the liver segments and create corresponding volumes of interest. To calculate the absorbed dose, Monte Carlo simulations were performed using Geant4 Application for Tomographic Emission (GATE). The absorbed dose and dose-volume histograms were calculated for all 6 spheres (diameters ranging from 10 to 37 mm) of the NEMA phantom, the liver segments, and the entire liver. Differences between the phantom doses and an analytic ground truth were quantified through the root mean squared error. Results: The uEXPLORER showed a higher signal-to-noise ratio at 10- and 13-mm diameters, consistent with its high spatial resolution and system sensitivity. The total liver-absorbed dose showed excellent agreement between the uEXPLORER and the mCT for both patients, with differences lower than 0.2%. Larger differences of up to 60% were observed when comparing the liver segment doses. All dose-volume histograms were in good agreement, with narrower tails for the uEXPLORER in all segments, indicating lower image noise. Conclusion: This patient study is compelling for the use of total-body 90Y PET for liver dosimetry. The uEXPLORER scanner showed a better signal-to-noise ratio than mCT, especially in lower-count regions of interest, which is expected to improve dose quantification and tumor dosimetry.

Personalising treatment plan quality review with knowledge-based planning in the TROG 15.03 trial for stereotactic ablative body radiotherapy in primary kidney cancer

IntroductionQuality assurance (QA) of treatment plans in clinical trials improves protocol compliance and patient outcomes. Retrospective use of knowledge-based-planning (KBP) in clinical trials has demonstrated improved treatment plan quality and consistency. We report the results of prospective use of KBP for real-time QA of treatment plan quality in the TROG 15.03 FASTRACK II trial, which evaluates efficacy of stereotactic ablative body radiotherapy (SABR) for kidney cancer.MethodsA KBP model was generated based on single institution data. For each patient in the KBP phase (open to the last 31 patients in the trial), the treating centre submitted treatment plans 7 days prior to treatment. A treatment plan was created by using the KBP model, which was compared with the submitted plan for each organ-at-risk (OAR) dose constraint. A report comparing each plan for each OAR constraint was provided to the submitting centre within 24 h of receiving the plan. The centre could then modify the plan based on the KBP report, or continue with the existing plan.ResultsReal-time feedback using KBP was provided in 24/31 cases. Consistent plan quality was in general achieved between KBP and the submitted plan. KBP review resulted in replan and improvement of OAR dosimetry in two patients. All centres indicated that the feedback was a useful QA check of their treatment plan.ConclusionKBP for real-time treatment plan review was feasible for 24/31 cases, and demonstrated ability to improve treatment plan quality in two cases. Challenges include integration of KBP feedback into clinical timelines, interpretation of KBP results with respect to clinical trade-offs, and determination of appropriate plan quality improvement criteria.

Revisiting 35 and 94 GHZ Millimeter Wave Exposure to the Non-Human Primate Eye.

A previous study reported thermal effects resulting from millimeter wave exposures at 35 and 94 GHz on non-human primates, specifically rhesus monkeys' (Macaca mulatta) corneas, but the data exhibited large variations in the observed temperatures and uncertainties in the millimeter wave dosimetry. By incorporating improvements in models and dosimetry, a non-human primate experiment was conducted involving corneal exposures that agreed well with a three-layer, one-dimensional, thermodynamic model to predict the expected surface temperature rise. The new data indicated that the originally reported safety margins for eye exposures were underestimated by 41 ± 20% over the power densities explored. As a result, the expected minimal visible lesion thresholds should be raised to 10.6 ± 1.5 and 7.1 ± 1.0 J cm at 35 and 94 GHz, respectively, provided that the power density is less than 6 W cm for subjects that are unable to blink. If the blink reflex was active, a power density threshold of 20 W cm could be used to protect the eye, although the eyelid could be burned if the exposure was long enough.

Small-field dosimetry with a high-resolution 3D scanning water phantom system for the small animal radiation research platform SARRP: a geometrical and quantitative study

Improvements in dosimetry in preclinical radiation research facilitate the application of results to the newest radiotherapy techniques, reducing gaps that hinder translation. Currently, guidelines for small-field kV photon dosimetry of small animal irradiators have not been published, and most of the publications are based on radiochromic film dosimetry. In this study, we evaluated the performance of four detectors, three ionization chambers (ICs): (PTW Advanced Markus, PTW Semiflex 31010, PTW PinPoint-3D 31016) and one solid-state detector (PTW 60017 unshielded Diode E) regarding their suitability for relative dosimetry of the small animal radiation research platform SARRP (220 kVp). The measurements were performed in a high-resolution 3D scanning phantom, centering the detectors in the field following the in-plane and cross-plane profiles method at two depths. Depth dose curves (PDDs) and profiles were measured in water for field sizes ranging from 40 × 40 mm2 to 5 × 5 mm2. Quantitative analysis was performed through global and local dose differences (DDs) between the PDDs and the Advanced Markus parallel plate IC data and through the gamma index (γ) criteria for profiles compared against data from EBT3 films provided by the manufacturer. Compared to the Advanced Markus IC, the PDD results suggest that PinPoint-3D is suitable for depth measurements at this beam quality, even near the surface, with agreements better than 1%. Semiflex 31010 was accurate to within 1.5% for measurements deeper than 5 mm. Diode E showed a dramatic DD and should not be recommended for the field sizes and kVp evaluated in this study. In agreement with γ analyses, PinPoint-3D and Diode E are good candidates for profile measurements of field sizes from 40 × 40 mm2 to 10 × 10 mm2. For 5 × 5 mm2 profiles, only Diode E showed good results, making it a recommended detector for profile measurements.

Improvement in Cardiac Dosimetry by Optimizing Heart-Sparing Breast Radiotherapy

Darby et al. demonstrated that cardiac events after breast radiation therapy (RT) are associated with mean heart dose (MHD). MHD is dependent on treatment fields and can be reduced by various techniques, such as deep inspiratory breath hold (DIBH), prone positioning, and cardiac blocks. The purpose of this study was to assess changes in MHD with advancements in modern RT by technique and treatment fields. This retrospective study included breast cancer patients treated from 2010 to 2018 at a single institution in an IRB approved registry. MHD was analyzed with respect to clinical variables, including laterality, cardiac sparing technique, and treatment fields, including regional nodal irradiation (RNI) with or without internal mammary nodal irradiation (IMNI). 765 patients (431 left, 315 right, 19 bilateral) were included. The average MHD was 1.87 Gy (SD 1.36 Gy, median 1.43 Gy) for left sided cases vs. 0.71 Gy (SD 0.80 Gy, median 0.51 Gy) for right sided cases (p<0.0001). Of the 43 patients that had a MHD > 4 Gy, bilateral cases were at a highest risk (21.1%), vs. left sided (7.7%) and right sided cases (1.9%) (p<0.0001). For left sided cases, average MHD without RNI, RNI without IMNI, and RNI with IMNI were 1.40 Gy (SD 0.98 Gy, median 1.16 Gy), 2.01 Gy (SD 1.15 Gy, median 1.63 Gy), and 3.48 Gy (SD 2.17 Gy, median 3.21 Gy), respectively. Following the 2013 publication of Darby et al, the average MHD significantly decreased for left sided RT cases (2.02 vs 1.82 Gy, p= 0.039) due to institutional adoption of cardiac-sparing techniques. For left sided cases w/o RNI, use of cardiac sparing techniques reduced average MHD from 1.61 Gy (SD 1.09 Gy, median 1.36 Gy) to 1.22 Gy (SD 0.99 Gy, median 0.99 Gy) with DIBH and 1.02 Gy (SD 0.56 Gy, median 0.78 Gy) with prone positioning respectively (p<0.0001), with no difference between techniques (p = 0.42). For left sided cases with RNI, DIBH reduced average MHD from 2.4 Gy (SD 0.13 Gy, median 2.02 Gy) down to 2.1 Gy (SD 1.57 Gy, median 1.6 Gy), p= 0.046. For left sided cases of RNI with IMNI, average MHD was 3.09 Gy (SD 2.38 Gy, median 2.57 Gy) with partially wide tangents compared to 3.99 Gy (SD 1.82 Gy, median 3.79 Gy) with matched electron fields (p= 0.053). For left sided cases with IMNI, the MHD was 3.48 Gy (SD 2.31 Gy, median 3.21 Gy) with DIBH compared to 3.64 Gy ( SD 2.16 Gy, median 3.37 Gy) without DIBH (p=0.27). The MHD for left sided RT with reconstruction was 1.94 Gy (SD 1.21 Gy, median 1.53 Gy) and without reconstruction was 1.85 Gy (SD 1.42 Gy, median 1.39 Gy). Cardiac doses were lower following the publication of Darby et al. Overall the average MHD was <1 Gy and <2 Gy for right and left breast cancers, respectively, by increased utilization of cardiac sparing techniques such as DIBH and prone positioning.

Evaluating improvements in cardiac dosimetry in breast radiotherapy and comparison of cardiac sparing techniques

Data from Darby et al. demonstrated that cardiac dose in patients undergoing breast radiation therapy is associated with cardiac events. Cardiac dose is primarily dependent on treatment laterality and treatment fields. More recently, techniques such deep inspiratory breath hold (DIBH) and prone positioning have been used as cardiac sparing techniques. The purpose of this study is to assess changes in cardiac dosimetry with cardiac sparing techniques. This retrospective study included breast cancer patients treated from 2010 to 2018 at a single institution. Mean heart dose (MHD) was analyzed with respect to treatment era, laterality, cardiac sparing technique, and treatment fields, including regional nodal irradiation (RNI) and internal mammary nodal irradiation (IMNI). Seven hundred sixty-five patients were included in this study. Average MHD was 1.87 Gy for left-sided cases and 0.71 Gy for right-sided cases (p < 0.0001). For left-sided cases, the average MHD without RNI, RNI without IMNI, and RNI with IMNI was 1.40 Gy, 2.01 Gy, and 3.48 Gy respectively. For left-sided cases without RNI, the average MHD decreased from 1.61 to 1.22 Gy using DIBH (p < 0.0001), and to 1.02 Gy with prone positioning (p < 0.0001). There was no difference in MHD between DIBH and prone techniques (p = 0.44). For left-sided cases with RNI, DIBH reduced the average MHD from 2.4 to 2.1 Gy (p = 0.04). Following the 2013 publication of Darby et al., the average MHD significantly decreased for left-sided RT cases (2.02 vs. 1.83 Gy, p = 0.03) due to increased institutional adoption of cardiac-sparing techniques. Cardiac doses were lower following the 2013 publication of Darby et al. due to greater use of cardiac sparing techniques. Overall, the average MHD was < 1 Gy and < 2 Gy for right and left breast cancers, respectively, with lower doses achieved using DIBH and prone positioning as cardiac sparing techniques.

Potential improvements in brain dose estimates for internal emitters

Background Element-specific biokinetic models are used to reconstruct doses to systemic tissues from internal emitters. Typically, a systemic model for a radionuclide explicitly depicts only its dominant repositories. Remaining tissues and fluids are aggregated into a pool called Other tissue in which the radionuclide is assumed to be uniformly distributed. In the systemic biokinetic models used in radiation protection, the brain usually is addressed as an implicit mass fraction of Other tissue rather than an explicitly depicted repository. Due to increasing interest in radiation effects on the brain, efforts are underway to improve brain dosimetry for internal radiation sources. Methods We assessed potential improvements in brain dosimetry for internal emitters by explicitly modeling brain kinetics rather than treating the brain as a mass fraction of Other tissue. We selected 10 elements for which brain kinetics can be modeled using published biokinetic data. Injection dose coefficients were calculated for a relatively long-lived radioisotope of each element using each of two versions of the ICRP’s latest systemic biokinetic model for the element, the original version and a modified version differing only in the treatment of brain. If the ICRP model contained an explicit brain pool, the modified version depicted brain instead as a mass fraction of Other tissue. If the ICRP model included brain in Other tissue, the modified version included an explicit brain pool with kinetics based on best available brain-specific data. Results The result for a given radionuclide is expressed as a ratio A:B, where A and B are the dose coefficients based on the versions of the model with and without an explicit brain pool, respectively. The following ratios A:B were obtained for the 10 radionuclides addressed here: 241Am, 0.13; 207Bi, 0.57; 234U, 0.81; 239Pu, 0.96; 203Hg (vapor), 1.4; 134Cs, 1.5; 54Mn, 1.7; 210Po, 1.7; 226Ra, 1.9; 210Pb, 3.3. These ratios indicate that a dose estimate for brain based on a biokinetic model with brain implicitly contained in Other tissue may substantially underestimate or substantially overestimate a dose estimate that reflects best available brain-specific biokinetic data. Of course, the reliability of the latter estimate depends on the quality of the underlying biokinetic data. Conclusions Where feasible, the brain should be depicted explicitly in biokinetic models used in epidemiological studies addressing adverse effects of ionizing radiation.

Intensity-modulated radiotherapy for paranasal sinuses and base of skull tumors

Paranasal sinus and skull base tumors are rare aggressive head and neck cancers, and typically present in the locally advanced stages. As a result, achieving wide surgical resection with clear margins is a challenge for these tumors, and radiotherapy is thus usually indicated as an adjuvant modality following surgery to optimize local control. Given the integral role of radiotherapy in the management of this subgroup of head and neck tumors, the advent of intensity-modulated radiotherapy (IMRT) has led to substantial improvement of clinical outcomes for these patients. This is primarily driven by the improvement in radiation dosimetry with IMRT compared to conventional two dimensional (2D)- and 3D-techniques, in terms of ensuring dose intensity to the tumor target coupled with minimizing dose exposure to critical organs. Consequently, the evident clinical benefits of IMRT have been in reduction of normal tissue toxicities, ranging from critical neurological symptoms to less debilitating but bothersome symptoms of eye infections and radiation-induced skin changes. Another domain where IMRT has potential clinical utility is in the management of a subset of non-resectable T4 paranasal sinus and skull base tumors. For these inoperable lesions, the steep dose-gradient between tumor and normal tissue is even more advantageous, given the crucial need to maintain dose intensity to the tumor. Innovative strategies in this space also include the use of induction chemotherapy for patient selection. In this review, we summarized the data for the aforementioned topics, including specific discussions on the different histologic subtypes of paranasal sinus and skull base tumors.

Evaluation of the UF/NCI hybrid computational phantoms for use in organ dosimetry of pediatric patients undergoing fluoroscopically guided cardiac procedures**This work was supported by Advanced Laboratory for Radiation Dosimetry Studies, University of Florida, American Association of University Women, National Cancer Institute Grant 1F31 CA159464.

Epidemiologic data demonstrate that pediatric patients face a higher relative risk of radiation induced cancers than their adult counterparts at equivalent exposures. Infants and children with congenital heart defects are a critical patient population exposed to ionizing radiation during life-saving procedures. These patients will likely incur numerous procedures throughout their lifespan, each time increasing their cumulative radiation absorbed dose. As continued improvements in long-term prognosis of congenital heart defect patients is achieved, a better understanding of organ radiation dose following treatment becomes increasingly vital. Dosimetry of these patients can be accomplished using Monte Carlo radiation transport simulations, coupled with modern anatomical patient models. The aim of this study was to evaluate the performance of the University of Florida/National Cancer Institute (UF/NCI) pediatric hybrid computational phantom library for organ dose assessment of patients that have undergone fluoroscopically guided cardiac catheterizations. In this study, two types of simulations were modeled. A dose assessment was performed on 29 patient-specific voxel phantoms (taken as representing the patient’s true anatomy), height/weight-matched hybrid library phantoms, and age-matched reference phantoms. Two exposure studies were conducted for each phantom type. First, a parametric study was constructed by the attending pediatric interventional cardiologist at the University of Florida to model the range of parameters seen clinically. Second, four clinical cardiac procedures were simulated based upon internal logfiles captured by a Toshiba Infinix-i Cardiac Bi-Plane fluoroscopic unit. Performance of the phantom library was quantified by computing both the percent difference in individual organ doses, as well as the organ dose root mean square values for overall phantom assessment between the matched phantoms (UF/NCI library or reference) and the patient-specific phantoms. The UF/NCI hybrid phantoms performed at percent differences of between 15% and 30% for the parametric set of irradiation events. Among internal logfile reconstructed procedures, the UF/NCI hybrid phantoms performed with RMS organ dose values between 7% and 29%. Percent improvement in organ dosimetry via the use of hybrid library phantoms over the reference phantoms ranged from 6.6% to 93%. The use of a hybrid phantom library, Monte Carlo radiation transport methods, and clinical information on irradiation events provide a means for tracking organ dose in these radiosensitive patients undergoing fluoroscopically guided cardiac procedures.

Ion chambers compliance results of Brazilian radiation therapy facilities

The Brazilian Nuclear Energy Commission (cnen) has been making a constant effort to keep up to date with international standards and national needs to strengthen the status of radiological protection of the country. The guidelines related to radiation therapy facilities have been revised in the last five years in order to take into consideration the most relevant aspects of the growing technology as well as to mitigate the accidents or incidents observed in practice. Hence, clinical dosimeters have gained special importance in this matter. In the present work, we discuss the effectiveness of regulation and inspections to the enforcement of instrument calibration accuracy for the improvement of patient dosimetry and quality control. As a result, we observed that the number of calibrated instruments, mainly well chambers, is increasing each year. The same behavior is observed for instruments employed in technologically advanced radiation treatments such as intensity modulated radiotherapy, volumetric therapy and stereotatic radiosurgery. We ascribe this behavior to the new regulation.