Search

Diffuse choroidal hemangioma (DCH) is a rare, benign vascular eye tumor that typically presents as part of Sturge-Weber syndrome. The tumor is clinically ill-defined with indistinct margins and blends subtly with the choroid. Associated exudative retinal detachment is a common complication that is reversible with management. External beam radiation therapy (EBRT) has traditionally been used for treatment. There have been limited reports on the use of radioactive eye plaque brachytherapy. A necessary component of eye plaque brachytherapy is accurate target delineation. Unfortunately, traditional computed tomography (CT) does not reveal the footprint of this vascular tumor, especially in the presence of retinal detachment. We report a case where magnetic resonance imaging (MRI) was used to aid in radiation target delineation for radioactive eye plaque brachytherapy. A thin-slice orbital MRI enhanced with gadolinium contrast was performed to differentiate the enhanced tumor from the unenhanced subretinal fluid, allowing for hemangioma delineation. Our patient was treated with 35Gy to the tumor apex over four days via radioactive iodine eye plaque. Subretinal fluid in the macula improved within a month and the exudative retinal detachment resolved within six months. There was no recurrence of subretinal fluid at three years. Our case illustrates radioactive iodine eye plaque brachytherapy is safe and effective for management of DCH-associated retinal detachment. MRI with contrast should be considered as an imaging modality to differentiate tumor from the surrounding subretinal fluid, allowing for improved delineation and targeted radiation.

Radiation oncology practices use a suite of dedicated software and hardware that are not common to other medical subspecialties, making radiation treatment history inaccessible to colleagues. A radiation dose distribution map is generated for each patient internally that allows for visualization of the dose given to each anatomic structure volumetrically; however, this crucial information is not shared systematically to multidisciplinary medical, surgery, and radiology colleagues. A framework was developed in which dose distribution volumes are uploaded onto the medical center’s picture archiving and communication system (PACS) to rapidly retrieve and review exactly where, when, and to what dose a lesion or structure was treated. The ability to easily visualize radiation therapy information allows radiology clinics to incorporate radiation dose into image interpretation without direct access to radiation oncology planning software and data. Tumor board discussions are simplified by incorporating radiation therapy information collectively in real time, and daily onboard imaging can also be uploaded while a patient is still undergoing radiation therapy. Placing dose distribution information into PACS facilitates central access into the electronic medical record and provides a succinct visual summary of a patient’s radiation history for all medical providers. More broadly, the radiation dose map provides greater visibility and facilitates incorporation of a patient’s radiation history to improve oncologic decision making and patient outcomes. Keywords: Brain/Brain Stem, CNS, MRI, Neuro-Oncology, Radiation Effects, Radiation Therapy, Radiation Therapy/Oncology, Radiosurgery, Skull Base, Spine, Technology Assessment Supplemental material is available for this article. © RSNA, 2021 See also commentary by Khandelwal and Scarboro in this issue.

Purpose To report early outcomes of patients with uveal melanoma treated with Eye Physics iodine-125 episcleral plaque therapy using modern biopsy techniques and intraoperative ultrasound guidance at our institution. Methods and materials A retrospective chart review was conducted for 48 consecutive patients with uveal melanoma who were treated with Eye Physics plaque brachytherapy performed by 1 ocular oncologist. All patients underwent intraoperative ultrasound for image guidance of plaque placement. A dose of 85 Gy was prescribed to the apical height of the tumor or 5 mm from the inner sclera, whichever was greater. Forty-five patients underwent biopsy. Visual acuity, complication data, and recurrence rates were recorded. Results Median age at presentation was 63.0 years (range, 19-86 years). Median follow-up was 21.6 months. Median tumor apical height was 3.3 mm (range, 1.8-11.5 mm). Median dose at apex for tumor height >5 mm was 85.0 Gy and 142.5 Gy for tumor height ≤5 mm. Mean percent decrease in tumor height from baseline at 12, 24, and 36 months was 39.6%, 51.8%, and 53.8%, respectively. At 24 months, 19/23 (82.6%) patients maintained vision within 3 lines of baseline visual acuity. Twelve patients developed radiation retinopathy, 6 of whom were treated with anti-vascular endothelial growth factor therapy in the context of a clinical trial. No patients to date have local failure. Three patients are alive with confirmed hepatic metastases. Conclusions We reported 0% early local failure rate and steady reduction in tumor height in 48 patients with uveal melanoma, ranging from small to large size, who were treated with Eye Physics iodine-125 episcleral plaque therapy using intraoperative ultrasound guidance. This promising result emphasizes the importance of image guided brachytherapy with intraoperative ultrasound at the time of plaque placement.

Aluminum oxide based optically stimulated luminescent dosimeters (OSLD) have been recognized as a useful dosimeter for measuring CT dose, particularly for patient dose measurements. Despite the increasing use of this dosimeter, appropriate dosimeter calibration techniques have not been established in the literature; while the manufacturer offers a calibration procedure, it is known to have relatively large uncertainties. The purpose of this work was to evaluate two clinical approaches for calibrating these dosimeters for CT applications, and to determine the uncertainty associated with measurements using these techniques. Three unique calibration procedures were used to calculate dose for a range of CT conditions using a commercially available OSLD and reader. The three calibration procedures included calibration (a) using the vendor‐provided method, (b) relative to a 120 kVp CT spectrum in air, and (c) relative to a megavoltage beam (implemented with 60Co). The dose measured using each of these approaches was compared to dose measured using a calibrated farmer‐type ion chamber. Finally, the uncertainty in the dose measured using each approach was determined. For the CT and megavoltage calibration methods, the dose measured using the OSLD nanoDot was within 5% of the dose measured using an ion chamber for a wide range of different CT scan parameters (80–140 kVp, and with measurements at a range of positions). When calibrated using the vendor‐recommended protocol, the OSLD measured doses were on average 15.5% lower than ion chamber doses. Two clinical calibration techniques have been evaluated and are presented in this work as alternatives to the vendor‐provided calibration approach. These techniques provide high precision for OSLD‐based measurements in a CT environment.

Purpose: The extensive use of computed tomography (CT) in diagnostic procedures is accompanied by a growing need for more accurate and patient-specific dosimetry techniques. Optically stimulated luminescent dosimeters (OSLDs) offer a potential solution for patient-specific CT point-based surface dosimetry by measuring air kerma. The purpose of this work was to characterize the OSLD nanoDot for CT dosimetry, quantifying necessary correction factors, and evaluating the uncertainty of these factors. Methods: A characterization of the Landauer OSL nanoDot (Landauer, Inc., Greenwood, IL) was conducted using both measurements and theoretical approaches in a CT environment. The effects of signal depletion, signal fading, dose linearity, and angular dependence were characterized through direct measurement for CT energies (80–140 kV) and delivered doses ranging from ∼5 to >1000 mGy. Energy dependence as a function of scan parameters was evaluated using two independent approaches: direct measurement and a theoretical approach based on Burlin cavity theory and Monte Carlo simulated spectra. This beam-quality dependence was evaluated for a range of CT scanning parameters. Results: Correction factors for the dosimeter response in terms of signal fading, dose linearity, and angular dependence were found to be small for most measurement conditions (

Purpose Accelerated partial breast irradiation (APBI) is an accepted treatment option in breast-conserving therapy for early stage breast cancer. However, data regarding outcomes of patients treated with multi-lumen catheter systems who have existing breast implants is limited. The purpose of this study was to report treatment parameters, outcomes, and possible dosimetric correlation with cosmetic outcome for this population of patients at our institution. Material and methods We report the treatment and outcome of seven consecutive patients with existing breast implants and early stage breast cancer who were treated between 2009 and 2013 using APBI following lumpectomy. All patients were treated twice per day for five days to a total dose of 34 Gy using a high-dose-rate (192)Ir source. Cosmetic outcomes were evaluated using the Harvard breast cosmesis scale, and late toxicities were reported using the Radiation Therapy Oncology Group (RTOG) late radiation morbidity schema. Results After a mean follow-up of 32 months, all patients have remained cancer free. Six out of seven patients had an excellent or good cosmetic outcome. There were no grade 3 or 4 late toxicities. The average total breast implant volume was 279.3 cc, received an average mean dose of 12.1 Gy, and a maximum dose of 234.1 Gy. The average percentage of breast implant volume receiving 50%, 75%, 100%, 150%, and 200% of the prescribed dose was 15.6%, 7.03%, 4.6%, 1.58%, and 0.46%, respectively. Absolute volume of breast implants receiving more than 50% of prescribed dose correlated with worse cosmetic outcomes. Conclusions Accelerated partial breast irradiation using a multi-lumen applicator in patients with existing breast implants can safely be performed with promising early clinical results. The presence of the implant did not compromise the ability to achieve dosimetric criteria; however, dose to the implant and the irradiated implant volume may be related with worse cosmetic outcomes.

Aluminium oxide (Al(2)O(3):C) is a common material used in optically stimulated luminescent dosemeters (OSLDs). OSLDs have a known energy dependence, which can impact on the accuracy of dose measurements, especially for lower photon energies, where the dosemeter can overrespond by a factor of 3-4. The purpose of this work was to characterise the response of Al(2)O(3):C using cavity theory and to evaluate the applicability of this approach for polyenergetic photon beams. The cavity theory energy response showed good agreement (within 2 %) with the corresponding measured values. A comparison with measured values reported in the literature for low-energy polyenergetic spectra showed more varied agreement (within 6 % on average). The discrepancy between these results is attributed to differences in the raw photon energy spectra used to calculate the energy response. Analysis of the impact of the photon energy spectra versus the mean photon energy showed improved accuracy if the energy response was determined using the entire photon spectrum rather than the mean photon energy. If not accounted for, the overresponse due to photon energy could introduce substantial inaccuracy in dose measurement using OSLDs, and the results of this study indicate that cavity theory may be used to determine the response with reasonable accuracy.

Optically stimulated luminescent dosimeters (OSLDs) are becoming increasingly popular for measuring an absorbed dose in clinical radiotherapy. OSLDs have known energy dependence, and this is accounted for by either calibrating the OSLD with a specific nominal energy, or using a standard energy correction factor to account for differences between the experimental beam photon energy and the photon energy used to establish the OSLD's sensitivity (e.g., (60)Co). This work is typically done under reference conditions (e.g., at d(max)). The impact of variations in photon spectra on the OSLD response is typically ignored for measurement positions that are different than the reference position. We determined that it is generally necessary to apply an additional non-reference energy correction factor to OSLD measurements made at locations that do not correspond to the reference position, particularly for OSLD measurements made out-of-field, where the photon spectra are softer. We determined this energy correction factor for a range of 6 MV photon spectra using two independent methods: Burlin cavity theory and measurements. The non-reference energy correction factor was found to range from 0.97 to 1.00 for in-field measurement locations and from 0.69 to 0.95 for out-of-field measurement locations. The use of a non-reference energy correction factor can improve the accuracy of OSLDs, especially when used out-of-field.

Purpose: Measurement of the absorbed dose from radiotherapy beams is an essential component of providing safe and reproducible treatment. For an energy-dependent dosimeter such as thermoluminescent dosimeters (TLDs), it is generally assumed that the energy spectrum is constant throughout the treatment field and is unperturbed by field size, depth, field modulation, or heterogeneities. However, this does not reflect reality and introduces error into clinical dose measurements. The purpose of this study was to evaluate the variability in the energy spectrum of a Varian 6 MV beam and to evaluate the impact of these variations in photon energy spectra on the response of a common energy-dependent dosimeter,TLD. Methods: Using Monte Carlo methods, we calculated variations in the photon energy spectra of a 6 MV beam as a result of variations of treatment parameters, including field size, measurement location, the presence of heterogeneities, and field modulation. The impact of these spectral variations on the response of the TLD is largely based on increased photoelectric effect in the dosimeter, and this impact was calculated using Burlin cavity theory. Measurements of the energy response were also made to determine the additional energy response due to all intrinsic and secondary effects. Results: For most in-field measurements, regardless of treatment parameter, the dosimeter response was not significantly affected by the spectral variations (

Mantle field irradiation has historically been the standard radiation treatment for Hodgkin lymphoma. It involves treating large regions of the chest and neck with high doses of radiation (up to 30 Gy). Previous epidemiological studies on the incidence of second malignancies following radiation therapy for Hodgkin lymphoma have revealed an increased incidence of second tumors in various organs, including lung, breast, thyroid and digestive tract. Multiple other studies, including the Surveillance, Epidemiology and End Results, indicated an increased incidence in digestive tract including stomach cancers following mantle field radiotherapy. Assessment of stomach dose is challenging because the stomach is outside the treatment field but very near the treatment border where there are steep dose gradients. In addition, the stomach can vary greatly in size and position. We sought to evaluate the dosimetric impact of the size and variable position of the stomach relative to the field border for a typical Hodgkin lymphoma mantle field irradiation. The mean stomach dose was measured using thermoluminescent dosimetry for nine variations in stomach size and position. The mean doses to the nine stomach variations ranged from 0.43 to 0.83 Gy when 30 Gy was delivered to the treatment isocenter. Statistical analyses indicated that there were no significant differences in the mean stomach dose when the stomach was symmetrically expanded up to 3 cm or shifted laterally (medial, anterior or posterior shifts) by up to 3 cm. There was, however, a significant (P > 0.01) difference in the mean dose when the stomach was shifted superiorly or inferiorly by ≥ 2.5 cm.

Hepatocellular carcinoma (HCC), the sixth most common cancer in the world, is a global health concern. Radiotherapy for HCC is uncommon, largely because of the likelihood of radiation-induced liver disease, an acute side effect that is often fatal. Proton beam therapy (PBT) and intensity-modulated radiation therapy (IMRT) may offer HCC patients a better option for treating the diseased liver tissue while largely sparing the surrounding tissues, especially the non-tumor liver. However, even advanced radiotherapies carry a risk of late effects, including second malignant neoplasms (SMNs). It is unclear whether PBT or IMRT confers less risk of an SMN than the other. The purpose of this study was to compare the predicted risk of developing an SMN for a patient with HCC between PBT and IMRT. For both treatments, radiation doses in organs and tissues from primary radiation were determined using a treatment planning system; doses in organs and tissues from stray radiation from PBT were determined using Monte Carlo simulations and from IMRT using thermo-luminescent dosimeter measurements. Risk models of SMN incidence were taken from the literature. The predicted absolute lifetime attributable risks of SMN incidence were 11.4% after PBT and 19.2% after IMRT. The results of this study suggest that using proton beams instead of photon beams for radiotherapy may reduce the risk of SMN incidence for some HCC patients.

An important but little examined aspect of radiation dosimetry studies involving organs outside the treatment field is how to assess dose to organs that are partially within a treatment field; this question is particularly important for studies intended to measure total absorbed dose in order to predict the risk of radiogenic late effects, such as second cancers. The purpose of this investigation was therefore to establish a method to categorize organs as in-field, out-of-field or partially in-field that would be applicable to both conventional and modern radiotherapy techniques. In this study, we defined guidelines to categorize the organs based on isodose inclusion criteria, developed methods to assess doses to partially in-field organs, and then tested the methods by applying them to a case of intensity-modulated radiotherapy for hepatocellular carcinoma based on actual patient data. For partially in-field organs, we recommend performing a sensitivity test to determine whether potential inaccuracies in low-dose regions of the DVH (from the treatment planning system) have a substantial effect on the mean organ dose, i.e. >5%. In such cases, we suggest supplementing calculated DVH data with measured dosimetric data using a volume-weighting technique to determine the mean dose.

Purpose: Optically stimulated luminescent dosimeters (OSLD) are becoming more popular for dose measurement in a clinical setting. The OSLD response is dependent on photon energy and that energy response is typically determined only for the photon spectrum at the reference dose calibration point (dmax on CAX for a 10cm×10cm field). Previous work has shown that variations exist in photon energy spectra as a result of measurement conditions and treatment parameters; however the effects of these energy variations on OSLD response have not been characterized. Method and Materials:Theoretical energy correction factors were calculated for a range of clinical conditions, including 6MV static and modulated (IMRT) fields, in‐field and out‐of‐field measurement positions, and in the presence of heterogeneous materials. These factors were calculated using previously determined photon energy spectra and Burlin cavity theory. Measured energy correction factors using OSLD nanoDots™ from Landauer, Inc. have also been determined under matching conditions, and the measured and calculated responses were compared. Results: When OSLD are used to measure dose for in‐field locations, the dosimeter response was as much as 5% different from the reference location due to perturbations in the spectra. The presence of heterogeneities at in‐field measurement locations did not significantly impact the OSLD response; however a substantial energy response occurred for the soft spectra that exist outside of the treatment field. At these measurement locations, OSLD may over‐respond by 20% or more, relative to the response at the dose calibration location. Conclusion: OSLD exhibit a non‐trivial energy response due to the increased effective atomic number. Variations in the photon energy spectra may impact the response of OSLD by as much as 20% and additional non‐reference energy correction factors may be necessary when measuring dose away from the dose calibration position. Work supported by PHS grant CA 10953 awarded by NCI, DHHS

Purpose: To test the sensitivity of the Eclipse anisotropic analytical algorithm (AAA) to expanded commissioning data that includes small‐field data and data corrected for detector size. Method and Materials: A 0.01 cm3ionization chamber was used to measure an extended commissioning data set for a 6 MV photon beam including open field profiles (OFP), percent depth dose (PDD), and output factors for field sizes ≥ 1×1 cm2. OFP were processed using mean‐value symmetry and adjusted for detector size effects. OFP were smoothed outside the penumbra region for noise reduction. PDD data were shifted to account for the effective point of measurement and then smoothed. Four unique beam models were commissioned to evaluate the impact of correcting the measured data for detector size as well as small‐field data inclusion. We compared the resulting AAA calculated models with the model based on Golden Beam Data (GBD) provided by Varian Medical Systems. Models were compared using a 1 mm calculation grid. Results: The various models proved to be insensitive to adjustments for detector size effects and also to the inclusion of small‐field data. All models, regardless of the penumbra of input profiles, exhibited nearly identical penumbra in the final calculated model. The algorithm narrowed the penumbra for the model commissioned with GBD i.e. with broad penumbra. Conversely, the algorithm broadened the penumbra for the model commissioned with measured data that were smoothed and corrected for volume averaging effects i.e. data with narrow penumbra. Conclusion: Results suggest that the TPS utilizes a generic model for the penumbra region in calculated models, thus ignoring measured data. The negligible impact of inclusion of small‐field data on the TPS's calculated model may be due to the large relative size of the penumbra region for those fields.

Purpose: Validation of dose calculation accuracy is essential for new radiotherapy techniques, such as volumetric modulated arc therapy (VMAT). The purpose of this project was to compare a VMAT system, Varian RapidArc, to the current standard of care, IMRT, using Radiological Physics Center (RPC) phantoms in terms of both treatment plan quality and dosimetricdelivery accuracy. Method and Materials:Treatment plans and dosedelivery accuracy were evaluated following procedures defined by the RPC for credentialing institutions for Radiation TherapyOncology Group (RTOG) clinical trials. Clinically relevant treatment plans were created for RPC prostate and head and neck phantoms from typical prescription and dose constraints for 6 MV IMRT and RapidArc. The treatment plans for head and neck radiotherapy were compared to determine if they were clinically comparable using several dosimetric criteria, including ability to meet dose objectives set by the RPC and conformity and homogeneity indices. The planned treatments were delivered to the phantoms and absolute doses and relative dose distributions were measured with thermoluminescent dosimeters and radiochromic film, respectively. The measured and calculated doses of each treatment plan were compared to determine if they were clinically acceptable based upon dose differences and distance‐to‐agreement. Results: All treatment plans were able to meet the dosimetric objectives set by the RPC for treatment volume dose coverage and critical structure dose constraints for both the prostate and head and neck phantoms. The IMRT and RapidArc plans for the head and neck phantom had similar conformity and homogeneity. The RapidArc plan for the prostate phantom met the RPC delivery accuracy requirements. Preliminary results for the head and neck phantom indicated that the IMRT and RapidArc plans were delivered with similar accuracy. Conclusion: Varian RapidArc is comparable to IMRT in treatment plan quality and the dose calculation accuracy is clinically acceptable.

Purpose: The purpose of this work was to quantify the discrepancy between the out‐of‐field doses as reported by a treatment planning system (TPS) to the actual measured doses.Method and Materials: Out‐of‐field doses were determined at the same location in phantom for a range of distances from the field edge using the treatment planning system (TPS) and thermoluminescent dosimeters(TLD). A typical radiation plan for Hodgkin lymphoma was created using Eclipse TPS (Varian Medical Systems, Palo Alto, CA) for an anthropomorphic male dosimetry phantom. TLD capsules were placed in the phantom at distances ranging from 1.25 cm to 18.75 cm inferior to the field edge. The phantom was irradiated with the full treatment plan dose.TLDs were read using an established laboratory protocol with an error of ⩽3%. For comparison, the out‐of‐field doses at the same positions were determined in the TPS using the point dose measurement tool. Results: As expected, the doses from both the TLD and TPS decrease exponentially as a function of distance from the field edge. Close to the field edge (within 1.25 cm), the TPS overestimated the actual dose by approximately 13%. At larger distances from the field edge the TPS underestimated dose with the magnitude of the underestimation increasing with increasing distance from the field edge. At a distance of 11.25 cm from the field edge, the TPS underestimated the dose by 53%. The TPS reported no dose at distances greater than 12 cm from the field edge. Conclusion: Studies requiring doses to organs out of the treatment field should not rely on the treatment planning system. Measurements using anthropomorphic phantoms or mathematical calculation models that are benchmarked for out‐of‐field doses should be used to determine doses to peripheral organs and tissues.

Purpose: Accurate dosimetry calculations are an important component of epidemiological studies of radiation induced late effects. It is impossible to perform individual dosimetry calculations for thousands of patients. Thus, patients are grouped using several criteria, and dose is calculated for a representative individual from each group. Within groups, the organs are assumed to be in the same location; however, this is complicated when the position of the organ of interest is known to vary between patients, as is the case for the stomach. The purpose of this work was to determine the impact of the size and position of the stomach on the mean organdose when the stomach is completely outside of the treatment field. This work focused on the dose received from a typical mantle field for Hodgkin lymphoma. Method and Materials: A treatment plan was created for an anthropomorphic male dosimetry phantom. Contouring tools in the treatment planning system were used to create five additional stomachs by modifying the size and position of the original stomach contour. The phantom was loaded with 550 thermoluminescent dosimeters(TLD) to encompass the six different stomachs. The phantom was irradiated with the treatment plan and the dosimeters were read using an established laboratory protocol. The mean dose to each of the six stomachs was determined using the appropriate TLD data points. An Analysis of Variance (ANOVA) was performed to determine whether the mean doses to each of the six samples were statistically different. Results: The mean out‐of‐field dose was determined for six common variations of the stomach. The ANOVA indicated that the means of the six stomachs were not statistically different. Conclusion: This study indicates that variations in organ position and size do not statistically change the mean organdose for out‐ of‐field organs.