Optically Stimulated Luminescence Detectors Research Articles

Assessment of fluence- and dose-averaged linear energy transfer with passive luminescence detectors in clinical proton beams

Objective. This work investigates the use of passive luminescence detectors to determine different types of averaged linear energy transfer ( LET― ) for the energies relevant to proton therapy. The experimental results are compared to reference values obtained from Monte Carlo simulations. Approach. Optically stimulated luminescence detectors (OSLDs), fluorescent nuclear track detectors (FNTDs), and two different groups of thermoluminescence detectors (TLDs) were irradiated at four different radiation qualities. For each irradiation, the fluence- ( LET―f ) and dose-averaged LET ( LET―d ) were determined. For both quantities, two sub-types of averages were calculated, either considering the contributions from primary and secondary protons or from all protons and heavier, charged particles. Both simulated and experimental data were used in combination with a phenomenological model to estimate the relative biological effectiveness (RBE). Main results. All types of LET― could be assessed with the luminescence detectors. The experimental determination of LET―f is in agreement with reference data obtained from simulations across all measurement techniques and types of averaging. On the other hand, LET―d can present challenges as a radiation quality metric to describe the detector response in mixed particle fields. However, excluding secondaries heavier than protons from the LET―d calculation, as their contribution to the luminescence is suppressed by ionization quenching, leads to equal accuracy between LET―f and LET―d . Assessment of RBE through the experimentally determined LET―d values agrees with independently acquired reference values, indicating that the investigated detectors can determine LET― with sufficient accuracy for proton therapy. Significance. OSLDs, TLDs, and FNTDs can be used to determine LET― and RBE in proton therapy. With the capability to determine dose through ionization quenching corrections derived from LET― , OSLDs and TLDs can simultaneously ascertain dose, LET― , and RBE. This makes passive detectors appealing for measurements in phantoms to facilitate validation of clinical treatment plans or experiments related to proton therapy.

Optically stimulated luminescence dosimeters for simultaneous measurement of point dose and dose-weighted LET in an adaptive proton therapy workflow.

To demonstrate the suitability of optically stimulated luminescence detectors (OSLDs) for accurate simultaneous measurement of the absolute point dose and dose-weighted linear energy transfer (LETD) in an anthropomorphic phantom for experimental validation of daily adaptive proton therapy. A clinically realistic intensity-modulated proton therapy (IMPT) treatment plan was created based on a CT of an anthropomorphic head-and-neck phantom made of tissue-equivalent material. The IMPT plan was optimized with three fields to deliver a uniform dose to the target volume covering the OSLDs. Different scenarios representing inter-fractional anatomical changes were created by modifying the phantom. An online adaptive proton therapy workflow was used to recover the daily dose distribution and account for the applied geometry changes. To validate the adaptive workflow, measurements were performed by irradiating Al2O3:C OSLDs inside the phantom. In addition to the measurements, retrospective Monte Carlo simulations were performed to compare the absolute dose and dose-averaged LET (LETD) delivered to the OSLDs. The online adaptive proton therapy workflow was shown to recover significant degradation in dose conformity resulting from large anatomical and positioning deviations from the reference plan. The Monte Carlo simulations were in close agreement with the OSLD measurements, with an average relative error of 1.4% for doses and 3.2% for LETD. The use of OSLDs for LET determination allowed for a correction for the ionization quenched response. The OSLDs appear to be an excellent detector for simultaneously assessing dose and LET distributions in proton irradiation of an anthropomorphic phantom. The OSLDs can be cut to almost any size and shape, making them ideal for in-phantom measurements to probe the radiation quality and dose in a predefined region of interest. Although we have presented the results obtained in the experimental validation of an adaptive proton therapy workflow, the same approach can be generalized and used for a variety of clinical innovations and workflow developments that require accurate assessment of point dose and/or average LET.

Experimental and Monte Carlo study of energy response of BEO-based OSL detectors within photon energy range up to 15 MeV.

Response of personal dosemeters to high energy photon radiation is of great interest nowadays due to a spread of new radiation technologies and the expansion of occupational exposure domains. ICRU95 publication has expanded the range of relevant photon energies upwards, setting new horizons for individual monitoring. Beryllium oxide (BeO) material is increasingly popular due to its excellent optically stimulated luminescence (OSL) properties, simple readout and reasonable energy response in the low energy (below 100keV) range. The study considers energy dependence of OSL response at higher photon energies. Energy deposition of monoenergetic photons with energy up to 15MeV in the BeO chips of various thickness was modeled with Monte Carlo MCNP 6.2 code. Benchmark experiments were conducted at LINAC with high voltage of 6, 10 and 15 MV resulting in respective incident photon spectra. The findings of this study add knowledge regarding behavior of BeO personal dosemeters in the photon fields within the energy range above 3MeV.

Optically stimulated luminescence detectors for dosimetry and LET measurements in light ion beams

Objective. This work investigates the use of Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) detectors to determine both the dose and the radiation quality in light ion beams. The radiation quality is here expressed through either the linear energy transfer (LET) or the closely related metric Q eff, which depends on the particle’s speed and effective charge. The derived LET and Q eff values are applied to improve the dosimetry in light ion beams. Approach. OSL detectors were irradiated in mono-energetic 1H-, 4He-, 12C-, and 16O-ion beams. The OSL signal is associated with two emission bands that were separated using a pulsed stimulation technique and subjected to automatic corrections based on reference irradiations. Each emission band was investigated independently for dosimetry, and the ratio of the two emission intensities was parameterized as a function of fluence- and dose-averaged LET, as well as Q eff. The determined radiation quality was subsequently applied to correct the dose for ionization quenching. Main results. For both materials, the Q eff determinations in 1H- and 4He-ion beams are within 5 % of the Monte Carlo simulated values. Using the determined radiation quality metrics to correct the nonlinear (ionization quenched) detector response leads to doses within 2 % of the reference doses. Significance. Al2O3:C and Al2O3:C,Mg OSL detectors are applicable for dosimetry and radiation quality estimations in 1H- and 4He-ions. Only Al2O3:C,Mg shows promising results for dosimetry in 12C-ions. Across both materials and the investigated ions, the estimated Q eff values were less sensitive to the ion types than the estimated LET values were. The reduced uncertainties suggest new possibilities for simultaneously estimating the physical and biological dose in particle therapy with OSL detectors.

Investigation of TL and OSL detectors in ultra-high dose rate electron beams

Objective. This work aims at investigating the response of various thermally stimulated luminescence detectors (TLDs) and optically stimulated luminescence detectors (OSLDs) for dosimetry of ultra-high dose rate electron beams. The study was driven by the challenges of dosimetry at ultra-high dose rates and the importance of dosimetry for FLASH radiotherapy and radiobiology experiments. Approach. Three types of TLDs (LiF:Mg,Ti; LiF:Mg,Cu,P; CaF2:Tm) and one type of OSLD (Al2O3:C) were irradiated in a 15 MeV electron beam with instantaneous dose rates in the (1–324) kGy s−1 range. Reference dosimetry was carried out with an integrating current transformer, which was calibrated in absorbed dose to water against a reference ionization chamber. Additionally, dose rate independent BeO OSLDs were employed as a reference. Beam non-uniformity was addressed using a matrix of TLDs/OSLDs. Main results. The investigated TLDs were shown to be dose rate independent within the experimental uncertainties, which take into account the uncertainty of the dosimetry protocol and the irradiation uncertainty. The relative deviation between the TLDs and the reference dose was lower than 4 % for all dose rates. A decreasing response with the dose rate was observed for Al2O3:C OSLDs, but still within 10 % from the reference dose. Significance. The precision of the investigated luminescence detectors make them suitable for dosimetry of ultra-high dose rate electron beams. Specifically, the dose rate independence of the TLDs can support the investigation of the beam uniformity as a function of the dose rate, which is one of the challenges of the employed beam. Al2O3:C OSLDs provided high precision measurements, but the decreasing response with the dose rate needs to be confirmed by additional experiments.

The role of capping agents on the trapping levels structure and luminescent emission of SrMoO4 phosphors

In the present work, we investigate the thermoluminescence (TL) and optically stimulated luminescence (OSL) from strontium molybdate SrMoO4 powders designed with different capping agents. The samples were prepared through co-precipitation and processed in a Microwave-Assisted Hydrothermal (MAH) system. The structural, optical, and morphological characteristics were investigated using Raman, Fourier transform infrared spectroscopy (FTIR), DRX, ultraviolet-visible (UV–vis) absorption, and Scanning electron microscopy (SEM). The TL glow curves recorded from as-prepared and irradiated samples with beta particles reveal that their intensity and profile depend on the used capping agent. The trapping depth energy, determined from the TL glows curves, ranges from 1.02 to 2.23 eV for the as-prepared samples and from 0.9 to 2.33 eV for the irradiated phosphors. The residual TL spectra, registered from successive readouts, reveal that the thermal treatment shifts the glow curve to lower temperatures suggesting the formation of shallower trap states. The results reveal that the OSL signal and its behaviors with the radiation dose depending on the employed capping agent. The results show the TL and OSL signal's dependence on the structural properties and support the potential application of SrMoO4 powders as an OSL detector.

Clinical Application of a Customized 3D-Printed Bolus in Radiation Therapy for Distal Extremities

In radiation therapy (RT) for skin cancer, tissue-equivalent substances called boluses are widely used to ensure the delivery of an adequate dose to the skin surface and to provide a radioprotective effect for normal tissue. The aim of this study was to develop a new type of three-dimensional (3D) bolus for RT involving body parts with irregular geometries and to evaluate its clinical feasibility. Two 3D-printed boluses were designed for two patients with squamous cell carcinoma (SCC) of their distal extremities based on computed tomography (CT) images and printed with polylactic acid (PLA). The clinical feasibility of the boluses was evaluated by measuring the in vivo skin dose at the tumor site with optically stimulated luminescence detectors (OSLDs) and comparing the results with the prescribed and calculated doses from the Eclipse treatment planning system (TPS). The average measured dose distribution for the two patients was 94.75% of the prescribed dose and 98.8% of the calculated dose. In addition, the average measured dose during repeated treatments was 189.5 ± 3.7 cGy, thus demonstrating the excellent reproducibility of the proposed approach. Overall, the customized 3D-printed boluses for the RT of distal extremities accurately delivered doses to skin tumors with improved reproducibility.

Development of a single sphere neutron spectrometer using α-Al2O3:C based optically stimulated luminescence detectors

A multi-shell single sphere moderating assembly has been designed and developed to measure the neutron spectra in which the optically stimulated luminescence (OSL) detector pairs (Al2O3:C + 6, 7LiF) were used. The response matrix of OSL detectors, covering 11 energy decades (from thermal to 100 MeV neutrons) at different depths of the sphere, was generated using FLUKA-Monte Carlo simulation. The testing and validation of the spectrometer was performed using 3 standard neutron sources, viz. 241AmBe, 252Cf and DT. Neutron spectra were generated using 2 different unfolding codes. The design of the moderating assembly has the flexibility of selecting the desired sphere size as per the end point energy of the neutron spectrum. This can be conveniently employed in the complex radiation environment around particle accelerators, where the time and the space for irradiations have limitations. The details of the spectrometer design, response matrix generation and unfolding results are presented here.

Fetal dose estimation for Virtual Tangential-fields Arc Therapy whole breast irradiation by optically stimulated luminescence dosimeters

Breast cancer is the most frequently diagnosed tumor in pregnant women and radiation therapy should carefully be weighted up because of the dose to the fetus. The aim of this study was to investigate fetal dose in a patient treated with Virtual Tangential-fields Arc Therapy (ViTAT), an innovative technique for whole breast irradiation. Optically stimulated luminescence detectors (OSLDs) were calibrated on a Varian TrueBeam linac, with both a 6X and 6XFFF beam quality, and used for out-of-field measurements. Fetal dose related with ViTAT technique was compared to the standard 3D conformal radiation therapy technique (3DCRT). The fetal dose delivered with a ViTAT technique planned with 6XFFF beam was also investigated. Measurements were taken on a phantom composed of Rando Alderson Phantom slices and solid water slabs. OSLDs were placed in a region identified by the height of the fundus from conception to the twentieth week using a custom made PMMA grid. Due to the higher number of monitor units, the peripheral dose of ViTAT delivered with 6X beams is higher than that of 3DCRT. However, nanoDots measurements prove that ViTAT can be used in place of 3DCRT while maintaining similar fetal dose levels if 6XFFF beams are used.

Improved simultaneous LET and dose measurements in proton therapy

The objective of this study was to improve the precision of linear energy transfer (LET) measurements using text {Al}_2text {O}_3text {:C} optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4–6.5) hbox {keV}, upmu hbox {m}^{-1} range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV (F^+-center) emission bands of text {Al}_2text {O}_3text {:C} and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

P61 - Metal oxide field effect transistors (MOSFETs) versus optically stimulated luminescence detectors (OSLDs) technology in total body irradiation

P61 - Metal oxide field effect transistors (MOSFETs) versus optically stimulated luminescence detectors (OSLDs) technology in total body irradiation

A customizable aluminum compensator system for total body irradiation.

PurposeTo develop a simplified aluminum compensator system for total body irradiation (TBI) that is easy to assemble and modify in a short period of time for customized patient treatments.MethodsThe compensator is composed of a combination of 0.3 cm thick aluminum bars, two aluminum T‐tracks, spacers, and metal bolts. The system is mounted onto a plexiglass block tray. The design consists of 11 fixed sectors spanning from the patient's head to feet. The outermost sectors utilize 7.6 cm wide aluminum bars, while the remaining sectors use 2.5 cm wide aluminum bars. There is a magnification factor of 5 from the compensator to the patient treatment plane. Each bar of aluminum is interconnected at each adjacent sector with a tongue and groove arrangement and fastened to the T‐track using a metal washer, bolt, and nut. Inter‐bar leakage of the compensator was tested using a water tank and diode. End‐to‐end measurements were performed with an ion chamber in a solid water phantom and also with a RANDO phantom using internal and external optically stimulated luminescent detectors (OSLDs). In‐vivo patient measurements from the first 20 patients treated with this aluminum compensator were compared to those from 20 patients treated with our previously used lead compensator system.ResultsThe compensator assembly time was reduced to 20–30 min compared to the 2–4 h it would take with the previous lead design. All end‐to‐end measurements were within 10% of that expected. The median absolute in‐vivo error for the aluminum compensator was 3.7%, with 93.8% of measurements being within 10% of that expected. The median error for the lead compensator system was 5.3%, with 85.1% being within 10% of that expected.ConclusionThis design has become the standard compensator at our clinic. It allows for quick assembly and customization along with meeting the Task Group 29 recommendations for dose uniformity.

Al2O3:C optically stimulated luminescence dosimeters (OSLDs) for ultra-high dose rate proton dosimetry

The response of Al2O3:C optically stimulated luminescence detectors (OSLDs) was investigated in a 250 MeV pencil proton beam. The OSLD response was mapped for a wide range of average dose rates up to 9000 Gy s−1, corresponding to a ∼150 kGy s−1 instantaneous dose rate in each pulse. Two setups for ultra-high dose rate (FLASH) experiments are presented, which enable OSLDs or biological samples to be irradiated in either water-filled vials or cylinders. The OSLDs were found to be dose rate independent for all dose rates, with an average deviation <1% relative to the nominal dose for average dose rates of (1–1000) Gy s−1 when irradiated in the two setups. A third setup for irradiations in a 9000 Gy s−1 pencil beam is presented, where OSLDs are distributed in a 3 × 4 grid. Calculations of the signal averaging of the beam over the OSLDs were in agreement with the measured response at 9000 Gy s−1. Furthermore, a new method was presented to extract the beam spot size of narrow pencil beams, which is in agreement within a standard deviation with results derived from radiochromic films. The Al2O3:C OSLDs were found applicable to support radiobiological experiments in proton beams at ultra-high dose rates.

Characterization of optically-stimulated luminescence properties by NaCl:Eu2+ crystal and the thermal response

In this paper, we report optically-stimulated luminescence (OSL) properties of Eu2+-doped NaCl single crystal as a candidate phosphor for use in near real-time radiation measurement and dosimetry. The crystal was grown by the vertical Bridgman–Stockbarger method. The obtained crystal shows a strong photoluminescence (PL) band peaking at 430 nm due to the parity-allowed 5d-4f transitions of Eu2+. After irradiating with X-rays, it demonstrates OSL also at 430 nm due to the Eu2+ ion acting as an emission center while stimulating by light (500 ± 30 nm). Compared with a commercial BaFBr:Eu2+ OSL detector, the sensitivity to X-ray dose is lower by about one order of magnitude. In addition, while the crystal is reused multiple times, the OSL response signal increases despite the same given radiation dose. The OSL decay curve can be decomposed into three exponential decay functions with the lifetimes of 0.6, 6.4, and 120.5 s, and the decomposition analyses revealed that only the intensity of intermediate component increases with the number of reused cycles. Further analyses with thermally-stimulated luminescence (TSL) revealed that the intermediate OSL component is related to a TSL glow signal originated from trapping centers having the activation energies of ~0.93 eV and ~1.27 eV and the frequency factors of ~7.52 × 108 s−1 and ~6.29 × 1011 s−1, respectively.

Synthesis, RL and OSL characterization of thulium doped NaMgF3 neighborite

The aim of this work is to study the dosimetric properties of tissue-equivalent thulium doped NaMgF3 neighborites and to determine their possible application as dosimeters in personal dosimetry. In this aspect, radioluminescence (RL) and optically stimulated luminescence (OSL) dosimetric properties of undoped and Tm3+ -doped NaMgF3 have been investigated for the first time. Samples were synthesized by solid state reaction and by considering a stoichiometric mixture of pure NaF and MgF2 reagents. Two emission peaks centered at 460 and 360 nm have been found in the RL emission spectrum of the doped samples, which can be ascribed to the 1D2 – 3F4 and 1D2 – 3H6 transitions of Tm3+ cations, respectively. Maximum OSL emission under blue light stimulation has been found for samples doped with 0.2 mol % of thulium. Furthermore, the OSL signal of this compound depends linearly on dose within the range 0.05–100 Gy. Besides, its OSL signal features satisfactory repeatability and a minimum detectable dose of 0.04 Gy. Finally, it has been found a low fading of the OSL signal of approximately 13% after the first 60 h, after which the OSL response remains constant. The obtained results suggest the feasibility of using this compound as an OSL detector in personal dosimetry.

Microwave-Assisted Growth of Silver Nanoparticle Films with Tunable Plasmon Properties and Asymmetrical Particle Geometry for Applications as Radiation Sensors

We report a simple and fast microwave-assisted method to grow silver nanoparticle films with tunable plasmon resonance band. Microwaving time controls nucleation and growth as well as particle agglomeration, cluster formation, particle morphology, and the plasmonic properties. Films produced with times shorter than 30 s presented a single well-defined plasmon resonance band (~ 400 nm), whereas films produced with times longer than 40 s presented higher wavelength resonances modes (> 500 nm). Plasmon band position and intensity can be easily tuned by controlling microwaving time and power. SEM and AFM images suggested the growth of asymmetrical silver nanoparticles. Simulated extinction spectra considering particles as spheres, hemispheres, and spherical caps were performed. The films were employed to enhance the sensitivity of ionizing radiation detectors assessed by optically stimulated luminescence (OSL) via plasmon-enhanced luminescence. By tuning the plasmon resonance band to overlap with the OSL stimulation (530 nm), luminescence enhancements of greater than 100-fold were obtained, demonstrating the importance of tuning the plasmon resonance band to maximize the OSL intensity and detector sensitivity. This versatile method to produce silver nanoparticle films with tunable plasmonic properties is a promising platform for developing small-sized radiation detectors and advanced sensing technologies.

Technical Note: A novel dosimeter improves total skin electron therapy surface dosimetry workflow.

PurposeThe novel scintillator‐based system described in this study is capable of accurately and remotely measuring surface dose during Total Skin Electron Therapy (TSET); this dosimeter does not require post‐exposure processing or annealing and has been shown to be re‐usable, resistant to radiation damage, have minimal impact on surface dose, and reduce chances of operator error compared to existing technologies e.g. optically stimulated luminescence detector (OSLD). The purpose of this study was to quantitatively analyze the workflow required to measure surface dose using this new scintillator dosimeter and compare it to that of standard OSLDs.MethodsDisc‐shaped scintillators were attached to a flat‐faced phantom and a patient undergoing TSET. Light emission from these plastic discs was captured using a time‐gated, intensified, camera during irradiation and converted to dose using an external calibration factor. Time required to complete each step (daily QA, dosimeter preparation, attachment, removal, registration, and readout) of the scintillator and OSLD surface dosimetry workflows was tracked.ResultsIn phantoms, scintillators and OSLDs surface doses agreed within 3% for all data points. During patient imaging it was found that surface dose measured by OSLD and scintillator agreed within 5% and 3% for 35/35 and 32/35 dosimetry sites, respectively. The end‐to‐end time required to measure surface dose during phantom experiments for a single dosimeter was 78 and 202 sec for scintillator and OSL dosimeters, respectively. During patient treatment, surface dose was assessed at 7 different body locations by scintillator and OSL dosimeters in 386 and 754 sec, respectively.ConclusionScintillators have been shown to report dose nearly twice as fast as OSLDs with substantially less manual work and reduced chances of human error. Scintillator dose measurements are automatically saved to an electronic patient file and images contain a permanent record of the dose delivered during treatment.

Relative dosimetry measurements in kilovoltage X-rays with OSLDs

Dosimetry for kilovoltage X-ray units requires a careful choice of equipment due a typically high energy dependence of standard detectors. The use of optically stimulated luminescence detectors (OSLDs) for in-vivo dosimetry and the measurement of relative output factors is investigated in this study. Supralinearity and the suitability of OSLDs for relative dose measurements are determined for the Landauer nanoDot OSLD system (Landauer, Inc., Greenwood, IL). OSLDs were found to exhibit supralinearity for therapeutic doses in kV X-rays, with the effect more pronounced in lower energy beams. Relative lead cutout factors measured with OSLDs were well within 5% of published values. OSLD measurements of applicator factors at the surface of a water phantom showed a systematic offset (> + 5%) to derived values and values measured with a PTW 23342 soft X-ray ionisation chamber (PTW, Freiburg, Germany), due to the change in source-to-skin distance (SSD) between the applicators used in this study. OSLDs are suitable for relative dosimetry in kilovoltage beams between 80 and 120 kVp when the SSD similar to the calibration/reference conditions.

Performance and Dosimetry of Total Body Irradiation Patients Using In Vivo Lung Dose Monitoring and Custom Lung Block Adaptation

Total body irradiation (TBI) prior to bone marrow transplant has been used for decades, but the details of delivery are institution dependent. We set out to establish decision support metrics by looking at respiratory outcomes based on measured lung dose. We hypothesize that individualized lung dose measurements and lung block adaptation may correlate with patient respiratory outcomes. This is a single institution retrospective study of 56 patients who received TBI from 2016-2018. Each patient received 1200 cGy (6 fractions; 200 cGy BID) with 3 optically stimulated luminescence detectors (OSLDs) placed on their body surface at the umbilicus, and left and right lungs. Lung dose was maintained between 700-900cGy by custom lung blocks. Supplemental oxygen requirements and clinical lung complications (shortness of breath (SOB) or cough requiring pharmacological intervention) were reviewed for the hospitalization period. Clinical respiratory complications (chronic cough, adventitious sounds on lung exam, new or worsening SOB) were also reviewed 120 days from irradiation. Median lung doses and patient anterior-posterior diameter (APD) at the umbilicus were compared for patients with and without respiratory complications using a Mann-Whitney U test. Forty-nine patients (age 40 years ± 12y; mean±SD) had lung dose data available for analysis. APD was positively correlated with OSLD umbilical dose (r=0.58, p<0.0001) confirming that larger patients received higher amounts of radiation than predicted during planning. The APD range did not correlate with OSLD lung doses. During hospitalization, patients who required any supplemental oxygen (N=7) or had clinically documented lung complications (N=8) did not have statistically different APD or lung doses compared to patients without respiratory complications. In the 120 day period following TBI, 8 patients had documented respiratory sequelae. Patients with reported respiratory complications in this period had larger APD than patients with no respiratory complications (median APD 31.5 vs 26.6, p=0.01), although this may reflect the effect of comorbidities (e.g., BMI) rather than the effect of radiation. Of the 27 patients with 1 year follow up data, only 2 had respiratory sequelae of chronic cough with corresponding inflammation on chest CT. Our overall rate of any respiratory complications using this technique was 22% (11/49) during hospitalization and 17% (8/48) at 120 days of TBI. The individualized planning technique described here achieved relatively uniform lung doses with no fatal lung complications in all 49 patients considered. Respiratory complications were minor, with the most significant intervention requiring high flow nasal cannula during the immediate hospitalization period.

Scintillator Target Imaging: A Novel Surface Dosimetry Method

The hypothesis of this work was that remote imaging of surface dose from small scintillators would be possible, suitable for clinical needs in soft tissue radiotherapy, and would minimize workflow of on-patient dosimetry due to automation of data analysis. An intensified, time-gated, camera synchronized to linear accelerator (linac) pulses was used to capture scintillation light from plastic discs directly attached to the skin surface of patients and phantoms undergoing whole breast (WB), head-neck (HN), and total skin electron (TSE) treatment. Scintillators were painted with reflective paint on the rear face and edges, coated with a protective film, and an adhesive strip was attached to the rear face. Optically stimulated luminescence detectors (OSLDs) were placed adjacent to the scintillators to provide reference surface dose measurements during all imaging. Two types of imaging apparatus were evaluated in this study: 1) a camera sensitive to both Cherenkov and scintillation emission, and 2) a camera with improved sensitivity to scintillation. Both of the scintillator dosimeter imaging systems were able to determine surface dose with <3% error compared to OSLDs during TSE, HN, and WB therapy. Furthermore, analysis of a human pilot study involving 242 instances of surface dose measured by scintillator and OSLD were linearly correlated with an R2 = 0.95. The 2nd version of the imaging system, tuned to maximize sensitivity to scintillation emission, was able to enhance scintillation intensity detection by 7x and suppress Cherenkov detection by 25x. Scintillator dosimeters were able to accurately track cumulative surface dose at a given anatomical site over the course of a full cycle of TSET. In the context of HN treatment, feasibility testing has shown that scintillation emission can be imaged through an optically-clear bolus and gaps of an immobilization mask. Application of a protective clear coating and adhesive backing had no significant effect on scintillator light output, allows for easy application of the dosimeter to the skin surface, and enables dosimeter re-use by standard clinical cleaning methods. Imaging scintillator dosimeters has been shown to be a viable method to obtain surface dose measurements in clinical radiotherapy. Improvements to the spectral sensitivity of the camera system permit reduction in dosimeter size and geometry for potential use in smaller-field treatment or for improved signal to noise. Since this technique requires simplified attachment, features a streamlined readout process, and automatically saves data to an electronic record – with capture of the anatomical position of dosimeter placement on the patient – error and time related to dosimeter readout and dose recording is minimized.