Measured Skin Dose Research Articles

Characterization of GafChromic EBT2 film dose measurements using a tissue-equivalent water phantom for a Theratron® Equinox Cobalt-60 teletherapy machine.

In vivo dosimetry is a quality assurance tool that provides post-treatment measurement of the absorbed dose as delivered to the patient. This dosimetry compares the prescribed and measured dose delivered to the target volume. In this study, a tissue-equivalent water phantom provided the simulation of the human environment. The skin and entrance doses were measured using GafChromic EBT2 film for a Theratron® Equinox Cobalt-60 teletherapy machine. We examined the behaviors of unencapsulated films and custom-made film encapsulation. Films were cut to 1 cm × 1 cm, calibrated, and used to assess skin dose depositions and entrance dose. We examined the response of the film for variations in field size, source to skin distance (SSD), gantry angle and wedge angle. The estimated uncertainty in EBT2 film for absorbed dose measurement in phantom was ±1.72%. Comparison of the measurements of the two film configurations for the various irradiation parameters were field size (p = 0.0193, α = 0.05, n = 11), gantry angle (p = 0.0018, α = 0.05, n = 24), SSD (p = 0.1802, α = 0.05, n = 11) and wedge angle (p = 0.6834, α = 0.05, n = 4). For a prescribed dose of 200 cGy and at reference conditions (open field 10 cm x 10 cm, SSD = 100 cm, and gantry angle = 0º), the measured skin dose using the encapsulation material was 70% while that measured with the unencapsulated film was 24%. At reference irradiation conditions, the measured skin dose using the unencapsulated film was higher for open field configurations (24%) than wedged field configurations (19%). Estimation of the entrance dose using the unencapsulated film was within 3% of the prescribed dose. GafChromic EBT2 film measurements were significantly affected at larger field sizes and gantry angles. Furthermore, we determined a high accuracy in entrance dose estimations using the film.

Comparison of Prospectively Generated Glioma Treatment Plans Clinically Delivered on Magnetic Resonance Imaging (MRI)-Linear Accelerator (MR-Linac) Versus Conventional Linac: Predicted and Measured Skin Dose.

Introduction: Magnetic resonance imaging-linear accelerator radiotherapy is an innovative technology that requires special consideration for secondary electron interactions within the magnetic field, which can alter dose deposition at air–tissue interfaces. As part of ongoing quality assurance and quality improvement of new radiotherapy technologies, the purpose of this study was to evaluate skin dose modelled from the treatment planning systems of a magnetic resonance imaging-linear accelerator and a conventional linear accelerator, and then correlate with in vivo measurements of delivered skin dose from each linear accelerator. Methods: In this prospective cohort study, 37 consecutive glioma patients had treatment planning completed and approved prior to radiotherapy initiation using commercial treatment planning systems: a Monte Carlo-based algorithm for magnetic resonance imaging-linear accelerator or a convolution-based algorithm for conventional linear accelerator. In vivo skin dose was measured using an optically stimulated luminescent dosimeter. Results: Monte Carlo-based magnetic resonance imaging-linear accelerator plans and convolution-based conventional linear accelerator plans had similar dosimetric parameters for target volumes and organs-at-risk. However, magnetic resonance imaging-linear accelerator plans had 1.52 Gy higher mean dose to air cavities (P < .0001) and 1.10 Gy higher mean dose to skin (P < .0001). In vivo skin dose was 14.5% greater for magnetic resonance imaging-linear accelerator treatments (P = .0027), and was more accurately predicted by Monte Carlo-based calculation (ρ = 0.95, P < .0001) versus convolution-based (ρ = 0.80, P = .0096). Conclusion: This is the first prospective dosimetric comparison of glioma patients clinically treated on both magnetic resonance imaging-linear accelerator and conventional linear accelerator. Our findings suggest that skin doses were significantly greater with magnetic resonance imaging-linear accelerator plans but correlated better with in vivo measurements of actual skin dose from delivered treatments. Future magnetic resonance imaging-linear accelerator planning processes are being designed to account for skin dosimetry and treatment delivery.

The efficiency of lead and non-lead shielding on breast dose in head CT

The aim of the study was to assess the effect of the shielding material and its thickness on the measured skin dose to the breasts during the CT examination of the head. The helical and axial head CT was performed on an anthropomorphic phantom (PBU 60). Two types of shielding were tested—lead and non-lead (antimony-bismuth) shielding. Measurements with different thicknesses were performed and the shielding efficiency of the materials was compared. Skin dose to the breasts was measured with an educational direct dosimeter (EDD-30). The shielding efficiency during both scanning protocols indicated an increased dose reduction with the thicker equivalent thickness in both shielding materials. Dose reduction was the highest at 0.5 mm equivalent thickness for both materials; lead shielding reduced the dose by 91% and 83%, the antimony-bismuth shielding by 90% and 86%, during the axial and helical head CT protocols, respectively. Statistically significant differences were found between the materials of the same equivalent thickness (0.175, 0.25 and 0.5 mm) during the helical protocol in favor of the antimony-bismuth shielding. During the axial protocol there were no statistically significant differences. Shielding of radiosensitive organs can prevent unnecessary exposure of radiosensitive organs outside the primary beam. Due to the significant decrease in radiation dose to the breasts, and many other positive attributes, use of the antimony-bismuth shielding instead of the lead shielding should be considered, especially during the helical CT scan of the head.

CN103 - Radiation dose variables related to the causes of skin toxicities in women with breast cancer: A study proposal

BackgroundDermatologic toxicities related to radiotherapy treatments affect substantially the patient’s quality of life. It is well stated that the causes are closely related to the radiotherapy treatment technique and to the individual genetic variation factors. More specifically, the received by each skin point is suggested as one of the most important among those causes. But there are still no studies proving this correlation as the skin radiation dose is only assessed within a 15% uncertainty using the current feasible procedures in a common department. On the contrary, we would expect a good correlation, even more, stating a skin-toxicities predicting method by assessing the skin dose using a feasible 5% uncertainty procedure. MethodsProspective transversal study of breast cancer patients receiving normofractionated external radiation therapy, without bolus compensator. This study uses a non-invasive innovative method to obtain accurate skin radiation doses based in a Software as a Service and radiochromic films.The prescribed dose, the dose report from the Treatment Planning System as well as its class and version, the irradiated volume and measured skin dose and extension by means of this innovative method at fractions 1, 2, 3, 15, 25 and end of treatment will be collected and correlated to acute skin toxicities of the patients. This will be performed using the Radiation Therapy Group gradation during the nurse visit ongoing- and post-treatment till 90 days since its ending. ResultsThis study will state a skin radiation dose – toxicity relationship for breast cancer patients as a result of a Pearson correlation coefficient analysis for each pair of variables. ConclusionsThe most common action in a nurse care plan is to treat signs and symptoms of the dermatologic toxicities but its causes are excluded, mainly due to a lack of knowledge. This study tries to formally state the skin radiation dose – toxicities relationship and, furthermore, the theoretical bases to determine and predict the skin radiation toxicities grade for each treatment. Even more, this will become a useful tool to improve the treatment success probability as well as empowering nursing for designing more accurate patient-specific radiotherapy care plans. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.

03:54 PM Abstract No. 369 Comparison of measured peak skin dose to scanner-reported dose indices during CT-guided interventions

CT-guided interventional procedures, in particular ablations and complex orthopedic procedures, can at times require the use of substantial radiation doses. A theoretical model for skin dose based on the definitions of CTDIvol and CTIDw has been published, but not validated experimentally. The aim of this study was to validate this model and benchmark against a typical mix of helical and axial scanning during CT-guided procedures. 68 patients were enrolled in this IRB-approved study. Radiochromic film was calibrated using standard methods and used to measure patient skin doses for consecutive ablation procedures performed on a single CT scanner. Procedural dose indices, including CTDIvol, were collected and compared to the measured skin doses using a paired t-test and Bland-Altman analysis. CTDIvol separated by axial and helical imaging was used to estimate skin doses using a published theoretical model, which were compared to measured doses. All data was log transformed for hypothesis testing. When a theoretical model was applied to the data, predicted skin doses were significantly different from measured skin doses according to a two-tailed t-test (p < 0.0001). However, skin dose was not significantly different from uncorrected total CTDIvol according to a two-tailed t-test (p = 0.29). Bland-Altman analysis revealed a bias of -3.75 for percent difference (standard deviation [SD] = 24.0) with limits of agreement (LoA) of [-50.7, 43.2] between measured skin dose and CTDIvol (measured skin dose – CTDIvol) and a bias of -18.1 (SD = 22.4) with LoA of [-62.0, 25.7] between measured skin dose and skin dose as calculated using a theoretical model. CTDIvol alone was a better predictor of skin dose than dose estimated using a theoretical model. This is likely a consequence of how CTDI is measured, with scatter contributing much of the signal, rather than primary radiation. Also, patient positioning during CT-guided procedures varies substantially, and patients are often off-center, meaning the skin surface may not match well to the surface of a phantom centered in the gantry. CTDIvol is reported by all CT scanners and is a simple index for monitoring skin dose.

54 Development of a model for predicting radiological risks in interventional cardiology

Introduction The aim of the study is to estimate, before intervention, the radiation dose that will be delivered to the patient during a recanalization of Chronic Total Occlusion (CTO). Relevant clinical indicators should be selected to predict, at best, the risk of deterministic effects and improve patient care. Methods 103 CTO procedures were performed in a department of interventional cardiology with a Siemens Artis Zee C-arm giving Air Kerma. The peak skin dose was measured for each intervention, using radiochromic films. Patient parameters, such as gender, age weight and height were recorded. The complexity index (J-CTO score) which is specific to each intervention, was determined by the cardiologist. A correlation study has clarified the impact of these indicators on the dose. A predictive model of the dose to the patient was found. Results Of the 103 patients studied, 5 were excluded from the study for clinical reasons, 2 others because radiochromic films were outside of the exposure field. Finally, 96 2D dose maps were used for the study. The factors showing the highest correlation with the peak skin dose are patient diameter and J-CTO score. The prediction model is therefore based on these two parameters. The comparison between the predicted skin dose and measured skin dose showed an average difference of 0.85 ± 0.55 Gy for doses less than 6 Gy. The average difference between Air-Kerma and peak skin dose is about 1.66 Gy ± 1.16 Gy. Conclusions An initial estimate of the skin dose to the patient is given prior to the start of the intervention. This indication helps the cardiologist to work effectively and safely. This predicted dose is more accurate than the estimate provided by the air-kerma.

Characterization of the effect of a new commercial transmission detector on radiation therapy beams

PurposeTo evaluate the influence of a new commercial transmission detector on radiation therapy beams. Methods and materialsA transmission detector designed for online treatment monitoring was characterized on a TrueBeam STx linear accelerator with 6-MV, 6-flattening filter free, 10-MV, and 10-flattening filter free beams. Measurements of percentage depth doses, in-plane and cross-plane off-axis profiles at different depths, transmission factors, and skin dose were acquired with 3 × 3, 5 × 5, 10 × 10, 20 × 20, and 40 × 40 cm2 field sizes at 100 cm and 80 cm source-to-surface distance (SSD). A CC04 chamber was used for all profile and transmission factor measurements. Skin dose was assessed at 100, 90, and 80 cm SSD using a variety of detectors (Roos and Markus parallel-plate chambers and optically stimulated luminescent dosimeters [OSLDs]). Skin dose was also assessed for various patient sample plans with OSLDs. ResultsThe percentage depth doses showed small differences between the unperturbed and perturbed beams for 100 cm SSD (≤4 mm depth of maximum dose difference, <1.2% average profile difference) for all field sizes. At 80 cm SSD, the differences were larger (≤8 mm depth of maximum dose difference, <3% average profile difference). The differences were larger for the flattened beams and larger field sizes. The off-axis profiles showed similar trends. Field penumbras looked similar with and without the transmission detector. Comparisons in the profile central 80% showed a maximum average (maximum) profile difference between all field sizes of 1.0% (2.6%) and 1.4% (6.3%) for 100 and 80 cm SSD, respectively. The average measured skin dose increase at 100 cm (80 cm) SSD for a 10 × 10 cm2 field size was <4% (<35%) for all energies. For a 40 × 40 cm2 field size, this increased to <31% (≤63%). For the sample patient plans, the average skin dose difference was 0.53% (range, -6.6% to 10.4%). ConclusionsThe transmission detector has minimal effect on clinically relevant radiation therapy beams for intensity modulated radiation therapy and volumetric arc therapy (field sizes 10 × 10 cm2 and less). For larger field sizes, some perturbations are observable that would need to be assessed for clinical impact.

Surface Dose Assessment for Different Clinical set up Parameters from High Energy Photon Beams

Introduction: The purpose of this study was to investigate surface doses of 6 and 10 MV energies of linear accelerator for different clinical setup parameters including (field size, gantry angle, SSD (source skin distance), PW (physical wedge), acrylic block tray and bolus), Comparison between measured surface dose by P.P (parallel plate) and calculated surface dose by TPS (Treatment Planning system). Comparison between surface doses measured by TLD (Thermo luminescence dosimeter) and P.P ion chamber, Comparison between the surface dose of 3DCRT and IMRT techniques. Materials and Methods: Surface dose measurements were carried out using a (PTW) Markus parallel-plate ion chamber in a plastic water plastic water phantom for various setup parameters using Primus Siemens (6, 10 MV) linear accelerator. For the normalization depth, i.e., the depth of maximum dose 1.5, 2.5 cm were chosen for 6, 10 MV photon beams, respectively. Results and Discussion: The measured skin dose values for 10 MV were lower than those of 6 MV, the skin dose increased as field size increased. The measured surface dose by P.P for 6 and 10 MV are 16%, 25%, for 10 × 10 cm2 square field size, within the first 2 millimetres of the build-up region, at field size 10 × 10 cm2 the PDD for a 6 and 10 MV photon beam increases from 24% to 62%, 16% to 44% respectively. With increasing the gantry angles (0 to 30) produces a minimal effect of dose, (40-70) gantry angles produce a significant increase. When studying the surface dose with different SSD found that the percentage of surface dose is nearly stable, the absolute surface dose (cGy) increased with decreasing SSD. The absolute skin dose for wedge fields were lower than for open fields, for field size 10 × 10 cm2, while the values of surface dose of wedge 30 are 20% and 14% for 6 and 10 MV respectively. The skin dose for a wedge field increased as field size increased. Bolus 1 cm material increased the surface dose for 10 × 10 cm2 from 24% to 96%, and from 16% to 87%, for 6 and 10 MV respectively. With the use of an acrylic block tray, the surface dose increased to the open fields for all field sizes higher than 10 cm2, but the increase was dominant for large fields, for field size 20 × 20 cm2 the surface dose increased from 29% to 41%, from 22% to 34% for 6 and 10 MV respectively. Conclusion: Agreement between skin doses calculated by multidata TPS and those measured by P.P ion chamber in water plastic water phantom was better than 20% for 96% of measurement points and this is indicate that the dose calculation in the build-up region using multidata TPS is good. For irregular tumor shape and closed OAR the IMRT is a good solution to cover the tumor and spare the critical organs without increasing the skin dose.

A Study on Skin Dose Changes with Changes in Body Weight From Tomotherapy for Head and Neck Cancer

Background/Objectives: When receiving radiation treatment in form of tomotherapy, most head and neck cancer patients show symptoms of weight loss caused by stomatitis and esophagitis, and skin burns. Weight loss may lead to a closer distance between the skin and the target, causing a change in the measured skin dose. This study was conducted to analyze such changes during the radiation treatment period. Methods/Statistical Analysis: The study also analyzed whether factors such as patient gender, age, diagnosis type, and treatment regimen, including surgery or chemotherapy in addition to radiotherapy, might influence the weight changes in patients, and collected values for changes in skin dose using thermoluminescence dosimeters. Findings: The study considered 20 patients with head and neck cancer, and all of these patients showed weight loss and an increase in measured skin dose. In addition, the gender or age of the patients had no direct relationship with their weight changes. Patients who hadn't undergone surgery prior to concurrent chemotherapy and radiation therapy showed a substantial weight loss. In comparison, the patients who had undergone surgery prior to concurrent chemotherapy and radiation therapy displayed the least amount of weight loss. As the amount of weight loss became larger, so did the skin dose that was measured during tomotherapy (p<.05). Application/Improvements: It appeared that greater weight loss led to an increase in measured skin dose, From this study, it is implied patients with large weight loss may benefit with an adjustment of their radiotherapy parameters while maintaining their target doses.

Patient UVA dosimetry using Gafchromic film

There is currently no method to measure the doses received by a patient during PUVA therapy. While some Monte Carlo modelling has been carried out, there is no measured data on the skin dose actually received by the patient. Commercially available electronic detectors are expensive, often only measure instantaneous irradiance rather than exposure values and cannot provide measurement at many different sites at the same time. Measured skin dose will allow further optimisation in the delivery of UVA radiation. This study investigates the use of Gafchromic EBT3 (Ashland, USA) as a patient UVA dosimeter. EBT3 Gafchromic film has been designed by its manufacturers as a tool for radiotherapy dosimetry. However, other studies have shown the film can be used to quantify solar UV dose. The film is easy to use and is minimally inconvenient for the patient. As the film is flat, it mimics skin in a geometry that cannot be matched using electronic detectors and allow simultaneous measurements at many sites. Absorption peaks of the film are located in the visible red region meaning a visual change in film colour will be observed upon sufficient exposure to UVA radiation. Scanning of the film using an Epson V800 scanner and analysis of the images using ImageJ and Microsoft Excel then provides UVA dosimetry information. The film was calibrated against a calibrated UVA radiometer and used in the field to provide an acceptable level of accuracy. The Epson V800 scanner was purchased using the YIG grant received from the IAPM

SU‐F‐T‐151: Measurement Evaluation of Skin Dose in Scanning Proton Beam Therapy for Breast Cancer

Purpose:To measure the skin dose and compare it with the calculated dose from a treatment planning system (TPS) for breast cancer treatment using scanning proton beam therapy (SPBT).Methods:A single en‐face‐beam SPBT plan was generated by a commercial TPS for two breast cancer patients. The treatment volumes were the entire breasts (218 cc and 1500 cc) prescribed to 50.4 Gy (RBE) in 28 fractions. A range shifter of 5 cm water equivalent thickness was used. The organ at risk (skin) was defined to be 5 mm thick from the surface. The skin doses were measured in water with an ADCL calibrated parallel plate (PP) chamber. The measured data were compared with the values calculated in the TPS. Skin dose calculations can be subject to uncertainties created by the definition of the external contour and the limitations of the correction based algorithms, such as proton convolution superposition. Hence, the external contours were expanded by 0, 3 mm and 1 cm to include additional pixels for dose calculation. In addition, to examine the effects of the cloth gown on the skin dose, the skin dose measurements were conducted with and without gown.Results:On average the measured skin dose was 4% higher than the calculated values. At deeper depths, the measured and calculated doses were in better agreement (&lt; 2%). Large discrepancy occur for the dose calculated without external expansion due to volume averaging. The addition of the gown only increased the measured skin dose by 0.4%.Conclusion:The implemented TPS underestimated the skin dose for breast treatments. Superficial dose calculation without external expansion would result in large errors for SPBT for breast cancer.

SU‐F‐T‐517: Determining the Tissue Equivalence of a Brass Mesh Bolus in a Reconstructed Chest Wall Irradiation

Purpose:To determine the tissue equivalence of a brass mesh bolus (RPD) in the setting of a reconstructed chest wall irradiationMethods:We measured breast skin dose delivered by a tangential field plan on an anthropomorphic phantom using Mosfet and nanoDot (Landauer) dosimeters in five different locations on the breast. We also measured skin dose using no bolus, 5mm and 10 mm superflab bolus. In the Eclipse treatment planning system (Varian, Palo Alto, CA) we calculated skin dose for different bolus thicknesses, ranging from 0 to 10 mm, in order to evaluate which calculation best matches the brass mesh measurements, as the brass mesh cannot be simulated due to artefacts.Finally, we measured depth dose behavior with the brass mesh bolus to verify that the bolus does not affect the dose to the breast itself beyond the build‐up region.Results:Mosfet and nanoDot measurements were consistent with each other.As expected, skin dose measurements with no bolus had the least agreement with Eclipse calculation, while measurements for 5 and 10 mm agreed well with the calculation despite the difficulty in conforming superflab bolus to the breast contour. For the brass mesh the best agreement was for 3 mm bolus Eclipse calculation. For Mosfets, the average measurement was 90.8% of the expected dose, and for nanoDots 88.33% compared to 83.34%, 88.64% and 93.94% (2,3 and 5 mm bolus calculation respectively).The brass mesh bolus increased skin dose by approximately 25% but there was no dose increase beyond the build‐up region.Conclusion:Brass mesh bolus is most equivalent to a 3 mm bolus, and does not affect the dose beyond the build‐up region. The brass mesh cannot be directly calculated in Eclipse, hence a 3mm bolus calculation is a good reflection of the dose response to the brass mesh bolus.

Evaluating the consistency of location of the most severe acute skin reaction and highest skin dose measured by thermoluminescent dosimeter during radiotherapy for breast cancer

We conducted this prospective study to evaluate whether the location of the most severe acute skin reaction matches the highest skin dose measured by thermoluminescent dosimeter (TLD) during adjuvant radiotherapy (RT) for patients with breast cancer after breast conservative surgery. To determine whether TLD measurement can reflect the location of the most severe acute skin reaction, 80 consecutive patients were enrolled in this prospective study. We divided the irradiated field into breast, axillary, inframammary fold, and areola/nipple areas. In 1 treatment session when obvious skin reaction occurred, we placed the TLD chips onto the 4 areas and measured the skin dose. We determined whether the highest measured skin dose area is consistent with the location of the most severe skin reaction. The McNemar test revealed that the clinical skin reaction and TLD measurement are more consistent when the most severe skin reaction occurred at the axillary area, and the p = 0.0108. On the contrary, TLD measurement of skin dose is less likely consistent with clinical observation when the most severe skin reaction occurred at the inframammary fold, breast, and areola/nipple areas (all the p > 0.05). Considering the common site of severe skin reaction over the axillary area, TLD measurement may be an appropriate way to predict skin reaction during RT.

SU-D-213-02: Characterization of the Effect of a New Commercial Transmission Detector On Radiotherapy Beams

Purpose: To evaluate the influence of a new commercial transmission detector on radiotherapy beams of various energies. Methods: A transmission detector designed for online treatment monitoring was characterized on a TrueBeam STx linear accelerator with 6MV, 6FFF, 10MV, and 10FFF beams. Measurements of beam characteristics including percentage depth doses (PDDs), inplane and crossplane off-axis profiles at different depths, transmission factors, and skin dose were acquired at field sizes of 3×3cm, 5×5m, 10×10cm, and 20×20cm at 100cm and 80cm source-to-surface distance (SSD). All measurements were taken with and without the transmission detector in the path of the beam. A CC04 chamber was used for all profile and transmission factor measurements. Skin dose was assessed at 100cm, 90cm, and 80cm SSD and using a variety of detectors (Roos and Markus parallel-plate chambers, and OSLD). Results: The PDDs showed small differences between the unperturbed and perturbed beams for both 100cm and 80cm SSD (≤4mm dmax difference and <1.2% average profile difference). The differences were larger for the flattened beams and at larger field sizes. The off-axis profiles showed similar trends. The penumbras looked similar with and without the transmission detector. Comparisons in the central 80% of the profile showed a maximum average (maximum) profile difference between all field sizes of 0.756% (1.535%) and 0.739% (3.682%) for 100cm and 80cm SSD, respectively. The average measured skin dose at 100cm (80cm) SSD for 10×10cm field size was <4% (<35%) dose increase for all energies. For 20×20cm field size, this value increased to <10% (≤45%). Conclusion: The transmission detector has minimal effect on the clinically relevant radiotherapy beams for IMRT and VMAT (field sizes 10×10cm and less). For larger field sizes, some perturbations are observable which would need to be assessed for clinical impact. The authors of this publication has research support from IBA Dosimetry.

SU-E-T-288: Skin Dose Measurement of Whole Brain with GAFCHROMIC EBT2 Films.

To measure skin dose of whole brain irradiation of a humanoid unsliced phantom treated by standard lateral fields with GAFCHROMIC EBT2 films. The head and neck of the whole body phantom was scanned at the slice thickness of 2mm. A whole brain plan using 6MV beam was created with standard parallel opposed lateral fields. The isocenter was placed at the outer canthus to avoid divergence to orbital structures. The plan was normalized to the calculation point and with = 95% of brain volume covered by = 95% of prescription dose. The EBT2 films were carefully cut and labeled with same orientation in the film calibration and skin dose measurement. EBT2 film was calibrated in the reference condition with various dose (0-10Gy). After the phantom was positioned for treatment and correct setup was verified by kV-kV imaging and CBCT, the films were placed at various sites and irradiated. An Epson flatbed color scanner was utilized and the scanner response from the red channel of the RGB image was used as the density value for the estimation of dose. The comparison was made between the measured dose and the planned dose for different head locations. Our preliminary results indicated that the measured skin dose agrees with the planned dose within 10% for the sites centered in the treatment fields such as mid right/left sphenoid bones. For the sites outside or near the edge of the treatment fields, such as the right/left orbits and low chin, the measured dose is significantly different from the planned dose (>15%). Skin dose of whole brain irradiation could be measured by GAFCHROMIC EBT2 films. The difference between the measured dose and the planned dose varies significantly depending on the location of interest relative to the treatment field. Further investigation is needed.

Skin-sparing Helical Tomotherapy vs 3D-conformal Radiotherapy for Adjuvant Breast Radiotherapy: In Vivo Skin Dosimetry Study

We investigated whether treatment-planning system (TPS)-calculated dose accurately reflects skin dose received for patients receiving adjuvant breast radiotherapy (RT) with standard three-dimensional conformal RT (3D-CRT) or skin-sparing helical tomotherapy (HT). Fifty patients enrolled in a randomized controlled trial investigating acute skin toxicity from adjuvant breast RT with 3D-CRT compared to skin-sparing HT, where a 5-mm strip of ipsilateral breast skin was spared. Thermoluminescent dosimetry or optically stimulated luminescence measurements were made in multiple locations and were compared to TPS-calculated doses. Skin dosimetric parameters and acute skin toxicity were recorded in these patients. With HT there was a significant correlation between calculated and measured dose in the medial and lateral ipsilateral breast (r = 0.67, P<.001; r = 0.44, P=.03, respectively) and the medial and central contralateral breast (r = 0.73, P<.001; r = 0.88, P<.001, respectively). With 3D-CRT there was a significant correlation in the medial and lateral ipsilateral breast (r = 0.45, P=.03; r = 0.68, P<.001, respectively); the medial and central contralateral breast (r = 0.62, P=.001; r = 0.86, P<.001, respectively); and the mid neck (r = 0.42, P=.04, respectively). On average, HT-calculated dose overestimated the measured dose by 14%; 3D-CRT underestimated the dose by 0.4%. There was a borderline association between highest measured skin dose and moist desquamation (P=.05). Skin-sparing HT had greater skin homogeneity (homogeneity index of 1.39 vs 1.65, respectively; P=.005) than 3D-CRT plans. HT plans had a lower skin(V50) (1.4% vs 5.9%, respectively; P=.001) but higher skin(V40) and skin(V30) (71.7% vs 64.0%, P=.02; and 99.0% vs 93.8%, P=.001, respectively) than 3D-CRT plans. The 3D-CRT TPS more accurately reflected skin dose than the HT TPS, which tended to overestimate dose received by 14% in patients receiving adjuvant breast RT.

In Vivo Dosimetry for Single-Fraction Targeted Intraoperative Radiotherapy (TARGIT) for Breast Cancer

In vivo dosimetry provides an independent check of delivered dose and gives confidence in the introduction or consistency of radiotherapy techniques. Single-fraction intraoperative radiotherapy of the breast can be performed with the Intrabeam compact, mobile 50 kV x-ray source (Carl Zeiss Surgical, Oberkochen, Germany). Thermoluminescent dosimeters (TLDs) can be used to estimate skin doses during these treatments. Measurements of skin doses were taken using TLDs for 72 patients over 3 years of clinical treatments. Phantom studies were also undertaken to assess the uncertainties resulting from changes in beam quality and backscatter conditions in vivo. The mean measured skin dose was 2.9 ± 1.6 Gy, with 11% of readings higher than the prescription dose of 6 Gy, but none of these patients showed increased complications. Uncertainties due to beam hardening and backscatter reduction were small compared with overall accuracy. TLDs are a useful and effective method to measure in vivo skin doses in intraoperative radiotherapy and are recommended for the initial validation or any modification to the delivery of this technique. They are also an effective tool to show consistent and safe delivery on a more frequent basis or to determine doses to other critical structures as required.

Acute Skin Toxicity following Radiosurgery for Metastatic Spine Tumors: A Prospective Study

Acute Skin Toxicity following Radiosurgery for Metastatic Spine Tumors: A Prospective Study

Thermoluminescence dosimetry for skin dose assessment during intraoperative radiotherapy for early breast cancer

Dosimetry for intraoperative radiotherapy (IORT) after wide local excision for breast cancer using a 50 kV X-ray needle (Intrabeam) was performed in vivo using thermoluminescence dosimetry. Eight LiF:Mg,Ti chips were placed on the skin around the incision site after wide local excision while the tumour bed was irradiated to a prescribed dose of 5 Gy 10 mm from the applicator surface. The maximum and mean measured skin dose for 57 patients ranged from 0.64 to 7.1 Gy and 0.56 to 4.78 Gy, respectively, reflecting different tissue thicknesses overlying the applicator. The average maximum dose of 2.93+/-1.46 Gy was below the threshold for severe radiation skin toxicity.

SU‐GG‐T‐266: Implementation of Total Skin Electron Irradiation (TSEI) Using High Dose Rate Mode at Siriraj Hospital

Purpose: To implement and commissioning of applied Stanford total skin electron irradiation (TSEI) technique using standard linear accelerator at our institute. Method and Materials: Patient was treated in six different upright patient positions using dual angle fields. This study was carried out on Varian 23EX linear accelerator with 6 MeV, 36×36 cm2 field size at collimator in HDTSe mode at a SSD of 400 cm behind a beam degrader. The dosimetric characteristics were verified experimentally using a parallel plate ion chamber, electron diodes, and TLD‐100 chip and rod types. The delivered dose is 36 Gy in 9 weeks. The basic dosimetric parameter consists of beam profile, depth dose curve and electron beam output in the treatment plane. The output and depth dose curve was measured by PTW23343 Markus chamber in solid phantom. Delivered dose from six dual fields technique in treatment position was verified on round phantom by TLD‐100. Results: The uniform vertical profile was obtained for gantry angulations of ± 17.5 degree above and below horizontal within 10% of the prescribed dose. The depth dose curve shows maximum dose at skin surface. The mean energy is 2.09 MeV with beam degrader 1 cm thick. The dose uniformity from six dual fields on round phantom is within 10%. The average measured skin dose in the anterior and posterior at the level of head, chest and pelvis on rando phantom is within 10% of prescribed point. Total X‐ray contamination in the rando phantom is about 1.35% of the delivered dose. Conclusion: The TSEI technique using six dual fields applied Stanford technique produced a uniformity at the whole patient's surface cannot be better than 15% of the prescribed dose because of variable skin distance, self‐shielding, and differences in curvature.