Peripheral Dose Measurements Research Articles

Monte Carlo flattening filter design to high energy intraoperative electron beam homogenization

Intraoperative radiotherapy using mobile linear accelerators is used for a wide variety of malignancies. However, when large fields are used in combination with high energies, a deterioration of the flatness dose profile is measured with respect to smaller fields and lower energies. Indeed, for the LIAC HWL of Sordina, this deterioration is observed for the 12 MeV beam combined with 10 cm (or larger) diameter applicator. Aimed to solve this problem, a flattening filter has been designed and validated evaluating the feasibility of its usage at the upper part of the applicator. The design of the filter was based on Monte Carlo simulations because of its accuracy in modeling components of clinical devices, among other purposes. The LIAC 10 cm diameter applicator was modeled and simulated independently by two different research groups using two different MC codes, reproducing the heterogeneity of the 12 MeV energy beam. Then, an iterative process of filter design was carried out. Finally, the MC designed conical filter with the optimal size and height to obtain the desired flattened beam was built in-house using a 3D printer. During the experimental validation of the applicator-filter, percentage depth dose, beam profiles, absolute and peripheral dose measurements were performed to demonstrate the effectiveness of the filter addition in the applicator. These measurements conclude that the beam has been flattened, from 5.9% with the standard configuration to 1.6% for the configuration with the filter, without significant increase of the peripheral dose. Consequently, the new filter-applicator LIAC configuration can be used also in a conventional surgery room. A reduction of 16% of the output dose and a reduction of 1.1 mm in the D50 of the percentage depth dose was measured with respect to the original configuration. This work is a proof-of-concept that demonstrates that it is possible to add a filter able to flatten the beam delivered by the Sordina LIAC HWL. Future studies will focus on more refined technical solutions fully compatible with the integrity of the applicator, including its sterilization, to be safely introduced in the clinical practice.

A novel technique for peripheral dose measurements in external beam radiation therapy

Abstract Introduction: In radiotherapy, the dose delivered outside the field is known as peripheral dose (PD). In this study, we have attempted to develop a dataset using the PD values measured with a two-dimensional array, IMatrixx. Methods: The IMatrixx was used to measure the PD up to a distance of 45 cm from the field edge, in a Varian Clinac 2100-C machine. Solid water slabs and water phantom were used to get the required geometry for the PD measurements. The measurements were done for different field sizes, collimator angles, source to surface distance (SSD) and depths. The influence of gantry angles and photon energies on the PD was studied. The surface dose measurements were carried out using thermoluminescent detectors (TLD). Results: The dataset shows that the PD increased significantly with field size and depth and its increase was insignificant for collimator rotation and SSD. The influence of gantry angle was less pronounced at dmax than at the surface. The TLD measurements at the surface of patients were in agreement with the IMatrixx measurements. Conclusions: The IMatrixx can be used for the generation of PD values and it is less time-consuming, accurate, and commonly available in all radiotherapy departments.

Measurement of peripheral dose to the pelvic region and the associated risk for cancer development after breast intraoperative electron radiation therapy

This study aimed to measure the received dose to the pelvic region of patients during breast intraoperative electron radiation therapy (IOERT). Furthermore, we compared the findings with those of external beam radiation therapy. Finally, secondary ovarian and uterus cancer risks following breast IOERT were estimated. In the current study, the received dose to the pelvic surface of 18 female patients during breast IOERT boosts were measured by thermoluminescent dosimeter (TLD-100) chips. All patients were treated with 12 Gy given in a single fraction. To estimate the dose to the ovary and uterus of the patients, conversion coefficients for depth from the surface dose were obtained in a Rando phantom. Given the received dose to the pelvic region of the patients, secondary ovarian and uterus cancer risks following breast IOERT were estimated. The received doses to the ovary and uterus surface of the patients were 0.260 ± 0.155 mGy to 31.460 ± 6.020 mGy and 0.485 ± 0.122 mGy to 22.387 ± 15.476 mGy, respectively. Corresponding intra-pelvic (ovary and uterus) regional doses were 0.012 ± 0.007 mGy to 1.479 ± 0.283 mGy and 0.027 ± 0.001 mGy to 1.164 ± 0.805 mGy, respectively. Findings demonstrated that the ratio of the received dose by the pelvic surface to the regional dose during breast IOERT was much less than external beam radiation therapy. The mean of the secondary cancer risks for the ovary in 8 and 10 MeV electron beam energies were 135.722 ± 117.331 × 10−6 and 69.958 ± 28.072 × 10−6, and for the uterus were 17.342 ± 10.583 × 10−6 and 2.971 ± 3.604 × 10−6, respectively. According to our findings, the use of breast IOERT in pregnant patients can be considered as a safe radiotherapeutic technique, because the received dose to the fetus was lower than 50 mGy. Furthermore, IOERT can efficiently reduce the unnecessary dose to the pelvic region and lowers the risk of secondary ovarian and uterus cancer following breast irradiation.

165. Periheral dose in a Cyberknife treatment: The case of a pregnant woman

PurposeWe present peripheral dose measurements in a Cyberknife brain treatment. This dosimetric study was applied to the clinical case of a pregnant woman and the dose to the fetus was estimated in order to verify the safety of the treatment [1]. MethodsDose evaluation at different distances from the target was achieved with the aid of a phantom resembling the human body. Two treatment plans were delivered to the phantom with prescription doses of 25 Gy and 14 Gy respectively. The dose was measured with two different detectors: gafchromic films and Farmer ionization chamber, which were positioned in different part of the phantom at various distances from the zone irradiated. The film measurement put in evidence the propagation of the beams after having hit the target while the ionization chamber gave a punctual detection of the dose. The two detection methods gave the same results at the common point of measurement. A shielding device was designed to further protect the patient and the radiation attenuation was estimated. ResultsThe dose sharply decreased with distance from the target: at a distance of 3 cm the dose was 6 times inferior with respect to the prescribed dose and the application of the shielding determined a reduction of the dose by a factor of three. In the case of a pregnant woman at the third trimester of gestation, the position of the embryo, evaluated with ultrasound imaging, laid from 56 cm (embryo head) to 72 cm (embryo legs) from the lesion. Following our simulation, for the first treatment plan the dose to the embryo was expected to be less than 5 cGy, for the second treatment less than 3 cGy. ConclusionsThe measured peripheral doses were below the threshold of 10 cGy for congenital malformations, mental and growth retardation effect. A brain treatment in pregnancy can therefore be safely administered after a careful evaluation of the dose to the embryo.

Commissioning and Peripheral Dose Measurements of the AccuBoost D-Shaped Skin Dose Optimized Applicators

Commissioning and Peripheral Dose Measurements of the AccuBoost D-Shaped Skin Dose Optimized Applicators

SU‐F‐SPS‐05: Experimental Validation of Peripheral Dose Distribution of Electron Beams for Eclipse Electron Monte Carlo Algorithm

Purpose:In this study, the two available calculation algorithms of the Varian Eclipse treatment planning system(TPS), the electron Monte Carlo(eMC) and General Gaussian Pencil Beam(GGPB) algorithms were used to compare measured and calculated peripheral dose distribution of electron beams.Methods:Peripheral dose measurements were carried out for 6, 9, 12, 15, 18 and 22 MeV electron beams of Varian Triology machine using parallel plate ionization chamber and EBT3 films in the slab phantom. Measurements were performed for 6×6, 10×10 and 25×25cm2 cone sizes at dmax of each energy up to 20cm beyond the field edges. Using the same film batch, the net OD to dose calibration curve was obtained for each energy. Films were scanned 48 hours after irradiation using an Epson 1000XL flatbed scanner. Dose distribution measured using parallel plate ionization chamber and EBT3 film and calculated by eMC and GGPB algorithms were compared. The measured and calculated data were then compared to find which algorithm calculates peripheral dose distribution more accurately.Results:The agreement between measurement and eMC was better than GGPB. The TPS underestimated the out of field doses. The difference between measured and calculated doses increase with the cone size. The largest deviation between calculated and parallel plate ionization chamber measured dose is less than 4.93% for eMC, but it can increase up to 7.51% for GGPB. For film measurement, the minimum gamma analysis passing rates between measured and calculated dose distributions were 98.2% and 92.7% for eMC and GGPB respectively for all field sizes and energies.Conclusion:Our results show that the Monte Carlo algorithm for electron planning in Eclipse is more accurate than previous algorithms for peripheral dose distributions. It must be emphasized that the use of GGPB for planning large field treatments with 6 MeV could lead to inaccuracies of clinical significance.

SU‐F‐T‐473: Evaluation of Off‐Axis And Peripheral Dose Using Different Detectors

Purpose:In radiation therapy, measurement of off‐axis and peripheral dose is a tedious task. The dose distribution along the beam central axis give only part of the information required for an accurate dose description inside the patient. Dose distributions in 2‐D and 3‐D are determined with central axis data in conjunction with off‐axis dose profiles. Combining a central axis dose distribution with off‐axis data results in volume dose matrix that provides 2‐D and 3‐D information on dose distribution. By considering the importance of these two parameters this study investigates and compares the off axis and peripheral dose measurement using Ionization chamber, MOSFET, Radiochromic film and EDR2 film.Methods:In the measurement of off‐axis and peripheral doses 0.6cc farmer type chamber, EDR‐2 film, MD‐55 radiochromic film and MOSFET detectors were used for both 6MV and 15MV beams. The off‐axis and peripheral dose was measured at every 1 cm interval by changing the position of the couch without disturbing the other experimental setup in particular, the phantom with detector position.Results:Readings were obtained for both 6MV and 15MV photon beams at SSD technique for various field size using MOSFET, Ionization chamber and Radiochromic film. The results shows the percentage difference between various detectors for various field sizes. For Peripheral dose measurement were taken from the edge of the field size and for off axis it is measured form central axis dose.Conclusion:In conclusion, our study shows that no detector is ideal and only a comparison between different detectors highlights the weaknesses of each detector. MOSFET provides adequate dose assessment in off‐axis and peripheral regions in 6MV and 15MV photon beams. Film dosimetry in general a convenient method to generate one‐ and two‐dimensional dose distributions. The result of this indicates that MOSFET is flexible tool for relative dosimetry as films.

The impact of dose calculatıon algorıthms for perıpheral dose dıstrıbutıons of enhanced dynamıc and physıcal wedges

Background : In radiaon therapy, the peripheral dose is important when anatomical structures with very low dose tolerances are involved. In this study, the two available calculaon algorithms of the Varian Eclipse 8.6 treatment planning system(TPS), the anisotropic analyc algorithm (AAA) and pencil-beam convoluon (PBC) was used to compare measured and calculated peripheral dose distribuon of physical wedged (PW) and enhanced dynamic wedged fields (EDW). Materials and Methods : Peripheral dose measurements were carried out for 6 and 18 MV photons using a 0.6cc Farmer-type ionizaon chamber in the slab phantom. Measurements were performed using 15°, 30°, 45° and 60° PW and EDW for three different field sizes at d max and up to a maximum distance of 50 cm beyond the field edges. peripheral dose was further computed using two different algorithms of a TPS. The measured and calculated datas were then compared to find which algorithm calculates peripheral dose distribuon more accurately. Results: Both algorithms from the TPS adequately model the peripheral dose distribuon up to 45 degrees. For large field sizes with 60 0 EDW, the largest deviaon between calculated and measured dose distribuon is less than 3.5% using the AAA, but can increase up to 9.7% of the distribuon using PBC. Conclusion: The AAA models wedged peripheral dose distribuons more accurately than the PBC does for all studied condions; the difference between the algorithms are more significant for large wedge angles and large field sizes. It must be emphasized that the use of PBC for planning large-field treatments with 60 0 EDW could lead to inaccuracies of clinical significance.

SU‐C‐207‐02: A Method to Estimate the Average Planar Dose From a C‐Arm CBCT Acquisition

Purpose:The planar average dose in a C‐arm Cone Beam CT (CBCT) acquisition had been estimated in the past by averaging the four peripheral dose measurements in a CTDI phantom and then using the standard 2/3rds peripheral and 1/3 central CTDIw method (hereafter referred to as Dw). The accuracy of this assumption has not been investigated and the purpose of this work is to test the presumed relationship.Methods:Dose measurements were made in the central plane of two consecutively placed 16cm CTDI phantoms using a 0.6cc ionization chamber at each of the 4 peripheral dose bores and in the central dose bore for a C‐arm CBCT protocol. The same setup was scanned with a circular cut‐out of radiosensitive gafchromic film positioned between the two phantoms to capture the planar dose distribution. Calibration curves for color pixel value after scanning were generated from film strips irradiated at different known dose levels. The planar average dose for red and green pixel values was calculated by summing the dose values in the irradiated circular film cut out. Dw was calculated using the ionization chamber measurements and film dose values at the location of each of the dose bores.Results:The planar average dose using both the red and green pixel color calibration curves were within 10% agreement of the planar average dose estimated using the Dw method of film dose values at the bore locations. Additionally, an average of the planar average doses calculated using the red and green calibration curves differed from the ionization chamber Dw estimate by only 5%.Conclusion:The method of calculating the planar average dose at the central plane of a C‐arm CBCT non‐360 rotation by calculating Dw from peripheral and central dose bore measurements is a reasonable approach to estimating the planar average dose.Research Grant, Siemens AG

TU‐F‐CAMPUS‐T‐03: Commissioning of a Custom Fetal Lead Shield for Radiotherapy

Purpose:To evaluate the peripheral dose (PD) to a fetus during radiation therapy of pregnant patients when using a newly designed fetal lead shield (FLS).Methods:A custom FLS has been designed and fabricated for our department. The FLS (1.1 TVLs for 6 MV) is mounted on a mobile frame and can be adjusted vertically with a motor actuator. PD measurements were acquired for multiple simple square fields and for a variety of potential treatment sites a pregnant patient may be treated for including brain, head and neck (H&N) and thorax. For measurements of the brain, H&N, and thorax, an ionization chamber and OSLDs were positioned on average at a distance of 48, 29 and 26 cm, respectively, from the edge of treatment fields to mimic the approximate position of the fundus.Results:Based on our measurements, applying a 90° collimator rotation and using tertiary MLCs to define the field aperture in combination with jaws resulted in an average dose reduction of 60%. When using these planning strategies in combination with the FLS, on average, the PD was reduced by additional 25% for simple square fields and 20% for clinical plans.Conclusion:The custom FLS is a safe, effective, and relatively easy system to position. Commissioning measurements have demonstrated that the PD to the fetus can be significantly reduced when using the FLS. The comprehensive dataset obviates the need for individual patient pre‐treatment dose measurements as long as the geometry falls within the commissioning limits.

EP-1377: IMRT and VMAT peripheral dose measurements

EP-1377: IMRT and VMAT peripheral dose measurements

Measurement of peripheral dose in high-energy electron beams used in external radiotherapy

Measurement of peripheral dose in high-energy electron beams used in external radiotherapy

Sci—Thur AM: YIS ‐ 05: 10X‐FFF VMAT for Lung SABR: an Investigation of Peripheral Dose

Flattening Filter Free (FFF) beams exhibit high dose rates, reduced head scatter, leaf transmission and leakage radiation. For VMAT lung SABR, treatment time can be significantly reduced using high dose rate FFF beams while maintaining plan quality and accuracy. Another possible advantage offered by FFF beams for VMAT lung SABR is the reduction in peripheral dose. The focus of this study was to investigate and quantify the reduction of peripheral dose offered by FFF beams for VMAT lung SABR.The peripheral doses delivered by VMAT Lung SABR treatments using FFF and flattened beams were investigated for the Varian Truebeam linac. This study was conducted in three stages, (1): ion chamber measurement of peripheral dose for various plans, (2): validation of AAA, Acuros XB and Monte Carlo for peripheral dose using measured data, and (3): using the validated Monte Carlo model to evaluate peripheral doses for 6 VMAT lung SABR treatments. Three energies, 6X, 10X, and 10X‐FFF were used for all stages.Measured data indicates that 10X‐FFF delivers the lowest peripheral dose of the three energies studied. AAA and Acuros XB dose calculation algorithms were identified as inadequate, and Monte Carlo was validated for accurate peripheral dose prediction. The Monte Carlo‐calculated VMAT lung SABR plans show a significant reduction in peripheral dose for 10X‐FFF plans compared to the standard 6X plans, while no significant reduction was showed when compared to 10X. This reduction combined with shorter treatment time makes 10X‐FFF beams the optimal choice for superior VMAT lung SABR treatments.

SU-E-T-145: Effects of Temporary Tachytherapy Inhibition Magnet On MOSFET Dose Measurements of Cardiovascular Implantable Electronic Devices (CIED) in Radiation Therapy Patients

Purpose: To determine the effects of temporary tachytherapy inhibition magnet on MOSFET dose measurements of cardiovascular implantable electronic devices (CIED) in radiation therapy patients. Methods: Infield and peripheral MOSFET dose measurements with 6MV photon beams were performed to evaluate dose to a CIED in the presence of a doughnut shaped temporary tachytherapy inhibition magnet. Infield measurements were done to quantify the effects of the magnetic field alone and shielding by the magnet. MOSFETs were placed inside a 20×20cm2 field at a depth of 3cm in the isocentre plane in the presence and absence of the magnet. Peripheral dose measurements were done to determine the impact of the magnet on dose to the CIED in a clinical setting. These measurements were performed at the centre, under the rim and half way between a 10×10cm2 field edge and the magnet with MOSFETS placed at the surface, 0.5cm and 1cm depths in the presence and absence of the magnet. Results: Infield measurements showed that effects of magnetic field on the MOSFET readings were within the 2% MOSFET dose measurement uncertainty; a 20% attenuation of dose under the magnet rim was observed. Peripheral dose measurements at the centre of the magnet show an 8% increase in surface dose and a 6% decrease in dose at 1cm depth. Dose under the magnet rim was reduced by approximately 68%, 45% and 25% for MOSFET placed at 0.0, 0.5 and 1.0cm bolus depths, respectively. Conclusions: The magnetic field has an insignificant effect on MOSFET dose measurements. Dose to the central region of CIED represented by centre of the magnet doughnut increases at the surface, and decreases at depths due to low energy scattering contributions from the magnet. Dose under the magnet rim, representing CIED edges, decreased significantly due to shielding.

Peripheral dose measurements in cervical cancer radiotherapy: a comparison of volumetric modulated arc therapy and step-and-shoot IMRT techniques

PurposeThe aim of this study was to investigate the peripheral doses resulting from volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) techniques in cervical cancer radiotherapy.MethodsNine patients with cervical cancer had treatment planned with both VMAT and IMRT. A specially designed phantom was used for this study, with ion chambers placed at interest points approximating the position of the breast, thyroid, and lens. The peripheral doses at the phantom interest points were measured and compared between the VMAT and IMRT techniques.ResultsVMAT provides a potential dosimetric advantage compared with IMRT. The mean (± standard deviation) peripheral dose to the breast point for 1 fraction (2 Gy) during VMAT measured 5.13 ± 0.96 mGy, compared with 9.04 ± 1.50 mGy for IMRT. At the thyroid and lens interest points, the mean (± standard deviation) peripheral dose during VMAT was 2.19 ± 0.33 and 2.16 ± 0.28 mGy, compared with 7.07 ± 0.76 and 6.97 ± 0.91 mGy for IMRT, respectively. VMAT reduced the monitor units used by 28% and shortened the treatment delivery time by 54% compared with IMRT.ConclusionWhile the dosimetric results are similar for both techniques, VMAT results in a lower peripheral dose to the patient and reduces the monitor-unit usage and treatment delivery time compared with IMRT.

Assessment of concomitant testicular dose with radiochromic film

To assess the suitability of EBT2 and XRQA2 Gafchromic film for measuring low doses in the periphery of treatment fields, and to measure the accumulative concomitant dose to the contralateral testis resulting from CT imaging, pre-treatment imaging (CBCT) and seminoma radiotherapy with and without gonadal shielding. Superficial peripheral dose measurements made using EBT2 Gafchromic film on the surface of water equivalent material were compared to measurements made with an ionisation chamber in a water phantom to evaluate the suitability and accuracy of the film dosimeter for such measurements. Similarly, XRQA2 was used to measure surface doses within a kilovoltage beam and compared with ionisation chamber measurements. Gafchromic film was used to measure CT, CBCT and seminoma treatment related testicular doses on an anthropomorphic phantom. Doses were assessed for two clinical plans, both with and without gonadal shielding. Testicular doses resulting from the treatment of up to 0.83 ± 0.17 Gy were measured per treatment. Additional doses of up to 0.49 ± 0.01 and 2.35 ± 0.05 cGy were measured per CBCT and CT image, respectively. Reductions in the testicular dose in the order of 10, 36 and 78% were observed when gonadal shielding was fitted for treatment, CT and CBCT imaging, respectively. Gafchromic film was found to be suitable for measuring dose in the periphery of treatment fields. The dose to the testis should be limited to minimise the risk of radiation related side effects. This can be achieved by using appropriate gonadal shielding, irrespective of the treatment fields employed.

Performance of KCl:Eu2+ storage phosphor dosimeters for low-dose measurements

Recent research has demonstrated that europium doped potassium chloride (KCl:Eu2+) storage phosphor material has the potential to become the physical foundation of a novel and reusable dosimetry system using either film-like devices or devices similar to thermoluminescent dosimeter chips. The purposes of this work are to quantify the performance of KCl:Eu2+ prototype dosimeters for low-dose measurements and to demonstrate how it can be incorporated into clinical application for in vivo peripheral dose measurements. Pellet-style KCl:Eu2+ dosimeters, 6 mm in diameter, and 1 mm thick, were fabricated in-house for this study. The dosimeters were read using a laboratory photostimulated luminescence detection system. KCl:Eu2+ prototype storage phosphor dosimeter was capable of measuring a dose-to-water as low as 0.01 cGy from a 6 MV photon beam with a signal-to-noise ratio greater than 6. A pre-readout thermal annealing procedure enabled the dosimeter to be read within an hour post-irradiation. After receiving large accumulated doses (∼10 kGy), the dosimeters retained linear response in the low-dose region with only a 20% loss of sensitivity comparing to a fresh sample (zero Gy history). The energy dependence encountered during low-dose peripheral measurements could be accounted for via a single point outside-field calibration per each beam quality. With further development the KCl:Eu2+−-based dosimeter could become a versatile and durable dosimetry tool with large dynamic range (sub-cGy to 100 Gy).

SU-E-T-139: Evaluation of Surface, Peripheral,and Buildup Dose in MR-IGRT

Purpose: To determine the effect of the magnetic field on surface and buildup dose in radiotherapy using MR-IGRT, specifically measured with a Co-60 system. Methods: A commercially-available MR-IGRT system was used to measure surface, peripheral, and build-up dose due to thermoplastic head immobilization masks. Both radiographic (Kodak EDR2) and radiochromic (EBT2) film types were used for surface measurements. A small-volume ionization chamber was used for peripheral dose measurements. Several types of thermoplastic masks from three different manufacturers were chosen; radiochromic film was used to measure possible dose to skin under the masks. Comparisons were made using these masks with 6-MV photon beams delivered by a Varian Truebeam machine. Results: For a 10×10 cm field size at 100 SSD, the surface dose as normalized to maximum dose (at 0.5 cm) was determined to be about 30% as measured by both EDR and EBT2 films. Peripheral dose with an open 10x10 field at 10 cm depth matched previously published data for Co-60. Skin dose due to thermoplastic mask buildup was at least 30% higher (depending on mask construction) with Co-60 as compared to 6-MV due to its lower energy. Conclusion: While the magnetic field of an integrated MR-IGRT system is expected to reduce skin dose by sweeping away contamination electrons, the use of Co-60 introduces the added challenge of carefully choosing immobilization devices in order to preserve the skin-sparing effect of the MR. Drs. Green, Hu, and Mutic have served as consultants to ViewRay, Inc.

TU‐C‐108‐06: Performance of KCl:Eu2+ Storage Phosphor Dosimeters for Low Dose Measurements

Purpose: Recent research has demonstrated that europium doped potassium chloride (KCl:Eu2+) storage phosphor material has the potential to become the physical foundation of a novel and reusable dosimetry system using either film‐like devices or devices similar to thermoluminescent dosimeter chips. In this work, we will quantify the low dose detection resolution of the KCl:Eu2+ prototype dosimeter and demonstrate how it can be incorporated into clinical application for in vivo peripheral dose measurements. Methods: The prototype KCl:Eu2+ dosimeters used in this study were manufactured according to standard materials processes, and had a physical makeup similar to thermoluminescent dosimeter chips. The lowest dose‐to‐water of 0.01 cGy in this work was achieved underneath a fully closed multileaf collimator at a source‐to‐surface distance of ∼200 cm. For doses greater than 100 Gy, prototype dosimeters were irradiated using the XRLM4 beamline at the Center for Advanced Mircrostructure and Devices synchrotron facility at Louisiana State University in Baton Rouge, LA. To compare sensitivity, two commercial storage phosphor detectors were also irradiated under the same conditions. The dosimeters were read using a laboratory photostimulated luminescence detection system. Results: KCl:Eu2+ prototype storage phosphor dosimeter is capable of measuring a dose‐to‐water as low as 0.01 cGy from a 6MV photon beam with a signal‐to‐noise ratio greater than 6. Agfa MD10, Fuji STIII and KCl:Eu2+ prototypes were within 10% in sensitivity. A pre‐readout thermal annealing procedure enables the dosimeter to be read within an hour post irradiation. The dosimeter retains a constant response after receiving large accumulated doses (∼10 kGy). The energy‐dependence encountered during low dose peripheral measurements can be accounted for via a single point outside‐field calibration per each beam quality. Conclusions: With further development the KCl:Eu2+− based dosimeter could become a versatile and durable dosimetry tool with large dynamic range (sub‐cGy to 100 Gy). This work was supported in part by NIH Grant No. R01CA148853.

Peripheral dose measurements with diode and thermoluminescence dosimeters for intensity modulated radiotherapy delivered with conventional and un-conventional linear accelerator

The objective of this paper was to measure the peripheral dose (PD) with diode and thermoluminescence dosimeter (TLD) for intensity modulated radiotherapy (IMRT) with linear accelerator (conventional LINAC), and tomotherapy (novel LINAC). Ten patients each were selected from Trilogy dual-energy and from Hi-Art II tomotherapy. Two diodes were kept at 20 and 25 cm from treatment field edge. TLDs (LiF:MgTi) were also kept at same distance. TLDs were also kept at 5, 10, and 15 cm from field edge. The TLDs were read with REXON reader. The readings at the respective distance were recorded for both diode and TLD. The PD was estimated by taking the ratio of measured dose at the particular distance to the prescription dose. PD was then compared with diode and TLD for LINAC and tomotherapy. Mean PD for LINAC with TLD and diode was 2.52 cGy (SD 0.69), 2.07 cGy (SD 0.88) at 20 cm, respectively, while at 25 cm, it was 1.94 cGy (SD 0.58) and 1.5 cGy (SD 0.75), respectively. Mean PD for tomotherapy with TLD and diode was 1.681 cGy SD 0.53) and 1.58 (SD 0.44) at 20 cm, respectively. The PD was 1.24 cGy (SD 0.42) and 1.088 cGy (SD 0.35) at 25 cm, respectively, for tomotherapy. Overall, PD from tomotherapy was found lower than LINAC by the factor of 1.2-1.5. PD measurement is essential to find out the potential of secondary cancer. PD for both (conventional LINAC) and novel LINACs (tomotherapy) were measured and compared with each other. The comparison of the values for PD presented in this work and those published in the literature is difficult because of the different experimental conditions. The diode and TLD readings were reproducible and both the detector readings were comparable.