TY - JOUR
AU1 - Esen, Nsikan
AU2 - Ramachandran, Prabhakar
AU3 - Geso, Moshi
AB - ABSTRACT Stereotactic Ablative Radiotherapy (SABR) remains one of the preferred treatment techniques for early-stage cancer. It can be extended to more treatment locales involving the sternum, scapula and spine. This work investigates SABR checks using Alanine and nanoDot dosimeter for three treatment sites, including sternum, spine and scapula. Alanine and nanoDot dosimeters’ performances were verified using a 6 MV photon beam before SABR pretreatment verifications. Each dosimeter was placed inside customized designed inserts into a Rod Phantom (in-house phantom) made of Perspex that mimics the human body for a SABR check. Electron Paramagnetic Resonance (EPR) spectrometer, Bruker EleXsys E500 (9.5 GHz) and Microstar (Landauer Inc.) Reader was employed to acquire the irradiated alanine and nanoDot dosimeters’ signal, respectively. Both dosimeters treatment sites are expressed as mean ± standard deviation (SD) of the measured and Eclipse calculated dose Alanine (19.59 ± 0.24, 17.98 ± 0.15, 17.95 ± 0.18) and nanoDot (19.70 ± 0.43, 17.05 ± 0.08, 17.95 ± 0.98) for spine, scapula and sternum, respectively. The percentage difference between alanine and nanoDot dosimeters was within 2% for sternum and scapula but 2.4% for spine cases. These results demonstrate Alanine and nanoDot dosimeters’ potential usefulness for SABR pretreatment quality assurance (QA). INTRODUCTION Stereotactic Ablative Radiotherapy (SABR) remains one of the preferred treatment techniques for early-stage bronchogenic carcinomas, and it can be extended to more treatment locales involving the sternum and scapula, as well as the spine [1, 2]. SABR uses small fields that mandate the use of a miniature for pretreatment checks. The pretreatment verification plan is a significant step in complex radiation treatment procedures, ensuring that the patient receives the planned dose while limiting excess dose to critical organs with healthy tissues. Recent advancements in radiation therapy have led to new treatment procedures that could achieve minimal efforts [3]. Different types of dosimeter devices have been used for treatment planning checks, including ionization chamber (IC), diode, thermoluminescence dosimeter (TLD) and 2D array [4–8]. Alanine is a relatively new class of dosimeter that needs to be checked for its use in patient-specific SABR procedures. Alanine dosimetry is most generally utilized in industry [9, 10]. Also, Alanine is a well-known dosimeter [11, 12] and is broadly used for mailed dosimetry services [13–15]. It has a near tissue-equivalence composition, dose rate independence, minimal fading and non-destructive readout procedure [16–20]. In 2011, Garcia et al. [21] reported about the verification of Alanine-Electron Paramagnetic Resonance (EPR) dosimetry for dose delivery checks. Several studies [22–24] have shown the importance of Alanine-based EPR dosimetry for radiotherapy [25, 26] and, in particular, for radiosurgery checks [27–29]. Indeed, this is a non-destructive, stable and reproducible method. The basic principle of the Alanine readout consists of measuring a number of major free radicals created during irradiation, which is proportional to the absorbed dose. Alanine pellets present the advantages for medical applications of being a near tissue-equivalent composition material [28, 29], easy to handle and small in size. The dosimeter is particularly suitable for the radiosurgery high dose range, and absorbed dose measurements with high accuracy [30, 31]. Also, several works have shown that the Alanine/EPR service is an excellent candidate for end-to-end testing of radiotherapy/radiosurgery treatments using a small field as passive dosimeters for reference dosimetry [32]. Although the characterization of Alanine has been well documented elsewhere, until now, it has not been researched as a tool for pretreatment checks in SABR procedures. On the other hand, nanoDot optical stimulated luminescence (OSL) dosimeters are gaining popularity, and have been widely used in personnel dosimetry for more than 10 years. The nanoDot OSL dosimeter (OSLD) has extensive applications in radiotherapy environmental monitoring, and other fields. The application of nanoDot OSLDs has been extended to verify output calibration in a linear accelerator, brachytherapy source verification, quality assurance (QA) of treatment plans and clinical dose measurements [24]. The basic principle of a nanoDot OSLD is derived from electrons that are freed after being irradiated by ionizing radiation and then trapped as energy inside the forbidden gap which is generated due to impurities within the crystalline structure [27]. Aluminium oxide doped with carbon (Al2O3: C) is the most widely used material in nanoDot OSL dosimetry [28]. Although the fundamental characteristics of nanoDot OSL dosimetry using aluminium oxide have been studied, the performance of commercial nanoDot dosimeters in clinical practice has not been investigated, particularly for SABR treatment verification. This study aimed to investigate the performance of alanine-EPR and nanoDot detectors as devices for SABR pretreatment checks. MATERIALS AND METHODS Alanine dosimeter The Alanine pellets dosimeter (Batch Number T030901) used in this report is commercially available from SynergyHealth™, Radeberg GmbH. The Alanine pellets have a diameter and height of 4.8 × 3.0 mm with a mass ratio and binder of 0.96 and 0.04, respectively [35]. The mass of the Alanine pellet was 67.5 ± 0.1 mg, with a mass dosimeter range of ±0.5 mg and 0.3 mg. Irradiation of Alanine dosimeters protocol (calibration) In total, 20 Alanine pellets were irradiated at our hospital, using Clinax 21ix, in compliance with the IAEA TRS-398 protocol. Two Alanine pellets were positioned at the central axis of a solid water phantom, RW3 (25 × 25 × 25 cm3) at 1.5 cm depth with a standard source-to-surface distance (SSD) of 100 cm in a field size (FS) of 10 × 10 cm (6 MV photon beam). The dose range of the irradiated alanine pellets lies between 5 and 40 Gy. The Alanine pellets were irradiated at 5, 7.5, 10, 15, 20, 25, 30, 35 and 40 Gy. A relative humidity effect that may influence the readout intensity was avoided by storing the irradiated dosimeters in a desiccator and then transferring them into a labelled pill-box for 24 hours to allow for the stable free radical process [33, 34]. The concentrations of the free radicals were studied using the EPR spectrometer (section II.A6). Since the irradiation temperature affects the Alanine absorbed dose measurement, the temperature of the solid phantom was recorded to enable the temperature coefficient of the Alanine EPR signal. Angular-dependency Alanine directional independence was checked using a 6 MV X-ray beam. The directional response of the Alanine dosimeter was measured at four different gantry angles: 0°, 30°, 45° and 90°, using 6 MV X-ray beams, the dosimeters were irradiated to 10 Gy at 600 cGy/min. The irradiated Alanine was stored in an air-tight container to avoid any known pre-irradiation or post-irradiation influences before EPR readout. The irradiated Alanine dosimeters were read using EPR ELEXSYS E500 based on the specification parameters (section II.A6). The exposed Alanine was positioned perpendicularly in a quartz tube by 10 mm of interior diameter, then situated centrally in the tube-shaped cavity for readout. Finally, the peak-to-peak of the highest spectrum was measured as the signal intensity with direct proportionality to the absorbed dose (Fig. 1). Fig. 1. Open in new tabDownload slide Cavity tunning of alanine-EPR (A) cavity tunning [35] (B) Working principle of alanine – EPR (B) spectrum illustrating the amplitude and single integration areas as utilize for the peak-to-peak analysis (Screenshot during EPR scanning). Fig. 1. Open in new tabDownload slide Cavity tunning of alanine-EPR (A) cavity tunning [35] (B) Working principle of alanine – EPR (B) spectrum illustrating the amplitude and single integration areas as utilize for the peak-to-peak analysis (Screenshot during EPR scanning). Dose rate and energy dependency Dose rate and energy dependency verification were also performed before applying Alanine-EPR dosimeter for pretreatment QA of SABR checks. In total, 12 Alanine dosimeters were irradiated at dose rates ranging from 100 to 600 cGy/min in steps of 100 cGy/min. Then, two Alanine pellets were placed simultaneously at the central beam axis on solid water (RW3) slab phantom™ and delivered with 10 Gy in a 6 MV X-ray beam (100 cm SSD) at 10 × 10 cm2 FS. The concentrations of the free radicals were obtained using the EPR spectrometer, as discussed in section II.A1. Similarly, the energy dependence of the alanine signal was evaluated by delivering a dose of 10 Gy to two-photon beams (6 MV and 18 MV) at 600 cGy/min. The selected alanine dosimeter samples were placed centrally at the beam axis on a solid phantom. For irradiation, the standard FS of 10 × 10 cm2, 100 cm SSD and 1.5 cm depth was applied to investigate the dependency of the EPR-Alanine signal. EPR measurements EPR-Alanine measurements were carried out using Bruker ELEXSYS E500 EPR spectrometer [36] in our hospital. The spectrometer operates in x-band with a microwave frequency of 9.5 GHz in a permissible temperature -10°C to 80°C linear relationship and humidity of 46%. The centre field was set to 3400 G with a sweep time of 10.50s at 150 mT sweep width. Also, to enable correct tunning of the cavity, the field amplitude and receiver-gain and modulation frequency were set to 4.0 mT, 75 dB and 100 kHz, respectively. The EPR readouts were done 24 hrs after the irradiation of the Alanine pellets in a laboratory to allow for the stabilization of Alanine signal [33]. A quartz tube with a 5 mm internal diameter was utilized for controlling the alanine pellet (4.8 × 3.0 mm) in the centre of the cavity. In order to facilitate the reading and the EPR spectral resolution, the first derivative of the absorption curve was recorded. The EPR-Alanine readout procedure was performed twice each at four different angles (90°, 180°, 270° and 360°) to enable averaging the EPR-Alanine readout variation of the absorption curve spatial resolution [21]. The acquired background (BKG) signal was subtracted from the irradiated EPR signal readout. The Alanine pellet EPR signal is the average of the central peak amplitude of the EPR-Alanine spectrum [12, 13, 29] for the four angles mentioned above. Before the exposed Alanine pellets’ readout, four non-irradiated Alanine pellets were scanned at four different orientations to obtain the BKG signal. The BKG is the mean of the EPR-Alanine signal of four irradiated Alanine pellets of the same batch. The mean BKG EPR-Alanine signal was subtracted from each EPR-Alanine pellet signal. The Alanine EPR signal is the mean value of the four Alanine pellet signals obtained from the BKG and divided by their respective mass and its associated composed uncertainty. All the irradiated Alanine pellets were stored in a tight container filled with a reusable silica gel desiccant moisture absorber to monitor the dosimeter’s percentage humidity before measurement to avoid having significant fading effects. The fading was estimated to be around 1% per year during dark and cold storage, which did not influence this work. The entire uncertainties of this work were determined using a 2 (k = 2) coverage factor. NanoDot OSLDs The OSLDs used in this work were nanoDots™ (Landauer, Glenwood, Illinois, USA), consisting of aluminium oxide doped with carbon (Al2O3: C) with sensitive material placed in a plastic disk. The dimension of the sensitive volume has a diameter of 5 mm and a thickness of 0.2 mm with a thin, flexible strip of plastic made of polyester film on both sides of the disk (binding foil). The total diameter of the disk is 0.3 mm. The active volume is 0.49 mm for both the top and bottom height of the air gap. The sensitive area is enclosed in a plastic casing with 10 × 10 × 2 mm thickness [37]. Irradiation protocol of nanoDot OSLDs The nanoDot OSLD was placed at the centre of a solid water phantom (RW3™) to investigate its suitability for SABR pretreatment verification. The nanoDot OSLDs were calibrated using Clinax 21iX with a 6 MV photon beam in the RW3 slab phantom at the standard experimental set-up of 1.5 cm depth (dmax), SSD of 100 cm and FS of 10 × 10 cm. After irradiation, the exposure was stored in a dark container void of UV light to avoid the exposed dosimeter’s bleaching before readout. The measurement of the nanoDot OSL was repeated three times to acquire the mean dose value. The standard deviation (SD) of three readings was calculated as the error in measurement. A Microstar reader at our institution was used to acquire the nanoDot readout. Dose rate and directional dependence of nanoDot OSLDs In total, eight nanoDot OSLDs were irradiated with 10 Gy in a 6 MV X-ray beam at 1.5 cm depth at the central axis of RW3 slab (solid water) phantom with 10 × 10 cm2 (SSD = 100 cm). Four different orientations of 0°, 30° 45° and 60° were selected for the nanoDot OSLD directional check. Two nanoDot OSLDs for the selected angles were exposed with the set parameters. The irradiated nanoDot dosimeter signal was read using a Microstar Landauer reader. NanoDot OSLDs were irradiated to several different dose rates between 100 cGy/min and 600 cGy/Min with 6 MV beam. At a depth of 1.5 cm, the SSD and FS was set to 100 cm and 10 × 10 cm, respectively. The signal of the exposed nanoDot OSLD was read using a Microstar reader. The uncertainty for nanoDot OSL measurements was determined based on equation (1). $$\begin{equation} \mathrm{percentage}\kern0.17em \mathrm{uncertainty}=\frac{\frac{\mathrm{range}}{\mathrm{n}}}{\mathrm{mean}\kern0.17em \mathrm{value}}\times 100\% \end{equation}$$(1) Where n is the total number of experimental readings. PHANTOM DESIGN AND SABR MEASUREMENTS An in-house phantom made of Perspex called Rod Phantom was initially designed to fit in a CC13 IC. The Rod Phantom simulates the thorax’s shape and has provisions to accommodate films and TLDs in the transverse place. The CC13 chamber enabled pin-point dose measurement. Before patient-specific quality assurance (PSQA) was carried out, chamber calibration was performed by irradiating a known dose to the IC at patient-specific beam energy. Steps involved in PSQA include exporting a SABR plan onto the Rod Phantom, calculating the dose and comparing it to the dose measured in Linac. Most of the SABR QAs were performed using the Rod Phantom in our hospital, which permitted the medical physicists to acquire absolute and relative dosimetry in a single measurement. Multiple slabs in the designed phantom enabled us to explore other commercially available detectors. Three-dimensional (3D) inserts were designed using the ViaCADTH 2D/3D software program to accommodate these dosimeters inside the phantom, and output files were exported in.stl format (Fig. 2a–c). The designed inserts were made of Acrylonitrile Butadiene Styrene (ABS) with a density of 1.04 g/cm3. The designed inserts were printed on a 3D printing machine (CreatBot™). Both dosimeters were individually placed into the space provided at the centre of the designed inserts and positioned in a phantom (in-house) made of Perspex that mimicked the human body [38], to perform treatment check measurement (Fig. 2a–f). Different treatment locales, including the sternum and scapula as well as the spine, were considered. This phantom was scanned on a Philips® Brilliance Big Bore computed tomography (CT) scanner, and the DICOM CT images were transferred to the Eclipse™ planning system. Treatment plans were generated with a 0 mm multileaf-collimator (MLC) margin to planning target volume (PTV). The approved treatment plans were then exported to Rod Phantom for dose verification (Fig. 3). The dose was calculated at treatment-specific gantry angles. The phantom has provisions for inserting an EBT film and TLDs for measuring both absolute and relative dosimetry, respectively. Two separate inserts, as described above, were designed to accommodate both dosimeters. Each insertion was individually scanned and exported onto the Rod Phantom for SABR treatment checks (Fig. 2). Fig. 2. Open in new tabDownload slide (A) printed 3-D nanoDot insert designed, (B) printed 3-D alanine insert, (C) designed inserts with cover, (D) designed insert(s) positioned centrally in one of the segment of Rod Phantom, (E) initial designed of Rod Phantom, (F) Top view segment of Rod Phantom, and (G) Assembled Rod Phantom ready for CT scanning. Fig. 2. Open in new tabDownload slide (A) printed 3-D nanoDot insert designed, (B) printed 3-D alanine insert, (C) designed inserts with cover, (D) designed insert(s) positioned centrally in one of the segment of Rod Phantom, (E) initial designed of Rod Phantom, (F) Top view segment of Rod Phantom, and (G) Assembled Rod Phantom ready for CT scanning. Fig. 3. Open in new tabDownload slide PSQA workflow: (A) transversal view of UFT treatment, (B) model, sagittal, frontal and model view of treatment sites, and (C) experimental setup of the designed insertion on a CT. Fig. 3. Open in new tabDownload slide PSQA workflow: (A) transversal view of UFT treatment, (B) model, sagittal, frontal and model view of treatment sites, and (C) experimental setup of the designed insertion on a CT. SABR ECLIPSE TREATMENT PLAN The dose delivery method for the scapula was a 3D-CRT-based SABR plan (Fig. 3). In total, nine beams with two non-coplanar arrangements were used with the FS ranging from 5.3 to 8.0 cm2, SSD from 88.3 to 94.1 cm and the computed monitor units (MUs) were between 262 and 627. The dose maximum for the Scapula (RT Scalp UFT) treatment plan (PTS) was 132%, and the mean dose in the final ptvt7 was 17.825 Gy. While the sternum technique was also 3D-CRT based SABR plan with field ID Beam = 9, Gantry angle = 9, Couch rotation = 4, SSD 79.8 to 94.2 and MU 168 to 496, The Sternum UFT treatment plan had a PTV mean dose of 17.768 Gy. At the same time, Spine treatment site techniques were based on the intensity modulated radiation therapy SABR Plan shown in Fig. 6, generated from eight different beam and gantry angles with 2 degrees. The SSD and MU ranges were set at 70 cm to 86.3 cm, and 156 to 523, respectively. The PTV mean dose for the Spine treatment plan was 17.830 Gy. The detector was placed at the centre of the target (Fig. 4). Fig. 4. Open in new tabDownload slide Spine T 7 UFT (thoracic vertebrae 7)—IMRT–based SABR plan. Fig. 4. Open in new tabDownload slide Spine T 7 UFT (thoracic vertebrae 7)—IMRT–based SABR plan. UNCERTAINTY FOR ALANINE-EPR AND NANODOT OSLDS EPR dosimetry sources of uncertainty are related to: (i) the spectrometer measurement, (ii) the analyzed Alanine-sample mass, and (iii) the irradiation protocols. The absorbed dose measurement uncertainty was 0.47%. The irradiation protocols, the combined uncertainties of all uncertainties related to IC measurements, and to Alanine dosimeter positioning uncertainty (i.e. source-to-distance and depth in water), which is 0.15%. EPR-spectrometer parameters have been studied to obtain excellent repeatability of measurement and relative uncertainty for reproducibility, including the sample positioning in the spectrometer cavity, which is equal to 0.3% at 10 Gy. At the same time, Alanine pellet reproducibility accounted for 0.2% in the measured dose. The correction factor KT (product of the Boltzmann constant, K) for the temperature irradiation (T) taken into account with a temperature coefficient relative uncertainty of 0.02%. The absorbed dose-to-water uncertainty on the EPR measurements has been taken into account for each linear regression calculation and thus for each slope and its associated uncertainty. All the uncertainties have been established according to the guidelines of the Expression of Uncertainties in Measurement [34] and are calculated with a coverage factor k = 2. NanoDot OSLDs measurement uncertainty has been taken into account for linear regression calculation and the slope and associated uncertainty. In terms of reproducibility of each nanoDot measurement, the readout was performed over a couple of hours with reader constancy checks performed pre- and post-readout to ensure a negligible reader drift. For all the irradiated nanoDot OSLDs in this manner, three readings were performed per dosimeter and evaluated as the readout SD. The uncertainty was calculated following the relationship discussed in 1.0. RESULTS Alanine and nanoDot linearity The Alanine EPR calibration curve was obtained from a straight line plot by the least square method. The results indicate that the dosimeter has a high degree of linearity within the range of 5 to 30 Gy for a 6 MV X-ray beam with a linearity determination coefficient of 0.9972 (Fig. 5). The calibration indicates that the least square fit gives a good trend with evenly distributed residual points. Fig. 5. Open in new tabDownload slide Scatter plot and corresponding residual plot of dose–response of Alanine EPR for 6 MV beam at 10 × 10cm2 with SSD 100 cm. Fig. 5. Open in new tabDownload slide Scatter plot and corresponding residual plot of dose–response of Alanine EPR for 6 MV beam at 10 × 10cm2 with SSD 100 cm. A linear response curve of nanoDot was derived, and the results indicate that the dosimeter has a good trend with a high degree of linearity within the range of 0.5 to 45 Gy with a linearity coefficient (R2 = 0.9979) for 6 MV energies and even distribution of residual scatters (Fig. 6). Fig. 6. Open in new tabDownload slide Scatter plot and corresponding residual plot of dose linearity of nanoDOT™ OSLDs. Dose–response for 6 MV beam at 10 × 10cm2 with at SSD of 100 cm. Fig. 6. Open in new tabDownload slide Scatter plot and corresponding residual plot of dose linearity of nanoDOT™ OSLDs. Dose–response for 6 MV beam at 10 × 10cm2 with at SSD of 100 cm. Angular-dependency The directional dependency of Alanine dosimeters determined by irradiated gantry angles 0°, 45° and 90° is presented in Table 1. The results show the less significant directional influence of the alanine dosimeters at the considered angles. The three geometry considered have a value of 3.08 × 106, 3.04 × 106 and 3.07 × 106 with an SD of ±0.02. The relative SD of the selected angles was recorded at 0.68%. Table 1 Directional dependence of Alanine-EPR and nanoDot dosimeters at an angle of 0o, 30°, 45° and 90°. The samples were placed in solid water (RW3) slab phantom, 10 Gy was delivered using 6 MV X-ray beam at 10 × 10cm2 FS with SSD = 100 cm. The SD was recorded at ±0.02, with a % RSD of ±0.6% Angle . Alanine (^6) . nanoDot(^3) . 0 3.05 7.45 30 3.06 7.51 45 3.07 7.55 90 3.07 7.61 Mean ± SD 3.063 ± 0.015 7.53 ± 0.058 Angle . Alanine (^6) . nanoDot(^3) . 0 3.05 7.45 30 3.06 7.51 45 3.07 7.55 90 3.07 7.61 Mean ± SD 3.063 ± 0.015 7.53 ± 0.058 *SD = standard deviation Open in new tab Table 1 Directional dependence of Alanine-EPR and nanoDot dosimeters at an angle of 0o, 30°, 45° and 90°. The samples were placed in solid water (RW3) slab phantom, 10 Gy was delivered using 6 MV X-ray beam at 10 × 10cm2 FS with SSD = 100 cm. The SD was recorded at ±0.02, with a % RSD of ±0.6% Angle . Alanine (^6) . nanoDot(^3) . 0 3.05 7.45 30 3.06 7.51 45 3.07 7.55 90 3.07 7.61 Mean ± SD 3.063 ± 0.015 7.53 ± 0.058 Angle . Alanine (^6) . nanoDot(^3) . 0 3.05 7.45 30 3.06 7.51 45 3.07 7.55 90 3.07 7.61 Mean ± SD 3.063 ± 0.015 7.53 ± 0.058 *SD = standard deviation Open in new tab The directional dependence of nanoDot OSLDs was verified in the 6 MV X-ray beams of a Variance 21iX linear accelerator PMCC. The uncertainty shows an SD between two angles (30° and 45°) to be ±0.03% and an RSD of 0.4%. When compared with the literature [35], the dependency of nanoDot dosimeters is not significant. Dose rate and energy dependency Table 2 shows the dose rate dependency curve from 100 to 600 cGy/Min for 6 MV X-ray beams. The Alanine dosimeters have a high dose rate independent signal response for the dose ranging from 100 to 600 cGy/Min with an SD of ±0.4% for 6 MV and SSD of 100 cm at 10 × 10 cm2 FS. This result was compared with the IC (0.6 cc) in energy dependence using the same methodology with 6 MV and 15 MV. The result indicates no significant difference between the energies considered. Table 2 Dose-rate dependence of Alanine- and nanoDot dosimeters. The dose-rate was selected between 100 cGy/min to 600 cGy/min with a relative SD of ±0.4%. Also, two Alanine samples were placed in an RW3 slab phantom, 10 Gy was delivered at 6 MV energy with 10 × 10 cm2 FS and standard SSD (= 100 cm) Dose rate . Alanine (^6) . nanoDot(^3) . 100 6.95 7.63 200 6.96 7.71 300 6.96 7.48 400 6.93 7.45 500 6.97 7.76 600 6.99 7.77 Mean ± SD 6.972 ± 0.027 7.633 ± 0.128 Dose rate . Alanine (^6) . nanoDot(^3) . 100 6.95 7.63 200 6.96 7.71 300 6.96 7.48 400 6.93 7.45 500 6.97 7.76 600 6.99 7.77 Mean ± SD 6.972 ± 0.027 7.633 ± 0.128 *SD = standard deviation Open in new tab Table 2 Dose-rate dependence of Alanine- and nanoDot dosimeters. The dose-rate was selected between 100 cGy/min to 600 cGy/min with a relative SD of ±0.4%. Also, two Alanine samples were placed in an RW3 slab phantom, 10 Gy was delivered at 6 MV energy with 10 × 10 cm2 FS and standard SSD (= 100 cm) Dose rate . Alanine (^6) . nanoDot(^3) . 100 6.95 7.63 200 6.96 7.71 300 6.96 7.48 400 6.93 7.45 500 6.97 7.76 600 6.99 7.77 Mean ± SD 6.972 ± 0.027 7.633 ± 0.128 Dose rate . Alanine (^6) . nanoDot(^3) . 100 6.95 7.63 200 6.96 7.71 300 6.96 7.48 400 6.93 7.45 500 6.97 7.76 600 6.99 7.77 Mean ± SD 6.972 ± 0.027 7.633 ± 0.128 *SD = standard deviation Open in new tab The dose rate dependence curve for nanoDot dosimeters from 100 to 600 cGy/Min for 6 MV X-ray beams illustrates a high dose rate independence response for the dose rates ranging from 100 to 600 cGy/min having an SD of 0.2% for 6 MV X-ray beams between the measured values. The comparison of measured and planned doses of Alanine and nanoDot dosimeters for various treatment sites (Table 3). The percentage difference trend of the dosimeters and different treatment sites for pretreatment verification for SABR patients. Table 3 shows a complete summary of Alanine and nanoDot measured and treatment planning doses with various sites, including the spine, sternum and scapula. Table 3 Summary of Alanine and nanoDot MD and TPS comparison . Alanine . . nanoDot . . . Sp . Sc . St . Sp . Sc . St . MD 19.83 18.12 18.12 20.13 17.67 18.12 TPS 19.35 17.83 17.77 19.27 17.83 17.77 Mean ± SD 19.59 ± 0.24 17.975 ± 0.15 17.945 ± 0.18 19.7 ± 0.43 17.75 ± 0.08 17.945 ± 0.98 % Diff. 2.00 0.40 2.40 1.05 1.30 1.05 . Alanine . . nanoDot . . . Sp . Sc . St . Sp . Sc . St . MD 19.83 18.12 18.12 20.13 17.67 18.12 TPS 19.35 17.83 17.77 19.27 17.83 17.77 Mean ± SD 19.59 ± 0.24 17.975 ± 0.15 17.945 ± 0.18 19.7 ± 0.43 17.75 ± 0.08 17.945 ± 0.98 % Diff. 2.00 0.40 2.40 1.05 1.30 1.05 *Sp = spine, Sc = scapula, St = sternum, MD = Measured Dose, TPS = Treatment planning system, SD = standard deviation. Open in new tab Table 3 Summary of Alanine and nanoDot MD and TPS comparison . Alanine . . nanoDot . . . Sp . Sc . St . Sp . Sc . St . MD 19.83 18.12 18.12 20.13 17.67 18.12 TPS 19.35 17.83 17.77 19.27 17.83 17.77 Mean ± SD 19.59 ± 0.24 17.975 ± 0.15 17.945 ± 0.18 19.7 ± 0.43 17.75 ± 0.08 17.945 ± 0.98 % Diff. 2.00 0.40 2.40 1.05 1.30 1.05 . Alanine . . nanoDot . . . Sp . Sc . St . Sp . Sc . St . MD 19.83 18.12 18.12 20.13 17.67 18.12 TPS 19.35 17.83 17.77 19.27 17.83 17.77 Mean ± SD 19.59 ± 0.24 17.975 ± 0.15 17.945 ± 0.18 19.7 ± 0.43 17.75 ± 0.08 17.945 ± 0.98 % Diff. 2.00 0.40 2.40 1.05 1.30 1.05 *Sp = spine, Sc = scapula, St = sternum, MD = Measured Dose, TPS = Treatment planning system, SD = standard deviation. Open in new tab DISCUSSION Alanine is considered one of the most reliable dosimeters, and its near tissue equivalence property makes it an ideal dosimeter for radiotherapy applications. It requires no energy correction for megavoltage beams used in radiotherapy. It has less fading and highly suitable for pretreatment QA of SABR treatment plans where the dose per fraction is usually greater than 10 Gy. OSLDs, on the other hand, are a potential alternative to TLDs and are increasingly being used in most radiotherapy centres. This study specifically chose Alanine and nanoDot OSLDs for patient-specific pretreatment verification of three treatment sites: spine, sternum and scapula. Both dosimeters were evaluated before SABR treatment by determining dose linearity, dose rate, energy, directional and FS dependencies, as well as measurement uncertainties. As discussed in section II, calibration curves were established for both alanine and nanoDot OSLDs using the EPR spectrometer and Microstar reader. The calibration curves for the absorbed dose-to-water for both dosimeters measured at our institutions are presented in Fig. 5 and Fig. 6, respectively. The obtained results indicate that both dosimetry systems have a linear dose–response relationship in the radiosurgery dose range. The intercepts of the two regression lines of Alanine and nanoDot dosimeters agree with zero points within the uncertainty. The residuals have an even distribution with an average value <0.1 cGy. The R2 values for both dosimeter calibration curves indicate excellent linearity for the values obtained for 0.5 to 40 Gy doses range and compared well with the literature [41]. Similarly, both dosimeters’ output factors showed a positive trend compared with the IC and Alanine from National Laboratory. The relative differences for a smaller field size – 2 cm × 2 cm between alanine and nanoDot dosimeters is ±0.07, which compared well with ion chamber and National Physical Laboratory (NPL) Alanine, but to unity at 10 × 10 cm2 (Fig. 7). Fig. 7. Open in new tabDownload slide Output factor of Alanine (blue), nanoDot (purple), NPL Alanine (green), and ionization chamber (red) at different collimator jaw-shaped FSs between 2 × 2 to 20 × 20 cm2 and 10 Gy. The SD between the square FSs is ±0.07, but normalized to unity with the Ion chamber and NPL alanine at 10 × 10 cm2. Fig. 7. Open in new tabDownload slide Output factor of Alanine (blue), nanoDot (purple), NPL Alanine (green), and ionization chamber (red) at different collimator jaw-shaped FSs between 2 × 2 to 20 × 20 cm2 and 10 Gy. The SD between the square FSs is ±0.07, but normalized to unity with the Ion chamber and NPL alanine at 10 × 10 cm2. SABR pretreatment verification is imperative in treatment workflow in SABR pretreatment verification. Presently there are a lot of dosimeters commercially available for patient QA. However, some dosimeters for physics’ QA available in the market require a specially made phantom for measurements. In this report, we have performed the verification of Alanine and nanoDot dosimeters. We have shown how these dosimeters were incorporated in an in-house designed phantom that mimics the shape of the thorax. Also, the customized insert has been designed to fit into the in-house phantom (Rod Phantom) to reduce physics’ QA by carrying out absolute dosimetry, 2D/3D dosimetry simultaneously and SABR treatment sites of the spine, scapula and sternum. This work indicates that both Alanine and nanoDot doses measured on the linac machine has a high degree of consistency to the calculated dose. An IMRT-based SABR plan was performed for the spine (T7 UFT–thoracic vertebrae 7). This treatment site’s eclipse treatment plan indicates a percentage uncertainty of 0.21% for Alanine and nanoDots dosimeters than the measured dose with a small SD of 0.24% and 0.43%, respectively. Spine SABR cases planned by IMRT showed a large SD for nanoDot OSLD (presented in Table 3), clearly indicating the variation coefficient. Similarly, the non-Spine (sternum and scapula) was delivered by 3D-CRT based SABR plan. The non-spine case treatment plan had mean doses in final ptvt7 of 17.77 and 17.83 Gy for both detectors. The sternum and scapula percentage uncertainties for both dosimeters were within 0.4%, with sternum higher in value of 0.98% for nanoDot OSLD. The percentage difference of alanine and nanoDot dosimeters was within 2%, within an acceptable range in radiation treatment. This work is a pilot study demonstrating the feasibility of using Alanine and OSLDs for pretreatment QA. Hence a limited number of cases were included in our study. Alanine-based dosimetry requires a dedicated EPR facility. Benchtop EPR readers could be used in radiotherapy settings for instant readout of alanine dosimeters. Our research shows that Alanine and OSLDs can be used as potential dosimeters for SABR QA. Alanine and nanoDot performances and their application for SABR checks have been studied. Both dosimeters show less significant dose-rate, energy and angular dependencies. The percentage difference of measured and Eclipse treatment plan dose for the two dosimeters and the applied treatment sites considered were coherent and gave a high degree of consistency. The consistency in the measured and Eclipse treatment plan dose of spine, sternum and scapula for both dosimeters confirm both dosimeters to be valuable for SABR pretreatment QA. ACKNOWLEDGEMENTS The authors acknowledge Engr. Paul Archer for his help during the 3-D phantom inserts design and Physics unit of the Physical science department of Peter Mac Cancer Centre, Melbourne, for allowing us protected time during the periodic experiments and designed work. The author would also like to thank Dr. N. J. 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Google Scholar OpenURL Placeholder Text WorldCat © The Author(s) 2021. Published by Oxford University Press on behalf of The Japanese Radiation Research Society and Japanese Society for Radiation Oncology. This article contains public sector information licensed under the Open Government Licence v3.0 (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).
TI - SABR pre-treatment checks using alanine and nanoDot dosimeters
JF - Journal of Radiation Research
DO - 10.1093/jrr/rrab056
DA - 2021-10-20
UR - https://www.deepdyve.com/lp/oxford-university-press/sabr-pre-treatment-checks-using-alanine-and-nanodot-dosimeters-0Wh9Zzrccw
SP - 1
EP - 1
VL - Advance Article
IS - 
DP - DeepDyve
ER -