Grid/lattice therapy: Consideration of small field dosimetry.

Small-field dosimetry used in special procedures such as gamma knife, Cyberknife, Tomotherapy, IMRT and VMAT has been in evolution after several radiation incidences with very significant (70%) errors due to poor understanding of the dosimetry. IAEA-TRS-483 and AAPM-TG-155 have provided comprehensive information on small-fields dosimetry in terms of code of practice and relative dosimetry. Data for various detectors and conditions have been elaborated. It turns out that with a suitable detectors dose measurement accuracy can be reasonably (±3%) achieved for 6 MV beams for fields > 1x1 cm2. For grid therapy, even though the treatment is performed with small fields created by either customized blocks, multileaf collimator (MLC) or specialized devices, it is multiple small fields that creates combined treatment. Hence understanding the dosimetry in collection of holes of small field is a separate challenge that needs to be addressed. It is more critical to understand the scattering conditions from multiple holes that form the treatment grid fields. Scattering changes the beam energy (softer) and hence dosimetry protocol needs to be properly examined for having suitable dosimetric parameters. In lieu of beam parameter unavailability in physical grid devices, MLC based forward and inverse planning is an alternative path for bulky tumors. Selection of detectors in small field measurement is critical and it is more critical in mixed beams created by scattering condition. Ramification of small field concept used in grid therapy along with major consideration of scattering condition is explored. Even though this review article is focused mainly for dosimetry for low energy megavoltage photon beam (6 MV) but similar procedures could be adopted for high energy beams. To eliminate small field issues, lattice therapy with the help of MLC is a preferrable choice.

The Italian young medical physicist scenario: Results from the young AIFM group survey.

PURPOSE: The young working group of the Italian Association of Medical and Health Physics (AIFM) designed a survey to assess the current situation of the under 35 AIFM members. METHODS: An online survey including 65 questions was designed to gather personal information, educational issues, working and research experience, and to evaluate the AIFM activities. The survey was distributed to the under 35 members between November 2022 and February 2023, through the young AIFM mailing list and social media. RESULTS: 160 answers from 230 affiliates (70%, 31 years median age) were obtained. The results highlighted that 87% of the respondents had a fixed term/permanent employment, mainly in public hospitals (58%). Regarding Medical Physicists (MPs) training, 54% of the students left their region of origin due to the training plan (40%) and the availability of scholarships (25%) in the chosen university. Most of the respondents have no Radiation Protection Expert title, while the remaining 20%, 6%, and 3% are qualified to the first, second, and third level, respectively. Several young MPs (62.2%) were involved in research activities; however, only 28% had teaching experience, mainly within their workplace (20%, safety courses), during AIFM courses (4%), or university lectures (3%). CONCLUSIONS: This survey reported the current situation of the under 35 AIFM members, highlighting the "brain drain" phenomenon from the south to the north of Italy, mainly due to the lack of post-graduate schools, scholarships, and job opportunities. The obtained results will help the future working program of the AIFM.

Validation of [Formula: see text]Tc and [Formula: see text]Lu quantification parameters for a Monte Carlo modelled gamma camera.

PURPOSE: Monte Carlo (MC) simulation in Nuclear Medicine is a powerful tool for modeling many physical phenomena which are difficult to track or measure directly. MC simulation in SPECT/CT imaging is particularly suitable for optimizing the quantification of activity in a patient, and, consequently, the absorbed dose to each organ. To do so, validating MC results with real data acquired with gamma camera is mandatory. The aim of this study was the validation of the calibration factor (CF) and the recovery coefficient (RC) obtained with SIMIND Monte Carlo code for modeling a Siemens Symbia Intevo Excel SPECT-CT gamma camera to ensure optimal [Formula: see text]Tc and [Formula: see text]Lu SPECT quantification. METHODS: Phantom experiments using [Formula: see text]Tc and [Formula: see text]Lu have been performed to measure spatial resolution and sensitivity, as well as to evaluate the CF and RC from acquired data. The geometries used for 2D planar imaging were (1) Petri dish and (2) capillary source while for 3D volumetric imaging were (3) a uniform filled cylinder phantom and (4) a Jaszczack phantom with spheres of different volumes. The experimental results have been compared with the results obtained from Monte Carlo simulations performed in the same geometries. RESULTS: Comparison shows good accordance between simulated and experimental data. The measured planar spatial resolution was 8.3[Formula: see text] mm for [Formula: see text]Tc and 11.8±0.6 mm for [Formula: see text]Lu. The corresponding data obtained by SIMIND for [Formula: see text]Tc was 7.8±0.1 mm, while for [Formula: see text]Lu was 12.4±0.4 mm. The CF was 110.1±5.5 cps/MBq for Technetium and 18.3±1.0 cps/MBq for Lutetium. The corresponding CF obtained by SIMIND for [Formula: see text]Tc was 107.3±0.3 cps/MBq, while for [Formula: see text]Lu 20.4±0.7 cps/MBq. Moreover, a complete curve RCs vs Volume (ml) both for Technetium and Lutetium was determined to correct the PVE for all volumes of clinical interest. In none of the cases, a RC coefficient equal to 100 was found. CONCLUSIONS: The validation of quantification parameters shows that SIMIND can be used for simulating both gamma camera planar and SPECT images of Siemens Symbia Intevo using [Formula: see text]Tc and [Formula: see text]Lu radionuclides for different medical purposes and treatments.

Validity of equivalent square field concept in small field dosimetry.

PURPOSE: The equivalent square (ES) concept has been used for traditional radiation fields defined by the machine collimating system. For small fields, the concept Sclin was introduced based on measuring dosimetric field width (full-width half maximum, FWHM) of the cardinal axis of the beam profiles. The pros and cons of this concept are evaluated in small fields and compared with the traditional ES using area and perimeter (4A/P) method based on geometric field size settings, for example, light field settings. METHODS: One hundred thirty-seven square and rectangular fields from 5-50 mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 50 mm) were utilized to measure FWHM for the validation of Sclin . Using a microSilicon detector and a scanning water tank, measurements were performed on an Elekta (Versa) machine with Agility head and a Varian TrueBeam with different MLC/Jaw design to evaluate the Sclin concept and to understand the effect of exchange factor in small fields. Field output factors were also measured for all 137 fields. RESULTS: The data fitting for fields ranging from 5-50 mm between the traditional 4A/P method and Sclin shows differences and indicates a linear relationship with distinct separation of slope for Elekta and Varian machines. For Elekta Agility machine ES based on 4A/P < Sclin and for the VarianTrueBeam  4A/P > Sclin for square fields. Our measured data show that both methods are equally valid but does vary by the machine design. The field output factor is dependent on the elongation factor as well as machine design. For fields with sides ≥10 mm, the exchange factor is nearly identical in both machines with magnitude up to 4%, which is close to measurement uncertainty (±3%), but for small fields (< 10 mm), the Elekta machine has higher exchange factors compared to the Varian machine. CONCLUSION: The results demonstrate that the two concepts for defining equivalent field (Sclin and 4A/P) are equivalent and can be directly related through an empirical equation. This study confirms that 4A/P is still valid for small fields except for very small fields (≤10 mm) where source occlusion is a dominating factor. The Sclin method is potentially sensitive to measurement uncertainty due to measurement of FWHM which is machine-, detector- and user-dependent, while the 4A/P method relies mainly on geometry of the machine and has less dependency on type of machine, detector, and user. The exchange factors are comparable for both types of machines. The conclusion is based on data from an Elekta with Agility head and a Varian TrueBeam machine that may have potential for bias due to light field/collimator set up and alignment. Care should be taken in extrapolating these data to any other machine.

Variable tilt-angle, parallel-hole collimation system for high-resolution molecular imaging gamma tomosynthesis.

PURPOSE: This study investigates a novel gamma tomosynthesis (GT) method based on a variable tilt-angle, parallel-hole collimator (VAPHC) which, mounting to a conventional gamma, is able to perform high-resolution three-dimensional imaging. METHODS: The VAPHC has the remarkable feature to be modular, consisting of independent collimation elements able to tilt according to variable angles [-45° to +45°]. Spatial resolutions were measured in reconstructed GT images using a point source at different source-to-collimator distances, while sensitivity was evaluated over the range of slant angles using a disk-source. Image contrast (IC) and contrast-to-noise-ratio (CNR) of sub-centimeters tumors were evaluated using a breast phantom containing a background activity and spheres filled with 99mTc to simulate lesions at two depths. Breast phantom GT images were compared with planar and circular-orbit SPECT acquisitions of equal scan-time. RESULTS: Planar spatial resolutions range from 9 to 14 mm over a depth range of 6-10 cm; spatial resolution in depth dimension becomes two times greater than those in the other dimensions. The measured sensitivity decreases from 9 cps/µCi to 6 cps/µCi varying the slant angle from 5° to 45°. The measured IC and CNR of GT reconstructed images demonstrated that it was possible to improve the spatial resolution/sensitivity trade-off. CONCLUSIONS: The proposed GT based VAPHC demonstrated the potential for superior spatial resolution and contrast compared to planar and SPECT acquisitions. A conventional gamma camera equipped with the VAPHC could be located at the minimum distance from the patient, thus improving detection, localisation and characterisation of sub-centimetre lesions.

Usefulness of iodine-123 whole-body scan in planning iodine-131 treatment of the differentiated thyroid carcinoma in children and adolescence.

OBJECTIVE: Radioiodine treatment (RAI-T) of differentiated thyroid carcinoma (DTC) is important to avoid disease progression, in particular in pediatric patients. For these reasons, a diagnostic scan may be useful to assess therapeutic tailored activity. The purpose of our study was to evaluate the usefulness of diagnostic whole-body scan (WBS) with iodine-123 (I) in combination with recombinant human thyroid-stimulating hormone (rh-TSH; Thyrogen) (rh-TSH-Dx-WBS), in planning RAI-T or further surgery before RAI-T in pediatric DTC. PATIENTS AND METHODS: Among 101 rh-TSH-Dx-WBS of 55 patients (21 males, mean age: 15 years, range: 5-18 years) followed at the Bambino Gesù Pediatric Hospital for DTC from February 2004 to December 2016, 41 rh-TSH-Dx-WBS scans of 41 patients (20 male and 21 female, mean age: 14 years, range: 5-18 years) performed for staging before RAI-T were retrospectively evaluated. Thyroglobulin was determined at baseline and on day 5. RESULTS: Receiver operating characteristic curve analysis showed that thyroglobulin alone is not a good predictor for staging modification (area under the curve=0.6855). rh-TSH-Dx-WBS showed both remnant and lymph node in 11 (27%), lymph node localization alone in one (2.5%), lung alone in 1/41 (2.5%), both lymph node and lungs in 2/41 (5%), and thyroid remnant alone in 26/41 (63%) patients. rh-TSH-Dx-WBS modified staging in 12/41 (29%): in 3/12 (25%) for the presence of lung metastases and in 9/12 (75%) for lymph node involvement. In all these patients, administered activity for RAI-T was then modified or further surgery was planned. CONCLUSION: Although further studies are needed, our data showed that combined use of rh-TSH and I-Dx-WBS allows an accurate and complete staging of disease, to implement the best therapeutic plan.

Quantification of scatter radiation from radiographic procedures in a neonatal intensive care unit.

BACKGROUND: In a neonatal intensive care unit (NICU), preterm infants are often exposed to a large number of radiographic examinations, which could cause adjacent neonates, family caregivers and staff members to be exposed to a dose amount due to scatter radiation. OBJECTIVE: To provide information on scatter radiation exposure levels in a NICU, to compare these values with the effective dose limits established by the European Union and to evaluate the effectiveness of radiation protection devices in this setting. MATERIALS AND METHODS: Radiation exposure levels due to scatter radiation were estimated by passive detectors (thermoluminescent dosimeters) and direct dosimetric measurements (with a dose rate meter); in the latter case, an angular map of the scatter dose distribution was achieved. RESULTS: The dose due to scatter radiation to staff in our setting is approximately 160 µSv/year, which is markedly lower than the effective dose limit for workers established by the European Union (20 mSv/year). The doses range between 0.012 and 0.095 µSv/radiograph. Considering a mean hospitalization period of 3 months and our NICU workload, the corresponding scatter radiation dose to an adjacent patient and/or his/her caregiver is at most 40 µSv. CONCLUSION: For distances greater than 1 m from the irradiation field, both scatter dose absorbed by a staff member during a year and that by an adjacent patient and/or his/her caregiver during hospitalization is less than 1 mSv, which is the exposure limit for public members in a year.

A novel method for CT dosimetry with a suspended phantom setup.

PURPOSE: This work presents a method for estimating CT dosimetric indices with a prototype designed for suspending the phantom/ion chamber system fixed at the CT isocenter. The purpose of this study was to validate the proposed methodology, which can be used to provide a direct assessment of dosimetric indices in helical scans. METHODS: The method is based on a reference setup in which the measuring system for CT dosimetry is in a stationary configuration, i.e. not bound to the CT table, and on a mathematical formalism developed for the proposed reference system. The reliability of the method was demonstrated through a set of experimental measurements. Firstly, dosimetric indices were measured with the new method and compared with the indices obtained with the procedure currently used for CT dosimetry (measuring system bound to the CT table). Secondly, dosimetric indices measured with the new method were compared with those displayed on the CT console. RESULTS: There is good agreement between the dosimetric indices obtained with the standard setup and those obtained with the suspended phantom setup, within the expected range of errors. The difference between dosimetric indices estimated with the proposed method and those displayed on the CT console is below 2%. CONCLUSIONS: The method enables CT dosimetry to be performed with the dose detector in a stationary longitudinal position thanks to the newly introduced suspended phantom setup. Using this approach, CT dose can be assessed for high pitch helical scans, acquisitions without complete tube rotation and for cases where dynamic collimation is used.

Non-vascular interventional procedures: effective dose to patient and equivalent dose to abdominal organs by means of DICOM images and Monte Carlo simulation.

This study evaluates X-ray exposure in patient undergoing abdominal extra-vascular interventional procedures by means of Digital Imaging and COmmunications in Medicine (DICOM) image headers and Monte Carlo simulation. The main aim was to assess the effective and equivalent doses, under the hypothesis of their correlation with the dose area product (DAP) measured during each examination. This allows to collect dosimetric information about each patient and to evaluate associated risks without resorting to in vivo dosimetry. The dose calculation was performed in 79 procedures through the Monte Carlo simulator PCXMC (A PC-based Monte Carlo program for calculating patient doses in medical X-ray examinations), by using the real geometrical and dosimetric irradiation conditions, automatically extracted from DICOM headers. The DAP measurements were also validated by using thermoluminescent dosemeters on an anthropomorphic phantom. The expected linear correlation between effective doses and DAP was confirmed with an R(2) of 0.974. Moreover, in order to easily calculate patient doses, conversion coefficients that relate equivalent doses to measurable quantities, such as DAP, were obtained.

A simplified edge illumination set-up for quantitative phase contrast mammography with synchrotron radiation at clinical doses.

This work presents the first study of x-ray phase contrast imaging based on a simple implementation of the edge illumination method (EIXPCi) in the field of mammography with synchrotron radiation. A simplified EIXPCi set-up was utilized to study a possible application in mammography at clinical doses. Moreover, through a novel algorithm capable of separating and quantifying absorption and phase perturbations of images acquired in EIXPCi modality, it is possible to extract quantitative information on breast images, allowing an accurate tissue identification. The study was carried out at the SYRMEP beamline of Elettra synchrotron radiation facility (Trieste, Italy), where a mastectomy specimen was investigated with the EIXPCi technique. The sample was exposed at three different energies suitable for mammography with synchrotron radiation in order to test the validity of the novel algorithm in extracting values of linear attenuation coefficients integrated over the sample thickness. It is demonstrated that the quantitative data are in good agreement with the theoretical values of linear attenuation coefficients calculated on the hypothesis of the breast with a given composition. The results are promising and encourage the current efforts to apply the method in mammography with synchrotron radiation.