Testing a 3-D radiation therapy planning program

This report describes a systematic effort to test all functions of a large 3-D radiation therapy planning program, including graphics and user interaction. Previous studies in quality assurance for radiation therapy programs do not adequately address the problem of programming errors. They compare dose estimates calculated by planning programs to actual doses measured in phantoms, so they cannot distinguish programming errors from measurement errors or physical unsoundness of the beam model. Moreover, they fail to exercise graphics and user interaction functions. This report describes a different methodology: test cases are derived from the program specification, results are calculated by an independent technique, and compared to program output. Derivation of test cases is described in detail. Effectiveness of testing is assessed by reporting the number of errors revealed by testing and comparing to the number of errors discovered during routine use in five successive program versions. The size of the test set is related to the total program size, and the effort devoted to deriving and performing tests is compared to the total program development effort. We conclude that systematic testing can reveal errors that are not found by informal testing, routine program use, or comparison with measurements. However, additional errors remain that are only discovered during use. This study suggests that a typical large planning system may include more than 100 errors when it is released for clinical use. Methods for increasing testing effectiveness are recommended.     

Surface scanning for 3D dose calculation in intraoperative electron radiation therapy

Background

Dose calculations in intraoperative electron radiation therapy (IOERT) rely on the conventional assumption of water-equivalent tissues at the applicator end, which defines a flat irradiation surface. However, the shape of the irradiation surface modifies the dose distribution. Our study explores, for the first time, the use of surface scanning methods for three-dimensional dose calculation of IOERT.

Methods

Two different three-dimensional scanning technologies were evaluated in a simulated IOERT scenario: a tracked conoscopic holography sensor (ConoProbe) and a structured-light three-dimensional scanner (Artec). Dose distributions obtained from computed tomography studies of the surgical field (gold standard) were compared with those calculated under the conventional assumption or from pseudo-computed tomography studies based on surfaces.

Results

In the simulated IOERT scenario, the conventional assumption led to an average gamma pass rate of 39.9% for dose values greater than 10% (two configurations, with and without blood in the surgical field). Results improved when considering surfaces in the dose calculation (88.5% for ConoProbe and 92.9% for Artec).

Conclusions

More accurate three-dimensional dose distributions were obtained when considering surfaces in the dose calculation of the simulated surgical field. The structured-light three-dimensional scanner provided the best results in terms of dose distributions. The findings obtained in this specific experimental setup warrant further research on surface scanning in the IOERT context owing to the clinical interest of improving the documentation of the actual IOERT scenario.

     

Diagnostic Reference Levels for nuclear medicine imaging in Austria: A nationwide survey of used dose levels for adult patients

PurposeTo assess dose levels in routine nuclear medicine (NUC) procedures in Austria as a prior to a legislative update of the National Diagnostic Reference Levels (NDRL).MethodAs part of a nationwide survey of common NUC-examinations between June 2019 and November 2019, data sets were collected from 33 Austrian hospitals with NUC equipment. All hospitals were asked to report the NUC imaging devices in use (model, type, year of manufacture, detector material, collimators), the standard protocol parameters for selected examinations (standard activity, collimator, average acquisition time, reconstruction type, use of time-of-flight) and to report data from 10 representative examinations (e.g. injected activity, weight), incl. the most common NUC-examinations for planar imaging/SPECT and PET. Median/mean values for injected activity were calculated and compared to current Austrian and international NDRL. A Pearson correlation coefficient was computed comparing different variables.ResultsIn total, all 33 hospitals (100% response rate) reported data for this study for 60 SPECT devices, 21 PET/CT devices and 23 scintigraphy devices. Fixed activity values for scintigraphy/SPECT and PET were employed by about 90% and 56% of the hospitals, respectively. The most widely performed examinations for scintigraphy/SPECT are bone imaging, thyroid imaging, renal imaging (with MAG3/EC) and lung perfusion imaging (in 88% of the hospitals) and F-18 FDG-PET studies for oncology indications (in 100% of the hospitals). Significant correlations were found for patient weight and injected activity (scintigraphy/SPECT), use of iterative reconstruction and injected activity (PET) as well as size of field-of-view and injected activity (PET).ConclusionsThe reported injected activity levels were comparable to those in other countries. However, for procedures for which NDRL exist, deviations in injected activities of >20% compared to the NDRL were found. These deviations are assumed to result mainly from advances in technology but also from deviations between NDRL and prescribed activities as given in the information leaflets of the radiopharmaceuticals.     

Bone metastases: assessment of therapeutic response through radiological and nuclear medicine imaging modalities

Radiological and nuclear medicine imaging modalities used for assessing bone metastases treatment response include plain and digitalised radiography (XR), skeletal scintigraphy (SS), dual-energy X-ray absorptiometry (DEXA), computed tomography (CT), magnetic resonance imaging (MRI), [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG-PET) and PET/CT. Here we discuss the advantages and disadvantages of these assessment modalities as evident through different clinical trials. Additionally, we present the more established response criteria of the International Union Against Cancer and the World Health Organization and compare them with newer MD Anderson criteria. Even though serial XR and SS have been used to assess the therapeutic response for decades, several months are required before changes are evident. Newer techniques, such as MRI or PET, may allow an earlier evaluation of response that may be quantified through monitoring changes in signal intensity and standard uptake value, respectively. Moreover, the application of PET/CT, which can follow both morphological and metabolic changes, has yielded interesting and promising results that give a new insight into the natural history of metastatic bone disease. However, only a few studies have investigated the application of these newer techniques and further clinical trials are needed to corroborate their promising results and establish the most suitable imaging parameters and evaluation time points. Last, but not least, there is an absolute need to adopt uniform response criteria for bone metastases through an international consensus in order to better assess treatment response in terms of accuracy and objectivity.     

Estimated collective effective dose to the population from nuclear medicine examinations in Slovenia

Background

A national survey of patient exposure from nuclear medicine diagnostic procedures was performed by Slovenian Radiation Protection Administration in order to estimate their contribution to the collective effective dose to the population of Slovenia.

Methods

A set of 36 examinations with the highest contributions to the collective effective dose was identified. Data about frequencies and average administered activities of radioisotopes used for those examinations were collected from all nuclear medicine departments in Slovenia. A collective effective dose to the population and an effective dose per capita were estimated from the collected data using dose conversion factors.

Results

The total collective effective dose to the population from nuclear medicine diagnostic procedures in 2011 was estimated to 102 manSv, giving an effective dose per capita of 0.05 mSv.

Conclusions

The comparison of results of this study with studies performed in other countries indicates that the nuclear medicine providers in Slovenia are well aware of the importance of patient protection measures and of optimisation of procedures.     

Analysis of the dose calculation accuracy for IMRT in lung: a 2D approach

The purpose of this study was to compare the dosimetric accuracy of IMRT plans for targets in lung with the accuracy of standard uniform-intensity conformal radiotherapy for different dose calculation algorithms. Tests were performed utilizing a special phantom manufactured from cork and polystyrene in order to quantify the uncertainty of two commercial TPS for IMRT in the lung. Ionization and film measurements were performed at various measuring points/planes. Additionally, single-beam and uniform-intensity multiple-beam tests were performed, in order to investigate deviations due to other characteristics of IMRT. Helax-TMS V6.1(A) was tested for 6, 10 and 25 MV and BrainSCAN 5.2 for 6 MV photon beams, respectively. Pencil beam (PB) with simple inhomogeneity correction and 'collapsed cone' (CC) algorithms were applied for dose calculations. However, the latter was not incorporated during optimization hence only post-optimization recalculation was tested. Two-dimensional dose distributions were evaluated applying the gamma index concept. Conformal plans showed the same accuracy as IMRT plans. Ionization chamber measurements detected deviations of up to 5% when a PB algorithm was used for IMRT dose calculations. Significant improvement (deviations approximately 2%) was observed when IMRT plans were recalculated with the CC algorithm, especially for the highest nominal energy. All gamma evaluations confirmed substantial improvement with the CC algorithm in 2D. While PB dose distributions showed most discrepancies in lower (<50%) and high (>90%) dose regions, the CC dose distributions deviated mainly in the high dose gradient (20-80%) region. The advantages of IMRT (conformity, intra-target dose control) should be counterbalanced with possible calculation inaccuracies for targets in the lung. Until no superior dose calculation algorithms are involved in the iterative optimization process it should be used with great care. When only PB algorithm with simple inhomogeneity correction is used, lower energy photon beams should be utilized.     

Image diagnosis: nuclear medicine

Delineation of malignant tumor by scintigraphy is divided into two categories; visualizing tumor as positive foci or negative foci. Our clinical experiences with 67Ga, 201Tl, 131I-MIBG and 131Imonoclonal antibodies including 111In-ZMEO18 were described and literatures relevant to positive delineation of malignant tumor were reviewed.     

Evaluation of a pencil-beam dose calculation technique for charged particle radiotherapy

: The purpose of this article is to evaluate a pencil-beam dose calculation algorithm for protons and heavier charged particles in complex patient geometries defined by computed tomography (CT) data and to compare isodose distributions calculated with the new technique to those calculated with conventional algorithms in selected patients with skull-base tumors.

: Monte Carlo calculations were performed to evaluate the pencil-beam algorithm in patient geometries for a modulated 150-MeV proton beam. A modified version of a Mont Carlo code described in a previous publication (18) was used for these comparisons. Tissue densities were inferred from patient CT data on a voxel-by-voxel basis, and calculations were peformed with an without tissue compensators. A dose calculation module using the new algorithm was written, and treatment plans using the new algorithm were compared to plans using standard ay-tracing techniques for 10 patients with clival chordoma and three patients with nasopharyngeal carcinoma who were treated with helium ions at Lawrence Berkeley National Laboratory (LBL).

: Pencil beam calculations agreed well with Monte Carlo calculations in the patient geometries. The pencil-beam algorithm predicted several multiple-scattering effects that are not modeled by conventional ray-tracing calculations. These includes (a) the widening of the penumbra as a function of beam penetration, (b) the degradation in the sharpness of the dose gradient at the end of the particle range in hgihly heterogeneous regions, and (c) the appearance of hot and cold dose regions in the shadow of cmplex heterogeneities. In particular, pencil-beam calculations indicated that the dose distribution within the target was not a homogeneous as expected on the basis of ray-tracing calculations. on average, for the 13 patients considered, only about 72% of the cone down target volume received at least 99% of the prescribed dose, whereas, 93% of the conedwn volume was contained within the 95% isodose surface. This may e significant because in standard charged particle dose calculations, the dose across the spread-Bragg peak is assumed to be uniform and equal to the maximum or prescribed dose.

: Dose distributions computed with the pencil-beam model are more accurate than ray-tracing calculations, providing additional information to clinicians, which may influence the doses they prescribe. In particular, these calculations indicate that for some patients with skull-base tumors, it may be advantageous to prescribe proton doses to a lower isodose level than is commonly done.     

New devices for imaging in nuclear medicine

Pinhole gamma camera imaging offers the ability to obtain high resolution images from single gamma ray emitting radiotracers playing a reasonable tradeoff between very small field of view (FoV) and sensitivity. On the other hand the total spatial resolution of a pinhole imaging device is predominantly affected by the detector intrinsic spatial resolution for reduced magnification factors. To design very compact pinhole SPET scanners with very high intrinsic spatial resolution, authors investigated a miniature gamma camera based on the newly developed Hamamatsu H8500 flat panel photomultiplier. The PSPMT was coupled to the following scintillation arrays: CsI(Tl) array with 0.2-mm, 1-mm, 1.4-mm pixel size and NaI (Tl) with 1-mm pixel size. The imaging performances were evaluated by 57Co spot and flood irradiations. NaI(Tl) array shows a better pixel identification for 1 mm pixel size, proving to be a good candidate to make a large area photodetector based on multi PSPMTs closely packed. Although CsI(Tl) array had the smallest pixel size, the low light output limited the best intrinsic spatial resolution to about 0.5 mm.     

Radiolabelled monoclonal antibodies: a new diagnostic tool in nuclear medicine

This review describes the state of the art for scintigraphic tumour detection using radiolabelled very pure (monoclonal) antibodies. In vivo imaging by scintigraphy may be useful for visualisation of cancer sites and treatment monitoring in oncologic patients. Imaging includes the computer-assisted processing of the scintigrams to remove background and non-target radioactivity. The clinical use of this method ("radioimmunoscintigraphy") depends, however, on the availability of the desired antibodies. Developments in the field of antibody labelling and emission tomography in the upcoming years are crucial for the usefulness of radioimmunoscintigraphy in daily practice.     

Localized current field hyperthermia in carcinoma of the cervix: 3-D computer simulation of SAR distribution

Software was developed for the 3D simulation of SAR distribution for a 500kHz localized current field hyperthermia system to be used in patients with carcinoma of the cervix. This hyperthermia system was specifically designed for use with a modified Fletcher-Suit intracavitary applicator. It consists of software modules for data input, tetrahedral grid generation and a numerical calculation of SAR distribution using an adaptive, multilevel finite element code. The AVS (Advanced Visual System, Inc.) system was used for the visual presentation of the results. A quasi-static approach was employed for the determination of SAR distribution. Results of the performed numerical tests were presented and they showed an important, clinically relevant ability to obtain a selective power deposition. This selective power deposition depended on the applicator geometry, i.e. the distance between the components of a Fletcher-Suit applicator and their relative position and the use of different modes of excitation.     

The development of nuclear medicine in Slovenia and Ljubljana; half a century of nuclear medicine in Slovenia

Background

Nuclear medicine began to be developed in the USA after 1938 when radionuclides were introduced into medicine and in Europe after radionuclides began to be produced at the Harwell reactor (England, 1947). Slovenia began its first investigations in the 1950s. This article describes the development of nuclear medicine in Slovenia and Ljubljana. The first nuclear medicine interventions were performed in Slovenia at the Internal Clinic in Ljubljana in the period 1954–1959. In 1954, Dr Jože Satler started using radioactive iodine for thyroid investigations. In the same year, Dr Bojan Varl, who is considered the pioneer of nuclear medicine in Slovenia, began systematically introducing nuclear medicine. The first radioisotope laboratories were established in January 1960 at the Institute of Oncology and at the Internal Clinic. Under the direction of Dr. Varl, the laboratory at the Internal Clinic developed gradually and in 1973 became the Clinic for Nuclear Medicine with departments for in vivo and in vitro diagnostics and for the treatment of inpatients and outpatients at the thyroid department. The Clinic for Nuclear Medicine became a teaching unit of the Medical Faculty and developed its own post-graduate programme – the first student enrolled in 1972. In the 1960s, radioisotope laboratories opened in the general hospitals of Slovenj Gradec and Celje, and in the 1970s also in Maribor, Izola and Šempeter pri Novi Gorici.

Conclusions

Nowadays, nuclear medicine units are modernly equipped and the staff is trained in morphological, functional and laboratory diagnostics in clinical medicine. They also work on the treatment of cancer, increased thyroid function and other diseases.     

宫颈癌IMRT计划独立三维剂量验算的初步应用与探讨

目的 评估自动计划验证系统Mobius3D (M3D)在宫颈癌IMRT中进行独立三维剂量验算的可行性。方法 随机选取20例宫颈癌病例,将其分别在Pinnacle 9.2和Eclipse13.5计划系统中进行7个野均分IMRT计划设计,达到临床要求后将两套计划系统中优化计划分别导入M3D中。观察两套TPS在传输计划过程中ROI体积变化、靶区及OAR剂量计算差异,结合γ通过率评估M3D验算计划的精确性。结果 Pinnacle9.2传输至M3D中各ROI体积差异远远小于Eclipse13.5,其最大变化差异为0.22%±0.69%,Eclipse13.5中最大变化差异为3.50%±1.89%。M3D中显示两套TPS的靶区及OAR剂量计算值差异在±1%内,经过3D重新计算后Pinnacle9.2与M3D计算结果差异小于Eclipse13.5,但其平均差异均在±3%内。靶区和OAR的γ通过率均值>95%。结论 利用自动计划验证系统进行计划验证,过程方便快捷。目前可作为计划的二次检查应用,提高IMRT计划验算精确性。     

Postimplant dosimetry using a Monte Carlo dose calculation engine: a new clinical standard

PURPOSE: To use the Monte Carlo (MC) method as a dose calculation engine for postimplant dosimetry. To compare the results with clinically approved data for a sample of 28 patients. Two effects not taken into account by the clinical calculation, interseed attenuation and tissue composition, are being specifically investigated. METHODS AND MATERIALS: An automated MC program was developed. The dose distributions were calculated for the target volume and organs at risk (OAR) for 28 patients. Additional MC techniques were developed to focus specifically on the interseed attenuation and tissue effects. RESULTS: For the clinical target volume (CTV) D(90) parameter, the mean difference between the clinical technique and the complete MC method is 10.7 Gy, with cases reaching up to 17 Gy. For all cases, the clinical technique overestimates the deposited dose in the CTV. This overestimation is mainly from a combination of two effects: the interseed attenuation (average, 6.8 Gy) and tissue composition (average, 4.1 Gy). The deposited dose in the OARs is also overestimated in the clinical calculation. CONCLUSIONS: The clinical technique systematically overestimates the deposited dose in the prostate and in the OARs. To reduce this systematic inaccuracy, the MC method should be considered in establishing a new standard for clinical postimplant dosimetry and dose-outcome studies in a near future.     

Localized current field hyperthermia in carcinoma of the cervix: 3-D computer simulation of SAR distribution.

Software was developed for the 3D simulation of SAR distribution for a 500 kHz localized current field hyperthermia system to be used in patients with carcinoma of the cervix. This hyperthermia system was specifically designed for use with a modified Fletcher-Suit intracavitary applicator. It consists of software modules for data input, tetrahedral grid generation and a numerical calculation of SAR distribution using an adaptive, multilevel finite element code. The AVS (Advanced Visual System, Inc.) system was used for the visual presentation of the results. A quasi-static approach was employed for the determination of SAR distribution. Results of the performed numerical tests were presented and they showed an important, clinically relevant ability to obtain a selective power deposition. This selective power deposition depended on the applicator geometry, i.e. the distance between the components of a Fletcher-Suit applicator and their relative position and the use of different modes of excitation.     

Internal radionuclide dosimetry: diagnostic and therapeutic nuclear medicine,occupational and environmental exposures. Differences and similarities

In diagnostic nuclear medicine, model-derived effective dose estimates have been considered adequate for risk estimates for various patient groups. Average anthropomorphic models (normally MIRD models) and representative biokinetic models are used, with the main uncertainty being due to limited information on the biokinetics of the substance in representative groups of patients. In nuclear medicine therapy it is necessary to make patient-specific absorbed dose estimates, especially to dose-limiting risk organs and to the tumor tissue. Together with information on the time-activity curve (which may differ for the low test activity and the high therapeutic activity) in different organs and tissues, there is a need for detailed anatomical information, normally collected through CT- and/or MR-imaging through the body volumes of interest. The wish to get the radionuclide localized in the tumor cells and preferentially in the cell nuclei makes it essential to consider the increased biological effect resulting from the nonuniform distribution of the absorbed energy in tumors as well as in dose-limiting organs such as bone marrow, liver, and kidneys. The situation in occupational and environmental internal dosimetry resembles that of diagnostic nuclear medicine. However, biokinetic models derived for the former purposes are often constructed for relatively long-lived isotopes, and cannot be used for the short-lived isotopes of the same element, which are used in diagnostic nuclear medicine. Similarities and differences in objectives and methods for dosimetry in the different areas are discussed.