The use of computed tomography (CT) has become a common practice in medical diagnosis in Indonesia. Its number, however, is not matched by the availability of dedicated-performance-check phantoms. This paper aims to describe the design, construction, and evaluation of an in-house phantom for CT performance check that accommodates both radiation dose measurement and image quality performance checks. The phantom is designed as laser-cut polymethyl methacrylate (PMMA) slabs glued together to form a standard cylindrical shape, with spaces to place dose measurement and image quality modules. In this paper, measurement results on both aspects are discussed and compared with standard phantoms and other works. For dose measurement, the constructed phantom exhibited the greatest absolute discrepancy against the reference standard phantom of 8.89 %. Measurement of the CT number linearity and modulation transfer function (MTF) yielded, at most, 7.51 % and 5.07 % discrepancies against Catphan 604, respectively. Meanwhile, although found to be more linear in the phantom-based contrast linearity test, the use of the in-house phantom for clinical image contrast threshold determination requires further study. For noise power spectrum (NPS) measurement, accurate results were obtained within a limited range of spatial frequency.

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Low Dose Computed Tomography (LDCT) is well-known for lung screening which administers low dose on the patient. In screening, intrapulmonary lymph node (IPLN) and lymph node in mediastinum (soft tissue) need special attention. In this research, nodule simulations with 36-85 Hounsfield units (HU) were made. IPLN was embedded inside lung simulation medium that was shaped as the module for 002LFC CIRS Thorax Phantom. The same method was also used for lymph node that was embedded in the soft tissue area. Image acquisition was conducted using LDCT and SDCT (Standard Dose Computed Tomography) methods with 100 kV and 120 kV exposure condition. The variations for mAs were 11, 25, 30, and 50 for LDCT and 70, 80, 90, 100 for SDCT. The result showed that IPLN image could be detected using LDCT method at 100 kV. Meanwhile, lymph node in soft tissue was not easily detected using LDCT because the noise in LDCT was relatively higher than in SDCT.

Abstract. DSSuperDose v.1.0 is an in-house treatment planning system (TPS) developed by Medical Physics and Biophysics Laboratory (LFMB) Universitas Indonesia as a treatment planning software for Cobalt-60 teletherapy unit. The main objective of this study was the validation of in-house TPS calculation as an essential part in quality assurance (QA) of radiotherapy. Validation of an in-house TPS was performed with two Cobalt-60 teletherapy units by comparison between in-house TPS and ISIS TPS and by measurements of absorbed dose. Mean dose deviations between in-house TPS and measurement were (1.97 ± 2.42)% for open field, (1.32 ± 1.30)% for tray field, and (2.91 ± 2.36)% for wedge field treatments. Inhouse TPS provide optimal planning for open and tray beam conditions with depth fewer than 10 cm (≤ 10 cm) and field sizes up to 20×20 cm 2 , while for wedge beam conditions with field sizes fewer than the physical size of the wedge. Comparison of in-house TPS and ISIS TPS demonstrated a good match of 96%. From the results, it is concluded that DSSuperDose v.1.0 is adequately accurate for treatment planning of radiotherapy.

A lutetium 177 (177Lu) radiopharmaceutical has been used for a theragnostic agent in molecular radiotherapies. This study aimed to investigate the image quality of SPECT image from 177Lu from Jaszczak Cylindrical Phantom based on tomographic uniformity, local-sphere uniformity, and signal-to-noise ratio (SNR). Data acquisitions were conducted using a SPECT/CT unit. For contrast measurement, six hollow sphere inserts with diameters of 9.9, 12.4, 15.6, 19.7, 24.8, and 31.2 mm were filled by 177Lu with radioactivity concentration 10 times higher than the warm background. Images were reconstructed using three different iterative reconstruction algorithms, including Flash3D, OSEM2D, and Wallis. All reconstructions were carried out with the same iteration number of 4, subset number of 4, and Gaussian Filter. Results for tomographic uniformity measurement were (112.47±8.40%), (114.30±9.59%), and (105.94±17.49%) counts for Flash3D, OSEM2D, and Wallis algorithms, respectively. Flash3D algorithm provided better tomographic uniformity than others, while Wallis algorithm yielded the highest noisy image with low SNR. Local-sphere uniformity and SNR tended to significantly increase for sphere diameters larger than 19.70 mm. It was concluded that the reconstruction method significantly affects the image quality in 177Lu quantification. Then, it seems that Flash3D is the best reconstruction method for 177Lu SPECT image acquisition.