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Dosimetric evaluation of VMAT automated breast treatment plans: Towards the establishment of an institutional plan acceptability criteria

Acquah George Felix, Hasford Francis, Tagoe Samuel Nii Adu, Diakite Adama, Adjenou Victor, Osei Ernest

Polish Journal of Medical Physics and Engineering

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2023

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Vol. 29, Iss. 4

185--194

EN

Introduction: To evaluate the clinical suitability of the current facility-based treatment plan protocol in establishing acceptability criteria. Material and methods: Automated Volumetric Arc Therapy (VMAT) treatment plans were retrospectively evaluated for intact breast and chest-wall cancer patients from January 2021 to January 2023. Results: A total of 94 patients were planned and treated using automated contouring and VMAT planning technique. The number of patients planned and treated for intact breast and chest-wall were 41 (43.6%) and 53 (56.4%), respectively. The mean intact breast volumes for optimization (Brst_opt) receiving 95% and 105% of the prescribed doses were 92.80% ± 1.11 and 1.54% ± 1.02, respectively. Their corresponding mean chest-wall volumes for optimization (Chst_opt) were 90.65% ± 3.19 and 2.28% ± 2.99, respectively. For left-sided cases, the mean heart dose received was 4.61 Gy ± 1.76 and 5.18 Gy ± 1.55 for intact breast plans and that for chest-wall plans, respectively. The mean ipsilateral lung volume receiving 20 Gy of the prescribed dose was 12.22% ± 3.86 and 13.19% ± 3.74 for intact breast plans and chest-wall plans, respectively. For the Brst_opt and Chst_opt dose metrics were calculated; the mean homogeneity index (HI) was 0.14 ± 0.03 and 0.15 ± 0.04, mean uniformity index (UI) was 1.09 ± 0.03 and 1.11 ± 0.03, and mean conformity index (CI) were 0.92 ± 0.04 and 0.91 ± 0.04, respectively. Conclusions: The dosimetric evaluation shows a good dose distribution in the target volumes with minimal doses to the organs at risk (OAR). Assessment of the current data affirms the clinical usefulness of the facility-adopted protocol in achieving quality treatment plans for intact breast and chest-wall irradiations. The establishment of plan acceptability criteria will help achieve improved overall treatment outcomes.

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Implementation of the Sievert integral for the calculation of dose distribution around the BEBIG Co-60 high dose rate brachytherapy source

Dumenya Castrol, Hasford Francis, Tagoe Samuel Nii Adu, Sasu Evans, Pokoo-Aikins Mark, Asamanyuah Belinda Buermle, Amuasi John Humphrey

Polish Journal of Medical Physics and Engineering

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2022

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Vol. 28, Iss. 2

90--98

EN

Introduction: In radiotherapy, a computerized treatment planning system (TPS) is used for performing treatment planning to estimate the dose distribution within a patient. To simplify the dose calculation, mathematical algorithms are employed. TG43 formalism is widely used for brachytherapy. Before the implementation of a particular dose calculation algorithm in clinical practice, it is imperative to acknowledge the limitations and uncertainties associated with the algorithm. Regarding this, outputs of the algorithm are compared to measurements or dose calculation approaches using simple source placement geometries. The manual dose calculation method has to be robust, straightforward, and devoid of complexities to reduce the likelihood of committing errors in the dose calculation process. A lot of manual dose calculation approaches have been proposed for Brachytherapy sources, but one needs to ascertain their reliability. Material and methods: Considering this, the output of an HDRplus treatment planning system dedicated to brachytherapy treatment planning and using the TG43 formalism to calculate the dose distribution around a BEBIG Co-60 source was validated with Sievert integral dose calculation approach. Simple source placement geometries were created with the TPS using the universal applicator, LLA1200-20, selected from the applicator library, and doses at various equidistant points from the applicator calculated with the TPS and the Sievert integral. Various steps to enhance the efficacy of the Sievert integral approach have been outlined. Results: The doses compared favourably well with deviations ranging from 0.03 – 10.51% (mean of 3.13%), and 0.03 – 5.63% (mean of 2.55%) for angles along the perpendicular bisector of the source, ranging from 0° < θ < 70° and 0° < θ < 48°, respectively. Conclusions: The Sievert integral breaks down at angles: θ ≥ 60°, and therefore, neglecting large angles, the Sievert integral would be an efficient, effective, and valid tool for quality control of the HDRplus TPS for the Co-60 source.

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Construction and pre-evaluation of an in-house cylindrical ionization chamber fabricated from locally available materials

Tagoe Samuel Nii Adu, Chaphuka Clement Dominic, Hasford Francis

Polish Journal of Medical Physics and Engineering

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2022

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Vol. 28, Iss. 4

188--199

EN

Introduction: The objectives of this study were to construct a very robust in-house cylindrical ionization chamber from locally available materials to minimize cost, and to assess its suitability for use in a clinical setting. Materials and Methods: The entire body of the constructed IC was composed of Perspex (PMMA). Other components of the IC were made from locally available materials, such as paper and discarded items. The in-house IC was made waterproof by passing the triaxial cable connecting its various electrodes through a plastic tube which once served as a drainage tube of a urine bag. This connection was made such that the chamber was vented to the environment. The completed in-house IC was evaluated for: polarity effect, ion recombination, ion collection efficiency, stability, dose linearity, stem effect, leakage current, angular, dose rate and energy dependences. Results: Although the pre-evaluation results confirmed that the in-house IC satisfied the stipulated international standards for ICs, there was a need to enhance the stem effect and leakage current characteristics of the IC. The in-house IC was found to have an absorbed dose to water calibration coefficient of 4.475 x 107 Gy/C (uncertainty of 1.6%) for cobalt 60 through a cross-calibration with a commercial 0.6 cc cylindrical IC with traceability to the Germany National Dosimetry Laboratory. Using a Jaffé diagram, the in-house IC was also found to have a recombination correction factor of 1.0078 when operated at the calibration voltage of + 400 V. In terms of beam quality correction factors for megavoltage beams, the in-house IC was found to exhibit characteristics similar to those of Scanditronix-Wellhofer IC 70 Farmer type IC. Conclusion: The constructed in-house Farmer-type IC was able to meet all the recommended characteristics for an IC, and therefore, the in-house IC is suitable for beam output calibration in external beam radiotherapy.

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Dose assessment in high dose rate brachytherapy with cobalt-60 source for cervical cancer treatment: a phantom study

Bour Bright Kwadwo, Inkoom Stephen, Tagoe Samuel Nii Adu, Amuasi John Humphrey, Sasu Evans, Hasford Francis

Polish Journal of Medical Physics and Engineering

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2020

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Vol. 26, Iss. 4

243--250

EN

Transition from low dose rate brachytherapy to high dose rate brachytherapy at our department necessitated the performance of dose verification test, which served as an end-to-end quality assurance procedure to verify and validate dose delivery in intracavitary brachytherapy of the cervix and the vaginal walls based on the Manchester system. An inhouse water phantom was designed and constructed from Perspex sheets to represent the cervix region of a standard adult patient. The phantom was used to verify the whole dose delivery chain such as calibration of the cobalt-60 source in use, applicator, and source localization method, the output of treatment planning with dedicated treatment planning system, and actual dose delivery process. Since the above factors would influence the final dose delivered, doses were measured with calibrated gafchromic EBT3 films at various points within the in-house phantom for a number of clinical implants that were used to treat a patient based on departmental protocol. The measured doses were compared to those of the treatment planning system. The discrepancies between measured doses and their corresponding calculated doses obtained with the treatment planning system ranged from -29.67 to 40.34% (mean of ±13.27%). These compared similarly to other studies.