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

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Bour B. K. , Inkoom S. , Tagoe S. N. A. , Amuasi J. H. , Sasu E. , Hasford F.

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2020

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tom 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.

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

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Acquah G. F. , Hasford F. , Tagoe S. N. A. , Diakite A. , Adjenou V. , Osei E.

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tom 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

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Dumenya C. , Hasford F. , Tagoe S. N. A. , Sasu E. , Pokoo-Aikins M. , Asamanyuah B. B. , Amuasi J. H.

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2022

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tom 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.