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To determine the feasibility of an anthropomorphic breast polyurethane-based three-dimensional (3D) dosimeter with cavity to measure dose distributions and skin dose for a commercial strut-based applicator strut-adjusted volume implant (SAVI™) 6–1.
Materials and methods
An anthropomorphic breast 3D dosimeter was created with a cavity to accommodate the SAVI™ strut-based device. 2 Gy was prescribed to the breast dosimeter having D95 to planning target volume evaluation (PTV_EVAL) while limiting 125% of the prescribed dose to the skin. Independent dose distribution verification was performed with GAFCHROMIC® EBT2 film. The dose distribution from the 3D dosimeter was compared to the distributions from commercial brachytherapy treatment planning system (TPS) and film. Point skin doses, line profiles and dose–volume histogram (DVHs) for the skin and PTV_EVAL were compared.
The maximum difference in skin dose for TPS and the 3D dosimeter was 4% whereas 41% between the TPS and EBT2 film. The maximum dose difference for line profiles between TPS, 3D dosimeter, and film was 4·1%. DVHs of skin and PTV_EVAL for TPS and 3D dosimeter differed by a maximum of 4% at 5 mm depth and skin differed by a maximum 1·5% between TPS and 3D dosimeter. The criterion for gamma analysis comparison was 92·5% at ±5%±3 mm criterion. The TPS demonstrated at least ±5% comparability in predicting dose to the skin, PTV_EVAL and normal breast tissue.
3D anthropomorphic polyurethane dosimeter with cavity gives comparable results to the TPS dose predictions and GAFCHROMIC® EBT2 film results in the context of HDR brachytherapy.
Accurate three-dimensional dosimetry is essential in modern radiotherapy techniques such as volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT). In this research work, the PRESAGE® dosimeter was used as quality assurance (QA) tool for VMAT planning for head and neck (H&N) cancer.
Material and method
Computer tomography (CT) scans of an Image Radiation Oncology Core (IROC) H&N anthropomorphic phantom with both IROC standard insert and PRESAGE® insert were acquired separately. Both CT scans were imported into the Pinnacle (9.4 version) TPS for treatment planning, where the structures [planning target volume (PTV), organs at risk) and thermoluminescent detectors (TLDs) were manually contoured and used to optimise a VMAT plan. Treatment planning was done using VMAT (dual arc: 182°–178°, 178°–182°). Beam profile comparisons and gamma analysis were used to quantify agreement with film, PRESAGE® measurement and treatment planning system (TPS) calculated dose distribution.
The average ratio of TLD measured to calculated doses at the four PTV locations in the H&N phantom were between 0·95 to 0·99 for all three VMAT deliveries. Dose profiles were taken along the left–right, the anterior–posterior and superior–inferior axes, and good agreement was found between the PRESAGE® and Pinnacle profile. The mean value of gamma results for three VMAT deliveries in axial and sagittal planes were found to be 94·24 and 93·16% when compared with film and Pinnacle, respectively. The average values comparing the PRESAGE® results and dose values calculated on Pinnacle were observed to be 95·29 and 94·38% in the said planes, respectively, using a 5%/3 mm gamma criteria.
The PRESAGE® dose measurements and calculated dose of pinnacle show reasonable agreement in both axial and sagittal planes for complex dual arc VMAT treatment plans. In general, the PRESAGE® dosimeter is found to be a feasible QA tool of VMAT plan for H&N cancer treatment.
Whole-breast external beam radiotherapy results in significant reduction in the risk for breast cancer-related death, but this may be offset by an increase in deaths from other causes and toxicity to surrounding organs. Partial breast irradiation techniques are approaches that treat only the lumpectomy area rather than the whole breast. Quality assurance in the radiation therapy treatment planning process is essential to ensure accurate dose delivery to the patient. For this purpose, this article compares the results from an anthropomorphic PRESAGE® dosimeter, radiation treatment planning system and from the GAFCHROMIC® EBT2 film.
Materials and methods
A breast dosimeter was created and a three-field partial plan was generated in the Pinnacle3 treatment planning system. Dose distribution comparisons were made between Pinnacle3 treatment planning system, GAFCHROMIC® EBT2 film and PRESAGE® dosimeter. Dose–volume histograms (DVHs), gamma maps and line profiles were used to evaluate the comparison.
DVHs of gross tumour volume, clinical tumour volume and planning tumour volume for the PRESAGE® dosimeter and Pinnacle3 treatment planning system shows that both measured and calculated statistics were in agreement, with a value of 97.8% of the prescribed dose. Gamma map comparisons showed that all three distributions passed 95% at the ±3%/±3 mm criteria. Comparisons of isodose line distribution between the PRESAGE® dosimeter, EBT2 film and planning system demonstrated agreement, with an average difference of 1.5%.
This work demonstrated the feasibility of PRESAGE® to function as an anthropomorphic phantom and laid the foundation for research studies in PRESAGE®/optical-computed tomography three-dimensional dosimetry with the most complex anthropomorphic phantoms.
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