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Improving Dose Accuracy of HDR Brachytherapy Treatment of Skin Lesions Using Freiburg Flap Applicator Based on Reference Radiochromic Film Dose Measurements
Abstracts / Brachytherapy 16 (2017) S14eS118 no serious complications detected during the follow-up period. Radioactive iodine-125 seed implantation can improve the target volume dose, with the high doses of radioactive iodine-125 seed, the tumor, which was refractory and insensitive to chemotherapy, can be effectively controlled and complications are less than conventional chemotherapy. Conclusions: CT-guided iodine-125 seed implantation appeared to be a safe, useful and less complicated treatment option for locally recurrent urothelial carcinoma after failure of conventional chemotherapy. However, the longterm efficacy of this treatment needs further follow-up.
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with respect to the phantom surface (Figure 1(a)). The impact of bolus (0, 0.5, 1, 2 and 3 cm thicknesses) placed on top of the applicator was investigated for two treatment plan loadings created using MasterPlanÔ (Ver 4.1): 5 cm 5 cm, and 11 cm 11 cm (Figure 1(b) top). The vertical axis in these top subfigures represents direction along which dose values were calculated at different depths. The measured and calculated dose values were compared in terms of percentage difference to the calculated dose. Dose prescription was 6 Gy at 1 cm depth and this choice was based on dose uncertainty established during film calibration. Results: Figure 1(b) (bottom) depicts the influence of bolus thickness on dose difference between TPS and film measurements. As expected, TPS systematically underestimated the actual delivered dose. For depths beyond 2 cm (for smaller targets, i.e. 5 cm 5 cm) and 1 cm (for larger targets, i.e. 11 cm 11 cm), the actual systematic error is less than 3%, which is also the uncertainty limit of our radiochromic film dosimetry system. At shallower depths, addition of 2 cm bolus for smaller lesions as well as 1 cm bolus for larger lesions will provide a dose difference of less than 3%. Conclusions: In this work, we investigated the impact of lack of full scattering conditions on the use of FF applicator and corresponding percent difference between calculated and measured doses using an EBT3 radiochromic film dosimetry system. Differences of up to 6% at the surface were observed if no bolus was added on top of the applicator. To reduce this dose error to less than 3% along the central axis (including surface), one needs to add at least a 2 cm bolus for lesions smaller than 5 cm 5 cm, and 1 cm bolus for larger lesions.
PO93 Improving Dose Accuracy of HDR Brachytherapy Treatment of Skin Lesions Using Freiburg Flap Applicator Based on Reference Radiochromic Film Dose Measurements Saad Aldelaijan, M.Sc.1,2,3, Hamed Bekerat, Ph.D.2,1, Ivan Buzurovic, Ph.D.4, Phillip Devlin, MD4, Francois Deblois, Ph.D.2,1, Jan Seuntjens, Ph.D.1, Louis Collins, Ph.D.5, Slobodan Devic, Ph.D.2,1. 1Medical Physics Unit, McGill University, Montreal, QC, Canada; 2Department of Radiation Oncology, Jewish General Hospital, Montreal, QC, Canada; 3 Biomedical Physics Department, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia; 4Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham and Women’s Hospital, Boston, MA, USA; 5McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, QC, Canada. Purpose: Current HDR brachytherapy treatment planning systems (TPS) utilize the AAPM TG-43 datasets which assume full water phantom approximation in dose calculations. For skin treatments with the Freiburg flap (FF) applicator, this represents a setup different than the actual clinical situation where contributions of backscatter originating above the applicator and air gaps between the applicator spheres are missing. Aims of this work are twofold: to experimentally evaluate the dose calculation accuracy during surface treatments with the FF applicator at different depths, and to suggest means of improving the delivered dose accuracy in light of experimental results. Materials and Methods: Absolute doses were measured using a reference EBT3 model GAFCHROMICÔ film dosimetry system within a Solid WaterÔ (SW) phantom at five different depths (0, 0.5, 1, 2 and 3 cm)
Figure 1. (a) Experimental setup with 3 cm bolus. Five slabs of Solid WaterÔ positioned below the applicator were indented to accommodate film pieces (1’’ 2’’ in size) to alleviate any impact of air gaps. Bottom 5 cm slab was added to provide sufficient backscatter to measurement films, (b) Impact of bolus thickness on dose difference between TPS calculation and film measurements for two experimental setups: 5 cm 5 cm (top-left), and 11 cm 11 cm (top-right); dose difference histograms with numbers in parentheses representing dose values calculated at corresponding depths (bottom).
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with respect to the phantom surface (Figure 1(a)). The impact of bolus (0, 0.5, 1, 2 and 3 cm thicknesses) placed on top of the applicator was investigated for two treatment plan loadings created using MasterPlanÔ (Ver 4.1): 5 cm 5 cm, and 11 cm 11 cm (Figure 1(b) top). The vertical axis in these top subfigures represents direction along which dose values were calculated at different depths. The measured and calculated dose values were compared in terms of percentage difference to the calculated dose. Dose prescription was 6 Gy at 1 cm depth and this choice was based on dose uncertainty established during film calibration. Results: Figure 1(b) (bottom) depicts the influence of bolus thickness on dose difference between TPS and film measurements. As expected, TPS systematically underestimated the actual delivered dose. For depths beyond 2 cm (for smaller targets, i.e. 5 cm 5 cm) and 1 cm (for larger targets, i.e. 11 cm 11 cm), the actual systematic error is less than 3%, which is also the uncertainty limit of our radiochromic film dosimetry system. At shallower depths, addition of 2 cm bolus for smaller lesions as well as 1 cm bolus for larger lesions will provide a dose difference of less than 3%. Conclusions: In this work, we investigated the impact of lack of full scattering conditions on the use of FF applicator and corresponding percent difference between calculated and measured doses using an EBT3 radiochromic film dosimetry system. Differences of up to 6% at the surface were observed if no bolus was added on top of the applicator. To reduce this dose error to less than 3% along the central axis (including surface), one needs to add at least a 2 cm bolus for lesions smaller than 5 cm 5 cm, and 1 cm bolus for larger lesions.
PO93 Improving Dose Accuracy of HDR Brachytherapy Treatment of Skin Lesions Using Freiburg Flap Applicator Based on Reference Radiochromic Film Dose Measurements Saad Aldelaijan, M.Sc.1,2,3, Hamed Bekerat, Ph.D.2,1, Ivan Buzurovic, Ph.D.4, Phillip Devlin, MD4, Francois Deblois, Ph.D.2,1, Jan Seuntjens, Ph.D.1, Louis Collins, Ph.D.5, Slobodan Devic, Ph.D.2,1. 1Medical Physics Unit, McGill University, Montreal, QC, Canada; 2Department of Radiation Oncology, Jewish General Hospital, Montreal, QC, Canada; 3 Biomedical Physics Department, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia; 4Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham and Women’s Hospital, Boston, MA, USA; 5McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, QC, Canada. Purpose: Current HDR brachytherapy treatment planning systems (TPS) utilize the AAPM TG-43 datasets which assume full water phantom approximation in dose calculations. For skin treatments with the Freiburg flap (FF) applicator, this represents a setup different than the actual clinical situation where contributions of backscatter originating above the applicator and air gaps between the applicator spheres are missing. Aims of this work are twofold: to experimentally evaluate the dose calculation accuracy during surface treatments with the FF applicator at different depths, and to suggest means of improving the delivered dose accuracy in light of experimental results. Materials and Methods: Absolute doses were measured using a reference EBT3 model GAFCHROMICÔ film dosimetry system within a Solid WaterÔ (SW) phantom at five different depths (0, 0.5, 1, 2 and 3 cm)
Figure 1. (a) Experimental setup with 3 cm bolus. Five slabs of Solid WaterÔ positioned below the applicator were indented to accommodate film pieces (1’’ 2’’ in size) to alleviate any impact of air gaps. Bottom 5 cm slab was added to provide sufficient backscatter to measurement films, (b) Impact of bolus thickness on dose difference between TPS calculation and film measurements for two experimental setups: 5 cm 5 cm (top-left), and 11 cm 11 cm (top-right); dose difference histograms with numbers in parentheses representing dose values calculated at corresponding depths (bottom).