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Use of radiochromic films in HDR Ir-192 brachytherapy dosimetry
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Abstracts/Physica Medica 32 (2016) e1–e70
90% of PD, respectively, was considered as providing the optimal clinical plan for PTV coverage. Liver Dmean, V7Gy and V12Gy were used against the PTV coverage (1-V100) to generate the fronts. Conformity index (CI = V100/PTV), gradient index (GI = V50/V100), homogeneity index (HI = D2%/PD) and healthy liver irradiation in terms of Dmean, V7Gy and V12Gy were calculated to compare different plans Results: About 150 plans per lesion were calculated to generate the fronts. The fronts for 1 mm MLC margin provided the best plans in terms of minimal liver irradiation. With 1 mm MLC margin, optimal clinical plans were obtained for IDS equal to 77–82%. GI shows a U-shaped behaviour with respect to prescribed IDS, CI and HI indexes, with minimum values at 1 mm for all metrics. The location of these minimal points was found independent of the tumour dimensions. Minimal GI values were found at HI values approximately equal to 1.3. Conclusions: Pareto fronts provide a rigorous strategy to choose clinical optimal plans in SBRT treatments. We show that a 1 mm MLC block margin provides the best results with regard to healthy liver tissue irradiation and steepness of dose fallout. http://dx.doi.org/10.1016/j.ejmp.2016.01.048
A.45 EPID-BASED IN-VIVO DOSIMETRY FOR VMAT TREATMENT DOSE VERIFICATION: INITIAL CLINICAL EXPERIENCE S. Cilla *,a, A. Ianiro a, F. Deodato a, G. Macchia a, C. Digesu a, A. Fidanzio b, L. Azario b, M. Craus a, P. Viola a, V. Valentini b, A.G. Morganti c, A. Piermattei b. a Fondazione di Ricerca e Cura Giovanni Paolo II – Università Cattolica del S. Cuore, Campobasso, Italy; b Policlinico Universitario A. Gemelli – Università Cattolica del S. Cuore, Roma, Italy; c DIMES Università di Bologna – Ospedale S. Orsola Malpighi, Bologna, Italy Purpose: To assess the usefulness of EPID-based in-vivo dosimetry (IVD) for complex VMAT treatments in clinical routine. Material and methods: 40 patients (20 with head–neck tumors and 20 with high-risk prostate cancer) treated with Elekta VMAT using simultaneous integrated boost were enrolled. IVD tests were evaluated by means of (i) R ratio between daily in-vivo isocenter dose and planned dose and (ii) γ-analysis between EPID integral portal images in terms of percentage of points with γ-value smaller than one (γ%) and mean γ-values (γmean), using a global 3%-3 mm criteria. Alert criteria of ±5% for R ratio, γ% < 90% and γmean > 0.67 were chosen. Results: A total of 620 transit EPID images were acquired during the treatment fractions. The mean R ratios were equal to 1.002 ± 0.018 and 0.993 ± 0.018 for HN and prostate treatments; in both cases, more than 95% of tests were within 5%. The 2D image γ-analysis showed γmean of 0.42 ± 0.16 and 0.43 ± 0.18 for HN and prostate treatments, respectively; 93.3% and 92.1% of tests were within alert criteria. Mean γ% were 92.9 ± 5.1% and 92.5 ± 5.8%. For HN and prostate treatments, 85.9% and 82.1% of tests were within alert criteria. Relevant discrepancies were observed in 3 HN patients: a set-up error was detected for one patient and two patients showed major anatomical variations (weight loss/tumor shrinkage) in the second half of treatment. For prostate treatments, most of tests outside the criteria were due to random anatomical changes (filling of rectum/bladder) and set-up uncertainties. All discrepancies would not have been detected by pretreatment verification. IVD results are displayed after 1 minute from the end of arc delivery. Conclusions: This procedure was able to detect when the delivery was inconsistent with the original plans, allowing physics and medical staff to promptly act in case of major deviations between measured and planned dose. http://dx.doi.org/10.1016/j.ejmp.2016.01.049
A.46 COMMISSIONING OF THE 4-D TREATMENT DELIVERY SYSTEM FOR ORGAN MOTION MANAGEMENT IN SCANNING PARTICLE BEAMS M. Ciocca *,a, S. Molinelli a, A. Mirandola a, A. Mairani a, S. Russo a, E. Mastella a, D. Panizza a, A. Pella a, P. Fossati a, M. Donetti a, F. Valvo a, G. Baroni b. a Fondazione CNAO, Pavia, Italy; b Politecnico di Milano, Milano, Italy
Introduction: The aim of this work was the clinical commissioning and validation of the dose delivery procedures for the treatment of moving targets in hadrontherapy with scanning pencil beams. Materials and methods: Radiochromic EBT3 films fixed to the moving Anzai respiratory phantom were exposed to mono-energetic carbon ion scanned homogeneous fields (E = 332 MeV/u, 6 × 6 cm2 field size, scanning step of 2 mm). To evaluate the interplay effect, field size and flatness for three different scenarios were compared to the static condition: gated irradiation alone, repainting alone and the combination of both. Respiratory signal was provided by the ANZAI pressure sensor or the optical tracking system (OTS) already in use at the CNAO. End-exhale phase and 1 s gating window were chosen (about 3 mm residual motion). Dose measurements were also performed using a PTW PinPoint ionization chamber inserted into the Brainlab ET Gating Phantom. Results: The combination of gating technique and repainting (N = 5) showed excellent results, being the only approach with a behavior close to the reference static condition (6% vs 4.3% flatness, identical field size and dose deviation within 1.5%). Treatment delivery time was comparably acceptable. The dose homogeneity for gated irradiation alone was poor (9% flatness). Both the Anzai pressure sensor and OTS appeared suitable for providing the respiratory signal. Conclusion: Results of measurements performed on different phantoms showed that the combination of gating and layered repainting techniques is suitable and safe to treat moving targets using scanning particle beams. Abdominal compression using thermoplastic masks has also been assessed as an additional strategy to mitigate the effect of patient respiration in the clinical practice. http://dx.doi.org/10.1016/j.ejmp.2016.01.050
A.47 USE OF RADIOCHROMIC FILMS IN HDR IR-192 BRACHYTHERAPY DOSIMETRY G. Compagnone *,a, F. Romani a, F. Bisello a, A.L. Angelini a, V. Mesisca a, S. Pini a, E. Lombardo a, A. Galuppi b, G. Frezza b, A.G. Morganti b. a UO Fisica Sanitaria, Azienda Ospedaliero – Universitaria di Bologna, Bologna, Italy; b UO Radioterapia, Azienda Ospedaliero – Universitaria di Bologna, Bologna, Italy Introduction: High-dose-rate (HDR) brachytherapy (BRT) procedures present difficult isodose measurements around the seeds due to steep dose gradient and narrow distances involved. Conventional detectors (ionization chambers or TLD) are inappropriate at small distances from the sources because of their relatively large sizes. In this contribution, the characterization of radiochromic films (RF) as a 2D dosimeter for clinical Ir-192 BRT systems was investigated. Time-offilm-readout (TFR), best response channel, calibration curve (CC), dose rate dependence and range-of-use were the focus of our study. Materials and methods: RF type EBT2 (ISP) was irradiated with two Ir192 BRT units (MicroSelectron V2 HDR and PDR, Nucletron). A Farmertype ionization chamber 0.6 cc TW30010 (PTW) was used for absolute dose measurements. TFR was evaluated for 1 and 10 Gy (2 films, scans after 1, 12, 24, 36, 72 h). The best response channel was chosen in the range of 1.3–12.4 Gy (5 films, scans after 24 h, 3 RGB channels). CC was determined in the range of 1–60 Gy (source–film distance 1 cm and 10 cm). Uncertainty analysis of the whole experimental chain and dose rate dependence (from 4.48 to 50.84 mGy/ h) was performed. All scans were carried out with a commercial flatbed scanner Epson Expression 1680ProCCD (Seiko). Results: Stability of the detector response within 2% was reached after 6 h (1 Gy exposure) and 8 h (10 Gy exposure). The calibration curve was established considering the green channel readout and interpolating the experimental data with a double exponential function. Dose rate independence of EBT2 film was proved. Uncertainty on the pixel values ranged from 1.1% to 6.0% (dose range: 3–30 Gy) and increased up to >10% for dose > 30 Gy. Conclusions: The feasibility of RF for Ir-192 BRT sources was assessed. An accurate calibration makes RF a suitable dosimeter for quality controls and dosimetry checks of clinical treatments. http://dx.doi.org/10.1016/j.ejmp.2016.01.051
Abstracts/Physica Medica 32 (2016) e1–e70
90% of PD, respectively, was considered as providing the optimal clinical plan for PTV coverage. Liver Dmean, V7Gy and V12Gy were used against the PTV coverage (1-V100) to generate the fronts. Conformity index (CI = V100/PTV), gradient index (GI = V50/V100), homogeneity index (HI = D2%/PD) and healthy liver irradiation in terms of Dmean, V7Gy and V12Gy were calculated to compare different plans Results: About 150 plans per lesion were calculated to generate the fronts. The fronts for 1 mm MLC margin provided the best plans in terms of minimal liver irradiation. With 1 mm MLC margin, optimal clinical plans were obtained for IDS equal to 77–82%. GI shows a U-shaped behaviour with respect to prescribed IDS, CI and HI indexes, with minimum values at 1 mm for all metrics. The location of these minimal points was found independent of the tumour dimensions. Minimal GI values were found at HI values approximately equal to 1.3. Conclusions: Pareto fronts provide a rigorous strategy to choose clinical optimal plans in SBRT treatments. We show that a 1 mm MLC block margin provides the best results with regard to healthy liver tissue irradiation and steepness of dose fallout. http://dx.doi.org/10.1016/j.ejmp.2016.01.048
A.45 EPID-BASED IN-VIVO DOSIMETRY FOR VMAT TREATMENT DOSE VERIFICATION: INITIAL CLINICAL EXPERIENCE S. Cilla *,a, A. Ianiro a, F. Deodato a, G. Macchia a, C. Digesu a, A. Fidanzio b, L. Azario b, M. Craus a, P. Viola a, V. Valentini b, A.G. Morganti c, A. Piermattei b. a Fondazione di Ricerca e Cura Giovanni Paolo II – Università Cattolica del S. Cuore, Campobasso, Italy; b Policlinico Universitario A. Gemelli – Università Cattolica del S. Cuore, Roma, Italy; c DIMES Università di Bologna – Ospedale S. Orsola Malpighi, Bologna, Italy Purpose: To assess the usefulness of EPID-based in-vivo dosimetry (IVD) for complex VMAT treatments in clinical routine. Material and methods: 40 patients (20 with head–neck tumors and 20 with high-risk prostate cancer) treated with Elekta VMAT using simultaneous integrated boost were enrolled. IVD tests were evaluated by means of (i) R ratio between daily in-vivo isocenter dose and planned dose and (ii) γ-analysis between EPID integral portal images in terms of percentage of points with γ-value smaller than one (γ%) and mean γ-values (γmean), using a global 3%-3 mm criteria. Alert criteria of ±5% for R ratio, γ% < 90% and γmean > 0.67 were chosen. Results: A total of 620 transit EPID images were acquired during the treatment fractions. The mean R ratios were equal to 1.002 ± 0.018 and 0.993 ± 0.018 for HN and prostate treatments; in both cases, more than 95% of tests were within 5%. The 2D image γ-analysis showed γmean of 0.42 ± 0.16 and 0.43 ± 0.18 for HN and prostate treatments, respectively; 93.3% and 92.1% of tests were within alert criteria. Mean γ% were 92.9 ± 5.1% and 92.5 ± 5.8%. For HN and prostate treatments, 85.9% and 82.1% of tests were within alert criteria. Relevant discrepancies were observed in 3 HN patients: a set-up error was detected for one patient and two patients showed major anatomical variations (weight loss/tumor shrinkage) in the second half of treatment. For prostate treatments, most of tests outside the criteria were due to random anatomical changes (filling of rectum/bladder) and set-up uncertainties. All discrepancies would not have been detected by pretreatment verification. IVD results are displayed after 1 minute from the end of arc delivery. Conclusions: This procedure was able to detect when the delivery was inconsistent with the original plans, allowing physics and medical staff to promptly act in case of major deviations between measured and planned dose. http://dx.doi.org/10.1016/j.ejmp.2016.01.049
A.46 COMMISSIONING OF THE 4-D TREATMENT DELIVERY SYSTEM FOR ORGAN MOTION MANAGEMENT IN SCANNING PARTICLE BEAMS M. Ciocca *,a, S. Molinelli a, A. Mirandola a, A. Mairani a, S. Russo a, E. Mastella a, D. Panizza a, A. Pella a, P. Fossati a, M. Donetti a, F. Valvo a, G. Baroni b. a Fondazione CNAO, Pavia, Italy; b Politecnico di Milano, Milano, Italy
Introduction: The aim of this work was the clinical commissioning and validation of the dose delivery procedures for the treatment of moving targets in hadrontherapy with scanning pencil beams. Materials and methods: Radiochromic EBT3 films fixed to the moving Anzai respiratory phantom were exposed to mono-energetic carbon ion scanned homogeneous fields (E = 332 MeV/u, 6 × 6 cm2 field size, scanning step of 2 mm). To evaluate the interplay effect, field size and flatness for three different scenarios were compared to the static condition: gated irradiation alone, repainting alone and the combination of both. Respiratory signal was provided by the ANZAI pressure sensor or the optical tracking system (OTS) already in use at the CNAO. End-exhale phase and 1 s gating window were chosen (about 3 mm residual motion). Dose measurements were also performed using a PTW PinPoint ionization chamber inserted into the Brainlab ET Gating Phantom. Results: The combination of gating technique and repainting (N = 5) showed excellent results, being the only approach with a behavior close to the reference static condition (6% vs 4.3% flatness, identical field size and dose deviation within 1.5%). Treatment delivery time was comparably acceptable. The dose homogeneity for gated irradiation alone was poor (9% flatness). Both the Anzai pressure sensor and OTS appeared suitable for providing the respiratory signal. Conclusion: Results of measurements performed on different phantoms showed that the combination of gating and layered repainting techniques is suitable and safe to treat moving targets using scanning particle beams. Abdominal compression using thermoplastic masks has also been assessed as an additional strategy to mitigate the effect of patient respiration in the clinical practice. http://dx.doi.org/10.1016/j.ejmp.2016.01.050
A.47 USE OF RADIOCHROMIC FILMS IN HDR IR-192 BRACHYTHERAPY DOSIMETRY G. Compagnone *,a, F. Romani a, F. Bisello a, A.L. Angelini a, V. Mesisca a, S. Pini a, E. Lombardo a, A. Galuppi b, G. Frezza b, A.G. Morganti b. a UO Fisica Sanitaria, Azienda Ospedaliero – Universitaria di Bologna, Bologna, Italy; b UO Radioterapia, Azienda Ospedaliero – Universitaria di Bologna, Bologna, Italy Introduction: High-dose-rate (HDR) brachytherapy (BRT) procedures present difficult isodose measurements around the seeds due to steep dose gradient and narrow distances involved. Conventional detectors (ionization chambers or TLD) are inappropriate at small distances from the sources because of their relatively large sizes. In this contribution, the characterization of radiochromic films (RF) as a 2D dosimeter for clinical Ir-192 BRT systems was investigated. Time-offilm-readout (TFR), best response channel, calibration curve (CC), dose rate dependence and range-of-use were the focus of our study. Materials and methods: RF type EBT2 (ISP) was irradiated with two Ir192 BRT units (MicroSelectron V2 HDR and PDR, Nucletron). A Farmertype ionization chamber 0.6 cc TW30010 (PTW) was used for absolute dose measurements. TFR was evaluated for 1 and 10 Gy (2 films, scans after 1, 12, 24, 36, 72 h). The best response channel was chosen in the range of 1.3–12.4 Gy (5 films, scans after 24 h, 3 RGB channels). CC was determined in the range of 1–60 Gy (source–film distance 1 cm and 10 cm). Uncertainty analysis of the whole experimental chain and dose rate dependence (from 4.48 to 50.84 mGy/ h) was performed. All scans were carried out with a commercial flatbed scanner Epson Expression 1680ProCCD (Seiko). Results: Stability of the detector response within 2% was reached after 6 h (1 Gy exposure) and 8 h (10 Gy exposure). The calibration curve was established considering the green channel readout and interpolating the experimental data with a double exponential function. Dose rate independence of EBT2 film was proved. Uncertainty on the pixel values ranged from 1.1% to 6.0% (dose range: 3–30 Gy) and increased up to >10% for dose > 30 Gy. Conclusions: The feasibility of RF for Ir-192 BRT sources was assessed. An accurate calibration makes RF a suitable dosimeter for quality controls and dosimetry checks of clinical treatments. http://dx.doi.org/10.1016/j.ejmp.2016.01.051