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Dosimetric properties of 3D-printed flat bolus for external radiotherapy
Abstracts/Physica Medica 32 (2016) e1–e70
relative to PFD, with a slight overestimation of the tails (<1%), due to the absence of the shielding. Output factors were in good agreement for fields up to 5 × 5 cm2 (<1%). Conclusions: The Razor diode has the same spatial resolution of SFD with the additional advantages of improved stability, becoming a possible candidate for small field dosimetry. http://dx.doi.org/10.1016/j.ejmp.2016.01.195 A.192 A PRELIMINARY DOSIMETRIC STUDY TO VALIDATE MULTI-SEGMENT PLAN (FIELD IN FIELD) FOR BREAST IRRADIATION USING IN VIVO DOSIMETRY (IVD) S. Riccardi *, R. Nigro, R. Maglio, M.G. Mangiacotti, R. Cassese. S. Camillo de Lellis Hospital, Rieti, Italy Purpose: IVD represents an independent check of the dose able to highlight the reproducibility of the treatment over time and able to help avoiding systematic errors during dose delivery. Moreover, IVD may be useful to validate a new technique. The aim of this study is to evaluate the accuracy and reproducibility of dose distributions of breast treatments using fieldin-field (FIF) technique (TPS Eclipse-Varian) with SOFTDISO (Best Medical Italy Srl). The FIF technique is a forward planning approach that uses multileaf collimator sub-fields to improve dose uniformity throughout the whole breast volume. Method and materials: We acquired the portal image during each session for all beams of seven breast FIF treatment planned. The treatments were delivered with 6 MV photon beam by a Varian Clinac 2100 C/D. CT images, RT plan and portal images of patients were imported in SOFTDISO. SOFTDISO is provided with an analysis module dedicated to the reconstruction of the dose at the point isocenter from the portal images signal. The value of the transit signal is converted to a dose value, Diso, and compared with the value of calculated dose, Diso,TPS. The comparison is performed through the index R = Diso/Diso,TPS. The acceptance criterion was: 0.95 ≤ R ≤ 1.05. The daily EPID images were compared to a reference image obtained in the first session of therapy. A further module is dedicated to the gammaanalysis between the reference and daily portal image. Results: The comparisons showed good results. The R values for 5 treatments were within 1.5%. In two treatments were within 4%. In particular the R average for all sessions valued was 1.016 ± 0.021. The gammaanalysis, performed with 3 mm/5% criteria, yielded Pg < 1 ≥ 93% in 80% of the tests, 20% of the tests supplied 88% ≤ Pg < 1 < 93% due to small setup variations. Conclusions: The IVD assures that the FIF treatment has a good reproducibility during treatment sessions and can replace the standard breast treatment with dynamic wedges. http://dx.doi.org/10.1016/j.ejmp.2016.01.196 A.193 INTRAFRACTION BREAST DISPLACEMENTS DURING HELICAL TOMOTHERAPY R. Ricotti *,a, D. Ciardo a, G. Fattori b,c, M.C. Leonardi a, A. Morra a, F. Pansini d, R. Cambria d, F. Cattani d, C. Spinelli e, C. Gianoli b,f, M. Riboldi b, G. Baroni b,g, B.A. Jereczek-Fossa a,h, R. Orecchia a,h. a Department of Radiation Oncology, European Institute of Oncology, Milan, Italy; b Dipartimento di Elettronica Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy; c Paul Scherrer Institut, Villigen, Switzerland; d Unit of Medical Physics, European Institute of Oncology, Milan, Italy; e Tecniche di Radiologia Medica, per Immagini e Radioterapia, University of Milan, Milan, Italy; f Ludwig Maximilians University, Munich, Germany; g Bioengineering Unit, Centro Nazionale di Adroterapia Oncologica, Pavia, Italy; h Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy Purpose: To investigate intra-fraction breast motion during long-lasting (10– 20 min) breast helical tomotherapy by means of optical tracking. Materials and methods: Twenty locoregional breast cancer patients underwent helical tomotherapy irradiation after receiving conservative surgery or mastectomy. Non-invasive monitoring of respiratory motion was achieved through infrared tracking of a passive marker placed near the surgical scar. In order to obtain the displacement deriving from the patient movement
e57
only, we subtracted the trace of an additional marker placed on the treatment couch. Respiratory signals were analyzed in terms of peak-to-peak amplitudes and baseline drifts, obtained by low-pass moving average filtering with a time window of 60 sec. Anisotropic clinical target volume (CTV) safety margin expansion due to the measured intra-fraction motion was calculated relying on a synthetic representation of the specific patient respiratory pattern, obtained by adding half of the most probable respiratory amplitude to the non-respiratory movement of the scar trace. Result: The most probable measured breathing amplitude was less than 2 mm along all anatomical directions. Intra-fraction baseline drifts were mostly in the posterior and inferior directions for all patients in most fractions, with the exception of one patient, who exhibited a countertendency behavior. The distribution of right–left shifts resulted in almost zero median, with a narrow interquartile range. Resulting anisotropic safety margin expansions across all patients with the exception of the outlier patient were 1.58–2.44 mm in right–left, 4.41– 3.65 mm in inferior–superior and 3.78–2.15 mm in the posterior–anterior directions, respectively. Conclusion: Non-respiratory motion during prolonged treatment induces notable uncertainties. Non-invasive continuous monitoring of patient setup variations including baseline drifts is considered necessary in order to minimize dosimetric deviations. http://dx.doi.org/10.1016/j.ejmp.2016.01.197
A.194 DOSIMETRIC PROPERTIES OF 3D-PRINTED FLAT BOLUS FOR EXTERNAL RADIOTHERAPY R. Ricotti *,a, A. Vavassori a, R. Spoto a,b, D. Ciardo a, F. Pansini c, A. Bazani c, S. Noris d, F. Cattani c, R. Orecchia a,b, B.A. Jereczek-Fossa a,b. a Department of Radiation Oncology, European Institute of Oncology, Milano, Italy; b Department of Oncology and Hemato-oncology, University of Milan, Milano, Italy; c Unit of Medical Physics, European Institute of Oncology, Milano, Italy; d Tecniche di Radiologia Medica, per Immagini e Radioterapia, University of Milan, Milano, Italy Purpose: Dosimetric property evaluation of acrylonitrile butadiene styrene (ABS) and polylactide (PLA) plastics, and their suitability for bolus 3D printing applied in high-energy radiotherapy to overcome the skin-sparing effect. Materials and methods: Eight flat boluses for the water-equivalent RW3 slab phantom were 3D printed using a commercial 3D printer (HP3DX100, Hamlet, Dublin, IE) using ABS and PLA. Flat boluses were sized at 8 × 8 × 1 cm (length × width × thickness). Each bolus was printed with different infill percentages (10%, 20% 40% and 60%). The mean value of Hounsfield unit (HU) of the 3D printed boluses was provided by analyzing their computed tomography (CT) scans. The measurements were performed with Vero® System (Brainlab AG, Feldkirchen, Germany) delivering 200 monitor units with a 6 MV photon beam, 5 × 5 cm open field with 90-degree gantry angle at 100 cm surface to surface distance on a water-equivalent phantom in three configurations: without bolus, with a commercial bolus and with the eight 3D printed boluses. Gafchromic EBT3 film (International Specialty Products, Wayne, NJ) placed between phantom slabs provided dose profile measurements. Results: Negative HU were due to the air gap inside the flat bolus infill pattern. The mean HU increased with the percentage infill, resulting in higher bolus density in a reduced distance from the surface of the phantom where the maximum dose occurs. Build-up peaks shifted toward the phantom surface when any bolus was used. ABS and PLA boluses with an infill percentage of 40% had comparable performance to the commercial bolus. Conclusion: 3D printed flat boluses can decrease the skin-sparing effect as a commercially available bolus. The performed analysis accurately describes the physical behavior of these plastic materials. Patient-specific boluses could be outlined from patient CT images and 3D printed shaping the actual anatomy of the patient and improving the fitting between bolus and skin surfaces. http://dx.doi.org/10.1016/j.ejmp.2016.01.198
relative to PFD, with a slight overestimation of the tails (<1%), due to the absence of the shielding. Output factors were in good agreement for fields up to 5 × 5 cm2 (<1%). Conclusions: The Razor diode has the same spatial resolution of SFD with the additional advantages of improved stability, becoming a possible candidate for small field dosimetry. http://dx.doi.org/10.1016/j.ejmp.2016.01.195 A.192 A PRELIMINARY DOSIMETRIC STUDY TO VALIDATE MULTI-SEGMENT PLAN (FIELD IN FIELD) FOR BREAST IRRADIATION USING IN VIVO DOSIMETRY (IVD) S. Riccardi *, R. Nigro, R. Maglio, M.G. Mangiacotti, R. Cassese. S. Camillo de Lellis Hospital, Rieti, Italy Purpose: IVD represents an independent check of the dose able to highlight the reproducibility of the treatment over time and able to help avoiding systematic errors during dose delivery. Moreover, IVD may be useful to validate a new technique. The aim of this study is to evaluate the accuracy and reproducibility of dose distributions of breast treatments using fieldin-field (FIF) technique (TPS Eclipse-Varian) with SOFTDISO (Best Medical Italy Srl). The FIF technique is a forward planning approach that uses multileaf collimator sub-fields to improve dose uniformity throughout the whole breast volume. Method and materials: We acquired the portal image during each session for all beams of seven breast FIF treatment planned. The treatments were delivered with 6 MV photon beam by a Varian Clinac 2100 C/D. CT images, RT plan and portal images of patients were imported in SOFTDISO. SOFTDISO is provided with an analysis module dedicated to the reconstruction of the dose at the point isocenter from the portal images signal. The value of the transit signal is converted to a dose value, Diso, and compared with the value of calculated dose, Diso,TPS. The comparison is performed through the index R = Diso/Diso,TPS. The acceptance criterion was: 0.95 ≤ R ≤ 1.05. The daily EPID images were compared to a reference image obtained in the first session of therapy. A further module is dedicated to the gammaanalysis between the reference and daily portal image. Results: The comparisons showed good results. The R values for 5 treatments were within 1.5%. In two treatments were within 4%. In particular the R average for all sessions valued was 1.016 ± 0.021. The gammaanalysis, performed with 3 mm/5% criteria, yielded Pg < 1 ≥ 93% in 80% of the tests, 20% of the tests supplied 88% ≤ Pg < 1 < 93% due to small setup variations. Conclusions: The IVD assures that the FIF treatment has a good reproducibility during treatment sessions and can replace the standard breast treatment with dynamic wedges. http://dx.doi.org/10.1016/j.ejmp.2016.01.196 A.193 INTRAFRACTION BREAST DISPLACEMENTS DURING HELICAL TOMOTHERAPY R. Ricotti *,a, D. Ciardo a, G. Fattori b,c, M.C. Leonardi a, A. Morra a, F. Pansini d, R. Cambria d, F. Cattani d, C. Spinelli e, C. Gianoli b,f, M. Riboldi b, G. Baroni b,g, B.A. Jereczek-Fossa a,h, R. Orecchia a,h. a Department of Radiation Oncology, European Institute of Oncology, Milan, Italy; b Dipartimento di Elettronica Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy; c Paul Scherrer Institut, Villigen, Switzerland; d Unit of Medical Physics, European Institute of Oncology, Milan, Italy; e Tecniche di Radiologia Medica, per Immagini e Radioterapia, University of Milan, Milan, Italy; f Ludwig Maximilians University, Munich, Germany; g Bioengineering Unit, Centro Nazionale di Adroterapia Oncologica, Pavia, Italy; h Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy Purpose: To investigate intra-fraction breast motion during long-lasting (10– 20 min) breast helical tomotherapy by means of optical tracking. Materials and methods: Twenty locoregional breast cancer patients underwent helical tomotherapy irradiation after receiving conservative surgery or mastectomy. Non-invasive monitoring of respiratory motion was achieved through infrared tracking of a passive marker placed near the surgical scar. In order to obtain the displacement deriving from the patient movement
e57
only, we subtracted the trace of an additional marker placed on the treatment couch. Respiratory signals were analyzed in terms of peak-to-peak amplitudes and baseline drifts, obtained by low-pass moving average filtering with a time window of 60 sec. Anisotropic clinical target volume (CTV) safety margin expansion due to the measured intra-fraction motion was calculated relying on a synthetic representation of the specific patient respiratory pattern, obtained by adding half of the most probable respiratory amplitude to the non-respiratory movement of the scar trace. Result: The most probable measured breathing amplitude was less than 2 mm along all anatomical directions. Intra-fraction baseline drifts were mostly in the posterior and inferior directions for all patients in most fractions, with the exception of one patient, who exhibited a countertendency behavior. The distribution of right–left shifts resulted in almost zero median, with a narrow interquartile range. Resulting anisotropic safety margin expansions across all patients with the exception of the outlier patient were 1.58–2.44 mm in right–left, 4.41– 3.65 mm in inferior–superior and 3.78–2.15 mm in the posterior–anterior directions, respectively. Conclusion: Non-respiratory motion during prolonged treatment induces notable uncertainties. Non-invasive continuous monitoring of patient setup variations including baseline drifts is considered necessary in order to minimize dosimetric deviations. http://dx.doi.org/10.1016/j.ejmp.2016.01.197
A.194 DOSIMETRIC PROPERTIES OF 3D-PRINTED FLAT BOLUS FOR EXTERNAL RADIOTHERAPY R. Ricotti *,a, A. Vavassori a, R. Spoto a,b, D. Ciardo a, F. Pansini c, A. Bazani c, S. Noris d, F. Cattani c, R. Orecchia a,b, B.A. Jereczek-Fossa a,b. a Department of Radiation Oncology, European Institute of Oncology, Milano, Italy; b Department of Oncology and Hemato-oncology, University of Milan, Milano, Italy; c Unit of Medical Physics, European Institute of Oncology, Milano, Italy; d Tecniche di Radiologia Medica, per Immagini e Radioterapia, University of Milan, Milano, Italy Purpose: Dosimetric property evaluation of acrylonitrile butadiene styrene (ABS) and polylactide (PLA) plastics, and their suitability for bolus 3D printing applied in high-energy radiotherapy to overcome the skin-sparing effect. Materials and methods: Eight flat boluses for the water-equivalent RW3 slab phantom were 3D printed using a commercial 3D printer (HP3DX100, Hamlet, Dublin, IE) using ABS and PLA. Flat boluses were sized at 8 × 8 × 1 cm (length × width × thickness). Each bolus was printed with different infill percentages (10%, 20% 40% and 60%). The mean value of Hounsfield unit (HU) of the 3D printed boluses was provided by analyzing their computed tomography (CT) scans. The measurements were performed with Vero® System (Brainlab AG, Feldkirchen, Germany) delivering 200 monitor units with a 6 MV photon beam, 5 × 5 cm open field with 90-degree gantry angle at 100 cm surface to surface distance on a water-equivalent phantom in three configurations: without bolus, with a commercial bolus and with the eight 3D printed boluses. Gafchromic EBT3 film (International Specialty Products, Wayne, NJ) placed between phantom slabs provided dose profile measurements. Results: Negative HU were due to the air gap inside the flat bolus infill pattern. The mean HU increased with the percentage infill, resulting in higher bolus density in a reduced distance from the surface of the phantom where the maximum dose occurs. Build-up peaks shifted toward the phantom surface when any bolus was used. ABS and PLA boluses with an infill percentage of 40% had comparable performance to the commercial bolus. Conclusion: 3D printed flat boluses can decrease the skin-sparing effect as a commercially available bolus. The performed analysis accurately describes the physical behavior of these plastic materials. Patient-specific boluses could be outlined from patient CT images and 3D printed shaping the actual anatomy of the patient and improving the fitting between bolus and skin surfaces. http://dx.doi.org/10.1016/j.ejmp.2016.01.198