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EP-1591: Normal tissue irradiation during micro-MLC based SRT or SRS: impact of the prescription isodose
ESTRO 33, 2014 Purpose/Objective: To perform an in silico comparative planning to evaluate IMRT versus 3D-CRT during irradiation of ipsilateral chest wall (CW), axilla/supraclavicular (AXSCF) and internal mammary (IM) regions in post-mastectomy breast cancers (PMBC). Materials and Methods: Twenty-five consecutive patients of PMBC, stages T2-3 with N1-3 were considered for this study. A total dose of 50 Gy/5 weeks/25 fractions were planned on identical target volumes and normal tissue contours by either IMRT or five-field 3D-CRT (Fig.). Treatment plans were evaluated for various dose-volume histogram parameters, namely D98, D90, D50, D2, homogeneity index(HI) to the CTV and PTV of the respective CW, AXSCF and IM along with V20 to lung and D33 to the heart. Differences in means were tested for significance by paired sample t-test.
S199 EP-1591 Normal tissue irradiation during micro-MLC based SRT or SRS: impact of the prescription isodose G. Delpon1, M. Dore2, S. Josset3, A. Lisbona3, F. Thillays2, S. Chiavassa1 1 Inserm, UMR892 CRCNA, Nantes, France 2 ICO, Radiotherapy, Saint-Herblain, France 3 ICO, Medical Physics, Saint-Herblain, France Purpose/Objective: For cerebral metastases treated by micro-MLC based stereotactic radiotherapy (SRT) or radiosurgery (SRS) with a Novalis (BrainLAB), three different prescription isodoses (PID) are currently used in the department depending on the number of fractions: 80%, 70% and 90% respectively for 1, 3 and 5 fractions. The aim of this study was to evaluate the impact of the prescription isodose on normal tissue irradiation. Materials and Methods: 40 cases were selected from patients treated in 2012 and 2013 to cover a large range of metastasis volume (0.3-30.2cc). For each case, 3 treatment plans were calculated with 5 dynamic arcs (Iplan RT Dose 4.5, BrainLAB). The prescribed dose was 23.1Gy corresponding to an isocenter dose equal to 33.0, 28.9 and 25.7 respectively for PID 70%, 80% and 90%. To obtain a satisfactory target coverage (V23.1Gy > 98%), MLC margin was 0.0mm for PID 70%, 0.5mm for PID 80% and 1.5mm or 2.0mm for PID 90%. The R50 index, used in extracerebral stereotactic radiotherapy is defined as the volume of the isodose 50% of the prescribed dose divided by the volume of the PTV, was calculated for each treatment plan.
Results: The DVH parameters for various target volumes and OARs show that IMRT plans have a significant dosimetric advantage over the 3D CRT plans in almost all key parameters (Table ). Even with the inclusion of IMC, the lung and cardiac doses are lower with IMRT. However, the mean dose to the opposite breast is higher with IMRT. None of the 25 patients treated with IMRT have not shown any loco-regional recurrence, pulmonary or cardiac toxicities at a median follow up of 2.9 years (range: 2.8 – 3.9 year).
Results: For a metastasis volume smaller than 5cc (14 cases), mean R50 (+/-1sd) was 3.36+/-0.52, 3.53+/-0.49 and 4.25+/-0.77 respectively for PID 70%, 80% and 90%. R50 was minimum for 12 cases with PID 70%. For PID 90%, R50 was systematically the highest, up to 40%. For a metastasis volume of between 5cc and 25cc (24 cases), mean R50 (+/-1sd) was 3.19+/-0.28, 3.09+/-0.25 and 3.36+/-0.33 respectively for PID 70%, 80% and 90%. R50 was minimum for 22 cases with PID 80%. For PID 70%, differences were mainly less than 5%, particularly for volume of between 5cc and 20cc. For PID 90%, R50 was systematically the highest, but differed by less than 10%. For a metastasis volume larger than 25cc (2 cases), PID 80% and PID 90% led to a lower R50 compared to PID 70%, but more cases will be needed to confirm this trend. The analysis showed the target volume had an important impact. For small size metastasis (diameter <20mm), for PID 90%, the larger irradiated surface led to increase the volume of the isodose 50% despite the lower prescribed dose. For large size metastasis (diameter >35mm), the irradiated surface had less impact than the prescribed dose, and the volume of the isodose 50% was larger for PID 70%. Conclusions: While maintaining the target coverage, and considering the R50, PID should be chosen according to the target volume. PID could be 70%, 80% respectively for metastasis diameter smaller than 20mm, and of between 20mm and 35mm. For larger metastasis, more cases are needed to conclude. EP-1592 Prone accelerated partial breast irradiation with MERT+IMRT using a Monte Carlo treatment planning system. E. Jiménez-Ortega1, L. Brualla2, A. Ureba1, J.A. Baeza1, A. González3, A.R. Barbeiro1, J. Roselló2, J. López-Torrecilla3, J. Ferrer4, A. Leal1 1 Universidad de Sevilla, Fisiología Médica y Biofísica, Seville, Spain 2 Hospital General de Valencia, Servicio de Radiofísica, Valencia, Spain 3 Hospital General de Valencia, Servicio de Radioterapia, Valencia, Spain 4 Hospital General de Valencia, Servicio de Medicina Nuclear, Valencia, Spain
Conclusions: In indications of irradiation to chest wall and all regional nodal sites in PMBC, IMRT provides significant dosimetric advantages over five field 3D-CRT. This was also evident clinically, on follow-up of these patients treated with IMRT.
Purpose/Objective: Accelerated partial breast irradiation (APBI) is well justified for early breast cancer, allowing early local and regional control, including a decrease in the radiation dose delivered to uninvolved portions of the breast and adjacent organs. Furthermore, APBI offers decreased overall treatment time. APBI clinical application is implemented using different techniques such as brachytherapy, external beam and intraoperative radiotherapy. We have proposed an external beam technique, using modulated electron beams (MERT) with a reduced SSD, alone or in combination with modulated photon beams (IMRT), delivered by using the same photon multi-leaf collimator (xMLC). This technique has been already clinically implemented in supine position with success by our group. Now, we suggest prone positioning for ensuring the exclusion of significant normal tissue from the treatment fields (e.g. lung and heart). Also, the prone positioning of patients considerably reduces the breast tissue motion associated with breathing. We used a treatment planning system based on full Monte Carlo simulations, called CARMEN, developed by our group. The use of Monte
S199 EP-1591 Normal tissue irradiation during micro-MLC based SRT or SRS: impact of the prescription isodose G. Delpon1, M. Dore2, S. Josset3, A. Lisbona3, F. Thillays2, S. Chiavassa1 1 Inserm, UMR892 CRCNA, Nantes, France 2 ICO, Radiotherapy, Saint-Herblain, France 3 ICO, Medical Physics, Saint-Herblain, France Purpose/Objective: For cerebral metastases treated by micro-MLC based stereotactic radiotherapy (SRT) or radiosurgery (SRS) with a Novalis (BrainLAB), three different prescription isodoses (PID) are currently used in the department depending on the number of fractions: 80%, 70% and 90% respectively for 1, 3 and 5 fractions. The aim of this study was to evaluate the impact of the prescription isodose on normal tissue irradiation. Materials and Methods: 40 cases were selected from patients treated in 2012 and 2013 to cover a large range of metastasis volume (0.3-30.2cc). For each case, 3 treatment plans were calculated with 5 dynamic arcs (Iplan RT Dose 4.5, BrainLAB). The prescribed dose was 23.1Gy corresponding to an isocenter dose equal to 33.0, 28.9 and 25.7 respectively for PID 70%, 80% and 90%. To obtain a satisfactory target coverage (V23.1Gy > 98%), MLC margin was 0.0mm for PID 70%, 0.5mm for PID 80% and 1.5mm or 2.0mm for PID 90%. The R50 index, used in extracerebral stereotactic radiotherapy is defined as the volume of the isodose 50% of the prescribed dose divided by the volume of the PTV, was calculated for each treatment plan.
Results: The DVH parameters for various target volumes and OARs show that IMRT plans have a significant dosimetric advantage over the 3D CRT plans in almost all key parameters (Table ). Even with the inclusion of IMC, the lung and cardiac doses are lower with IMRT. However, the mean dose to the opposite breast is higher with IMRT. None of the 25 patients treated with IMRT have not shown any loco-regional recurrence, pulmonary or cardiac toxicities at a median follow up of 2.9 years (range: 2.8 – 3.9 year).
Results: For a metastasis volume smaller than 5cc (14 cases), mean R50 (+/-1sd) was 3.36+/-0.52, 3.53+/-0.49 and 4.25+/-0.77 respectively for PID 70%, 80% and 90%. R50 was minimum for 12 cases with PID 70%. For PID 90%, R50 was systematically the highest, up to 40%. For a metastasis volume of between 5cc and 25cc (24 cases), mean R50 (+/-1sd) was 3.19+/-0.28, 3.09+/-0.25 and 3.36+/-0.33 respectively for PID 70%, 80% and 90%. R50 was minimum for 22 cases with PID 80%. For PID 70%, differences were mainly less than 5%, particularly for volume of between 5cc and 20cc. For PID 90%, R50 was systematically the highest, but differed by less than 10%. For a metastasis volume larger than 25cc (2 cases), PID 80% and PID 90% led to a lower R50 compared to PID 70%, but more cases will be needed to confirm this trend. The analysis showed the target volume had an important impact. For small size metastasis (diameter <20mm), for PID 90%, the larger irradiated surface led to increase the volume of the isodose 50% despite the lower prescribed dose. For large size metastasis (diameter >35mm), the irradiated surface had less impact than the prescribed dose, and the volume of the isodose 50% was larger for PID 70%. Conclusions: While maintaining the target coverage, and considering the R50, PID should be chosen according to the target volume. PID could be 70%, 80% respectively for metastasis diameter smaller than 20mm, and of between 20mm and 35mm. For larger metastasis, more cases are needed to conclude. EP-1592 Prone accelerated partial breast irradiation with MERT+IMRT using a Monte Carlo treatment planning system. E. Jiménez-Ortega1, L. Brualla2, A. Ureba1, J.A. Baeza1, A. González3, A.R. Barbeiro1, J. Roselló2, J. López-Torrecilla3, J. Ferrer4, A. Leal1 1 Universidad de Sevilla, Fisiología Médica y Biofísica, Seville, Spain 2 Hospital General de Valencia, Servicio de Radiofísica, Valencia, Spain 3 Hospital General de Valencia, Servicio de Radioterapia, Valencia, Spain 4 Hospital General de Valencia, Servicio de Medicina Nuclear, Valencia, Spain
Conclusions: In indications of irradiation to chest wall and all regional nodal sites in PMBC, IMRT provides significant dosimetric advantages over five field 3D-CRT. This was also evident clinically, on follow-up of these patients treated with IMRT.
Purpose/Objective: Accelerated partial breast irradiation (APBI) is well justified for early breast cancer, allowing early local and regional control, including a decrease in the radiation dose delivered to uninvolved portions of the breast and adjacent organs. Furthermore, APBI offers decreased overall treatment time. APBI clinical application is implemented using different techniques such as brachytherapy, external beam and intraoperative radiotherapy. We have proposed an external beam technique, using modulated electron beams (MERT) with a reduced SSD, alone or in combination with modulated photon beams (IMRT), delivered by using the same photon multi-leaf collimator (xMLC). This technique has been already clinically implemented in supine position with success by our group. Now, we suggest prone positioning for ensuring the exclusion of significant normal tissue from the treatment fields (e.g. lung and heart). Also, the prone positioning of patients considerably reduces the breast tissue motion associated with breathing. We used a treatment planning system based on full Monte Carlo simulations, called CARMEN, developed by our group. The use of Monte