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EP-1560: Left breast cancer planning with VMAT technique: the dosimetric trade-offs
S840 ESTRO 36 _______________________________________________________________________________________________
constraints seem suboptimal for sparing rectum when using IMRT. However, tighter dose constraints may result in higher dose inhomogeneities in the PTV. The treatment modalities that had lower NTCP values were inferior in many cases regarding the risk for secondary malignancies. Consequently, the optimization of different treatment modalities and plans should be complemented by the estimation of the corresponding risks for developing secondary malignancies. EP-1560 Left breast cancer planning with VMAT technique: the dosimetric trade-offs A. Fogliata1, J. Seppala2, G. Reggiori1, F. Lobefalo1, V. Palumbo1, F. De Rose1, D. Franceschini1, M. Scorsetti3, L. Cozzi3 1 Humanitas Research Hospital, Radiation Oncology, Milan-Rozzano, Italy 2 Kuopio University Hospital, Cancer Center, Kuopio, Finland 3 Humanitas Cancer Center and Humanitas University, Radiation Oncology, Milan-Rozzano, Italy Purpose or Objective : Intensity modulation with volumetric modulated arc therapy (VMAT) for breast cancer treatment has been explored, proving that, as a trade-off of improved target dose distributions, larger volumes of the surrounding tissues receive a more or less pronounced low dose bath. Clinical results demonstrating a detrimental effect of the low-dose bath, related to volume and dose levels, with respect to the two-tangential beam dose delivery, or the associated risk of secondary cancer induction, are currently not available. In the absence of such data, a good approach is to drive the inverse VMAT optimization processes to decrease the dose to all the critical structures as much as possible, and to maximize the target dose homogeneity. This can be primarily achieved by means of adequate beam arrangement, and by highly restrictive planning objectives, more restrictive than the clinical need. Scope of this work is to evaluate the possible trade-offs in breast VMAT planning, exploring the degree of achievable dosimetric sparing of different organs at risk (OAR) by using two quite similar VMAT plan settings. Material and Methods CT scans of 20 patients presenting left sided breast cancer, in deep inspiration breath hold, were studied. VMAT plans were optimized for the RapidArc technique in the Eclipse treatment planning system (Varian) using the PO algorithm and were calculated with Acuros, to deliver 40.05Gy to mean target dose in 15 fractions. Two partial arcs were arranged for 6MV, Millennium MLC from a TrueBeam linac (Varian). Two plans per patient were optimized: RA_full, where the optimizer used the entire partial arc trajectory, and RA_avoid, where sectors (set from ~0 to ~105 degree) of MU=0 were set. Common dose objectives included a stringent dose homogeneity, mean dose to heart <5Gy, ipsilateral lung <8Gy, contralateral lung <2Gy, contralateral breast <3Gy. Results RA_full showed a better dose conformity, lower high dose volumes in healthy tissue and lower skin dose. The NTHD (normal tissue high dose, defined as the uninvolved tissue receiving 90% of the dose prescription relative to the volume of the target) resulted in 18% and 31% for RA_full and RA_avoid, respectively. RA_avoid presented a reduction of the mean doses for all critical structures: 51% to heart, 12% to ipsilateral lung, 81% to contralateral lung, 73% to contralateral breast. All differences were significant with p<0.0001. Conclusion The adaptation of VMAT options to planning objectives reduced significantly the healthy tissue dose levels at the price of some high dose spillage. Evaluation of the trade-
offs to apply to the different critical structures should drive in improving the usage of the VMAT technique for breast cancer treatment, as the choice of the trade-offs would affect the possible future late toxicity and secondary cancer induction risk. EP-1561 Comparison of heart, lung doses, and skin toxicity from different breast cancer RT techniques. M. Lizondo1, N. Jornet2, M.J. Fuentes-Raspall3, P. Carrasco2, A. Latorre-Musoll2, A. Ruiz-Martinez2, T. Eudaldo2, P. Delgado-Tapia2, C. Cases2, M. Ribas2 1 Institut de Recerca Hospital de la Santa Creu i Sant Pau, Servei de Radiofíosica i Radioprotecció, Barcelona, Spain 2 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain 3 Hospital de la Santa Creu i Sant Pau, Servei d'Oncologia Radioteràpica, Barcelona, Spain Purpose or Objective The aim of this study was to assess whether there are significant differences in lung and heart doses for different breast cancer radiotherapy techniques. This study is based on a plan comparison from the dosimetric and patient data prospectively collected in a breast RT treatment database. Patient and treatment risk factors for acute skin toxicity were analysed. Material and Methods Patient, treatment variables and treatment-related outcomes were abstracted for 469 breast cancer patients who completed radiotherapy treatment from 2013 to 2016. We selected patients with similar nominal dose to the whole breast (50 Gy) and to the boost (EQD2 66 Gy), patients with no electron boost were excluded. We also included patients with lymph nodes(LN), irradiation(50Gy). The available techniques were 3DCRT and IMRT and from April 2016 onwards, deep inspiration breath hold (DIBH) is used for all left breast patients. Following our technique decision criteria, all boost areas deeper than the range of our highest e- energy, are treated with integrated boost using IMRT. And till 2016, left breast cancer patient not fulfilling heart and/or lung dose restrictions with 3DCRT were moved to IMRT. For each patient, the technique was chosen in order to maximize PTV coverage and homogeneity while keeping doses to OAR as low as possible. Heart dose (Dmean ,V25) and the ipsilateral lung dose (V20) values were compared separately as a function of laterality for patients undergoing 3DCRT (with and without DIBH) or IMRT. Correlation tests were made between maximum acute skin toxicity and technique, season, skin photo-type, breast volume and smoking habits.Results Table I shows mean values and significance results. For right-sided breast patients, heart Dmean was significantly lower for 3DCRT techniques than for IMRT techniques, while heart V25 and lung V20 are not significantly different. For left-sided breast patients heart Dmean was lower but heart V25 was higher with the 3DCRT techniques than with IMRT techniques when LN were not included, and heart Dmean also when LN were included. Lung V20 was not significantly different. For those patients treated with DIBH, heart Dmean and heart V25 were considerably lower. Skin toxicity shows a significant correlation with breast volume (p=0.01) but not with technique, smoking habits, skin photo type or period of the year in which the patient was treated.
constraints seem suboptimal for sparing rectum when using IMRT. However, tighter dose constraints may result in higher dose inhomogeneities in the PTV. The treatment modalities that had lower NTCP values were inferior in many cases regarding the risk for secondary malignancies. Consequently, the optimization of different treatment modalities and plans should be complemented by the estimation of the corresponding risks for developing secondary malignancies. EP-1560 Left breast cancer planning with VMAT technique: the dosimetric trade-offs A. Fogliata1, J. Seppala2, G. Reggiori1, F. Lobefalo1, V. Palumbo1, F. De Rose1, D. Franceschini1, M. Scorsetti3, L. Cozzi3 1 Humanitas Research Hospital, Radiation Oncology, Milan-Rozzano, Italy 2 Kuopio University Hospital, Cancer Center, Kuopio, Finland 3 Humanitas Cancer Center and Humanitas University, Radiation Oncology, Milan-Rozzano, Italy Purpose or Objective : Intensity modulation with volumetric modulated arc therapy (VMAT) for breast cancer treatment has been explored, proving that, as a trade-off of improved target dose distributions, larger volumes of the surrounding tissues receive a more or less pronounced low dose bath. Clinical results demonstrating a detrimental effect of the low-dose bath, related to volume and dose levels, with respect to the two-tangential beam dose delivery, or the associated risk of secondary cancer induction, are currently not available. In the absence of such data, a good approach is to drive the inverse VMAT optimization processes to decrease the dose to all the critical structures as much as possible, and to maximize the target dose homogeneity. This can be primarily achieved by means of adequate beam arrangement, and by highly restrictive planning objectives, more restrictive than the clinical need. Scope of this work is to evaluate the possible trade-offs in breast VMAT planning, exploring the degree of achievable dosimetric sparing of different organs at risk (OAR) by using two quite similar VMAT plan settings. Material and Methods CT scans of 20 patients presenting left sided breast cancer, in deep inspiration breath hold, were studied. VMAT plans were optimized for the RapidArc technique in the Eclipse treatment planning system (Varian) using the PO algorithm and were calculated with Acuros, to deliver 40.05Gy to mean target dose in 15 fractions. Two partial arcs were arranged for 6MV, Millennium MLC from a TrueBeam linac (Varian). Two plans per patient were optimized: RA_full, where the optimizer used the entire partial arc trajectory, and RA_avoid, where sectors (set from ~0 to ~105 degree) of MU=0 were set. Common dose objectives included a stringent dose homogeneity, mean dose to heart <5Gy, ipsilateral lung <8Gy, contralateral lung <2Gy, contralateral breast <3Gy. Results RA_full showed a better dose conformity, lower high dose volumes in healthy tissue and lower skin dose. The NTHD (normal tissue high dose, defined as the uninvolved tissue receiving 90% of the dose prescription relative to the volume of the target) resulted in 18% and 31% for RA_full and RA_avoid, respectively. RA_avoid presented a reduction of the mean doses for all critical structures: 51% to heart, 12% to ipsilateral lung, 81% to contralateral lung, 73% to contralateral breast. All differences were significant with p<0.0001. Conclusion The adaptation of VMAT options to planning objectives reduced significantly the healthy tissue dose levels at the price of some high dose spillage. Evaluation of the trade-
offs to apply to the different critical structures should drive in improving the usage of the VMAT technique for breast cancer treatment, as the choice of the trade-offs would affect the possible future late toxicity and secondary cancer induction risk. EP-1561 Comparison of heart, lung doses, and skin toxicity from different breast cancer RT techniques. M. Lizondo1, N. Jornet2, M.J. Fuentes-Raspall3, P. Carrasco2, A. Latorre-Musoll2, A. Ruiz-Martinez2, T. Eudaldo2, P. Delgado-Tapia2, C. Cases2, M. Ribas2 1 Institut de Recerca Hospital de la Santa Creu i Sant Pau, Servei de Radiofíosica i Radioprotecció, Barcelona, Spain 2 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain 3 Hospital de la Santa Creu i Sant Pau, Servei d'Oncologia Radioteràpica, Barcelona, Spain Purpose or Objective The aim of this study was to assess whether there are significant differences in lung and heart doses for different breast cancer radiotherapy techniques. This study is based on a plan comparison from the dosimetric and patient data prospectively collected in a breast RT treatment database. Patient and treatment risk factors for acute skin toxicity were analysed. Material and Methods Patient, treatment variables and treatment-related outcomes were abstracted for 469 breast cancer patients who completed radiotherapy treatment from 2013 to 2016. We selected patients with similar nominal dose to the whole breast (50 Gy) and to the boost (EQD2 66 Gy), patients with no electron boost were excluded. We also included patients with lymph nodes(LN), irradiation(50Gy). The available techniques were 3DCRT and IMRT and from April 2016 onwards, deep inspiration breath hold (DIBH) is used for all left breast patients. Following our technique decision criteria, all boost areas deeper than the range of our highest e- energy, are treated with integrated boost using IMRT. And till 2016, left breast cancer patient not fulfilling heart and/or lung dose restrictions with 3DCRT were moved to IMRT. For each patient, the technique was chosen in order to maximize PTV coverage and homogeneity while keeping doses to OAR as low as possible. Heart dose (Dmean ,V25) and the ipsilateral lung dose (V20) values were compared separately as a function of laterality for patients undergoing 3DCRT (with and without DIBH) or IMRT. Correlation tests were made between maximum acute skin toxicity and technique, season, skin photo-type, breast volume and smoking habits.Results Table I shows mean values and significance results. For right-sided breast patients, heart Dmean was significantly lower for 3DCRT techniques than for IMRT techniques, while heart V25 and lung V20 are not significantly different. For left-sided breast patients heart Dmean was lower but heart V25 was higher with the 3DCRT techniques than with IMRT techniques when LN were not included, and heart Dmean also when LN were included. Lung V20 was not significantly different. For those patients treated with DIBH, heart Dmean and heart V25 were considerably lower. Skin toxicity shows a significant correlation with breast volume (p=0.01) but not with technique, smoking habits, skin photo type or period of the year in which the patient was treated.