ESTRO 37 Abstract book

S1073

ESTRO 37

Changes in mean, minimum and maximum dose (D mean , D min , D max ) are listed in Table 1. For the IMRT plans, changes in mean prescribed dose for the PTV were clinically irrelevant for both PTV and boost volumes, with a maximum observed change of 0.25%. Changes in minimum and maximum dose and dose to the organs at risk could reach up to 3%, which is still acceptable in virtually all clinical settings. Treated STX volumes ranged from 4.95 to 183.6 cm 3 . While the mean change of D 99% was 2.1 to 4.6% depending on the linac, this increased drastically for smaller volumes, resulting in a change of up to 11.1% for the smallest volume. The change in D mean was less pronounced, with a mean deviation of 0.34 to 0.68% from the originally planned dose.

at-risk. Healthy tissue was defined as whole body minus PTVbr. Only left sided patients were included in order to evaluate also the heart irradiation. All patients were simulated and treated using the Active Breath Coordinator (Elekta), a spirometer enabling a temporary controlled interruption of patient breathing at the end of inspiration phase. HMRT plans were inversely optimized by combining two open fields with six-eights subfields in two tangential beam. Open fields were setup to include the whole breast with a 2 cm flash region and to carry the 80% of beams weight. HMRT plans were compared with conventional wedged-field tangential plans (WF), field-in-field forward planned tangential plans (FiF) and volumetric modulated arc therapy (VMAT) plans. Dosimetric differences among the plans were evaluated using a Kruskal-Wallis one-way analysis of variance. The Bonferroni correction was applied for pairwise comparisons; an adjusted value of p<0.0083 was considered as statistically significant. Delivery efficiency was analysed based on number of monitor units (MUs) and estimated delivery time. Results No significant differences were found among the four techniques for PTVbr an PTVcav coverage in terms of mean dose, minimal dose (D98%), target coverage (D95% and V95%). The HMRT technique showed statistically significant reduction of healthy tissue irradiation with respect to WF and FiF techniques: V 55Gy : 89cc vs 155cc and 143cc; V 60Gy : 18cc vs 40cc and 34cc. No significant differences were found in lung and heart irradiation between the three tangential technique. VMAT supplied the best conformity dose distribution for both PTVs but the worst results for contralateral breast irradiation, ipsilateral lung and heart in the low dose region (V 5Gy ). With respect to other three techniques, HMRT reported the minimal time for planning optimization and the minimal number of monitor unit delivery. Conclusion HMRT plans resulted in superior target dose conformity and homogeneity with respect to WF and FiF techniques. In addition, due to fast planning time HMRT can be applied for all patients, minimizing the impact on human or departmental resources. EP-1971 Can SBRT-VMAT be an alternative to HDR brachytherapy for vaginal cuff boost? A dosimetric study S. Cilla 1 , G. Mattiucci 2 , F. Deodato 3 , L. Azario 4 , A. Ianiro 1 , R. Frakulli 5 , A. Galuppi 5 , A. Arcelli 5 , S. Ciabatti 5 , S. Cammelli 5 , E. Galofaro 5 , G. Frezza 6 , V. Valentini 2 , A. Morganti 5 , G. Macchia 3 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy 2 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy 3 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy 4 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Medical Physics Department, Roma, Italy 5 Department of Experimental- Diagnostic and Specialty Medicine - DIMES- University of Bologna- S.Orsola- Malpighi Hospital, Radiation Oncology Center, Bologna, Italy 6 Bellaria Hospital, Radiation Oncology Unit, Bologna, Italy Purpose or Objective To evaluate the role of stereotactic body radiotherapy (SBRT) using VMAT technique as an alternative to high- dose rate brachytherapy (HDR-BRT) in the treatment of vaginal cuff in postoperative endometrial cancer.

Conclusion For large volumes, isocenter movements have little impact on RT treatment delivery, as observed changes in PTV coverage and OAR dose are too smalll to give rise to concern. However, for small-volume PTV in STX settings, isocenter shifts may lead to inadequate PTV coverage. EP-1970 Hybrid-IMRT as an optimal class solution for whole breast planning with boost to lumpectomy area S. Cilla 1 , F. Deodato 2 , A. Ianiro 1 , M. Boccardi 2 , P. Viola 1 , M. Craus 1 , M. Romanella 2 , I. Djan 3 , M. Buwenge 4 , R. Frakulli 4 , G. Siepe 4 , A. Arcelli 4 , S. Cammelli 4 , D. Smaniotto 5 , G. Frezza 6 , V. Valentini 5 , A. Morganti 4 , G. Macchia 2 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy 2 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy 3 Medical Faculty- University of Novi Sad, Institute of Oncology Vojvodina, Novi Dad, Serbia 4 Department of Experimental- Diagnostic and Specialty Medicine - DIMES- University of Bologna- S.Orsola- Malpighi Hospital, Radiation Oncology Department, Bologna, Italy 5 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy 6 Bellaria Hospital, Radiation Oncology Unit, Bologna, Italy Purpose or Objective The aim of this study was to dosimetrically evaluate a robust semiautomatic treatment planning approach for whole breast irradiation with simultaneous integrated boost (SIB) using an hybrid IMRT (HMRT) class solution. Material and Methods Twenty-five consecutive patients with left breast cancer were included in the study. All patients received 50Gy (2 Gy/fraction) to the whole breast (PTVbr) and an additional simultaneous 10 Gy (2.4 Gy/fraction) to the tumour cavity (PTVcav) over 25 fractions. Ipsilateral lung, heart and contralateral breast were contoured as organs-