ESTRO 38 Abstract book

S1018 ESTRO 38

brain was better spared with Elements® DCAT than with the Cyberknife and VMAT. VMAT gave significantly higher doses to the brain than the 2 other techniques (Table 1). Mean estimated delivery time was 78 min, 20 min and 25min for the Cyberknife®, DCAT and VMAT techniques, respectively. Logfile analysis showed that VMAT plans had more MUs than DCAT plans (8477±1651 vs 5037±1090), smaller segments, and more important fluctuations in dose rate and gantry speed.

The hydrogel spacer was effective at reducing rectal doses in the intermediate dose range, with very little volume receiving 60Gy and above for all plan types. Using MCO on the post-implantation plans resulted in even lower rectal doses alongside a significant reduction in bladder doses compared to the spacer alone. Conclusion The implantation of a hydrogel spacer can significantly reduce rectal doses for patients treated with moderately hypofractionated prostate radiotherapy without compromising PTV coverage. Using multi-criteria optimisation alongside the hydrogel spacer can further reduce these rectal doses and results in lower bladder doses than are achieved using the spacer only. EP-1874 Multiple brain metastasis radiosurgery using dedicated treatment planning system: a dosimetric study M. Biston 1 , M. Ayadi 1 , P. Dupuis 1 , T. Baudier 2 , C. Malet 1 , M. Sunyach 1 1 Léon Bérard Cancer Center, Radiotherapy, Lyon, France ; 2 Lyon university, Creatis, Lyon, France Purpose or Objective The objective was to compare the performances of conventional versus dedicated linear accelerator for the stereotactic treatment of multiples brain metastases. Cyberknife® plans were compared to those obtained with a treatment planning system (TPS) designed for treating multiple brain metastases on conventional linac and to another one used in routine for volumetric modulated arc therapy planning (VMAT). Material and Methods Eight previously treated patients with 2 to 8 tumors representing 37 gross target volumes (GTV) were selected. GTV-to-Planning target volume (PTV) margins were 2 mm in all directions. PTV sizes were under 2 cm 3 . The prescribed dose was 20 Gy in single fraction prescribed at the isodose 80% and covering 96-99% of the PTVs. The original treatments planned with Multiplan® (V3.2.0, Accuray) delivered on a Cyberknife® (Accuray) using 2 or 3 fixed-size collimators were replanned in dynamic conformal arctherapy (DCAT) with dedicated automated brain metastases TPS Elements® (v.1.5, Brainlab) and with Monaco TPS (V 5.11.02, Elekta) using VMAT. Plans were delivered using 6-MV photons with an Elekta Versa HD® Linac equipped with an Agility® MLC consisting of 80 paired leaves each measuring 5 mm in width at the isocenter. The dose distributions were compared using Paddick conformity index (CI), mean dose to the PTVs, and volume of healthy brain receiving 10 (V10), 12 (V12) and 5 (V5) Gy. Delivery efficiency was compared throughout the number of monitor units (MUs), delivery time and logfiles analyses. Results A better CI was found with the Cyberknife (1.26 ±0.06) than with Elements® DCAT (1.29 ±0.12) or Monaco VMAT (1.33 ±0.11). Mean dose to the PTVs were found higher for Cyberknife (22.47 Gy±0.29) and VMAT (22.27 Gy±0.43) plans than for DCAT plans (22.06 Gy±0.55). The healthy

Conclusion Elements® DCAT is a robust automatic planning solution for treating multiple brain metastasis. The planning time is considerably reduced compared to the 2 other techniques, and the system is nearly operator independent. For clinically acceptable plan quality the delivery efficiency is considerably better with linac-based stereotactic radiosurgery than with Cyberknife. Further investigations are in progress to examine whether tumor size/location and number of lesions have an impact on the results. EP-1875 Compare OAR dose of breast cancer using sequential boost and simultaneous integrated boost technique L. Chou 1 , T. Wang 2 , C. Shiau 1 , P. Huang 1 , Y. Lin 1 , C. Lin 1 1 Taipei Veterans General Hospital, Oncology, Taipei City, Taiwan ; 2 China Medical University Hospital, Radiation Oncology, Taichung, Taiwan Purpose or Objective Thanks to advances in treatment and diagnosis, the mortality of breast cancer has decreased. Radiotherapy is an indispensable part in adjuvant treatment for patients undergoing breast-conserving surgery. However, inevitable radiation exposure to the heart and lung may cause serious long-term toxicities. Besides whole breast irradiation, tumor bed boost can be delivered in sequential (SEQ) or simultaneously integrated boost (SIB) techniques. This study aimed to compare the dosimetric outcome of two techniques. Material and Methods Eighty node-negative left breast cancer patients receiving breast-conserving surgery were evaluated, of which 47 patients received 45Gy in 25 fractions to the whole breast and then 10 Gy in 5 fractions to tumor bed, while 33 patients received 55Gy to tumor bed and 45Gy to whole breast in 25 fractions using SIB technique. All treatment plans were based on CT imaging and consisted of two tangential fields with 6MV photon to whole breast and 1-2 beams to tumor bed. If necessary, we used 1-2 additional beams to improve whole breast homogeneity and normal organ sparing. Conformal index, homogeneity index, heart dose, ipsi-lateral lung dose were compared between SEQ and SIB technique. (Table 1) Results The median age of SEQ and SIB group were 48 (25-71) and 54 (33-74) respectively and the PTV boost volume were similar (110.7±84.6 c.c. for SEQ and 108.7±66.4 c.c. for SIB). Both SEQ and SIB plans demonstrated similar homogeneity (p > 0.05) but significant difference of conformity (p<0.01). In addition, SEQ plans provided significantly less lung radiation exposure (V5, V10 and mean left lung dose) than SIB plans (p < 0.05). Heart dose were similar in two groups crossing V5, V10, V30, and mean heart dose (all p > 0.05).