ESTRO 36 Abstract Book

S1001 ESTRO 36 _______________________________________________________________________________________________

Results IMRT and VMAT significantly improved the conformity to the Planning Target Volume (PTV) and increased the volume of PTV covered with 50Gy. This effect was clearly illustrated in the region of the lateral field edges since it is difficult to achieve in 3D-CRT due to the dose building up effect. The lung volume received 20Gy in IMRT and VMAT were higher than that of 3D-CRT but the result was found to be not significant. The treatment time in terms of number of monitor unit (MU) was found to be significantly lower in 3D-CRT but the time required for setting up the patient to the treatment position was almost doubled to other two techniques. Conclusion IMRT and VMRT are well-accepted techniques and able to provide encouraging dosimetric results for bilateral breast irradiation. VMAT could further reduce the overall treatment time because of the simple setup procedure and the relatively small number of MU. This study suggested that VMAT technique is feasible and is recommended for bilateral breast irradiation. EP-1828 Mean Dose in healthy lung for chest tumors treated with Stereotactic Body Radiation Therapy (SBRT) J.l.Monroy Anton 1 , M. Asensio Martinez 2 , V. Borreda Talon 2 , J. Hernandis Barbera 2 , M. Marco Collado 2 1 Hospital universitario de la ribera, radiation oncology, alzira, spain 2 hospital universitario de la ribera, radiation protection and radiophysics dpt, Alzira, Spain Purpose or Objective Stereotactic body radiotherapy (SBRT) is considered treatment of choice in patients with pulmonary lesions not candidates for surgical treatment. High doses of radiation, both total and per fraction , requires a dose limitation in healthy organs at risk (contralateral lung, heart, spine) Our objectives were: -- To evaluate the mean dose (Dm) received by the contralateral lung in SBRT for thoracic lesions. -- To analyze if PTV volume and/or total dose (TD) are related to the Dm achieved in the contralateral lung. Material and Methods A total of 26 pulmonary lesions treated with SBRT were evaluated. Simulation was performed with CT 4D respiratory gating and customized immobilization devices. PTV was designed with an isotropic margin of 0.5 cm from the GTV. Treatment was delivered with Linear Accelerator ( CLINAC, Varian), and verification done with internal fiducial markers surrogates. Results Total Dose (TD) (Gy): range 20 – 45 Gy. Most cases (18; 69%) received a TD of 45Gy. Dose/fraction: range 10-20 Gy/fr. The most frequent fractionation was 15 Gy (20; 77%). PTV volumen (cc): range between 10.18 - 99.33cc, with a mean: 36.14cc ; median: 26.65cc Healthy lung Dm (Gy): range 0.23 - 9.8 Gy; mean: 1.75Gy; median: 1.25Gy The increase in PTV volume did not associate an increase in the average dose to the contralateral lung. Fig 1 An increase in total dose not involved an associated increase in the dose to the healthy lung. Fig. 2

Conclusion The Mean Dose received by the contralateral healthy lung is minimal. No relationship was found between the increase in total dose and increased in contralateral lung Dmean No relationship was found between the volume of PTV and Dmean reached in contralateral lung The parameters PTV and TD do not appear to relate to the dose received to the contralateral lung. We can conclude that SBRT technique can be applied safely largely preserving the healthy lung. EP-1829 Dose delivery accuracy in total body irradiation delivered with Step and Shoot IMRT T. Berlon 1 , L. Specht 1 , P.M. Petersen 1 , L.S. Fog 1 1 Rigshospitalet, Clinic of Oncology- Department of Radiotheraphy, Copenhagen, Denmark Purpose or Objective In total body irradiation (TBI) delivered with step and shoot IMRT (SS IMRT), the dose conformity is considerably improved compared with the more widely used TBI delivered with open fields. This conformity is achieved through the use of multiple fields defined by multileaf collimators (MLCs). We aim to quantify the accuracy with which TBI patients treated at our clinic were positioned, and to determine the effect any positioning errors may have had on the delivered dose. Material and Methods Images acquired as a routine part of the patient treatment with the Theraview ™ (Theraview Technology, Leuden, The Netherlands) imaging system were used to determine the positioning shift in the cranio-caudal direction. Images for 11 consecutive patients, each receiving 6 fractions, were analysed and the shifts recorded (figure 1). For 3 of the patients, only images for 5 of the 6 fractions were available.