[P278] The use of flattening filter free irradiation mode in normo-fractionated treatments

[P278] The use of flattening filter free irradiation mode in normo-fractionated treatments

180 Abstracts / Physica Medica 52 (2018) 99–187 Results. For the phantom plans, the following range deviations relative to the metal-free reference ...

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180

Abstracts / Physica Medica 52 (2018) 99–187

Results. For the phantom plans, the following range deviations relative to the metal-free reference plan (uncorrected CT, oMAR, kerMAR) were observed: Plan 1: (0.6, 0.6, 0.6)%; plan 2: ( 4, 1.8, 2.1)%. The patient plans showed the following deviations from the uncorrected CT plan: kerMAR: (10, 8, 7, 11)%; oMAR: (3, 0.1, 10, 0.2)%. Conclusions. Proton range calculations on a phantom showed similar improvements compared to the uncorrupted reference with kerMAR and oMAR. Similar calculations on HN patients, however, displayed systematic proton range increases when applying kerMAR as compared to oMAR. https://doi.org/10.1016/j.ejmp.2018.06.553

[P277] Investigation of mean heart dose reduction inter-fraction variation in left-sided breast cancer radiotherapy using active breath coordinator moderate deep inspiration breath hold Chryssa Paraskevopoulou *, Efi Koutsouveli, Nikos Giakoumakis, Giorgos Kollias, Pantelis Karaiskos Hygeia Hospital, Medical Physics Department, Athens, Greece Corresponding author.



Purpose. Left-sided breast radiotherapy is associated with increased risk of coronary artery disease. Active Breathing Coordinator (ABC) reduces radiation dose to the heart and preserves local control in patients with left breast cancer. The aim of this study is to estimate the dose reduction to the heart and its inter-fraction variation in moderate deep inspiration breath hold (mDIBH) breast radiotherapy using ABC (Elekta). Methods. Ten patients with left-sided breast cancer with tangential radiotherapy plans and ten patients with VMAT plans performed using to Monaco (Elekta) TPS, where included in the study. All the patients were trained on ABC procedure to enhance patient compliance and to determine individual (mDIBH) levels, which was set at 70–80% of maximum inspiratory capacity. During simulation two sets of CT images were acquired for each patient, one with mDIBH with ABC system and the other with free breathing. Treatment plans were performed for both scans and the mean dose to the heart was recorded. Treatment was performed using the ABC system. 200 cone-beam CT (CBCT) scans were acquired for all patients investigated throughout their course of treatment to take into account inter-fraction patient set-up inaccuracies. CBCTs were exported to Monaco TPS for registration and mean heart dose determination after the application of the original patient plan. Results. For all patients evaluated, compared to free breathing, mDIBH with ABC significantly reduced mean dose to the heart by 20% or greater independently of the planning technique (tangential fields or VMAT). This reduction remains the same with minor differences (on average <1 cGy per fraction) throughout the treatment course. Conclusion. Moderate deep inspiration breath hold (mDIBH) breast radiotherapy using ABC (Elekta) can significantly reduce mean dose to the heart. Variation in mean heart dose was minor and mean dose remains significantly reduced throughout the treatment course without being affected by inter-fraction variations. https://doi.org/10.1016/j.ejmp.2018.06.554

[P278] The use of flattening filter free irradiation mode in normofractionated treatments Barbara Dobler a,*, Marius Treutwein a, Judit Alvarez Moret a, Tina Obermeier b, Johannes Maier c, Oliver Koelbl a

a Regensburg University Medical Center, Department of Radiotherapy, Regensburg, Germany b Regensburg University Medical Center, Department of Radiology, Regensburg, Germany c Regensburg Center of Biomedical Engineering (Rcbe), Medical Image Computing, Regensburg, Germany ⇑ Corresponding author.

Purpose. The aim of this study was to identify general advantages and disadvantages of the flattening filter free irradiation mode in normo-fractionated intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Methods. Various studies have been performed at our department to identify specific advantages and disadvantages of the use of the flattening filter free irradiation mode for the normo-fractionated treatment of different tumor sites. Volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans were created with and without flattening filter for at least 10 patients for each tumor site. All treatment plans were verified by a 2D-ionization-chamber-array and delivery times were measured from first beam on to last beam off. Peripheral doses were determined with an ionization chamber as a measure of radiation induced second cancer risk. Differences were evaluated in terms of plan quality, irradiation time, and radiation induced second cancer risk. The results of these studies were reviewed to assess general advantages or disadvantages independent on the specific tumor entity or treatment technique. Results. Differences in plan quality and irradiation time were dependent on the tumor entity and treatment technique. The peripheral dose as a measure of radiation induced second cancer risk, however, was significantly reduced in the flattening filter free mode for all tumor sites and treatment techniques. The reduction ranged from 17% to 33%. Conclusion. The only general advantage of the flattening filter free irradiation mode observed for all tumor sites and treatment techniques was a reduction in dose to peripheral organs corresponding to a reduction in radiation induced second cancer risk in these organs. No general advantage or disadvantage could be observed in terms of plan quality or treatment time. https://doi.org/10.1016/j.ejmp.2018.06.555

[P279] Inter- and intra-fraction tumor motion in lung SBRT Ismail Faruk Durmus *, Bora Tas Yeni Yuzyil University Gaziosmanpasa Hospital, Radiation Oncology, Istanbul, Turkey ⇑ Corresponding author. Purpose. In Lung SBRT treatments, inter- and intra-fraction movement management are very important. The aim of the study is to determine the tumor movement as inter-fraction and intra-fraction. Methods. For 8 lung SBRT patients, CT scans were performed at 1 mm slice intervals. Breath Hold CT was performed using the CatalystTM surface scanning system in 2 patients and 4DCT scanning was performed in all 6 patients with respiratory phases. In the Monaco 5.11 treatment planning system, plans were prepared using 4–5 non-coplanar VMAT fields. The field to be scanned for intra-fraction CBCT was set to full rotation of 360°. Pre-CBCT scanning had performed in the XVI system before the patient began treatment and the amount of deviation in the tumor was determined in three dimensions. CBCT imaging was then performed intra-fraction while the 360° field was being treated both in the treatment. CBCT imaging was performed with 3 dimensional tumor tracking until the VMAT field was completed. After the VMAT field was completed, the