ESTRO 38 Abstract book

S1061 ESTRO 38

Results Figure 1 shows the averaged target volumes' DHVs on CBCTs and original dosimetry CT match each other in both arms. There are some discrepancies for rectum and bladder in both arms. DVHs of the CBCTs bladder are always lower than dosimetry because the bladder is empty during the original dosimetric scanner (CBCTs mean volume is 125 cc and 97.4 cc for the original CT), leading to higher relative volume doses. Rectum DVHs are on average higher on CBCTs, with an important uncertainty due to the high variation in rectum shape. Calypso SV, bladder and rectum DVHs are lower than those of the standard arm because of the lower irradiated volume induced by the reduced PTV margin. For instance, Calypso bladder D50 is 14 Gy (23 Gy for standard arm) and V70 is 5% (13%). There is also a 6 Gy lower rectum D50% on the Calypso patients, and V72 is 6% versus 10.5% for the standard arm.

Results A total of 787 sessions were analyzed. An intrafraction motion ≥ 3mm was detected for 77 fractions (9.8%). Visually, the shifts were unpredictable and varied from a transient evolution (left figure) continuous drift to a continuous drift (right figure). For each patient, from 0% to 23% of fractions were impacted by a displacement ≥ 3mm. 12,4% of movements were in the lateral direction, 48,8% in the axial direction and 38.8% in the longitudinal one. The mean time of the treatment interruption was ranged from 0.01’ to 09.52 minutes and increased the mean session time of 24.7% in comparison with a fraction without motion. Forty six percent of 77 fractions required couch shift corrections using kV imaging (as mandatory in our protocol) and explained a longer treatment.

Conclusion The intrafraction motions of the prostate are unpredictable and not negligible during the treatment. The Calypso system performs an accurate and continuous monitoring of the target and allows a safe margin reduction. EP-1947 RCMIGI randomized phase II study using Calypso system. First dosimetric results on CBCT acquisitions P. DebuirE 1 , J. Prunaretty 1 , N. Ailleres 1 , O. Riou 1 , D. Azria 1 , P. Fenoglietto 1 1 Institut du Cancer de Montpellier ICM, Radiothérapie, Montpellier, France Purpose or Objective In the RCMI-GI randomized phase II study, two treatment techniques of prostate cancer are compared in terms of radiation late toxicities, depending on the irradiated volumes. One of these techniques is a non-irradiative real- time tracking which uses electromagnetic implanted transponders (Calypso, Varian Medical System) to detect and follow submillimetric motions of a target . This way, the margin around the prostate can be reduced and a correlation may be found with late toxicities by studying the daily patient treatment deliveries. Here we present the results of dose calculation on daily CBCT images leading to the real treatment delivery knowledge. Material and Methods 25 prostate cancer patients were treated using RapidArc technique on a TrueBeam linear accelerator (Varian Medical System). In each arm of the study, 80 and 56 Gy were prescribed to the prostate and seminal vesicles (SV) in 40 fractions. The Calypso arm included 14 patients, each with 3 transponders implanted in the prostate that can be tracked before and during the irradiation. This allows to reduce the margin used to create the Planning Target Volume (PTV2 = Prostate + 3 mm). Eleven patients were included in the standard arm, without real-time tracking and with standard margins (1 cm, 0.5 cm posterior). For every patient, Cone Beam Computed Tomography (CBCT) imaging was performed at each fraction before irradiation. Target volumes and Organs at Risk (OAR) were contoured and the original Eclipse (Varian medical system) treatment plan was calculated on the CBCT images. Thus 40 daily Dosimetric Volume Histograms (DVHs) were obtained per patient (1000 CBCTs in total). The averaged prostate, SV, bladder and rectum DVHs were then compared to the original treatment plan DVHs, for both arms of the study.

Conclusion Calypso system allows submillimeric tracking of the prostate and therefore a reduction in the irradiated volume as shown in these first patient dosimetric results. Associated with long-term life quality follow-up, this could lead to the correlation of late toxicities versus dose statistics. EP-1948 Deep-inspiration breath-hold and free- breathing in left breast cancer irradiation:a dosimetric study D. Aiello 1 , G.R. Borzì 2 , L. Marino 2 , V. Umina 2 , A.M. Di Grazia 2 1 Fondazione Istituto Oncologico del Mediterraneo, Radiotherapy, Viagrande, Italy ; 2 REM Radioterapia, Radiotherapy, Viagrande, Italy Purpose or Objective To analyze organs at risk dose reduction between voluntary deep inspiration breath hold (DIBH) and free- breathing (FB) techniques in left breast irradiation. Material and Methods Between January 2018 and October 2018, eighty RT plans, based on DIBH and FB scans, were generated for forty breast left cancer patients who received three- dimensional conformal (3D) adjuvant RT and were retrospectively analyzed. Treatment plans were generated on both DIBH and FB CT scans. The scans were monitored by the Varian RPM TM respiratory gating system. The patients were asked to breathe freely and then inhale and hold their breath at a comfortable level, for at least 15 seconds. The treatment planning was performed with conformal tangential fields by means of 6, 10, or 15 MV photon fields. Treatment schedule were 40.05 Gy in 15 fractions (hypofractionated schedule) or 50 Gy in 25 fractions (conventional schedule) with or without sequential boost to tumor bed. Dose-volume histograms (DVHs) were compared for all plan. For the comparison, we considered: the mean dose to the heart (D meanheart ), left anterior descending coronary artery (D meanLADCA ) and ipsilateral lung (D meanlung), the volume receiving 20 Gy (V 20Gylung ) and the volume receiving 30 Gy (V 30Gylung ) for the ipsilateral lung, the volume receiving 20 Gy for LADCA (V 20GyLADCA ) in conventional schedule, the volume receiving