172. Predictors of cardiac dose reduction achieved with deep inspiration breath hold technique over free breathing technique in left breast radiotherapy

Abstracts / Physica Medica 56 (2018) 133–278

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a

Ospedale San Pietro FBF, U.O.C. Radioterapia Oncologica, Italy UPMC San Pietro FBF, Centro di Radioterapia ad alta specializzazione, Italy b

Half Dmax of a single-isocenter VMAT radiosurgery treatment for multiple intracranial lesions shifted during a single session for repositioning. The implementation of single-isocenter volumetric modulated arc therapy (VMAT) radiosurgery technique for multiple intracranial lesions allows a significant reduction of treatment times, as well as enhancing accuracy by reducing the potential intrafraction motion [1]. Methods. For 20 patients treated with VMAT for multiple brain metastases we have analyzed the treatment process. Each case had different number and distribution of metastases. We performed a CT simulation scan with 1.25 mm thickness slice for all patients. The simulation images were registered with a MR in order to define the targets. For each case we compared the VMAT single-isocenter technique plan with the sums of the plans of every single lesion. Plans were evaluated using Dose Volume Histograms, Conformity and Uniformity Indexes. All the plans were optimized with 6 MV flattened filter free arcs. Set up checks were performed using both BrainLAB ExacTrac and Varian Cone Beam CT (CBCT). For 10 patients we also evaluated the intrafraction motion. Results. No significant difference was detected between the two techniques. The single-isocenter technique comes out better for the dose distributions especially for low doses. We discovered a good agreement between ExacTrac and CBCT and a minimum intrafraction movement (<1 mm) which was dosimetrically insignificant also for peripheral lesions. We underline a very significant reduction of treatment times. Conclusions. Both methods achieve good dosimetric results. Single-isocenter VMAT radiosurgery treatment for multiple metastases is a faster technique and could be performed safely using image guided radiotherapy treatment thus relieving patient discomfort. Reference Jay Morrison et al. Is a single isocenter sufficient for volumetric modulated arc therapy radiosurgery when multiple intracranial metastases are spatially. https://doi.org/10.1016/j.meddos.2016. 06.007. https://doi.org/10.1016/j.ejmp.2018.04.181

171. Dosimetric validation for an automatic multiple brainmetastases planning system using a single isocenter and conformal arc Randa El Gawhary a,b, Giorgio Hamid Raza a,b, Barbara Nardiello b, Federico Bianciardi a,b, Giuseppe Minniti a,b, PierCarlo Gentile a,b

Purpose. A commercial planning software using this technique, called Multiple Brain Mets SRS (MBM) Element from Brainlab AG (Feldkirchen, Germany), version 1.5, has been installed in our institution. It uses a preconfigured set of dynamic noncoplanar, conformal arcs to treat up to 15 brain-metastases with a single isocenter. It optimizes the weight of each arc to achieve the best conformity for all targets. Planning time for optimization and dose calculation is 24 min, which improves the planning efficiency dramatically in our clinic. In this study we describe the method used in our clinic to measure the delivered dose and then compare to the calculated dose distribution. Methods. We included in this study 10 patients whith multiple brain mets. For these 10 pz the number of lesions planned ranges from a minimum of two to a maximum of six. The verification plan is calculated by Brainlab Element for the QA and measured in Easycube phantom equipped with a CC01 ionization chamber and EBT film. Furthermore the comparison of the plans, computed by MBM Element and Varian Eclipse, version 13.0, is realised. Results. The percentage difference between calculated by MBM Element and measured is included in 5%.Treatment plans generated using MBM Element and Eclipse resulted in a good agreement, the difference of the maximun dose is lower 2%. The PTV mean dose values difference between MBM Element and Eclipse have resulted less 1,7%. Conclusions. Satisfactory absolute dose and distribution agreement were observed. We conclude that MBM Element was in clinical use after these validations. https://doi.org/10.1016/j.ejmp.2018.04.182

172. Predictors of cardiac dose reduction achieved with deep inspiration breath hold technique over free breathing technique in left breast radiotherapy M. Maddalo a, G. Benecchi a, C. Grondelli b, E. Calabri a, R. Rossi a, P. Losardo b, M.L. Bergamini b, C. Dell’Anna b, G. Ceccon b, S. Nurmahomed b, S. Gianni b, R. Rossi b, M. Manicone b, S. Andreani b, F. Ghetti b, F. Salaroli b, C. Ghetti a, N. D’Abbiero b a b

AOU di Parma, Medical Physics Department, Parma, Italy AOU di Parma, Radiotherapy Department, Parma, Italy

Purpose. Deep inspiration breath-hold (DIBH) has been routinely applied in left breast radiotherapy to reduce cardiac exposure. The purpose of this study was to compare deep inspiration breath hold and free breathing techniques (FB) in terms of heart and left-lung doses and to determine possible predictors of the dose reduction achieved with DIBH (DDBH-FB). Methods. Ten patients with left breast cancer have been treated with postoperative radiotherapy in Parma Hospital. For each patient both the FB and the DIBH planning CT were acquired. 3DCRT treatment plans using tangential field-in-field beams were developed for both FB and DIBH. FB and DIBH dose distributions were compared in terms of Dmean, V5Gy, V20Gy, V30Gy of the heart and V5Gy, V20Gy of the left-lung. Many geometric/anatomical parameters were measured in the FB condition: heart and left-lung volumes (Vheart, Vlung-L), maximum thickness of the same organs inside the tangential fields (dheart, dlung-L), axial and para-sagittal cardiac contact distances (CCDax, CCDps), maximum tangential distance between beam-entrance and beam-exit (dentrance-exit), maximum anteroposterior diameter of the chest. Results. DIBH plans showed a significant reduction of Dmean ( 60.9%), V5Gy ( 82.5%), V20Gy ( 93.6%) and ( 95.8%) of the heart (p < 0.01, Wilcoxon signed-rank test), while no significant difference

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in target coverage and left-lung V5Gy, V20Gy. The parameters that significantly correlated with DDBH-FB were: Vheart (0.041 < p < 0.049, 0.63 < R < 0.65), dheart (p < 0.001, 0.96 < R < 0.97), CCDps (0.036 < p < 0.045, 0.64 < R < 0.66) and dentrance-exit (0.036 < p < 0.048, 0.64 < R < 0.67). Conclusions. This study confirmed how DIBH for left breast cancer treatment can decrease cardiac dose. The benefit of DIBH over FB strictly depends on chest shape, heart size and heart position. However, most of the parameters showed a weak correlation with DDBHFB, so they cannot be used to effectively predict DDBH-FB. Only dheart seems to be a good predictor of DDBH-FB, but more cases must be included to confirm/reject these findings. https://doi.org/10.1016/j.ejmp.2018.04.183

173. Dosimetrical evaluation of interplay effect for lung cancer treatments with Vero system: Comparison between three different techniques S. Comi a, A. Bazani a, F. Emiro a,d, G. Piperno b, F. Baldini b, B.A. Jereczek-Fossa b,c, F. Cattani a a

Unit of Medical Physics, European Institute of Oncology, Milan, Italy Division of Radiation Oncology, European Institute of Oncology, Milan Italy c Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy d University of Milan, Milan, Italy b

Purpose. To evaluate interplay effect on delivered dose distributions for lung cancer treatments using treatment techniques (DynamicWaveArc [1,2], DynamicConformalArc and DynamicTumorTracking) performed with VERO system. Methods. For each patient with lung nodules selected for stereotactic treatments a 4DCT with RPM Varian System was acquired. Internal Target Volume (ITV) was created on maximum intensity projection reconstructed from a dataset of ten phases and enlarged to PTV (5 mm margins). For each plan an extreme hypo-IGRT schedule was applied (36 Gy/3fz) with a prescription of D95% PTV = 100%. DWA planning was performed with Collapsed Cone Convolution Superposition on Raystation (v.6.1.1.2) (2 full arcs, GenericX1 template), while DCA and DTT with Monte Carlo algorithm on iPlannet RT Dose (v.4.5.4) (1 full arc and 5 conformal beams, respectively). Plans were recalculated as pre-treatment QA and delivered on BrainLab Respiratory Gating Phantom, applying real patients’ breathing patterns. Dose maps were acquired with EBT3 Gafchromic, applying a single scan protocol for absolute dose measurements [3,4]. All films were read with an EPSON XL10000 scanner in transmission mode (48-bit RGB and 72 dpi resolution) and analyzed with FilmQAProÒ 2016 (Ashland). For each technique, absolute dose c analysis was performed between static and moving delivery, applying 2%-2 mm criteria and no dose threshold. Evaluations were performed considering single and 3-fractions schedule and a mean c passing rate for 5 patients. Results. Results obtained from analysis of all treatment techniques and both schedules are reported in Table 1.

Conclusions. From preliminary studies, the interplay effect is more pronounced in DWA treatments than in other cases, as expected. However as the number of fractions is increased, the c passing rates become almost acceptable also for DWA. We also started to investigate the interplay effect varying patients’ breathing patterns [5]. Results suggest using this technique for moving targets could lead to better OARs sparing.

References 1. Mizowaki T et al.. Feasibility evaluation of a new irradiation technique: three-dimensional unicursal irradiation with the Vero4DRT (MHI-TM2000). J Rad Res 2013;54:330–6. 2. Burghelea M et al.. Initial characterization, dosimetric benchmark and performance validation of Dynamic Wave Arc. Radiat Oncol 2016;11:63. 3. Micke A, Lewis D, Yu X. Multichannel film dosimetry with nonuniformity correction. Med Phys 2011;38:2523–34. 4. Lewis D, Micke A, Yu X, Chan MF. An efficient protocol for radiochromic film dosimetry with flatbed CCD scanners combining calibration and measurement in a single scan. Med Phys 2012;39:6339–50. 5. Garibaldi C et al.. Geometric and dosimetric accuracy and imaging dose of the real-time tumour tracking system of a gimbal mounted linac. Med Phys 2015;31:501–9. https://doi.org/10.1016/j.ejmp.2018.04.184

174. Large scale adoption of statistical process control for patient-specific VMAT quality assurance S. Cilla a, A. Ianiro a, P. Viola a, M. Craus a, F. Deodato b, G. Macchia b, M. Buwenge c, V. Valentini b,d, A.G. Morganti c a Medical Physics Unit, Foundation for Research and Cure ‘‘John Paul II”, Campobasso, Italy b Radiation Oncology Unit, Foundation for Research and Cure ‘‘John Paul II”, Campobasso, Italy c Radiation Oncology Department, DIMES, S.Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy d Radiation Oncology Department, Foundation University Hospital ‘‘A. Gemelli”, Catholic University of Sacred Heart, Roma, Italy

Purpose. Statistical Process Control (SPC) is a tool widely used in industrial engineering for monitoring, controlling and improving a process through statistical analysis. We applied this strategy for patient-specific VMAT pre-treatment verification. Methods. From 2009, more than 1700 patients were treated with Elekta VMAT at our institution. Plans were re-grouped according to treatment technique and disease sites Group 1: 736 complex treatments using SIB for head-neck, pelvic, brain and other sites; (2) 441 low-risk prostate treatments and (3) 558 extracranial metastasis treated with SBRT. 4942 planar dose measurements were performed with the PTW Seven29 array/Octavius phantom. Three metrics were simultaneously evaluated: (a) c%: points-percentage with c-value less than one, (b) cmean and (c) c1%: the near-maximum gamma. Clinical specifications were: c% > 90%, cmean < 0.67 and c1% < 2. Shewhart charts were used to calculate the central (CL), upper control (UCL) and lower control limits (LCL). The capability of the processes was evaluated by means of Cpk indexes. Results. Using 3%/3 mm c-analysis, results significantly depend on plan complexity. For c%, CL and LCL were 93.8%, 99.1%, 99.5% and 87.9%, 96.6%, 97.9%, for group 1,2 and 3 respectively. For cmean, CL and UCL were 0.42, 0.36, 0.29 and 0.54, 0.49, 0.40, for groups 1, 2 and 3 respectively. For the groups 2 and 3, all processes are in