ESTRO 38 Abstract book

S658 ESTRO 38

Conclusion Even with the new target delineation method, VMAT provides dosimetric advantages in carotids, bulbs and in the most of OARs sparing respect to 3DCRT in T1 GC. EP-1187 Different carotid contouring results in dosimetric variability and significant anatomical missing L. Ferella 1 , F. Vittorini 2 , E. Varrassi 3 , P. Franzese 3 , M. Di Staso 3 , F. Marampon 4 , C. Sorce 5 , A. Chalaszczyk 5 , G. Grimaldi 5 , E. Di Cesare 6 , E. Orlandi 7 , V. Tombolini 4 , C. Masciocchi 6 , G.L. Gravina 5 1 Fondazione IRCC Istituto Nazionale dei Tumori Milan- University of L'Aquila-, Radiotherapy 2 Unit. Department of Biotechnological and Applied Clinical Sciences- Division of Radiotherapy. Laboratory of Radiobiology L'Aquila, Milano, Italy ; 2 San Salvatore Hospital- L'Aquila, Service of Medical Physics, L'Aquila, Italy ; 3 S. Salvatore Hospital- University of L'Aquila, Department of Radiation Oncology, L'Aquila, Italy ; 4 Policlinico Umberto I Hospital- Sapienza- University of Rome, Department of Radiation Oncology, Rome, Italy ; 5 University of L'Aquila, Department of Biotechnological and Applied Clinical Sciences- Division of Radiotherapy. Laboratory of Radiobiology, L'Aquila, Italy ; 6 University of L'Aquila, Department of Biotechnological and Applied Clinical Sciences, L'Aquila, Italy ; 7 Fondazione IRCC Istituto Nazionale dei Tumori, Radiotherapy 2 Unit- Radiotherapy 1 Unit, Milano, Italy Purpose or Objective Carotid Artery (CA) sparing approach is a field of increasing interest owing to long life expectancy of patients with early glottic cancer (EGC). A CA delineation consensus lacks with no internationally recognized dose constraints for this structure. Here we compare, in terms of anatomical and dosimetric variability, three of the most common CA delineation methods found in literature. Material and Methods CA of 10 cT1a N0 EGC patients were outlined using 3 different approaches: 1) the whole CA from its origin up to the internal carotid entry into skull base (Contour 1); 2) the tract of CA from its origin up to at least 2.5 cm above the hyoid bone (Contour 2); 3) the tract of CA 1 cm superior and inferior to PTV (Contour 3). The carotid bulb (CB) was contoured 2 cm inferiorly and superiorly to carotid bifurcation according Framingham Heart definition due to its role in the radio-induced atherosclerosis. A 1 mm isotropic carotid and bulb margin was added to compensate the changes during cardiac cycle. Thirty VMAT carotid sparing plans were generated and CA Dmax, Dmean, V35 and V50 were compared across the different contouring approaches. T-test for paired data with logarithmic transformation was used to compare dosimetric parameters. A two-sided p-value< 0.05 was the significance threshold Results In terms of carotid structures missing, Contour 3 did not include the entire bulb in 100% of contoured carotids while Contour 1 and 2 always included it entirely. A significant variability in ipsilateral and contralateral CA Dmean and ipsilateral CA V35 were found among the three contouring approaches with the lowest, intermediate and highest mean values found for Contour 1, Contour 2 and Contour 3, respectively (Table 1). No consistent variability was found for bilateral CA Dmax and V50 and for contralateral CA V35 across the three contouring approaches (Table 1).

Conclusion Here we document the need for a standardized CA delineation since a relevant dosimetric variability and a significant missing of important structures has been documented among the three most frequent used contouring approaches. Based on our Institutional preference, we suggest to delineate the whole bulb and whole CA from its origin up to the skull base entry to decrease interobserver variability among clinicians. EP-1188 Carbon ion radiotherapy for recurrent pleomorphic adenoma at CNAO: preliminary results. S. Ronchi 1 , B. Vischioni 1 , V. Vitolo 1 , M. Bonora 1 , A. Hasegawa 2 , M.R. Fiore 1 , A. Iannalfi 1 , E. D'Ippolito 1 , R. Petrucci 1 , A. Barcellini 1 , S. Molinelli 1 , D. Maestri 1 , G. Viselner 3 , A. Facoetti 1 , M. Ciocca 1 , L. Preda 3 , F. Valvo 1 , R. Orecchia 1,4 1 National Center of Oncological Hadrontherapy, Radiotherapy Unit, Pavia, Italy ; 2 Osaka Heavy Ion Therapy Center, Radiation therapy Unit, Osaka, Japan ; 3 National Center of Oncological Hadrontherapy, Diagnostic Imaging Unit, Pavia, Italy ; 4 European Institute of Oncology, Radiation therapy Unit, Milan, Italy Purpose or Objective To evaluate response and toxicity of carbon ion radiotherapy (CIRT) for recurrent pleomorphic adenoma patients (pts). Material and Methods Inclusion criteria based on the CNAO phase II clinical protocol CNAOS10/2012/C were: (1) prior histological diagnosis of pleomorphic adenoma; (2) relapse after at least one previous surgical approach; (3) further surgery excluded (due to high risk of facial nerve damage/medical contraindications/refusal of the patient); (4) no previous radiotherapy. CIRT prescription dose was 65.6 Gy[RBE] in 16 fractions (4.1 Gy[RBE]/fraction). Local response and toxicity (tox) were respectively evaluated using RECIST and CTCAE v.4.0 criteria. MRI was performed after treatment every 3-4 months (mo.) in the first 2 years, every 6 mo. in the third year, then once a year. Results Between November 2012 and May 2017, 24 pts were treated. Median age was 47 years (range 20-68). Median time from first diagnosis to CIRT was 17.4 years (range 1– 33.5). Median number of previous surgeries was 3 (range 1-6). Median time from last surgery to CIRT was 16.8 mo. (range 9.8–274.4). Two and 22 pts were treated for uninodular and plurinodular recurrence, respectively. Mean GTV was 19.8 cc (range 1.1–91.1). Mean CTV was 83.5 cc (range 25.6–148.6). Median follow-up (FU) time was 23.3 mo.(range 7.8–64.4). Radiological response at first FU was partial response and stabilization in 2 and 22 pts, respectively. At last FU, all pts were alive with local control maintained. Only 1 patient treated for plurinodular tumor had out-field recurrence at 4.5 years after CIRT. Tox during/at the end of treatment was G0, G1, G2 for 3 (12.5%), 9 (37.5%), and 12 (50%) pts, respectively. Acute tox within 3 months was G0, G1, G2 for 10 (41.7%), 11 (45.8%), and 3 (12.5%) pts, respectively.