CT images in target volume delineation of the breast boost

ESTRO 33, 2014 1

Humanitas Centro Catanese di Oncologia, Radiotherapy, Catania, Italy Humanitas Centro Catanese di Oncologia, Medical Physics, Catania, Italy 3 Humanitas Centro Catanese di Oncologia, Nuclear Medicine, Catania, Italy 2

Purpose/Objective: The aim of this paper is the evaluation of the feasibility of Head & Neck radiation therapy in nasopharynx carcinoma using PET/CT simulation and VMAT delivery. Materials and Methods: From February 2012 to September 2013 ten consecutive patients with nasopharynx carcinoma have been treated using RapidArc® technology with Unique Performance Edition linear accelerator (Varian Palo Alto, California, USA). They all have been planned using twofull (360°) arcs with a beam energy of 6 MV and a dose rate of 600 MU/min. All patients were performed to a 18F-FDGPET\CT imaging as part of the initial staging workup. Patients were scanned with Time Of Flight PET\CT scanner (GE Discovery 690, GE Healthcare, Milwaukee, WI) 60 minutes after3 MBq/kg 18F-FDG intravenous injection. The Gross Tumour Volume (GTV) was defined as the gross extent of tumour contoured using SUV 30% threshold relative to the SUVmax, that we named Biological Target Volume (BTV). The high-risk Clinical Target Volume (CTV1) was defined as BTVplus a margin for microscopic spread, while the low-risk Clinical Target Volume (CTV2) included uninvolved nodes. A margin for Planning Target Volume (PTV) was generated by expanding the CTV2 of 5 mm in all directions. Dose prescription was 54.45Gy at Planning Target Volumes (PTV) and 69.96 Gy to CTV1 using simultaneous integrated boost in 33 fractions. All patients received concomitant weekly cisplatin chemotherapy.

Results: Concerning planning optimization strategies and constraints, as per PTV coverage, D98%>95% and V95%>99%. As for organs at risk, all planning objectives were respected, and this was correlated with observed acute toxicity rates. Only 3 pts. experienced G3 mucositis, none G3 dermitis and 4 pts. G3 dysphagia. Nobody required feeding tubes to be placed during treatment. Acute toxicity is also related to chemotherapy. No patient interrupted the course of radiotherapy because of a quick worsening of general clinical conditions. Six patients underwent 18F-FDG-PET/CT three months after the end of radiation therapy course as follow-up exam: one of them had a negative PET scan on primary site but a single liver metastasis; four of them showed a complete response and one had a partial response on primary site with complete node negativization. Conclusions: These preliminary results state that volumetric modulated arc therapy with 18F-FDG PET\CT simulation in Nasopharynx cancers is feasible and effective, with acceptable toxicities. Furthermore, PET scan is useful for the revaluation of patients after radiation therapy, asit can be compared to the one acquired at the very beginning of the treatment. EP-1415 Dosimetry of incidental irradiation, level I and II lymph nodes in breast cancer. E. Jorda Sorolla1, D. Dualde Beltrán1, M. Alcalá Gimenez1, J. Pinazo Bensach1, R. Algás Algás1, M. Maroñas1, M. Ferri1, C. Domingo1, E. Ferrer1 1 Hospital Clinico Universitario, Department of Radiation Oncology, Valencia, Spain

S127 Purpose/Objective: To evaluate dose distribution and coverage of level I and II lymph nodes in three-dimensional conformal radiotherapy (3DCRT) standard irradiation via opposed tangential fields. Materials and Methods: A retrospective study was made of 50 patients treated for breast cancer during 2013. Mean age of patients was 62 years (42-84). 70% of patients had invasive ductal carcinoma (IDC). (10% DCIS, 20% other infiltrating carcinomas). The majority of patients were treated for tumors <2 cm (N=32). Hormone receptor positive (ER: 41/50, PR: 45/50) and HER2-Negative (41/50). 34 patients were treated by lumpectomy + sentinel lymph node biopsy (SLNB). One patient, with postive sentinel lymph node, also recieved axillary node dissection. The 5 patients diagnosed with DCIS were treated by lumpectomy without SLNB. The remainder of the patients (N=11) underwent immediate axillary node dissection (positive lymph node biopsy, no tracer migration, surgery at other centers) Breast radiotherapy (RT) was administered exclusively via tangential fields (mean dose recieved: V95 was 93%), excluding irradiation of axillary and supraclavicular lymph nodes. All patients recieved a total dose (TD) of 50 Gy to 200 cGy/fraction/day. Once RT treatment was completed, the level I and II axillary lymph nodes were contoured independently based on the Breast Cancer Contouring Atlas of the Radiation Therapy Oncology Group (RTOG). Results: The mean level I lymph node volume was 46.73 cc. The mean level II lymph node volume was 43.26 cc. The mean dose received by level I and II was 39.38 Gy and 20.92 Gy respectively. The maximum dose received by level I and II was 49.17 Gy and 46.34 Gy respectively. The mean V95 of the level I and II axillary lymph nodes was 43.26 Gy and 8.68 Gy respectively. The level I and II axillary lymph nodes received 79% and 42% repectively of the prescribed dose for breast irradiation (50 Gy). Conclusions: The results demonstrate that incidental irradiation of the level I and II axillary lymph nodes is more than negligible, although possibly insufficient, therefore in patients with positive SLNB who have not received axillary dissection, locoregional treatment of the axilla should be considered. New prospective studies should be made to determine whether the incidental dose received by the level I and II axillary lymph nodes is sufficient to exclude locoregional treatment of the axilla. EP-1416 Impact of PET-CT simulation in lung cancer patients treatment. Preliminary results J. Pardo1, A.M. Mena1, C. Chiaramello1, M. Giménez2, F. Romero3, P. Mateos3, M. Sintes3, I. Alastuey4, N. Aymar4, C. Peña5 1 Hospital Universitari Son Espases, Radiation Oncology. Radiation Oncology Research Group (IBSE), Palma de Mallorca, Spain 2 Hospital Universitari Son Espases, Nuclear Medicine. Radiation Oncology Research Group (IBSE), Palma de Mallorca, Spain 3 Hospital Universitari Son Espases, Medical Physics. Radiation Oncology Research Group (IBSE), Palma de Mallorca, Spain 4 Hospital Universitari Son Espases, Radiation Oncology. Radiation Oncology Research Group (IBSE), Palma de Mallorca, Spain 5 Hospital Universitari Son Espases, Nuclear Medicine. Radiation Oncology Research Group (IBSE), Palma de Mallorca, Spain Purpose/Objective: PET-CT is being increasingly used in radiation oncology. 18Fluorodeoxyglucose is the most commonly employed radiotracer for diagnosis, staging, recurrent disease detection and monitoring of tumor response to therapy. In radiotherapy, improvement in target delineation allows tumor margins reduction and, consequently, decrease the volume of normal tissue irradiated. Our purpose is to analyze the impact of simulation by means of PET-CT versus CT on tumor volume target (TVT) and normal tissue organs at risk (OARs) in RTP in lung cancer patients (pts). Materials and Methods: From 04/2012 to 10/2013, 37 lung cancer pts (stage IIIA- IIIB) underwent PET-TC with intravenous contrast for staging and radiotherapy treatment planning at our center. Our staging protocol is: Standard PET-TC Initial Acquisition (50-110min post-injection of 610mCi of 18-FDG; 2min/bed; *GE ST70). If no images suggestive of metastasis have proven, we proceeded to acquisition of images for 3DCRT treatment planning using laser positioning and the required immobilization devices. Mean total dose administered: 63 Gy (range, 6066Gy) in in 30-33 fractions with concurrent chemotherapy. Regarding lung, the following parameters were analyzed: V20, Dmax, MLD, V35 homolateral lung and PTV volume (cc). Regarding OARs, V45 Esophagus, V45 heart and V45 cord were analyzed. Results: Age: Mean 57 years (range 43-92). Gender: 32 males and 5 females. Histology: 18 pts had NSCLC and 14 pts SCLC. Metastatic disease was detected in 16 (43%) pts, therefore 21 pts underwent radical treatment and were analyzed. Comparing PET-CT respect CT simulation,

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ESTRO 33, 2014

Lung: PTV was reduced in 19 pts (mean 184.9 cc), and increased in 2 pts (mean 6.3cc).V20 was reduced in 19 pts (mean 8 Gy), and increased in 2 pts (mean 1.53 Gy). Dmax was reduced in 17 pts (mean 2.52Gy), and increased in 4 pts (mean of 1.13 Gy). MLD was reduced in 19 pts (mean 5.63 Gy), and increased in 2 pts (0.47 Gy). V30homolateral was reduced in 19 pts (mean 12.16 Gy), and increased in 2 pts (mean 3 Gy). OARs: V45esophageal was reduced in 19 pts (mean 10.69 Gy), and increased in 2 pts (mean 11.6 Gy). V45heart was reduced in 13 pts (mean 11 Gy), no increase was observed. V45cord was reduced in 3 pts (mean 2.19 Gy), no increase was observed.

Materials and Methods: 18F-FDG PET/CT was performed in RT treatment planning position in 38 patients before breast conserving surgery for stage I – II invasive ductal breast cancer. The tumor size ranged from 0.5 – 2.6 cm (median 1.6). Following surgery an additional treatment planning CT was fused to the preoperative 18F-FDG PET/CT. Three experienced radiation oncologists defined the GTV based on CT (GTVCT) and in a second time using the fused PET/CT datasets (GTVPET/CT). All clinical history and previous imaging studies were provided. Overlap analysis was conducted to assess geographic mismatch between the GTVs.

Conclusions: In the group of patients analyzed, PET-CT planning allows to significantly reducing PTV volume, which results in lower OAR received doses and, therefore, in lower toxicity, and better treatment adherence and tolerance.

Results: The median SUVMax was 3.6 (range 1.4 – 9.6). The inclusion of the 18F-FDG PET added substantial tumor extension outside the GTVCT and changed the GTVs significantly in 24 patients. Compared with the GTVCT the GTVPET/CT was increased of median 17.80% (range: 0.0 – 82.5%). Interobserver variability for GTV delineation was high using CT images only and could be significantly reduced using the fused PET/CT (p=0.04). PET/CT revealed additionally 3 axillairy lymph node metastases and 1 bone metastases.

EP-1417 The effect of tumor volume and pathology on diffusion-weighted MRI during radiotherapy of lung cancer E. Weiss1, J.C. Ford1, K. Olsen2, K. Karki1, G.D. Hugo1 1 Virginia Commonwealth University, Radiation Oncology, Richmond VA, USA 2 Virginia Commonwealth University, Radiology, Richmond VA, USA Purpose/Objective: Diffusion-weighted MRI (DW-MRI) has been demonstrated to monitor response to therapy and to potentially predict outcome in several tumor locations, including early reports for lung cancer. The apparent diffusion coefficient (ADC) as a quantitative measure for the diffusion of water molecules, depends on the tissue composition, including cell size, density, and integrity. In this study, the correlation of initial tumor volumes and volume changes during radiotherapy, and the effect of lung cancer pathology on ADC values were investigated. Materials and Methods: Seventeen patients with non-small cell lung cancer underwent MRI with DW-MRI and 4D CT imaging prior to radiochemotherapy. Imaging was repeated in 10 patients after 30 Gy and 60 Gy. Respiratory navigated DW-MRIs were acquired on a 1.5T scanner in axial planes with eight b-values ranging from 0-1000 s/mm2. Primary tumors were contoured on CT, post gadolinium T1-weighted ultrafast gradient echo volume interpolated breath hold (VIBE), and diffusionweighted images. Initial ADC values and variations thereof during treatment were correlated with tumor regression and pathology. Results: The initial primary tumor volume ranged between 0.5 and 455 cm3. The mean tumor volume regression after 6 weeks was 46%±13%. The initial ADC value ranged between 933 and 1663 µm2/s. The mean ADC increase during therapy was 25%±14%. ADC values in patients with larger than median primary tumor volumes were not significantly different from those with smaller volumes (1314 µm2/s ± 214 µm2/s versus 1355 µm2/s ± 251 µm2/s, p=0.75). Also, percent ADC increase was not significantly different in patients with larger versus those with smaller than median volume regression during therapy (22% ± 4% versus 28% ± 21%, p=0.77). Mean ADC values were higher in patients with adenocarcinoma than squamous cell cancer (1406 µm2/s ± 169 µm2/s versus 1247 µm2/s ± 217 µm2/s , p=0.26). After 60 Gy, patients with adenocarcinoma had less mean ADC value increase than squamous cell cancer (17% ± 7% versus 30% ± 16%, p=0.3). Conclusions: Pretreatment ADC values and ADC response to therapy appear to be independent from the initial tumor volume and tumor regression during therapy in this small patient cohort which suggests ADC is an independent measure of tumor response to radiotherapy in lung cancer. Interestingly, ADC values were higher and responded less in adeno- than squamous cell cancers. These data need to be confirmed in larger cohorts including correlation of ADC response with clinical outcome. EP-1418 Impact of preoperative 18FDG PET/CT images in target volume delineation of the breast boost O. Fargier-Bochaton1, V. Vinh-Hung1, O. Ratib2, C. Tabouret-Viaud2, R. Miralbell2, H. Vees2 1 Hôpitaux Universitaires de Genève, Radiation Oncology, Geneva, Switzerland 2 Hôpitaux Universitaires de Genève, Nuclear Medecine, Geneva, Switzerland Purpose/Objective: Geographical uncertainties in gross tumour volume (GTV) delineation for the breast boost volume are high. We therefore evaluated the impact of 18F-FDG PET/CT in radiotherapy (RT) treatment planning in these tumors.

Conclusions: The use of fused PET/CT images for target volume delineation for the boost volume after breast conserving surgery alters RT treatment volume in a majority of patients and reduced interobserver variability significantly with respect to CT only. EP-1419 Magnetic resonance imaging rigid and deformable pelvic registration accuracy related to the tabletop shape M. Pastor1, S. Sabater2, I. Andrés2, E. Lozano1, R. Berenguer3, M.M. Sevillano2, M. Arenas4 1 Hospital General de Albacete, Radiology, Albacete, Spain 2 Hospital General de Albacete, Radiation Oncology, Albacete, Spain 3 Hospital General de Albacete, Radiation Physics, Albacete, Spain 4 Hospital Sant Joan, Radiation Oncology, Reus, Spain Purpose/Objective: While CT remains the gold standard on radiation therapy treatment planning, due to the electron density provided as well as its geometric accuracy, MRI is increasingly used for prostate delineation due to its greater soft-tissue contrast which improves pelvic segmentation. Flat tables are used during radiation procedures. Diagnostic MRI (MRI-DX) scans are performed on curved couches, so patient positions differ. Our purpose was to verify registration accuracy of the rigid and deformable registration of pelvic MRI-DX related to MRI scans acquired with flat tables (MRI-RT). Materials and Methods: Six prostate cancer patients underwent T2 weighted MRI scan in two different positions with identical MRI parameters with a flat tabletop (MRI-RT) immediately followed by a standard diagnostic scan using the curved couch (MRI-DX) (Philips Intera 1.5 T; TE 120 ms; TR 3000 ms; Field of view 180mm; Matrix 256x512; Slice thickness 3 mm; Number of signal averages 4; Number of slices 24; Scan percentage 80%; TSE factor 16; Scan duration 5:12. Some patients required 30 slices). MRI-RT scans were undergone with a four-channel flexible body coil. MRI-DX were performed using a five-channel cardiac coil. Images were imported into the 3D-SLICER package for a rigid registration followed by a non-rigid (b-spline) registration. The MRI-RT was considered the fixed set and the MRI-DX was the moving image. At the end 3 image sets were compared: the MRI-RT and two sets produced after rigid registration (MRI-rigid) and deformable registration (MRI-def). Registered images were compared to the RM-flat using intensity based metrics (mutual information (MI), cross-correlation (CC) and sum of squared differences (SSD)). Prostate and rectum were segmented on every image set. Volume differences using 3D vectors, Hausdorff distance (HD) and the Dice similarity coefficient (DSC) were computed. Paired non-parametric tests were used for comparisons. Results: All image metrics showed significant differences between rigid and deformed images related to RM-flat (all p=0.028). No significance was seen for median 3D prostate vectors (median 105.6, 105.9 and 105.6 for RM-flat, rigid and deformable images) nor 3D rectal vectors (median 92.1, 93.4 and 93.7). DSC did not show significant differences for prostate (median, rigid, 0.8411; deformable, 0.9174). Significance was seen for rectal DSC (median, rigid, 0.7828; deformable, 0.9054, p=0.028) and 95% prostate and rectal HD distance (median prostate, rigid, 3.135; deformable, 2,255; p=0.028; median rectum, rigid, 4,005, deformable, 2.655, p=0.028). Conclusions: Differences on image intensities between RM-flat, RM-rigid and RM-def were seen. Despite the lack of differences among 3D vectors, divergences on HD and DSC metrics are of concern. Additional studies are need before to use images acquired with curved couches on RT treatments.