Alexander V. Kirichenko

A region growing method for tumor volume segmentation on PET images for rectal and anal cancer patients.

The application of automated segmentation methods for tumor delineation on 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) images presents an opportunity to reduce the interobserver variability in radiotherapy (RT) treatment planning. In this work, three segmentation methods were evaluated and compared for rectal and anal cancer patients: (i) Percentage of the maximum standardized uptake value (SUV% max), (ii) fixed SUV cutoff of 2.5 (SUV2.5), and (iii) mathematical technique based on a confidence connected region growing (CCRG) method. A phantom study was performed to determine the SUV% max threshold value and found to be 43%, SUV43% max. The CCRG method is an iterative scheme that relies on the use of statistics from a specified region in the tumor. The scheme is initialized by a subregion of pixels surrounding the maximum intensity pixel. The mean and standard deviation of this region are measured and the pixels connected to the region are included or not based on the criterion that they are greater than a value derived from the mean and standard deviation. The mean and standard deviation of this new region are then measured and the process repeats. FDG-PET-CT imaging studies for 18 patients who received RT were used to evaluate the segmentation methods. A PET avid (PETavid) region was manually segmented for each patient and the volume was then used to compare the calculated volumes along with the absolute mean difference and range for all methods. For the SUV43% max method, the volumes were always smaller than the PETavid volume by a mean of 56% and a range of 21%-79%. The volumes from the SUV2.5 method were either smaller or larger than the PETavid volume by a mean of 37% and a range of 2%-130%. The CCRG approach provided the best results with a mean difference of 9% and a range of 1%-27%. Results show that the CCRG technique can be used in the segmentation of tumor volumes on FDG-PET images, thus providing treatment planners with a clinically viable starting point for tumor delineation and minimizing the interobserver variability in radiotherapy planning.

Hepatocellular carcinoma with child Pugh-A Cirrhosis treated with stereotactic body radiotherapy

AIM To evaluate the control, survival, and hepatic function for Child Pugh (CP)-A patients after Stereotactic body radiotherapy (SBRT) in hepatocellular carcinoma (HCC). METHODS From 2009 to 2016, 40 patients with Barcelona Liver Clinic (BCLC) stages 0-B HCC and CP-A cirrhosis completed liver SBRT. The mean prescription dose was 45 Gy (40 to 50 Gy in 4-5 fractions). Local relapse, defined as recurrence within the planning target volume was assessed with intravenous multiphase contrast computed tomography or magnetic resonance imaging every 4-6 mo after completion of SBRT. Progression of cirrhosis was evaluated by CP and Model for End Stage Liver Disease scores every 3-4 mo. Toxicities were graded per the Common Terminology Criteria for Adverse Events (v4.03). Median follow-up was 24 mo. RESULTS Forty-nine HCC lesions among 40 patients were analyzed in this IRB approved retrospective study. Median tumor diameter was 3.5 cm (1.5-8.9 cm). Six patients with tumors ≥ 5 cm completed planned selected transarterial chemoembolization (TACE) in combination with SBRT. Eight patients underwent orthotropic live transplant (OLT) with SBRT as a bridging treatment (median time to transplant was 12 mo, range 5 to 23 mo). The Pathologic complete response (PCR) rate in this group was 62.5%. The 2-year in-field local control was 98% (1 failure). Intrahepatic control was 82% and 62% at 1 and 2 years, respectively. Overall survival (OS) was 92% and 60% at 1 and 2 years, with a median survival of 41 mo per Kaplan Meier analysis. At 1 and 2 years, 71% and 61% of patients retained CPA status. Of the patients with intrahepatic failures, 58% developed progressive cirrhosis, compared to 27% with controlled disease (P = 0.06). Survival specific to hepatic failure was 92%, 81%, and 69% at 12, 18, and 24 mo. There was no grade 3 or higher toxicity. On univariate analysis, gross tumor volume (GTV) < 23 cc was associated with freedom from CP progression (P = 0.05), hepatic failure-specific survival (P = 0.02), and trended with OS (P = 0.10). CONCLUSION SBRT is safe and effective in HCC with early cirrhosis and may extend waiting time for transplant in patients who may not otherwise be immediate candidates.

TH‐E‐220‐08: Flattening Filter Removal for Improved Megavoltage Imaging of Fiducial Markers

Purpose: Removal of the LINAC flattening filter enables a high rate of dose deposition with reduced treatment time. When used for megavoltage imaging, an unflat beam has reduced primary beam scatter resulting in sharper images. In fluoroscopic imaging mode, a higher photon count per image frame yields higher contrast‐to‐noise ratio. We investigated the effects of an unflat beam on the image quality of megavoltage portal and fluoroscopic images. The impact of flattening filter removal on imaging of moving fiducial markers also was investigated. Methods: 6MV projection images were acquired in fluoroscopic and portal modes using an electronic flat‐panel imager. Portal images also were acquired using XV film. The effects of the flattening filter on the pre‐sampling MTF, relative MTF and contrast‐to‐noise ratio were quantified using the QC3 phantom and tungsten wire. The ability of observers to visualize fiducial markers using flat versus unflat beams also was studied. Results: The unflat beam had improved contrast resolution, up to 40% increase in MTF contrast at the highest frequency measured (0.75 line pairs per mm). The contrast‐to‐noise ratio was increased as expected from the increased photon flux. The visualization of fiducial markers was markedly better using the unflat beam enabling visualization of thin gold fiducial markers, the thinnest of which was not visible using the unflat beam. Conclusions: The removal of the flattening filter from a clinical LINAC leads to quantifiable improvements in the image quality of megavoltage projection images. These gains enable observers to more easily visualize thin fiducial markers and track their motion on fluoroscopic images.

Feasibility of intensity-modulated radiation therapy (IMRT) with PET-defined simultaneous integrated boost (SIB) for distal rectal adenocarcinoma (DRA).

550 Background: PET/CT guided preoperative IMRT is being used with increasing frequency in standard practice but reports of methods, efficacy, and toxicity are limited. We report the AGH experience from 2007-2010 of IMRT with SIB for DRA.nnnMETHODSn22 pts with stage IB-IV DRA (8 with anal canal involvement) were treated with preoperative concurrent IMRT with SIB, 5FU-based chemotherapy. 15 received weekly oxaliplatin. All had PET/CT simulation. The planned target volume included PET-avid primary tumor and LNs with median margins of 3mm (range, 0-13), in a median of 24 fx (range, 20-28), a median dose of 2.25 Gy/fx (range, 1.9-2.4 Gy) to a median total dose of 53.3 Gy (range, 50.6-57.2 Gy). Clinical target volume included non PET-avid 1st echelon LNs with a median dose of 2.0 Gy/fx (range, 1.6-2.3 Gy) to a total median dose of 47 Gy (range, 40.7-54.04 Gy). Median follow-up was 18 mos (range, 4-35). Late toxicities were scored using CTCAE v. 3.0.nnnRESULTSn17 of 22 patients (TNM stages IB (3), IIA (3), IIB (1), IIIA (2), IIIB (7), IV (1)) were treated curatively. The remaining 5 pts were treated palliatively. The median length of time from completion of radiation to surgery was 81 days (range, 48-398). 5 pts did not have surgery due to advanced metastatic disease (3), death (1) or biopsy proven complete response (CR) (1). R0 resection was accomplished in 15 of 17 surgical pts including 13/14 curative and 2/3 palliative cases. R1 resection occurred in 2 pts; 1 with stage IIIB and 1 with stage IV. No pts had R2 resection. 6 pts (5 with T2 lesions and 1 with a T4 lesion) had a pathologic CR. 2 of 3 non-surgical pts with metastatic disease had LRF at 5 and 11 mos. 9/22 pts had no late toxicity, 9/22 ≤ grade 2 and 4/22 had grade 3 late toxicity. No patients with T2 tumors had grade 3 late toxicity, and this appeared to be related to lower GTV. Kaplan-Meier freedom from grade 3late toxicity was 85% at 18 mos.nnnCONCLUSIONSnIMRT with SIB is an accurate targeting technique in pts with DRA that showed a pathologic CR in 100% of T2 lesions. Advanced T stage and larger GTV were possible risk factors for grade 3 late toxicity. [Table: see text] No significant financial relationships to disclose.

TU‐C‐204B‐10: Beam's‐Eye‐View MV Fluoroscopy during SBRT for Tumor Tracking and Treatment Verification

Purpose The radiotherapy treatment beam captured in megavoltage fluoroscopy (MVF) mode contains a record of tumor motion during treatment. This studys objectives were to use MVF to: 1) verify whether a tumor remains fully within the treatment beam; and 2) assess the reduction of tumor motion during the beam‐on period by respiratory gating. Method and Materials Electronic portal imaging was used to capture beams‐eye ‐view fluoroscopic movies of target movement within the treatment beam during SBRT.Dose rate was 300 MU/min; no imagingdose beyond the treatment dose was required. Images were captured at 7–13 frames/sec. Three lungcancer and 2 livercancer patients were studied over 5 fractions each; 2 were respiratory gated. For livertumors, implanted gold fiducial markers and surgical clips provided surrogates of tumor motion. Custom image analysis and tracking software was written using MeVisLab/VTK/ITK. Deformable registration between image frames was used to warp tumor contours and compute the tumor center of mass and tumor borders relative to the ITV/PTV as a function of time. Results MVF tumor tracking yielded tumor range‐of‐motion measurements of 4–10 mm in the lungcancer patients, and liver fiducial tracking yielded motion measurements of 14mm and 11mm in the livercancer patients. Large tumor motions due to infrequent large inspirations were reduced by respiratory gating with 75% inspiration threshold. Ungated motion was measured from pre‐treatment cone‐beam projection data. Gating reduced the tumor range of motion from 14mm to 9mm for the lung patient and from 17mm to 14mm for liver patient. Conclusions Motion measured via MV fluoroscopy during SBRT can be used to verify whether planned margins are adequate and evaluate the effectiveness of respiratory gating. Future work towards real ‐time processing could provide control signals for gating or dynamic multi ‐leaf collimators. Research sponsored by Siemens Corporation.