Commissioning of the world's first compact pencil-beam scanning proton therapy system.

This paper summarizes clinical commissioning of the world's first commercial, clinically utilized installation of a compact, image-guided, pencil-beam scanning, intensity-modulated proton therapy system, the IBA Proteus® ONE, at the Willis-Knighton Cancer Center (WKCC) in Shreveport, LA. The Proteus® ONE is a single-room, compact-gantry system employing a cyclotron-generated proton beam with image guidance via cone-beam CT as well as stereoscopic orthogonal and oblique planar kV imaging. Coupling 220° of gantry rotation with a 6D robotic couch capable of in plane patient rotations of over 180° degrees allows for 360° of treatment access. Along with general machine characterization, system commissioning required: (a) characterization and calibration of the proton beam, (b) treatment planning system commissioning including CT-to-density curve determination, (c) image guidance system commissioning, and (d) safety verification (interlocks and radiation survey). System readiness for patient treatment was validated by irradiating calibration TLDs as well as prostate, head, and lung phantoms from the Imaging and Radiation Oncology Core (IROC), Houston. These results confirmed safe and accurate machine functionality suitable for patient treatment. WKCC also successfully completed an on-site dosimetry review by an independent team of IROC physicists that corroborated accurate Proteus® ONE dosimetry.

A Model for Secondary Monitor Unit Calculations of PBS Proton Therapy Treatment Plans.

PURPOSE: This article summarizes a volume-based method by which secondary monitor unit (MU) calculations may be performed for pencil beam scanning, single field uniform dose (SFUD) proton therapy treatment plans. MATERIALS AND METHODS: Treatment planning system (TPS) simulations were performed by using the local beam model to define relationships between planning target volume (PTV) characteristics and the MUs required to deliver a uniform dose for a given beam orientation. Relevant target attributes included volume, depth (ie, beam range), range-shifter air gap, and the projected area of the target volume in the beam's eye view (BEV). The proposed model approximates the PTV as a simplified cuboid region of interest as defined by its volume and BEV projected area. Output factors (cGy/MU) were then tabulated for the idealized geometry through TPS simulations using region of interests with a range of dimensions expected to be seen clinically. Correction factors were applied that account for differences between the PTV and the idealized conditions, and MUs for each beam were then scaled according to the measured spread out Bragg peak (SOBP) dose in water. RESULTS: Our model was applied to various treatment sites, including pelvis, brain, lung, and head and neck. Monitor units prescribed by the TPS were compared to those predicted by using the model for 78 treatment beams. The total mean percentage difference for all beams was -0.2% ± 3.8%. CONCLUSION: This work demonstrates the potential for reasonably accurate secondary verification of MUs in pencil beam scanning proton therapy for SFUD treatment plans with the proposed method. Required inputs are few, and are readily accessible, facilitating automation and clinical application. Further investigation will expand the current model to accommodate a broader range of potential optimization problems, and intensity-modulated proton therapy treatment plans.

Overview of dosimetry for Systemic Targeted Radionuclide Therapy (STaRT).

The purposes of systemic targeted radionuclide therapy dosimetry include compiling a database of normal organ radiation-absorbed doses that are carrier- and radionuclide-specific, and assuring that the normal organ radiation doses are within a safe range before therapy. Also of importance is quantitation of radiation delivery to tumors vs. normal tissues to correlate absorbed dose with tumor control. For agents with significant and variable excretion, estimates of individual patient distribution/clearance may be needed to optimize the dose-response relationship.

Helical image-guided stereotactic body radiotherapy (SBRT) for the treatment of early-stage lung cancer: a single-institution experience at the Willis-Knighton Cancer Center.

AIMS AND BACKGROUND: Our aim is to report on the clinical methods and outcomes of helical intensity-modulated stereotactic body radiotherapy (SBRT) for the treatment of early-stage non-small cell lung cancer (NSCLC). METHODS AND STUDY DESIGN: Seventy-nine patients with stage I NSCLC underwent helical SBRT with 48 Gy in 4 fractions or 60 Gy in 5 fractions. All patients underwent 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) or FDG-PET/computed tomography (CT) scanning in the immobilized treatment position for planned fusion with a separate kilovoltage (KV) CT simulation prior to treatment. Megavoltage CT images were obtained on the treatment unit prior to therapy and repeated at mid-fraction with comparison and fusion to the KV CT simulation planning images to assure setup accuracy. Serial follow-up with FDG-PET or FDG-PET/CT was performed at 3-4 months and every 6 months thereafter. RESULTS: Median follow-up was 27 months (range, 4-82 months). Overall local control rate (LCR) was 93.6% (95% confidence interval [CI], 86.0-97.3%) and 3-year overall survival (OS) was 58.4% (95% CI, 47.2-69.5%). For patients with T1N0M0 disease (n = 59) the LCR was 94.9% (95% CI, 86.1-98.3%) and the 3-year OS was 62.8% (95% CI, 49.9-73.9%). Patients treated with 60 Gy had longer 3-year OS than patients treated with 48 Gy (65.2% vs 37.5%; P = 0.044). SBRT-related toxicity was modest, with 10 patients developing grade 1/2 chest wall toxicity based on the Common Terminology Criteria for Adverse Events (CTCAE). CONCLUSION: Image-guided SBRT with helical IMRT delivered in 4 or 5 fractions of 12 Gy with rigid immobilization, FDG-PET-assisted targeting, and repeat mid-fraction CT scan is an effective treatment for early NSCLC.

Influence of patient characteristics on survival following treatment with helical stereotactic body radiotherapy (SBRT) in stage I non-small-cell lung cancer.

BACKGROUND: To determine the influence of patient and tumor characteristics on clinical outcomes in patients with early-stage non-small cell lung cancer (NSCLC) treated with helical intensity modulated stereotactic body radiotherapy (SBRT). METHODS: From March 2005 to August 2010 a total of 62 patients with biopsy proven Stage I NSCLC underwent helical SBRT with 48 Gy in 4 fractions or 60 Gy in 5 fractions. Patient and tumor characteristics including tumor stage, age, sex, tumor histology, maximal tumor diameter, and smoking history, were evaluated in regard to local control and overall survival using Kaplan-Meier survival curves and the Cox proportional hazard method. Treatment related toxicity in the patient subgroups was evaluated. RESULTS: The median follow-up was 28 months. Total cohort local control was 93.55% and 3-year overall survival (OS) was 53.4%. Those patients with Stage IA disease had a 3-year OS of 64.4% versus 32.1% for Stage IB disease (P = 0.042). Tumors classified as T1a (≤20 mm) and T1b (20-30 mm) had significantly increased overall survival compared to T2 (>30 mm) tumors (P = 0.046). There was a slight survival advantage in those patients with adenocarcinoma. No correlation between age, gender or smoking history, and overall survival was found. Nine patients had radiation related toxicity, which was increasingly more common with advancing age. CONCLUSION: Helical SBRT is an effective method to treat NSCLC and the most significant prognostic factors were tumor stage and size. There was no correlation between age, gender, and smoking history.

An automatic method for PET target segmentation using a lookup table based on volume and concentration ratio.

Accurate evaluation of functionally significant target volumes in combination with anatomic imaging is of primary importance for effective radiation therapy treatment planning. In this study, a method for rapid and accurate PET image segmentation and volumetrics based on phantom measurements and independent of scanner calibration was developed. A series of spheres ranging in volume from 0.5 mL to 95 mL were imaged in an anthropomorphic phantom of human thorax using two commercial PET and CT/PET scanners. The target to background radioactivity concentration ratio ranged from 3:1 to 12:1 in 11 separate phantom scanning experiments. The results confirmed that optimal segmentation thresholding depends on target volume and radioactivity concentration ratio. This information can be derived from a generalized pre-determined "lookup table" of volume and contrast dependent threshold values instead of using fitted curves derived from machine specific information. A three-step method based on the PET image intensity information alone was used to delineate volumes of interest. First, a mean intensity segmentation method was used to generate an initial estimate of target volume, and the radioactivity concentration ratio was computed by a family of recovery coefficient curves to compensate for the partial volume effect. Next, the appropriate threshold value was obtained from a phantom-generated threshold lookup table. Lastly, a threshold level set method was performed on the threshold value to further refine the target contour by reducing the limitation of global thresholding. The segmentation results were consistent for spheres greater than 2.5 mL which yielded volume average uncertainty of 11.2% in phantom studies. The results of segmented volumes were comparable to those determined by contrast-oriented method and iterative threshold method (ITM). In addition, the new volume segmentation method was applied clinically to ten patients undergoing PET/CT volume analysis for radiation therapy treatment planning of solitary lung metastases. For these patients, the average PET segmented volumes were within 8.0% of the CT volumes and were highly dependent on the extension of functionally inactive tumor volume. In summary, the current method does not require fitted threshold curves or a priori knowledge of the CT/MRI target volume. This threshold method can be universally applied to radiation therapy treatment planning with comparable accuracy, and may be useful in the rapid identification and assessment of plans containing multiple targets.