Linda Ding

Initial Experience With Volumetric IMRT (RapidArc) for Intracranial Stereotactic Radiosurgery

PURPOSE Initial experience with delivering frameless stereotactic radiotherapy (SRT) using volumetric intensity-modulated radiation therapy (IMRT) delivered with RapidArc is presented. METHODS AND MATERIALS Treatment details for 12 patients (14 targets) with a mean clinical target volume (CTV) of 12.8 ± 4.0 cm(3) were examined. Dosimetric indices for conformality, homogeneity, and dose gradient were calculated and compared with published results for other frameless, intracranial SRT techniques, including CyberKnife, TomoTherapy, and static-beam IMRT. Statistics on setup and treatment times and per patient dose validations were examined. RESULTS Dose indices compared favorably with other techniques. Mean conformality, gradient, and homogeneity index values were 1.10 ± 0.11, 64.9 ± 14.1, 1.083 ± 0.026, respectively. Median treatment times were 4.8 ± 1.7 min. CONCLUSION SRT using volumetric IMRT is a viable alternative to other techniques and enables short treatment times. This is anticipated to have a positive impact on radiobiological effect and for facilitating wider use of SRT.

Hybrid IMRT for Treatment of Cancers of the Lung and Esophagus

PURPOSE To report on a hybrid intensity-modulated radiation therapy (IMRT; static plus IMRT beams treated concurrently) technique for lung and esophageal patients to reduce the volume of lung treated to low doses while delivering a conformal dose distribution. METHODS Treatment plans were analyzed for 18 patients (12 lung and 6 esophageal). Patients were treated with a hybrid technique that concurrently combines static (approximately two-thirds dose) and IMRT (approximately one-third dose) beams. These plans were compared with conventional three-dimensional (3D; non-IMRT) plans and all IMRT plans using custom four- and five-field arrangements and nine equally spaced coplanar beams. Plans were optimized to reduce V13 and V5 values. Dose-volume histograms were calculated for the planning target volume, heart, and the ipsilateral, contralateral, and total lung. Lung volumes V5, V13, V20, V30; mean lung dose (MLD); and the generalized equivalent uniform dose (gEUD) were calculated for each plan. RESULTS Hybrid plans treated significantly smaller total and contralateral lung volumes with low doses than nine-field IMRT plans. Largest reductions were for contralateral lung V5, V13, and V20 values for lung (-11%, -15%, -7%) and esophageal (-16%, -20%, -7%) patients. Smaller reductions were found also for 3D and four- and five-field IMRT plans. MLD and gEUDs were similar for all plan types. The 3D plans treated much larger extra planning target volumes to prescribed dose levels. CONCLUSIONS Hybrid IMRT demonstrated advantages for reduction of low-dose lung volumes in the thorax for reducing low dose to lung while also reducing the potential magnitude of dose deviations due to intrafraction motion and small field calculation accuracy.

Volume Modulated Arc Therapy (VMAT) for pulmonary Stereotactic Body Radiotherapy (SBRT) in patients with lesions in close approximation to the chest wall

Purpose: Chest wall pain and discomfort has been recognized as a significant late effect of radiation therapy in historical and modern treatment models. Stereotactic Body Radiotherapy (SBRT) is becoming an important treatment tool in oncology care for patients with intrathoracic lesions. For lesions in close approximation to the chest wall with motion management, SBRT techniques can deliver high dose to the chest wall. As an unintended target of consequence, there is possibility of imposing significant chest wall pain and discomfort as a late effect of therapy. The purpose of this paper is to evaluate the potential role of Volume Modulated Arc Therapy (VMAT) technologies in decreasing chest wall dose in SBRT treatment of pulmonary lesions in close approximation to the chest wall. Materials and Methods: Ten patients with pulmonary lesions of various sizes and tomography in close approximation to the chest wall were selected for retrospective review. All volumes including tumor target, chest wall, ribs, and lung were contoured with maximal intensity projection maps and four-dimensional computer tomography planning. Radiation therapy planning consisted of static techniques including Intensity Modulated Radiation Therapy compared to VMAT therapy to a dose of 60 Gy in 12 Gy fraction dose. Dose volume histogram to rib, chest wall, and lung were compared between plans with statistical analysis. Results: In all patients, dose and volume were improved to ribs and chest wall using VMAT technologies compared to static field techniques. On average, volume receiving 30 Gy to the chest wall was improved by 74%; the ribs by 60%. In only one patient did the VMAT treatment technique increase pulmonary volume receiving 20 Gy (V20). Conclusions: VMAT technology has potential of limiting radiation dose to sensitive chest wall regions in patients with lesions in close approximation to this structure. This would also have potential value to lesions treated with SBRT in other body regions where targets abut critical structures.

Target delineation for radiosurgery of a small brain arteriovenous malformation using high-resolution contrast-enhanced cone beam CT

Three years following endovascular embolization of a 3 mm ruptured arteriovenous malformation (AVM) of the left superior colliculus in a 42-year-old man, digital subtraction angiography showed continuous regrowth of the lesion. Thin-slice MRI acquired for treatment planning did not show the AVM nidus. The patient was brought back to the angiography suite for high-resolution contrast-enhanced cone beam CT (VasoCT) acquired using an angiographic c-arm system. The lesion and nidus were visualized with VasoCT. MRI, CT and VasoCT data were transferred to radiation planning software and mutually co-registered. The nidus was annotated for radiation on VasoCT data by an experienced neurointerventional radiologist and a dose/treatment plan was completed. Due to image registration, the treatment area could be directly adopted into the MRI and CT data. The AVM was completely obliterated 10 months following completion of the radiosurgery treatment.

Diaphragm injury after liver stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) is an increasingly common treatment for lung and liver malignancies. Chest wall toxicity following SBRT for peripheral tumors has been reported and there are published dose constraint guidelines to minimize the risk for rib fracture, chest wall necrosis, and cutaneous ulceration.1-4 There are no documented reports of diaphragm injury after SBRT and no defined tolerance dose. We describe in this report the clinical course of a patient who developed severe back pain following liver SBRT and was found to have focal necrosis, fibrosis, and atrophy of the diaphragm in the high-dose region on autopsy.

SU‐FF‐T‐164: Radiochromic EBT Film Characterization and Applicability for IMRT QA Verification

Purpose: Characterization of ISPs new EBT radiochromic film for clinical dosimetry, with emphasis on the usefulness for routine QA of IMRT treatments. Method and Materials: EBT is a new formulation of radiochromic film by ISP. Sheets were exposed to 6 MV and 18 MV photons from a Varian 2300C/D accelerator over clinically useful dose ranges. Density was measured by scanning the film in a Vidar VXR‐16 Dosimetry Pro scanner and the data analyzed using RIT113 v4 software. The reproducibility, stability, and temperature sensitivity were investigated. Dose distributions for IMRT treatments delivered with a Millinieum 120 leaf MLC were measured with the EBT film and compared to those of Kodak EDR2 film and to the predictions of the Eclipse treatment planning system. Results: EBT films from the same batch have a consistent response to doses ranging from 50 to 500 cGy for 6 MV and 18 MV photons. The density readings are stable from 1 to 75 hours post exposure when stored in the dark at room temperature. Beyond 75 hours, the density slowly increases. The film is insensitive to cold, but shows significant degradation when exposed to 60 C for as little as two hours. For IMRT dose distributions where the dose is below 200 cGy, the EBT film has similar responses as Kodaks EDR2 film and very close agreement to the Eclipse predictions. In regions of IMRT doses greater than 200 cGy, the EBT film loses sensitivity as compared to EDR2 film and to the Eclipse calculations. Conclusion: ISPs EBT radiochromic film is reproducible and stable under normal clinical conditions. For IMRT dose verification, the EBT film is in close agreement with calculations and EDR2 film for doses less than 200 cGy. Further research is needed to understand the reduced response of EBT to IMRT doses above 200 cGy.

P-017 Radiation target delineation of micro brain arteriovenous malformations using high-resolution flat-detector cone-beam Computed Tomography (CBCT)

Purpose Radiation therapy has shown to be an effective treatment of brain arteriovenous malformations (bAVMs).1 2 Target delineation is commonly performed on volumetric image data, such as MRI or CT data. However, the nidi of micro-AVMs may not be visualized adequately by these modalities due to their limited image resolution. In this report, we show a novel usage of high-resolution contrast-enhanced cone-beam computed tomography (CBCT) imaging and multi-modal image registration3 for radiation target delineation of a micro-AVM, a technique previously suggested for larger AVMs.4 Case A 42-year-old male presented with intraparenchymal hemorrhage in the mesencephalic tectum and left posterior thalamus. Conventional angiography revealed a left superior collicular AVM with a nidus of 3 mm. The AVM was successfully embolized but follow-up angiography examinations at 36 months demonstrated a small re-growth of the AVM (Abstract P-017 figure 1A). The patient was thus referred to radiosurgery. Thin slice contrast and non-contrast MRI acquired for target delineation did not show the AVM nidus. Therefore, the patient was transferred to the angiography suite for high resolution contrast-enhanced CBCT. Data was acquired using the angiography c-arm system with a reduced detector size of 22 cm. Contrast was injected with 2 ml/s for a total of 64 ml and a 2 sec delay) using a coupled power injector into the left vertebral artery with a 5Fr catheter. Volumetric CBCT data (FOV: 703 mm3, matrix: 0.143 mm3) was generated using a non-binned reconstruction algorithm. Lesion and nidus were visualized with CBCT. MRI, CT-simulator and CBCT data was then transferred to the radiation planning software and mutually co-registered. The nidus was delineated on CBCT data by an experienced neurointerventional radiologist for radiation therapy and dose/treatment plan was completed. Due to image registration, the target area could be directly transferred to MRI and CT data (Abstract P-0017 figure 1B). The patient received a total of 4 radiation sessions.Abstract P-017 Figure 1 Discussion and Conclusion Radiation target delineation of micro AVMs can be challenging with conventional 3D imaging techniques as their spatial resolution is relatively low for the application of visualization of the nidus. We were able to demonstrate the complementary value of high resolution contrast enhanced CBCT in radiation target delineation of a micro brain AVM. Multi-modal image registration of CBCT with MRI and CT-simulator has shown to be an effective method for radiation target delineation. Competing interests I van der Bom: None. A Wakhloo: Philips Healthcare. A Kuhn: None. L Ding: None. D Goff: None. M Gounis: None. References 1. AJNR 1995;16:299. 2. J Neurosurg 2002;97:779–84. 3. vanderBom IMJ, et al. J NeuroIntervent Surg 2011. In press. 4. Radvany MG, et al. J NeuroIntervent Surg 2011. In press.

SU‐FF‐T‐350: Dose in Buildup Region of Flash: PBC, AAA Calculation Vs Measurement

Purpose: In this paper, results are presented comparing AAA and PBC dose calculation algorithms with dose measured in the buildup region where flash is of concern. Flash is of primary interest for breast, sarcomas, and whole brainradiotherapy treatments. Method and Materials: A cylindrical phantom was scanned on a GE LightSpeed Advantage Sim with slice thickness of 2.5 mm. On an Eclipse TPS (Version 8.2.24), AAA and PBC (Modified Batho inhomogeneity correction) dose calculation algorithms were used to calculate the dose distribution for photon beam energies of 6 MV and 18 MV and field size 12 × 12 cm2 with a calculation grid size of 2.5 mm. The fields were arranged as parallel opposed pair incident on a cylindrical phantom with 3 cm of flash. Dose profiles were compared at 1.5, 4.0, 6.5, and 9.0 mm depths from the end of the cylindrical phantom. Gafchromic EBT film was exposed, in the same dose planes, on a Varian Trilogy Clinac. Measured and calculated dose profiles were compared using RIT113 V5.0 Radiation TherapyDosimetry Software. Results: Calculations show a difference in excess of 7% in dose between the two algorithms at a depth of 4 mm. The AAA produces dose distributions better resemble the measured dose distribution. Conclusion: Preliminary results indicate that the AAA algorithm more closely calculates dose in the buildup region where flash is of concern.

SU‐FF‐T‐444: Variability of EDR2 Dose Calibration Films Taken for IMRT Dose Verification

Purpose: To report the consistency of EDR2 calibration films taken for IMRT absolute dose verification. Method and Materials: 180 sets of dose‐optical (OD) calibration films for IMRT dose validation were taken on 4 Linacs on two campuses using Kodak EDR2 film from Nov. 2005 to Dec. 2006. Each calibration datum contained at least 5 dose points (i.e. 0 cGy, 60 cGy, 120 cGy, 180 cGy and 240 cGy). All calibration films were processed on the same Kodak film processor, were scanned with the same Vidar 1600Pro film scanner, and analyzed using RIT dosimetrysoftware. A second order polynomial function was applied to create the H‐D curve using averaged dose‐OD data from each Linac separately. The range of dose variation (maximum, minimum and standard deviation) was determined. Results: Overall, one standard deviation of the OD corresponded to ±5.3 cGy at 60 cGy, ±8.1 cGy at 120 cGy, ±11.1 cGy at 180 cGy, and ±11.7 cGy at 240 cGy. The maximum and minimum recorded OD numbers of 180 cGy dose point corresponded to 221.4 cGy and 152.5 cGy respectively. Variability was greater for the films taken at one campus and transported (usually overnight) to the main campus for processing and analysis. Had a single dose point film (e.g. 180 cGy) been taken, dose errors (2 SD) of ±24.4 cGy at 240 cGy and ±16.5 cGy at 120 cGy would have occurred. There was no correlation of consistency with processor service. Conclusions: The OD calibration curves with EDR2 film varied significantly, not only in absolute OD value but also in curvature. In order to achieve +/−3% accuracy for IMRT dose verification films, EDR2 calibration films must be taken for each set of IMRT films.