Purpose: We investigate the feasibility of surface guided radiation therapy (SGRT) for accelerated partial breast irradiation (APBI) by comparing it with in-room, fan beam kV computed tomography on rails (CTOR) imaging of the targeted region. The uniqueness of our study is that all patients have multiple daily CTOR scans to compare corresponding SGRT AlignRT (VisionRT, United Kingdom) images to. Methods/materials: Twelve patients receiving APBI were enrolled in this study. Before each treatment fraction, after patients were setup on tattoos, SGRT was performed using AlignRT, and then target matching was performance using CTOR. The average and maximum difference in shifts between SGRT and CTOR were calculated and analyzed for each patient, so as the correlation between surgical cavity size and shift difference. Results: Our study showed that SGRT agreed well with CTOR for patients with small surgical cavity volume changes (<10%). There were nine patients who had a ≥5 mm maximum shift difference between SGRT and CTOR along any direction, and in two patients the difference was more than 10 mm (one patient with surgical cavity change 44.3% and one patient with 27 cc cavity volume decrease). All patients, except one, had a mean shift difference < 5 mm along any direction. Conclusion: For the patients studied here, SGRT appears to be a reasonable and potentially valuable image guidance approach for APBI for patients who experience small changes in surgical cavity volume (<10%) between CT simulation and treatment. However, there is potential for larger alignment errors (up to 11 mm) when using SGRT for patients who experience larger surgical cavity changes.

Recently, there has been a resurgence of interest in arc-based IMRT, through the use of 'conventional' multileaf collimator (MLC) systems that can treat large tumor volumes in a single, or very few pass(es) of the gantry. Here we present a novel 'burst mode' modulated arc delivery approach, wherein 2000 monitor units per minute (MU min(-1)) high dose rate bursts of dose are facilitated by a flattening-filter-free treatment beam on a Siemens Artiste (Oncology Care Systems, Siemens Medical Solutions, Concord, CA, USA) digital linear accelerator in a non-clinical configuration. Burst mode delivery differs from continuous mode delivery, used by Elekta's VMAT (Elekta Ltd, Crawley, UK) and Varian's RapidArc (Varian Medical Systems, Palo Alto, CA, USA) implementations, in that dose is not delivered while MLC leaves are moving. Instead, dose is delivered in bursts over very short arc angles and only after an MLC segment shape has been completely formed and verified by the controller. The new system was confirmed to be capable of delivering a wide array of clinically relevant treatment plans, without machine fault or other delivery anomalies. Dosimetric accuracy of the modulated arc platform, as well as the Prowess (Prowess Inc., Concord, CA, USA) prototype treatment planning version utilized here, was quantified and confirmed, and delivery times were measured as significantly brief, even with large hypofractionated doses. The burst mode modulated arc approach evaluated here appears to represent a capable, accurate and efficient delivery approach.

Purpose: To present our preliminary experience with the recently released Calypso lung beacons to track lung tumor location during stereotactic body radiation therapy (SBRT). Materials/Methods: Five recent lung SBRT patients had Calypso lung beacons implanted for tumor tracking during treatment. Beacons were placed by a pulmonologist using fluoroscopic navigation within 1 week prior to planning four-dimensional computed tomography (4DCT) acquisition. Patients were immobilized in a full-body double-vacuum bag. For the first three patients, a verification 4DCT was obtained prior to the first fraction with the patient in the treatment position to assess both beacon migration and motion of tumor and beacons relative to planning day. For each treatment fraction, Calypso was used to position the patient. A verification cone-beam CT (CBCT) confirmed the Calypso-defined target position was appropriate. Real-time Calypso tracking information was also acquired and compared to an action level that was used to determine if the tumor migrated outside of the planning target volume. Results: For four patients, the implant procedure was well tolerated, with average CBCT-based shifts being within 0.2 mm of the shifts reported by Calypso at the time of imaging. The other patient had a small pneumothorax due to very peripheral tumor location and experienced beacon migration. However, the patient quickly recovered from the pneumothorax, and after deactivating that beacon, motion tracking was possible throughout his treatment. Conclusions: All patients were successfully treated with SBRT using the newly released Calypso lung beacons, with initial positioning confirmed by this clinic's current clinical standard of CBCT. The system allowed us to validate, with real-time confirmation, that the planned internal target volumes were appropriate to each day's extent of actual tumor motion. An efficient and effective workflow for utilizing the new lung beacons for SBRT treatments was developed.

PurposeThis is a proof-of-principle study investigating the feasibility of using late gadolinium enhancement magnetic resonance imaging (LGE-MRI) to detect left atrium (LA) radiation damage.Methods and materialsLGE-MRI data were acquired for 7 patients with previous external beam radiation therapy (EBRT) histories. The enhancement in LA scar was delineated and fused to the computed tomography images used in dose calculation for radiation therapy. Dosimetric and normal tissue complication probability analyses were performed to investigate the relationship between LA scar enhancement and radiation doses.ResultsThe average LA scar volume for the subjects was 2.5 cm3 (range, 1.2-4.1 cm3; median, 2.6 cm3). The overall average of the mean dose to the LA scar was 25.9 Gy (range, 5.8-49.2 Gy). Linear relationships were found between the amount of radiation dose (mean dose) (R2 = 0.8514, P = .03) to the LA scar-enhanced volume. The ratio of the cardiac tissue change (LA scar/LA wall) also demonstrated a linear relationship with the level of radiation received by the cardiac tissue (R2 = 0.9787, P < .01). Last, the normal tissue complication probability analysis suggested a dose response function to the LA scar enhancement.ConclusionsWith LGE-MRI and 3-dimensional dose mapping on the treatment planning system, it is possible to define subclinical cardiac damage and distinguish intrinsic cardiac tissue change from radiation induced cardiac tissue damage. Imaging myocardial injury secondary to EBRT using MRI may be a useful modality to follow cardiac toxicity from EBRT and help identify individuals who are more susceptible to EBRT damage. LGE-MRI may provide essential information to identify early screening strategy for affected cancer survivors after EBRT treatment.

To compare finite-size pencil beam/equivalent path-length (FSPB/EPL) and Monte Carlo (MC) SBRT dose computations for serial tomotherapy and to quantitatively assess dose differences between the dose calculation methods. Based on 72 SBRT plans for pulmonary targets, FSPB/EPL, considering the inhomogeneous lung environment, and MC calculations were performed to establish differences between FSPB/EPL predicted dose and MC derived doses. Compared with MC, FSPB/EPL consistently overestimated minimum doses to the clinical target volume and planning target volumes by an average of 18.1+/-7.15% (range 4 to 33.4%), and 21.9+/-10.4% (range 1.2 to 45.5%), respectively. The respective mean target dose differences were 15.5+/-7.4% (2.8-36.4%) and 19.2+/-7.6% (3.6-40.1%). Deviations from MC doses were lesion size and location dependent, with smaller lesions completely embedded into lung parenchyma being most susceptible. Larger lesion in contact with mediastinum and chest wall showed lesser differences. In comparison with MC dose calculation, FSPB/EPL overestimates doses delivered to pulmonary SBRT targets. The observed dose differences may have impact on local tumor control rates, and may deserve consideration when using fast, but less accurate dose calculation methods.