A novel method for radiotherapy patient identification using surface imaging.

Performing a procedure on the wrong patient or site is one of the greatest errors that can occur in medicine. The addition of automation has been shown to reduce errors in many processes. In this work we explore the use of an automated patient identification process using optical surface imaging for radiotherapy treatments. Surface imaging uses visible light to align the patient to a reference surface in the treatment room. It is possible to evaluate the similarity between a daily set-up surface image and the reference image using distance to agreement between the points on the two surfaces. The higher the percentage overlapping points within a defined distance, the more similar the surfaces. This similarity metric was used to intercompare 16 left-sided breast patients. The reference surface for each patient was compared to 10 daily treatment surfaces for the same patient, and 10 surfaces from each of the other 15 patients (for a total of 160 comparisons per patient), looking at the percent of points overlapping. For each patient, the minimum same-patient similarity score was higher than the maximum different-patient score. For the group as a whole a threshold was able to classify correct and incorrect patients with high levels of accuracy. A 10-fold cross-validation using linear discriminant analysis gave cross-validation loss of 0.0074. An automated process using surface imaging is a feasible option to provide nonharmful daily patient identification verification using currently available technology.

Surface imaging-based analysis of intrafraction motion for breast radiotherapy patients.

Breast treatments are becoming increasingly complex as the use of modulated and partial breast therapies becomes more prevalent. These methods are predicated on accurate and precise positioning for treatment. However, the ability to quantify intrafraction motion has been limited by the excessive dose that would result from continuous X-ray imaging throughout treatment. Recently, surface imaging has offered the opportunity to obtain 3D measurements of patient position throughout breast treatments without radiation exposure. Thirty free-breathing breast patients were monitored with surface imaging for 831 monitoring sessions. Mean translations and rotations were calculated over each minute, each session, and over all sessions combined. The percentage of each session that the root mean squares (RMS) of the linear translations were outside of defined tolerances was determined for each patient. Correlations between mean translations per minute and time, and between standard deviation per minute and time, were evaluated using Pearson's r value. The mean RMS translation averaged over all patients was 2.39 mm ± 1.88 mm. The patients spent an average of 34%, 17%, 9%, and 5% of the monitoring time outside of 2 mm, 3 mm, 4 mm, and 5 mm RMS tolerances, respectively. The RMS values averaged over all patients were 2.71 mm ± 1.83 mm, 2.76 ± 2.27, and 2.98 mm ± 2.30 mm over the 5th, 10th, and 15th minutes of monitoring, respectively. The RMS values (r = 0.73, p = 0) and standard deviations (r = 0.88, p = 0) over all patients showed strong significant correlations with time. We see that the majority of patients' treatment time is spent within 5 mm of the isocenter and that patient position drifts with increasing treatment time. Treatment length should be consid- ered in the planning process. An 8 mm margin on a target volume would account for 2 SDs of motion for a treatment up to 15 minutes in length. 

Commissioning and validation of BrainLAB cones for 6X FFF and 10X FFF beams on a Varian TrueBeam STx.

Small field dosimetry is a challenging task. The difficulties of small field measurements, particularly stereotactic field size measurements, are highlighted by the large interinstitution variability that can be observed for circular cone collimator commissioning measurements. We believe the best way to improve the consistency of small field measurements is to clearly document and share the results of small field measurements. In this work we report on the commissioning and validation of a BrainLAB cone system for 6 MV and 10 MV flattening filter-free (FFF) beams on a Varian TrueBeam STx. Commissioning measurements consisted of output factors, percent depth dose, and off-axis factor measurements with a diode. Validation measurements were made in a polystyrene slab phantom at depths of 5 cm, 10 cm, and 15 cm using radiochromic film. Output factors for the 6xFFF cones are 0.689, 0.790, 0.830, 0.871, 0.890, and 0.901 for 4 mm, 6 mm, 7.5 mm, 10 mm, 12.5 mm, and the 15 mm cones, respectively. Output factors for the 10xFFF cones are 0.566, 0.699, 0.756, 0.826, 0.864, and 0.888 for 4 mm, 6 mm, 7.5 mm, 10 mm, 12.5 mm, and the 15 mm cones, respectively. The full width half maximum values of the off-axis factors agreed with the nominal cone size to within 0.5 mm. Validation measurements showed an agreement of absolute dose between calculation and plan of < 3.6%, and an agreement of field sizes of ≤ 0.3 mm in all cases. Radiochromic film validation measurements show reasonable agreement with beam models for circular collimators based on diode commissioning measurements.