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In this chapter, small field dosimetry for two dedicated radiosurgery treatment delivery devices, the CyberKnife and the ZAP-X, are presented. After a short technical overview and introduction to the respective device, small field dosimetry beam data is discussed. For each device, the adaptation of reference dosimetry protocols for the machine-specific reference field is covered. Measurement methods to collect data for output factors, percent depth dose (PDD) or tissue-phantom ratio (TPR), and off-axis factors are presented. Suitable detectors for measuring each beam data type are listed. Sample data to visualize the specific characteristics of each beam dataset are provided. This chapter covers the difference between beam data from the fixed cones, IRIS collimator and multi-leaf collimator (M6) for the CyberKnife, including selected comparison data plots.

Background A variety of catheter-based energy modalities are used for cardiac ablation to treat arrhythmias. Robotic radiosurgery is increasingly being utilized to successfully accomplish precise tissue ablation in anatomically remote areas. Objective The purpose of this study was to examine the experimental feasibility of a noninvasive method using stereotactic robotic radiosurgery (SRS) to create cardiac lesions. Methods Sixteen (16) Hanford-Sinclair mini swine (weight 40–70 kg) under general anesthesia were studied. Baseline computed tomographic scans were performed, followed by electroanatomic mapping using the CARTO system. Stereotactic robotic radiosurgery was performed using the CyberHeart system, with predetermined targets at the cavotricuspid isthmus, AV node, pulmonary vein–left atrial junction, or left atrial appendage. From 25 to 196 days after treatment, the animals were investigated with repeat electroanatomic voltage mapping and transesophageal echocardiography, when possible. The animals then were sacrificed and pathology specimens taken. Results Dose ranging suggested that 25 Gy was needed to produce an electrophysiologic effect. The time course showed an electrophysiologic effect consistently by 90 days. The method was feasible for producing bidirectional cavotricuspid isthmus block and AV nodal conduction block. The pulmonary vein–left atrial junction and left atrial appendage showed marked voltage reduction to less than 0.05 mV. No spontaneous arrhythmias were observed. Pathology specimens showed no evidence of radiation damage outside the target. Histology samples from target sites showed effects consistent with X-beam radiation. Conclusion Stereotactic robotic radiosurgery can produce cavotricuspid isthmus block, AV nodal block, and significant decreased voltage at the pulmonary vein–left atrial junction. No other organ damage was seen. The study findings demonstrate the feasibility of this noninvasive treatment method for creating cardiac lesions. This approach merits further investigation in the treatment of arrhythmias.