Multi-institutional clinical experience with the Calypso System in localization and continuous, real-time monitoring of the prostate gland during external radiotherapy

The aim of this study was to evaluate the differences in target localization between Calypso®, kV orthogonal imaging and cone‐beam computed tomography (CBCT) for combined translations and rotations of an anthropomorphic pelvic phantom. The phantom was localized using all three systems in 50 different positions, with applied translational and rotational offsets randomly sampled from representative normal distributions of prostate motion. Lin's concordance correlation coefficient (ρc) and 95% confidence intervals were calculated to assess the agreement between the localization systems. Mean differences and difference vectors between the three systems were also calculated. Agreement between systems for lateral, vertical, and longitudinal translations was excellent, with ρc values of greater than 0.98 between all three systems in all axes. There was excellent agreement between the systems for rotations around the lateral axis (pitch) (ρc > 0.99), and around the vertical axis (yaw) (ρc > 0.97). However, somewhat poorer agreement for rotations around the longitudinal axis (roll) was observed, with the lowest correlation observed between Calypso and kV orthogonal imaging (ρc = 0.895). Mean differences between the phantom position reported by Calypso and the radiographic systems were less than 1 mm and 1° for all translations and rotations. The results for translations are consistent with the publications of previous authors. There is no comparable published data for rotations. While there is lower correlation between the three systems for roll than for the other angles, the mean differences in reported rotations are not clinically significant.

Section: Discussionsupporting

confidence: 89%

“…Patient and animal studies have also demonstrated strong correlation between transponder‐based systems and radiographic systems 5, 11, 13, 15, 16, 17, 18. Foster et al 15.…”

Section: Introductionmentioning

confidence: 99%

Comparison between electromagnetic transponders and radiographic imaging for prostate localization: A pelvic phantom study with rotations and translations

Hamilton

McKenzie

Perkins

2017

“…However, patients will receive additional radiation due to repeated exposures, especially for long treatment procedures. The Calypso 4D localization system (Calypso Medical Technologies, Seattle, WA) uses miniaturized, nonionizing implanted fiducial devices, 16 , 17 , 18 which are electromagnetic transponders, called Beacons, to set up the patient efficiently and to track the location of the treatment target during external beam radiotherapy. This will allow for accurate localization of the treatment target both before and during the treatment, and real‐time tracking of the target during treatment.…”

Section: Introductionmentioning

confidence: 99%

“…It will be more useful to know what percentage of a regular patient population will exhibit such large prostate motion and benefit from real‐time motion tracking. Based on the results of 35 patients, Kupelian et al (18) reported that approximately 15% of fractions (83% of patients) exhibited a 5 mm shift for cumulative 30 s. However, detailed analyses showed that the majority of patients did not exhibit substantial prostate movements in any fractions, while some patients had up to 56% of fractions with

> 5 mm

shifts for

> 30 s

. It will be clinically important to identify such patients with substantial prostate movements and design “personalized” treatment strategies for them.…”

Section: Introductionmentioning

confidence: 99%

Intrafractional prostate motion during external beam radiotherapy monitored by a real‐time target localization system

Chen

et al. 2015

This paper investigates the clinical significance of real‐time monitoring of intrafractional prostate motion during external beam radiotherapy using a commercial 4D localization system. Intrafractional prostate motion was tracked during 8,660 treatment fractions for 236 patients. The following statistics were analyzed: 1) the percentage of fractions in which the prostate shifted 2−7 mm for a certain duration; 2) the proportion of the entire tracking time during which the prostate shifted 2−7 mm; and 3) the proportion of each minute in which the shift exceeded 2−7 mm. The ten patients exhibiting maximum intrafractional‐motion patterns were analyzed separately. Our results showed that the percentage of fractions in which the prostate shifted by >2,3,5,and 7 mm off the baseline in any direction for >30 normals was 56.8%, 27.2%, 4.6%, and 0.7% for intact prostate and 68.7%, 35.6%, 10.1%, and 1.8% for postprostatectomy patients, respectively. For the ten patients, these percentages were 91.3%, 72.4%, 36.3%, and 6%, respectively. The percentage of tracking time during which the prostate shifted >2,3,5,and 7 mm was 27.8%, 10.7%, 1.6%, and 0.3%, respectively, and it was 56.2%, 33.7%, 11.2%, and 2.1%, respectively, for the ten patients. The percentage of tracking time for a >3 mm posterior motion was four to five times higher than that in other directions. For treatments completed in 5 min (VMAT) and 10 min (IMRT), the proportion for the prostate to shift by >3 mm was 4% and 12%, respectively. Although intrafractional prostate motion was generally small, caution should be taken for patients who exhibit frequent large intrafractional motion. For those patients, adjustment of patient positioning may be necessary or a larger treatment margin may be used. After the initial alignment, the likelihood of prostate motion increases with time. Therefore, it is favorable to use advanced techniques (e.g., VMAT) that require less delivery time in order to reduce the treatment uncertainty resulting from intrafractional prostate motion.PACS number: 87.50.S‐, 87.53.Kn, 87.55.N‐, 87.55.ne

“…Prostate position during treatment can be monitored using a variety of methods, including megavoltage (MV) imaging,1 ultrasound,2 Calypso electromagnetic guidance,3 the BrainLAB ExacTrac x‐ray system,4 the Cyberknife platform,5, 6, 7 and Navotek radioactive fiducials 8. Adjustments to either the patient or the beam position can then be made during treatment to correct for the motion observed.…”

Section: Introductionmentioning

confidence: 99%

Technical note: TROG 15.01 SPARK trial multi‐institutional imaging dose measurement

Legge

Greer

Keall

et al. 2017

PurposeThe Trans‐Tasman Radiation Oncology Group (TROG) 15.01 Stereotactic Prostate Adaptive Radiotherapy utilizing Kilovoltage intrafraction monitoring (SPARK) trial is a multicenter trial using Kilovoltage Intrafraction Monitoring (KIM) to monitor prostate position during the delivery of prostate radiation therapy. KIM increases the accuracy of prostate radiation therapy treatments and allows for hypofractionation. However, an additional imaging dose is delivered to the patient. A standardized procedure to determine the imaging dose per frame delivered using KIM was developed and applied at four radiation therapy centers on three different types of linear accelerator.MethodsDose per frame for kilovoltage imaging in fluoroscopy mode was measured in air at isocenter using an ion chamber. Beam quality and dose were determined for a Varian Clinac iX linear accelerator, a Varian Trilogy, four Varian Truebeams and one Elekta Synergy at four different radiation therapy centers. The imaging parameters used on the Varian machines were 125 kV, 80 mA, and 13 ms. The Elekta machine was measured at 120 kV, 80 mA, and 12 ms. Absorbed doses to the skin and the prostate for a typical SBRT prostate treatment length were estimated according to the IPEMB protocol.ResultsThe average dose per kV frame to the skin was 0.24 ± 0.03 mGy. The average estimated absorbed dose to the prostate for all five treatment fractions across all machines measured was 39.9 ± 2.6 mGy for 1 Hz imaging, 199.7 ± 13.2 mGy for 5 Hz imaging and 439.3 ± 29.0 mGy for 11 Hz imaging.ConclusionsAll machines measured agreed to within 20%. Additional dose to the prostate from using KIM is at most 1.3% of the prescribed dose of 36.25 Gy in five fractions delivered during the trial.