1. INTRODUCTION RESULTS DATA ANALYSIS DISCUSSION METHODS REFERENCES
Implementation of the TG-147 Protocol in Conjunction with the Calypso GPS tracking system for
Higher Confidence of Prostate Patients Being Treated on RTOG Study 0938
A Morris1*, B Hasson2, P Sullivan3, C Hand4, S Philbrook3,
1Bucknell University, Lewisburg, PA, 2Anne Arundel Medical Center, Annapolis, MD, 3Abington Memorial Hospital, Abington, PA
4Albert Einstein Medical Center, Philadelphia, PA, (5) ,Jenkintown, PA,
2,3,4Drexel College of Medicine
INTRODUCTION
RESULTS
The increased use of SBRT with hypofractionated doses requires optimal precision and accuracy in target alignment. Hypofractionated prostate treatment protocols such as RTOG Study 0938 require corrective action for target volume movement greater than 2mm. To account for intrafractional motion, various localization and tracking systems are being adopted.
The GPS based Calypso system is a non-radiographic localization and tracking system used for alignment and tracking. Calypso functions through the use of three Beacon transponders, each implanted into the patient. An electromagnetic array is aligned using an infrared camera system. The array produces an oscillating electromagnetic field, which produces resonance in the beacons. The array excites the beacons sequentially, detecting emitted signals of three different frequencies one at a time. The signals are used to determine position and orientation, updated at a rate of 10Hz. The three signals are triangulated to determine the position of the PTV isocenter. When the target volume moves beyond the allowed boundary, the console emits an alarm.
In order to ensure these systems are localizing and tracking with the high degree of accuracy needed, a set of robust quality assurance procedures are required. Task Group Report (TG-147) of the AAPM describes daily, monthly, annual, and commissioning QA for non-radiographic localization systems. The purpose of this work was to implement TG-147 with the Calypso 4D, and use the system for patients entered onto the RTOG 0938 study.
Based on the review of TG-147 recommendations for daily, monthly, and annual QA tests new departmental QA procedures were implemented. New monthly QA tests consisted of a camera check, rigorous static localization test, a dynamic localization, and a radiographic analysis comparing the Calypso system’s isocenter with that of the linac’s portal imaging system. The dynamic localization test consisted of having Calypso track the movement of the phantom as it was shifted over known distances.
New yearly QA tests consisted of a rigorous safety check, a position stability test, a static localization test, a dynamic localization test, and a data transfer check. The static localization test consisted of a full end-to-end radiographic analysis.
Using Calypso, prostate movement during treatment was analyzed. The data showed definitive trends in total distance over the period of a treatment. (Figure 1) It was seen that there was typically no lateral movement, between 0 and 3 mm of inferior movement, and between 0 and 2 mm of posterior movement during treatment. No definitive trends in time of movement were detected with IMRT patients. However, for the longer SBRT treatments there was a time dependent change in the vertical displacement. (Figure 2) Typically, there was minimal movement after 2 to 3 minutes post setup.
DATA ANALYSIS
DISCUSSION
METHODS
The TG-147 recommendations provided a robust set of QA procedures that confirmed the Calypso’s accuracy within 1mm. The system consistently passed the tests without problem. Several tests are reliant on other systems such as the linac imaging systems and treatment planning systems. These tests should be performed with these systems’ accuracy confirmed. The new QA procedures have increased the confidence for tracking prostate movement during treatments, and allowed for the detection of movement trends which can be used to preemptively adjust for intrafractional motion. More data will be needed to confirm a time correlation for SBRT patient treatments.
The Calypso system consists of three Beacon transponders that are implanted into the patient, an electromagnetic array, a console, and an infrared camera system. Calypso was used in conjunction with a Siemens Oncor accelerator to deliver IMRT and SBRT treatments.
The implementation of TG-147 with the Calypso system recommends numerous tests to be performed on a daily, monthly, and yearly basis, including tests for static localization, dynamic localization, and stability (See Table 1). The TG-147 recommended tests were analyzed in regards to their application to the Calypso system. The manufacturer-recommended QA tests were used as a starting point upon which the other tests were adapted. The provided QA tools were adapted to the TG-147 recommendations.
With the enhanced tests in place, Calypso was used to track prostate movement during standard IMRT and SBRT treatments. The total lateral, longitudinal, and vertical movement of the beacons were measured from the setup of patients daily treatment till the end of treatment.
Table 1. Prostate Vertical Shift Trends
REFERENCES
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Fig.1. Lateral, Longitudinal, and Vertical Prostate Movement During IMRT
Fig 2. Vertical Prostate Movement Over Time During IMRT