Prostate Movement Evaluation During Treatment Delivery Period for Prostate Cancer
J Zhang12*, S Azawi2, R Williams2, E Frank12, (1) Photon Physics Services, Inc., Rolling Hill Estates, CA, (2) VA Long Beach Medical Center, Long Beach,, CASU-E-J-19 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To evaluate the intra-fractional prostate movement during the beam delivery period using orthogonal KV image pairs.
Methods: To understand the prostate internal motion range during the beam delivery period of conventional treatment, 11 conventional treatments were utilized. We followed RTOG 0815. The total dose is about 75.6 to 79.2 Gy with 1.8 Gy per fraction. The PTV margin is 5 to 10 mm. 2-arc RapidArc plans are used for the treatment. Once the first arc was delivered, another orthogonal KV image pair was performed to setup the patient based on the prostate seeds. The shift data and the interval time between the first and second orthogonal KV image pair were recorded.
Results: The relative error results of OBI QA were within 1mm. The average shift between two arc beam deliveries was 0.38cm (0.20cm ~ 0.85cm). The interval time between two orthogonal KV image pairs was 6.71 min (4.64min ~ 9.22 min). For conventional treatment delivery, the 2 arc beam delivery time is within 3 minutes. Hypofractionated treatment will double the beam delivery time. Accordingly, prostate movement might be larger and impair the targeting of cancer tissue. Studies about the prostate movement during longer treatment period will be carried out in the future. Real time tracking method can be employed to verify patient setup during long treatment. However, the orthogonal KV image pair can be an alternative if real time tracking method is not available.
Conclusion: Hypofractionated prostate treatment or prostate SBRT need longer beam delivery time. Also the PTV margin is much less than conventional treatment. Therefore verification of patient setup during the beam delivery is critical. Real time tracking system or orthogonal KV image pairs should be used during the beam delivery period to improve treatment delivery quality.