Couch and multileaf collimator tracking: A clinical feasibility study for pancreas and liver treatment

Abstract

Real-time tumor tracking through active correction by the multileaf collimator or treatment couch offers a promising strategy to mitigate delivery uncertainty due to intrafractional tumor motion. This study evaluated the performance of MLC and couch tracking using the prototype iTools Tracking system in TrueBeam Developer Mode and the application for abdominal cancer treatments. Methods: Experiments were carried out using a phantom with embedded Calypso transponders and a motion simulation platform. Geometric evaluations were performed using a circular conformal field with sinusoidal traces and pancreatic tumor motion traces. Geometric tracking accuracy was retrospectively calculated by comparing the compensational MLC or couch motion extracted from machine log files to the target motion reconstructed from real-time MV and kV images. Dosimetric tracking accuracy was measured with radiochromic films using clinical abdominal VMAT plans and pancreatic tumor traces. Results: Geometrically, the root-mean-square errors for MLC tracking were 0.5 and 1.8 mm parallel and perpendicular to leaf travel direction, respectively. Couch tracking, in contrast, showed an average of 0.8 mm or less geometric error in all directions. Dosimetrically, both MLC and couch tracking reduced motion-induced local dose errors compared to no tracking. Evaluated with five pancreatic tumor motion traces, the average 2%/2 mm global gamma pass rate of eight clinical abdominal VMAT plans was 67.4% (range: 26.4%-92.7%) without tracking, which was improved to 86.0% (range: 67.9%-95.6%) with MLC tracking, and 98.1% (range: 94.9%-100.0%) with couch tracking. In 16 out of 40 deliveries with different plans and motion traces, MLC tracking did not achieve clinically acceptable dosimetric accuracy with 3%/3mm gamma pass rate below 95%. Conclusions: This study demonstrated the capability of MLC and couch tracking to reduce motioninduced dose errors in abdominal cases using a prototype tracking system. Clinically significant dose errors were observed with MLC tracking for certain plans which could be attributed to the inferior MLC tracking accuracy in the direction perpendicular to leaf travel, as well as the interplay between motion tracking and plan delivery for highly modulated plans. Couch tracking outperformed MLC tracking with consistently high dosimetric accuracy in all plans evaluated, indicating its clinical potential in the treatment of abdominal cancers.

Realistic CT data augmentation for accurate deep‐learning based segmentation of head and neck tumors in kV images acquired during radiation therapy

“…62,63 It is thought that this 3D position estimation method can be adapted such that markerless 3D position and motion estimation is possible, either by using the location of the segmentation centroid or points on the segmentation outline instead of the marker locations. 64 An accurate estimation of the 3D position and motion of the tumor would allow for improved dose delivery through the use of beam adaptation methods 65 or gated treatments. 63 Currently for H&N cancer RT treatments, kV images are mainly acquired prior to treatment to assist in accurately positioning the patient.…”

Evaluation of OrthoChromic OC-1 films for photon radiotherapy application

“…The calibration film of each case extended about 10–20% higher than the maximum dose of the case to anticipate the full dynamic dose range [ 2 ]. For EBT3, calibration was performed following our departmental procedure [ 15 ]. The calibration curve was generated with twelve points with a dose range from 0 cGy to 110% of the maximum dose of the clinical fields.…”

Robotic Systems in Radiotherapy and Radiosurgery

“…3. While good dosimetric accuracy has been reported [50,51], couch movement can cause unconscious physiological response. Still, Jöhl et al found acceptable levels of stress in healthy participants [52].…”