About the lead author:
Gustavo Olivera, PhD
21st Century Oncology ATD
Madison, WI 53719
The Reviewer’s Viewpoint
Matthew Abramowitz, MD
Assistant Professor, Co-Chairperson Genitourinary Site Disease Group, Director of Compliance, Department of Radiation Oncology, Sylvester Comprehensive Cancer Center University of Miami
Why is this article contemporary?
Rapid advances in the technological development of precise and conformal radiation therapy and its incorporation into the clinic have generally outpaced our ability to test these technologies in a clinical trial format. With improvements in conformity utilizing intensity modulation and set-up accuracy utilizing stereotactic techniques and tumor motion management, margins continue to shrink. We hope this will translate into improved patient outcomes by allowing higher tumor doses and decreased morbidity by improved avoidance of critical structures.
However, these advances create new questions. Respiratory motion management based upon modeling and fiducial tracking assume minimal changes in the patient’s respiratory cycle, both during a single fraction and during a course of therapy. In addition, how changes in body shape that are attributed to weight loss, bowel gas, or slight differences in patient body position that may occur inter-or intra-fraction affect the delivered dose when using these new modalities remains unclear.
This study is contemporary in how it utilizes existing resources in a massive data set to evaluate the implications of these changes measured in delivered dose to patients. With the growing integration of adaptive dose recalculation, identification and correction of these issues may now be possible.
Background and Purpose:
In vivo dosimetry and verification (IVV) in conjunction with adaptive dose recalculation (ADR) is a synergistic set of processes that provides insight into actual treatment. Our intent was to test an automatic, multicenter procedure for IVV and ADR for all patients and all fractions treated on 14 helical TomoTherapy units across the United States. Additionally, our secondary goal was to create a system with metrics to flag for possible issues, establish trending, and determine possible clinical impact. Establishment of this system could both provide internal recommendations for daily IGRT and clinical improvements using IV and ADR findings. Moreover, our final goal was to evaluate deviations of the cumulative dose at the end of the treatment using Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) recommenda-tions for organs at risk.
Materials and Methods:
A system for IVV and ADR that retrieves and processes machine and patient information during treatment was created. The IVV portion includes (1) checking consistency values using machine encoders and (2) using the imaging detector data and comparing a reference frac-tion with respect to daily treatment deliveries using the Gamma metric. The ADR component computes daily and cumulative doses; DVH data are compared plan data and the flagging system. Thus, a reviewer can (1) identify machine, setup, and/or anatomical issues and (2) infer possible clinical impact.
Results and Conclusions:
Across multi-center clinics (n=14), 153,330 IVV and 66,294 ADR fractions were analyzed. The extent of in vivo flags was independent of an individual clinic’s volume. The number of in vivo flags considerably decreases as a function of the length of time that the system is used. This was accomplished by tailoring IGRT procedures to specific anatomical sites and specific patients. With respect to disease site, 5% of all prostate treatments and more than 20% of head and neck treatments triggered some IVV action level. ADR results demonstrated that cumu-lative doses at the end of treatment for head and neck patients exceed QUANTEC limits for 9% of parotids glands and 2% larynxes. Following treatment for breast cancer, approximately 10.5% of patients exceeded QUANTEC limits for lung and 3% for heart at the end of treatment. Thus, these data suggest ADR and IV are a synergistic set of processes that allows flagging and quantifying potential clinical impact to analyze dosimetrical information on patient registries.
Radiotherapy has evolved from three-dimensional conformal radiotherapy (3D), to intensity modulated radiotherapy (IMRT)1,2
and many forms of image-guided radiotherapy (IGRT).1
Comprehensive quality assurance (QA) procedures are evolving as the technology evolves.3-8
In IMRT, the typical QA procedures involve the use of phantom measurements or the delivery of a plan to a portal imager.9
IMRT QA is typically performed before clinical treatment.