Leakage radiation and room shielding considerations increase significantly for intensity-modulated radiation therapy (IMRT) treatments due to the increased beam-on time to deliver modulated fields. Tomotherapy, with its slice by slice approach to IMRT, further exacerbates this increase. Accordingly, additional shielding is used in tomotherapy machines to reduce unwanted radiation. The competing effects of the high modulation and the enhanced shielding were studied. The overall room leakage radiation levels are presented for the continuous gantry rotations, which are always used during treatments. The measured leakage at 4 m from the isocenter is less than 3 x 10(-4) relative to calibration output. Primary radiation exposure levels were investigated as well. The effect of forward-directed leakage through the beam-collimation system was studied, as this is the leakage dose the patient would receive in the course of a treatment. A 12-min treatment was calculated to produce only 1% patient leakage dose to the periphery region. Longer treatment times might yield less patient dose if the field width selected is correspondingly narrower. A method for estimating the worst-case leakage dose a patient would receive is presented.
Helical tomotherapy is a relatively new modality with integrated treatment planning and delivery hardware for radiation therapy treatments. In view of the uniqueness of the hardware design of the helical tomotherapy unit and its implications in routine clinical practice, the Therapy Physics Committee (TPC) of the American Association of Physicists in Medicine (AAPM) commissioned Task Group 148 (TG‐148) to review this modality and make recommendations for quality assurance related methodologies. This report summarizes the findings of the Task Group and aims to provide the practicing clinical medical physicist with the insight into the technology that is necessary to establish an independent and comprehensive quality assurance program for a helical tomotherapy unit. In this task group report an overview of the TomoTherapy system and its unique aspects is provided. Delivery, imaging, and treatment planning quality assurance are discussed in three separate chapters of this report. Lastly quality assurance aspects are summarized according to their recommended frequency.
History: Helical tomotherapy is a relatively new modality with integrated imaging, planning and delivery hardware for radiation therapy treatments. In view of the unique hardware design and its implications for routine quality assurance, the Therapy Physics Committee (TPC) of the AAPM commissioned Task Group 148 to review this modality and to make quality assurance recommendations. General Outline: Initial chapters provided a brief overview of the technology and describe unique aspects of the technology. These chapters are followed by three chapters that are dedicated to the delivery, imaging, and planning aspects. A final chapter summarizes the QA recommendations and details daily, monthly, quarterly, and annual procedures. Major Highlights: This report is designed to provide guidance to the physicist that is charged with establishing a routine QA program for helical tomotherapy. Since the imaging and treatment planning aspects are intimately connected to the physical machine hardware, each of these aspects is covered in this report such that TG-148 provides comprehensive guidelines. Implementation Plan: The summary chapter list daily, monthly, quarterly, and annual tests. This chapter is designed to facilitate the implementation of the recommended QA procedures. Timeline for the Report Release: This task group was submitted in February 2010 to the Medical Physics Journal for review. Conflict of Interest: Gustavo Olivera is an employee of TomoTherapy, Inc.; John Balog owns TomoTherapy stock; Katja Langen hold a research agreement with TomoTherapy, Inc. Learning Objectives: 1. Understand the unique aspects of helical tomotherapy 2. Understand QA aspects of the delivery, imaging, and planning components of helical tomotherapy 3. Implement a routine QA program for helical tomotherapy
