The management of imaging dose during image‐guided radiotherapy: Report of the AAPM Task Group 75

Abstract

Radiographic image guidance has emerged as the new paradigm for patient positioning, target localization, and external beam alignment in radiotherapy. Although widely varied in modality and method, all radiographic guidance techniques have one thing in common--they can give a significant radiation dose to the patient. As with all medical uses of ionizing radiation, the general view is that this exposure should be carefully managed. The philosophy for dose management adopted by the diagnostic imaging community is summarized by the acronym ALARA, i.e., as low as reasonably achievable. But unlike the general situation with diagnostic imaging and image-guided surgery, image-guided radiotherapy (IGRT) adds the imaging dose to an already high level of therapeutic radiation. There is furthermore an interplay between increased imaging and improved therapeutic dose conformity that suggests the possibility of optimizing rather than simply minimizing the imaging dose. For this reason, the management of imaging dose during radiotherapy is a different problem than its management during routine diagnostic or image-guided surgical procedures. The imaging dose received as part of a radiotherapy treatment has long been regarded as negligible and thus has been quantified in a fairly loose manner. On the other hand, radiation oncologists examine the therapy dose distribution in minute detail. The introduction of more intensive imaging procedures for IGRT now obligates the clinician to evaluate therapeutic and imaging doses in a more balanced manner. This task group is charged with addressing the issue of radiation dose delivered via image guidance techniques during radiotherapy. The group has developed this charge into three objectives: (1) Compile an overview of image-guidance techniques and their associated radiation dose levels, to provide the clinician using a particular set of image guidance techniques with enough data to estimate the total diagnostic dose for a specific treatment scenario, (2) identify ways to reduce the total imaging dose without sacrificing essential imaging information, and (3) recommend optimization strategies to trade off imaging dose with improvements in therapeutic dose delivery. The end goal is to enable the design of image guidance regimens that are as effective and efficient as possible.

Technical note: TROG 15.01 SPARK trial multi‐institutional imaging dose measurement

“…In one Cyberknife fraction, between 30 and 50 image pairs are normally acquired, and the entrance surface dose per projection is between 0.25 and 2 mGy, depending on the treatment site and imaging method used 21. The maximum entrance dose per projection measured for KIM in this study is slightly lower than the lowest Cyberknife value, however, at least three times as many images are likely to be taken when using KIM during a VMAT treatment, and so the overall surface dose is likely to be on the same order of magnitude.…”

Technical note: No increase in effective dose from half compared to full rotation pelvis cone beam CT

“…The advantage of image‐guided radiation therapy (IGRT) is the application of more conformal plans and therefore, a reduction of the irradiated volume. The additional dose received by the patient1 raises concerns about late effects such as second primary cancers. Hence, the quantification of CBCT dose is an important issue.…”

Contrast enhancement for portal images by combination of subtraction and reprojection processes for Compton scattering

“…Various systems, e.g., in‐treatment‐room computed tomography (CT‐on‐rails), kilovoltage cone beam CT (kV‐CBCT), portal imaging and megavoltage cone beam CT (MV‐CBCT) are currently available for the IGRT 1, 2…”