AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

Abstract

The introduction of advanced techniques and technology in radiotherapy has greatly improved our ability to deliver highly conformal tumor doses while minimizing the dose to adjacent organs at risk. Despite these tremendous improvements, there remains a general concern about doses to normal tissues that are not the target of the radiation treatment; any "nontarget" radiation should be minimized as it offers no therapeutic benefit. As patients live longer after treatment, there is increased opportunity for late effects including second cancers and cardiac toxicity to manifest. Complicating the management of these issues, there are unique challenges with measuring, calculating, reducing, and reporting nontarget doses that many medical physicists may have limited experience with. Treatment planning systems become dramatically inaccurate outside the treatment field, necessitating a measurement or some other means of assessing the dose. However, measurements are challenging because outside the treatment field, the radiation energy spectrum, dose rate, and general shape of the dose distribution (particularly the percent depth dose) are very different and often require special consideration. Neutron dosimetry is also particularly challenging, and common errors in methodology can easily manifest as errors of several orders of magnitude. Task Group 158 was, therefore, formed to provide guidance for physicists in terms of assessing and managing nontarget doses. In particular, the report: (a) highlights major concerns with nontarget radiation; (b) provides a rough estimate of doses associated with different treatment approaches in clinical practice; (c) discusses the uses of dosimeters for measuring photon, electron, and neutron doses; (d) discusses the use of calculation techniques for dosimetric evaluations; (e) highlights techniques that may be considered for reducing nontarget doses; (f) discusses dose reporting; and (g) makes recommendations for both clinical and research practice.

Measurement and modeling of out-of-field doses from various advanced post-mastectomy radiotherapy techniques

“…Therefore IC’s over-response in the out-of-field region is negligible, which is also consistent with the literature (Kry et al , 2017). To quantify K OBOF and K IBOF for all PMRT techniques, we transferred PMRT treatment plans from the anthropomorphic phantom to a water phantom in Pinnacle TPS and performed out-of-field dose measurements with TLDs and an IC in solid water phantoms.…”

Radiation treatment planning and delivery strategies for a pregnant brain tumor patient

“…The TrueBeam plans had an isocenter placed as far cranially as possible to maximize the separation between the treatment head and the fetus9; additionally, couch kicks were avoided to maximize separation between the treatment head and the fetus and to avoid beam divergence toward the fetus. Beam energy was limited to 6 MV to reduce scatter, head leakage, and neutron contamination, and the flattening filter‐free beam was investigated to assess head leakage reductions from the removal of the flattening filter from the beamline 5, 10. The TrueBeam plans used minimal monitor units (MU) by avoiding highly modulated IMRT or volumetric modulated arc therapy (VMAT), minimizing the number of fields, and using SnS rather than sliding‐window technique for IMRT beams.…”

“…It may be possible to achieve a clinically acceptable plan while substantially reducing peripheral dose by modifying these standard treatment planning strategies. Numerous reports have detailed planning strategies to reduce peripheral dose 4, 5, 6, 7, 8, 9, 10. While IMRT is a common choice for intracranial treatments, IMRT often results in higher peripheral dose than 2D‐ or 3D‐conformal treatment techniques 5, 10…”

“…While prior reports have provided estimates of peripheral dose for various combinations of beam energy and geometry, these reports often apply to a prior generation of treatment delivery system 1, 4, 5, 6, 10, 11, 12, 13, 14. The present manuscript details fetal dose measurements on current‐generation treatment delivery systems and summarizes the anticipated risks to the patient's fetus using published guidance.…”

Executive summary of AAPM Report Task Group 113: Guidance for the physics aspects of clinical trials

“…Therefore, definitions and dose goals across trials to the same body site should be standardized as much as possible with the expectation of evolution of care over time. In addition, the protocol should specify any additional limits to doses to organs outside the treatment field 15. A final critical concern is that some systems ignore the volume of an organ outside the dose calculation grid when reporting dose‐volume parameters.…”