International Journal of Radiation Oncology*Biology*Physics
Physics ContributionDeep Inspiration Breath Hold—Based Radiation Therapy: A Clinical Review
Introduction
Several recent developments in linear accelerator–based photon radiation therapy (RT), such as intensity modulated RT (IMRT) (1) and volumetric modulated arc therapy (VMAT) 2, 3, allow the application of highly complex treatment plans with steep dose gradients. Photon dose distributions in rigid treatment volumes have approached physically achievable complexity and accuracy limits as a consequence of the introduction of precise dose calculation algorithms (4), daily online soft tissue–based 3-dimensional (3D) image guided patient and target positioning for image guided RT (IGRT) 5, 6, and continuously improved delivery devices with fast collimators (7). Flattening filter-free (FFF) high-dose-rate applications 1, 8, 9, 10, 11, 12, 13 have dramatically accelerated small-field delivery, particularly for the stereotactic body RT (SBRT) paradigm, while maintaining biological properties of the beam 14, 15. It has several further advantages such as less scatter from the treatment source, less leaf transmission, and less head leakage 1, 16.
The combination of all these technical possibilities has refined and accelerated (8) the therapy of both large stationary targets like head and neck cancer 17, 18 and smaller mobile targets, resulting in clinical benefits such as excellent local control rates in the treatment of early non-small cell lung cancer (NSCLC) or lung and liver metastases with SBRT 19, 20, 21, 22, 23, 24, with very reasonable total treatment times now in the range of 15 minutes per treatment fraction.
Proton therapy is now applied with increasing frequency, with new treatment facilities being activated on a regular basis. It has made significant technological progress recently with more widespread use of scanned beams and the introduction of 3D image guidance. Nine times rescanning of a 1-L volume within 1 minute is now technically feasible, bringing into reach treatment deliveries during the time span of 1 breath hold (25). An innovative design for image guidance is the integration of a beams-eye view imager at Gantry 2 at the Paul Scherrer Institute in Switzerland, which is a fast parallel beam scanning proton therapy unit with small spot size and penumbra, allowing x-ray imaging in fluoroscopy mode during treatment delivery 25, 26. However, target motion implies a much bigger challenge for proton therapy than for photon therapy, especially for a scanned delivery, where interplay effects can significantly disturb the planned dose distribution (27). Furthermore, image guided approaches are much more advanced in photon RT, and online 3D motion monitoring has not been realized for particle therapy to date (28).
Despite constant efforts to mitigate motion effects 29, 30, 31 in both advanced photon therapy and proton therapy of body regions that are affected by breathing motion with motion amplitudes of up to 2 to 3 cm and potentially including hysteresis and deformations (32), methodical improvements are still needed. Resolving remaining issues may improve the treatment of several disease entities and clinical situations, among which are these:
- 1.
RT of locally advanced NSCLC, where escalated doses in combination with chemotherapy may improve local control 33, 34 but are limited by normal lung tolerance and methodical imprecisions. Insufficient target coverage prompted by concerns about lung toxicity may have contributed to a lack of efficacy of dose escalation in the treatment of locally advanced lung cancer in the randomized Radiation Therapy Oncology Group (RTOG) trial 0617 35, 36.
- 2.
Exposed lung volume also plays a role in considerations regarding secondary malignancy after RT of all mediastinal tumors 37, 38. Exposed heart volume after mediastinal or breast RT is linked to long-term cardiac toxicity 39, 40, 41, 42, 43, 44.
- 3.
Treatment of nonstatic targets with passively scattered proton beams, which currently is not unlocking its full potential because of limitations on image guidance.
- 4.
Treatment of nonstatic targets with scanned proton beams, which has been performed clinically only rarely to date because of concerns regarding interplay effects (45).
This review describes the different methods and characteristics of available motion management strategies in photon and proton RT and then outlines how deep inspiration breath hold (DIBH) can be efficiently performed and where it may resolve or mitigate the issues and unmet methodical needs just described. Table 1 provides a synopsis of the dosimetric and clinical characteristics of DIBH treatments and compares them with other currently available motion management strategies regarding their advantages and disadvantages.
Section snippets
Breathing Motion Management Strategies and Methods
Even for short beam-on times now achievable with FFF treatments, motion management strategies are necessary to compensate for intrafractional breathing motion. Different strategies aim at a reduction of margins between clinical target volume (CTV) and planning target volume (PTV) and/or improved geometrical precision of dose delivery.
- 1.
Motion amplitude of free breathing (FB) can be reduced by mechanical abdominal compression (46). Recently, however, it has been shown to be beneficial only for
Methods for Establishing DIBH
DIBH can be achieved by repeated voluntary breath hold or with computer-controlled commercially available devices, which can assist DIBH through airway blocking, feedback approaches, or both. Breath hold gating signals now automatically trigger treatments across all major treatment device manufacturers.
Possibility to image under DIBH
Serpa et al (119) have shown that markerless EPID tracking is principally suitable for treatment verification of gated SBRT, but marker-based EPID imaging is also being used. For Cyberknife SBRT, breath hold imaging was performed after implantation of 2 to 4 fiducials directly into the tumor, and a maximal tumor vector movement of 3.8 mm (detected by kV flat-panel detectors) was reported (120).
Linac-mounted CBCTs currently on the market provide the possibility to interrupt imaging and image
Recent Developments That Have Facilitated the Use of DIBH, and Outlook
Quality assurance and workflow for breath hold application is fast and easy 8, 82. Frequently voiced concerns regarding DIBH have concentrated on the necessity for optimal patient collaboration and compliance with the procedure, sufficient pulmonary reserve, and the longer treatment time in comparison with nongated or tracked treatments (187). With the advent of fast multileaf collimators, VMAT, and particularly the FFF technology, the prolongation of treatment time of a gated over a nongated
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Cited by (0)
J. Boda-Heggemann and A.-C. Knopf contributed equally to this work.
Conflict of interest: Dr Boda-Heggemann, Dr L. Jahnke, Dr A. Jahnke, A. Arns, Dr Blessing, Dr Wenz, Dr Lohr, and Dr Simeonova-Chergou received personal fees from Elekta AB, Sweden, during the conduct of the study, and Dr Lohr received grants and personal fees from IBA and personal fees from C-RAD during the conduct of the study. The other authors report no conflict of interest.