GuidelinesThe Canadian Association of Radiation Oncology Scope of Practice Guidelines for Lung, Liver and Spine Stereotactic Body Radiotherapy
Introduction
The principle of stereotactic body radiotherapy (SBRT) is to deliver in a few fractions an equivalent, or greater, biologically effective dose as compared to a standard 5–7 week fractionated course that would otherwise be considered radical. SBRT is possible as a result of modern radiation technologies that allow for highly conformal radiation treatment planning that maximises the dose within the target volume, while optimising the steep dose gradients beyond the target boundaries to minimise the dose to the surrounding organs at risk (OAR), and delivery precision in the order of millimetres [1]. The main technical requirements for SBRT include modern linacs with integrated inter- and intra-fractional image guidance solutions [2], sophisticated immobilisation systems [3], advanced treatment planning software and some level of adaptive patient realignment capabilities, such as robotic positioning technologies.
SBRT is being investigated as definitive treatment for an increasing selection of primary tumours that include lung cancers [4], [5], hepatocellular cancers [6], prostate cancers [7], pancreatic cancers [8], selected primary spinal tumours [9] and the list is growing. In particular, SBRT has been a major advance in the management of early stage lung cancers [4]. Local control rates for lung SBRT are dramatically greater than those reported from protracted conventional radiation treatment, and judging from the favourable therapeutic ratio seen in phase II trials [4] SBRT has become a de facto standard therapeutic option.
SBRT is as a treatment for extracranial metastatic disease, analogous to stereotactic radiosurgery (SRS) for brain metastases [10]. Lung [11], liver [12] and spinal metastases [13], [14] are the predominant targets of mainstream SBRT practice; however, its applicability to a wide variety of extracranial metastatic sites is continuously evolving [11]. The philosophical shift specific to metastatic indications is to deliver a ‘locally radical’ dose in order to achieve long-term local control. This is contrary to the current practice of delivering a ‘locally palliative’ conventional dose of radiation aimed at symptom control. SBRT is also increasingly being considered in the re-irradiation metastatic patient, and the bulk of the re-irradiation SBRT experience in the treatment of spinal metastases [15], [16].
SBRT is increasingly being practiced in North America. A recent survey in the USA reported that 64% of the 551 respondents (40% response rate) are currently practicing SBRT [17]. Of SBRT practitioners, the most common sites were lung (89.3%), liver (54.5%) and spine (67.5%), and most started to practice SBRT as of 2007. In Canada, the use of SBRT has also emerged with 14 of 41 cancer centres currently practicing SBRT [18]. Lung (13/14), liver (9/14) and spine (6/14) were the most common sites of SBRT practice, and 77% of practicing centres had adopted SBRT within the last 3 years. The adoption of SBRT is increasing year by year [17], and has occurred despite a lack of randomised clinical trial evidence to support the proposed benefits of SBRT.
Until evidence of safety and efficacy of SBRT matures for metastatic disease, the widespread adoption of SBRT is cautioned, as there is potential for serious toxicities from high-dose exposure to the normal tissues [11], [19], [20], [21], [22]. Furthermore, unlike for brain metastases, chemotherapy traditionally has been the main modality of therapy to control extracranial metastatic disease that does not require urgent local therapy. Therefore, toxicities associated with SBRT for metastases may not only cause local toxicities that can harm a patient's quality of life, but affect overall survival should delivery of systemic therapy be compromised.
Scope of practice has been defined as ‘…the activities for which the professional is educated, and authorized to perform; and is influenced by the setting in which the professional practices, the requirements of care delivery organizations, the needs of the patients or clients’ [23]. Thus, the notion of scope of practice reflects essentially the practice of the profession, and is used as a guide for the profession and public. The purpose of this document was to define for the Canadian Association of Radiation Oncology (CARO) a Canadian perspective on SBRT, and those considerations for safe SBRT practice in the areas of lung, liver and spine tumours (Figure 1). The aim was also to describe the particular requirements on the part of a radiation oncologist and radiation oncology department to consider for safe practice, and to clarify the role of the radiation oncologist and allied health professionals in the process of treating patients with SBRT. Our mandate was not to explicitly define the indications for SBRT, nor to summarise the evidence in support of SBRT.
Section snippets
Definition of Stereotactic Body Radiotherapy
This CARO task force has considered SBRT to be defined as:
The precise delivery of highly conformal and image-guided hypofractionated external beam radiotherapy, delivered in a single or few fraction(s), to an extracranial body target with doses at least biologically equivalent to a radical course when given over a protracted conventionally (1.8–3.0 Gy/fraction) fractionated schedule.
Our definition is consistent with those reported by other national working groups, which include:
- 1.
The American
Basic Principles of Stereotactic Body Radiotherapy
SBRT is distinct from three-dimensional conformal radiotherapy or conventionally fractionated intensity-modulated radiotherapy (IMRT), regardless of the intent being palliative or curative. We outline the fundamental principles of SBRT as follows.
- •
Complex simulation and target definition may include:
- ○
Multi-modal imaging and image registration for both target and OAR delineation.
- ○
For selected indications, tumour motion assessment is incorporated into simulation. For example, four-dimensional
- ○
Treatment Delivery Units
Currently in Canada, the most common technology in use for SBRT is that of an isocentric S-band linac using a multileaf collimator (MLC) for beam shaping, coplanar and/or non-coplanar beam arrangements (typically six to 15 beams) and conformal treatment planning. Although IMRT is commonly used for SBRT treatments, inverse planning has not been a necessary requirement for some indications. For example, SBRT has been delivered using three-dimensional conformal radiotherapy for lung primary
Spine
Spine SBRT studies have reported that intra-fraction motion in the order of millimetres can significantly affect the actual dose delivered to the spinal cord [39], and this is a reflection of the steepest dose gradient intentionally maximised at the PTV–spinal cord interface. Given that near-rigid body immobilisation minimises the potential for intra-fraction motion, as compared with more simple devices [3], it is highly suggested for MLC-linac-based treatments. For robotic non-isocentric
Image-guided Radiotherapy Practice
SBRT is an image-guided therapy, and the target position must be verified before treatment. Tolerance, or action levels, for repositioning the patient should be set based on the applied preferably patient-specific PTV margin, and knowledge of the couch motion tolerance. Strict action thresholds for patient positioning corrections have been shown to improve the overall precision of the treatment and, for example, a 1 mm and 1 degree action level is standard for spine SBRT at the University of
Patient Selection and Dose Limits to Organs at Risk
In Table 1, the most common indications currently practiced for lung, spine and liver tumours are summarised. The list is not all-inclusive and the purpose of this document is not to review the current evidence of SBRT for each indication. With respect to dose limits to the OAR, we direct the interested reader to a comprehensive reference specific to SBRT [21], and the recently published Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) report [47].
Role Definitions
The radiation oncologist is ultimately responsible for all aspects of care when patients undergo SBRT, and is expected to have knowledge of the specific indications for the tumour site to be treated and expertise with the technology to be used for both simulation and delivery. More specifically, the radiation oncologist should understand the limitations of the technology, the required quality assurance, and sources of inaccuracies such that the appropriate PTV margin is applied. He or she must
Quality Assurance
SBRT is less tolerant to error in delivery and especially geometric errors [40], [48]. Each radiation department should have a programmatic approach to quality. The quality assurance of SBRT will fall under the purview of the department's treatment quality assurance committee. In this regard, CARO is party to the Canadian Partnership for Quality Radiotherapy and endorses its proposed guidelines [49]. Key points are as follows:
- •
Quality assurance should encompass the entire treatment process from
Conclusion
This CARO scope of practice guideline for SBRT is specific to liver, lung and spine tumours with principles applicable to SBRT in general. We detail the minimum requirements to consider for simulation and image guidance, recommend SBRT-specific team(s) to be developed within a department and specify role definitions and quality assurance measures to consider for safe practice. The task force recommendations are designed to assist departments in establishing a safe and robust SBRT program.
Acknowledgements
We thank Dr David Larson MD. PhD and Lijun Ma PhD from the University of California San Francisco for their expert advice as external reviewers. We thank Mrs Dana Hiraldo-Santos for assistance with manuscript preparation.
References (55)
- et al.
Spine stereotactic body radiotherapy utilizing cone-beam CT image-guidance with a robotic couch: intrafraction motion analysis accounting for all six degrees of freedom
Int J Radiat Oncol Biol Phys
(2012) - et al.
Technique for stereotactic body radiotherapy for spinal metastases
J Clin Neurosci
(2011) - et al.
Stereotactic body radiotherapy for medically inoperable lung cancer: prospective, single-center study of 108 consecutive patients
Int J Radiat Oncol Biol Phys
(2012) - et al.
Gemcitabine chemotherapy and single-fraction stereotactic body radiotherapy for locally advanced pancreatic cancer
Int J Radiat Oncol Biol Phys
(2008) - et al.
Stereotactic body radiotherapy is effective salvage therapy for patients with prior radiation of spinal metastases
Int J Radiat Oncol Biol Phys
(2009) - et al.
Spinal cord tolerance for stereotactic body radiotherapy
Int J Radiat Oncol Biol Phys
(2010) - et al.
Reirradiation human spinal cord tolerance for stereotactic body radiotherapy
Int J Radiat Oncol Biol Phys
(2012) - et al.
Brachial plexopathy from stereotactic body radiotherapy in early-stage NSCLC: dose-limiting toxicity in apical tumor sites
Radiother Oncol
(2009) - et al.
American Society for Therapeutic Radiology and Oncology (ASTRO) and American College of Radiology (ACR) practice guideline for the performance of stereotactic body radiation therapy
Int J Radiat Oncol Biol Phys
(2010) - et al.
Stereotactic body radiotherapy. Guidelines for commissioners, providers and clinicians: a national report
Clin Oncol
(2011)