Stereotactic Body Radiation Therapy:
The Report of AAPM Task Group 101
JOURNAL CLUB
Slides prepared By Dr Wang Fuqiang, Registrar, Radiation Oncology,
NCCS
Daniel Tan
Course Director
Associate Consultant
Department of Radiation Oncology
National Cancer Centre Singapore
Stereotactic Body Radiation Therapy:
The Report of AAPM Task Group 101
Aims:
1) Know the existence of this resource
2) Know the contents of this resource
3) Briefly run through this resource to make a
mental note
Stereotactic Body Radiation Therapy:
The Report of AAPM Task Group 101
I. Introduction and Scope
I. Introduction and Scope
Contents
I. Introduction and Scope

SBRT

emerging RT procedure for the treatment of early stage
primary and oligometastatic cancer

delivery of large doses in few fractions resulting in high
biological effective dose

to minimise normal tissue toxicity, need to ensure high
conformity and rapid fall-off doses away from the target

therefore high level confidence in accuracy of treatment is
required for SBRT

this is achievable by integrating modern imaging, simulation
and treatment planning and delivery technologies
I. Introduction and Scope
 ‘In SBRT, confidence in this accuracy is accomplished by
the integration of modern imaging, simulation,
treatment planning, and delivery technologies into all
phases of the treatment process; from treatment
simulation and planning, and continuing throughout
beam delivery. ‘
II. History and Rationale of SBRT

outcomes of SBRT for both primary and metastatic disease
compare favourably to surgery

many conceptual theories:

sites of gross disease containing highest number of
clonogenic cells not eliminated by chemotherapy

oligometastatic disease which can be eradicated if
numbers are limited

Norton-Simon hypothesis whereby cancer increases from
low undetectable level to a phase of exponential growth
and a lethal plateau, therefore SBRT may aid in the
reduction of systemic burden to delay lethal tumour
burden
II. History and Rationale of SBRT
 immunomodulation
 palliative treatment
 clinical patient outcomes first published in 1995
 initially focused on liver and lung lesions
 subsequently other studies included spinal lesions
III. Patient Selection Criteria
 mostly lung/ liver/ spinal lesions
 well circumscribed tumours up to 5cm
 SBRT has been used as a boost in addition to
regional nodal irradiation
 careful evaluation of normal tissue function
and dose distribution (typically pulmonary
function and volume of liver irradiated)
 important structures should be avoided
III. Patient Selection Criteria
 Recommendations
 formal group trials with appropriate protocols
 or an institution treatment protocol/ guidelines as
developed by radiation oncologists and physicists
IV. Simulation Imaging and Planning
 A. Simulation Imaging
 CT/ 4D CT/ MRI/ PET
 Recommendation:
 simulation done in treatment position
 cover target and all OARs
 5-10cm superior and inferior of normal treatment
borders (~15cm if non-coplanar treatment
techniques)
 tomographic slice thickness of 1-3mm
IV. Simulation Imaging and Planning B
 B. Data Acquisition
 Multiple sources for organ/ tumour motion during
simulation
 Population based margins may be incorrectly applied
 refer to AAPM Task Group 76 report on various
tumour motion strategies
IV. Simulation Imaging and Planning
 C. Imaging Artifacts
 If target and radiosensitive critical structures cannot
be localised on section imaging modality with
sufficient accuracy because of motion and/ or metal
artifacts, SBRT should not be pursued as a treatment
option
IV. Simulation Imaging and Planning
 D. Treatment Planning
 Limited volume of tissues containing the
gross tumour and close vicinity are
targeted for high dose per fraction
treatment, hot spots within the target are
deemed acceptable
 Volume of normal tissue receiving high
doses should be minimised by a sharp
dose fall-off outside of the target
IV. Simulation Imaging and Planning
 D. Treatment Planning
 ICRU 50/ 62
 GTV/CTV considered identical
 Variation in CTV due to motion/ organ filling
accounted for by ITV
 PTV
IV. Simulation Imaging and Planning

D. Treatment Planning

1. Dose Heterogeneity, gradient and fall-off and beam geometry
 dose prescription specified at lower isodose with small or no
margins for penumbra
 hotspots within target deemed acceptable and clinically
desirable
 use of multiple nonoverlapping beams to achieve sharp dose
fall-off
 beam energy (6MV smaller penumbra)
 resolution of beam shaping (as determined by MLC leaf
width-> 5mm adequate)
IV. Simulation Imaging and Planning
 D. Treatment Planning
 2. Beam selection and beam geometry
 restricting entrance dose to <30% of
cumulative dose and avoiding beam
overlaps to prevent acute skin reactions
 increased number of beams yield better
conformity but not practical (VMAT may
overcome this issue)
IV. Simulation Imaging and Planning

D. Treatment Planning

3. Calculation grid size
 2mm grids required for IMRT
 Recommendation: 2mm of finer for SBRT, >3mm not acceptable
 a 2.5 mm isotropic grid produces an accuracy of about 1% in the
high-dose region of an IMRT plan consisting of multiple fields
 Another report indicated an accuracy of +/- 5% for an isotropic
grid resolution of 4 mm.
 Chung et al. found a dose difference of 2.3% of the prescribed
dose for 2 mm calculation grids as compared to 1.5 mm grids,
rising to 5.6% for 4 mm grids.
 conclusion is that 2 mm grids are required for IMRT procedures,
especially in high-dose gradient areas.
IV. Simulation Imaging and Planning
 D. Treatment Planning
 4. Bioeffect-based treatment planning
 NTD derived from conventional RT unlikely to be
applicable to SBRT
 Bioeffect measures (BED/ NTD/ EUD) required to rank
and compare SBRT plans with conventional plans
IV. Simulation Imaging and Planning
 D. Treatment Planning
 5. Normal Tissue Dose Tolerance
 Recommendation: Normal tissue dose tolerance in the
context of SBRT still evolving , limited experiences to
draw recommendations
IV. Simulation Imaging and Planning
IV. Simulation Imaging and Planning
IV. Simulation Imaging and Planning E
 E. Treatment plan reporting
 prescription dose/ ICRU reference point / number of
fractions/ total treatment delivery period/ target
coverage
 plan conformity
 heterogeneity index
 dose fall-off outside of target
 notable areas of high/ low dose outside of PTV
 dose to OARs
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
 B. Image-guided localisation
 For SBRT, image guided localisation techniques
should be used to guarantee the spatial accuracy of
delivered dose distribution
 gantry mounted kV units capable of fluoroscopy,
radiographic localisation and cone beam imaging
 implantation of fiducials
 ultrasound imaging
 radiofrequency tracking
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
 C. localisation, tumour tracking and gating
techniques for respiratory motion
management
 1. Image-guided techniques
 Cone beam imaging with acquisition
time >60s
 fast CT less ideal because position of
tumour may be captured at random
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
 C. localisation, tumour tracking and gating
techniques for respiratory motion management
 2. Optical tracking techniques
 stereoscopic infrared cameras and video
photogrammetry used to track 3D coordinates of
points on patient’s skin
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
 C. localisation, tumour tracking and gating
techniques for respiratory motion management
 3. Respiratory gating techniques
 delivery of dose at certain phases of
breathing
 issue of reproducibility
 recommend patient-specific tumour motion
assessment for thoracic/ abdominal targets
V. Patient Positioning, Immobilisation, Target
Localisation and Delivery
 D. Delivery data reporting
 report that QA process is in use and proper
documentation for accurate treatment delivery
VI. Special Dosimetry Considerations
 A. Problems associated with dosimetry of small/
narrow field geometry
 an appropriate dosimeter with a spatial resolution of
~1mm or better
 maximum inner diameter of a detector should be
<half the FWHM of smallest beam measure
VI. Special Dosimetry Considerations
 B. Problems associated with small-field
heterogeneity calculations
 when target is surrounded by low-density tissue
 Monte Carlo precalculated dose-spread kernels and
employing convolution/ superposition techniques
 AAPM Task Group 65 recommend inhomogeneity
corrections be used for patient dose calculation
VII. Clinical Implementation of SBRT
 Critical steps involved
1. establish scope of program
2. determine treatment modality
3. equipment requirements
4. personnel needed
5. acceptance/ commissioning
6. establish work flow guidelines/ reporting/ QA
7. conduct personnel training
VII. Clinical Implementation of SBRT
 A. Establishing the scope and clinical Goals
 1. Equipment considerations
 integration of treatment machines with pre-existing
planning system and imaging localisation
VII. Clinical Implementation of SBRT
 A. Establishing the scope and clinical Goals
 2. Time and personnel considerations
 additional physicist involvement
VII. Clinical Implementation of SBRT
 B. Acceptance, commissioning and QA
 acceptance test procedures by vendors
 commissioning tests developed by physicists
 QA procedures for both treatment and patient
VII. Clinical Implementation of SBRT
 C. Patient safety and the medical physicist
 recommend one medical physicist to be present
throughout first treatment fraction and available for
subsequent fractions
VII. Clinical Implementation of SBRT
 D. Quality process improvement: Vigilance in the
error reduction process in the treatment planning
and delivery process
 regular review of existing QA procedures with the
objective of assessing and critiquing the current QA
practice
VIII. Future Directions

incorporation of strategies for the adaptive conformation of treatment
fields

incorporation of bioeffect knowledge into treatment process

incorporation of improvements in small field dosimetry performance in
clinical treatment planning system

incorporation of chemotherapy

incorporation of molecular imaging

incorporation of tumour-motion effects into the treatment planning
and the methods of evaluation for the delivered SBRT dose to a
dynamic target

volumetric modulated arc therapy

proton and heavy ion therapies
Goldmine