Classes of Contouring Tools
- Manual
- Image greyscale interrogation
- Body atlas based methods
- Statistical Shape modelling
ART Limitations
• Time and resource intensive process – financial burden
• More clinical outcome studies needed
• Appropriate patient selection
• What is the optimal number of replans? – Clinical benefit vs time and resources spent
• Consensus guidelines lacking
o Online vs Offline vs Hybrid
o Technical and QA considerations
• Patient-specific margins
• Plan of the day (multiply planning and staff training & education intensive)
• Extensive re-contouring required (more automation)
Speciality Image Sets
- feature that combines 2 or more image sets to make a specialty image:
Maximum Intensity Projection
Minimum Intensity Projection
Average Intensity Projection
What is MIP?
- maximum image projectory
- displays the max no. of all pixels at the same locatin over the respiratory cycle
- shows entire extent of tumour motion
- caution for tumour close to diaphragm and chest wall
What is MinIP?
- minimum image projectory
- displays the min no. of all pixels at the same sptial location over the respiratory cycle
- shows where some of the tumour always is
- useful for liver tumours that present at low density
What is AvgIP?
- average image projectory
- displays the avg no. of all pixels at the same sptial location over the respiratory cycle
- considered appropriate for planning which reduces the need for additional scan and thus dose
Define sterotactic
- high precision image guided dose delivery (1mm, 1 degree)
- highly conformal dose with steep dose drop off
- intrafraction motion management
What is SBRT?
- sterotactic body radiotherapy
- dose escalation for targets close to OAR (extracranial e.g. spine, prostate)
- 1 to 5 #
- > 8Gy per fraction
What is SABR?
- sterotactic ablative body radiotherapy
- for ablation (extracranial e.g. liver, lung, renal)
- 1 to 5 #
- > 8Gy per fraction
What is SRS?
- sterotacitc radiosurgery
- historically intracranial but can be extracranial
- single fraction
- 12 to 90+ Gy per fraction
- can use gamma, cyber or linac
What is SRT?
- stereotactic radiotherapy
- for large cranial lesions not suited for SRS (e.g. post operative cavities)
- 2 to 5 #
- lower BED then SRS
What does conventional dose fractionation allow?
- normal cell repair
- re-population after RT
- re-distribution in cell cycle
- re-oxygenation
- radiosensitivity
What body areas move?
- skeletal/muscle: stabilisation
- respiratory (lungs, ribs, abdomen): 4DCT, breath hold or gating
- cardiac: remains
- peristalsis: compression
- bladder and bowel: preparation or catherisation
Abscopal effect?
Localised irradiation perturbs the organism as a whole with consequences that can either be beneficial or detrimental
Motion Management strategies?
- Breath hold – DIBH / EEBH (end expiratory breath hold)
- Elekta BodyFix
- Compression Belt
- Compression Plate
- Gating
Dose Response graph?
draw graph
Rapidly proliferating cells, high a/b?
- Not very sensitive to changes in fraction size or dose rate
- True for most types of tumour
- Evidence now that this is not true for prostate tumours
Slowly proliferating cells, with low a/b?
- Plenty of repair capability
- Very sensitive to dose/fractionation
- Late responding normal tissues are therefore sensitive to large dose / fraction
Advantages of Brachy
- Outpatient treatment
- Dose optimisation - adaptive B/T planning
- Reduced radiation exposure for staff under normal situations
- More stable positioning
- Smaller applicators
- High dose rate = short treatment time
Disadvantages of Brachy
- More complex treatment and planning techniques
- Compressed time frame for planning
- Greater potential for error due to a much higher dose being delivered over a short timeframe
- Potential for high radiation dose to staff and patient with source failure
