site specific ART Flashcards
bladder ART - clinical problem
- Organ motion
- Bladder is a mobile, hollow organ that can change significantly in size, shape and position during treatment
- Leads to use of generous margins (2-3cm) and resultant irradiation of large amounts of surrounding healthy tissue
- Dose limiting toxicity to small bowel and bladder
itself
- Dose limiting toxicity to small bowel and bladder
prescribed dose to the bladder
50-66Gy
Bladder ART - IGRT
- Leads to marked reduction in required margins
- without correction 2cm margin required to ensure 95% of CTV covered – with IGRT margin isotropically reduced to 1.2cm
- However bladder shape and size can also change between fractions
- This is where adaptive radiotherapy approach is utilised
bladder ART - online ART
- pre treatment daily CBCT
- selection of the most appropriate ‘plan of the day’ for the day
bladder ART - offline ART
- adaptive PTV is delineated from the first 5 CBCTs
- utilisation of patient specific margins
prostate ART - clinical problems
- the size, shape and the motion of the prostate is highly dependent on the neighbouring structures (eg. bladder and rectum filling)
- can lead to under dose or over dosage of prostate or overdosing of bladder and rectum –> increased side effects
prostate ART - offline ART
- delivered dose and the variation of organs of interest is accounted for in the planning objective function –> dose distribution accomplished in the adaptive plan is optimised for the remaining treatments
prostate ART - online ART
- CBCT is suboptimal for prostate IGRT due to poor soft tissue contrast
- the MRI Linac enhances the online image guidance capability and subsequently improve treatment accuracy
lung ART - clinical problem
- NSCLC has poor prognosis
- dose escalation shows promising results (improved loco-regional control and survival), however dose escalation is restricted by surrounding dose limiting structures
lung ART - affect of motion
- is very patient dependent and can vary from <1cm to >2cm
- Affects accuracy of tumour delineation
- Potential of increased side effects
- Potential of tumour moving in and out of treatment field
- Bones good surrogates for nodal disease but may lead to misalignment of primary tumour
lung ART - ART assists to improve
- target delineation and margin selection
- Treatment delivery techniques
- Volumetric imaging during treatment responding to tumour and surrounding tissue changes
- ART for dose maintenance
- ART for normal tissue sparing
- Adaptation of treatment plan due to biological and functional response
- ART for dose escalation
lung ART - treatment delivery
- Active motion compensation techniques
- Gating
- Breath control
- Tumour tracking
- Techniques adapt the treatment to maintain constant target position in the beam’s eye view when the beam is on
lung ART - gating + methods
- imaging and treatment devices are periodically turned on and off, in phase with the patient breathing pattern, in order to restrict the range of positions of the tumour and internal anatomy during imaging and radiation delivery
- managing a long and reproducible breath hold
- real time monitoring of free breathing
lung ART - tumour tracking
Dynamically shifting dose in space so as to follow the tumour’s changing position during free breathing
tumour tracking methods should be able to…
- identify the tumour in real time
- anticipate tumour motion to allow for time delays in beam response
- reposition the beam
- adapt dosimetry to allow for changing lung volume and critical structure locations during breathing cycle
lung ART - PET FDG
- FDG-PET increasingly used to monitor tumour response in NSCLC patients
- Quantitative assessment of therapy-induced changes in tumour FDG uptake may allow prediction of tumour response and/or radiation- induced lung toxicity
- Early identification of non-responding patients or patients at high risk for radiation-induced lung
toxicity has potential to reduce side effects and costs of ineffective or toxic treatment
lung ART - SPECT
- assess lung function
- Can be used to design and adjust treatment plan to limit dose to functional, healthy lung tissue
lung ART - ventilation and perfusion scans
Ventilation - the movement of air between the atmosphere and alveoli and the distribution of air within the lungs to maintain appropriate concentrations of oxygen and carbon dioxide in the blood
Perfusion - The movement of blood through though the pulmonary capillaries
Can be used before, during and after treatment to design, adapt and assess treatment
H&N ART - clinical problems
- tumour size and shape change
- change in OAR size and shape
- patient anatomy change (eg. weight loss)
- post operative changes (oedema)
H&N ART - impacts
- Changes can have detrimental impact on dose distribution
- Inadequate coverage of tumour volume by prescribed dose
- OAR volumes exceeding tolerance dose
- Dosimetric impact –> clinical impact
- Potential loco-regional recurrence
- Increased severity of side effects
