H&N I Patient Outcomes Flashcards
Spinal Cord - QUANTEC myelopathy
With conventional fractionation of 2Gy per day including the full cord cross section, a total dose of 50Gy, 60Gy and 69Gy are associated with a 0.2, 6, and 50% rate of myelopathy
Spinal Cord - in cases where bilateral cervical lymph nodes are irradiated
- Lhermitte’s Syndrome (2-4 months) -> tingling in the extremities electric shop type tingling, very common late effect in H&N tx
- Chronic progressive myelitis
- DVC: 50Gy in 2Gy/# if length of cord <10cm
- Dmax as serial organ BUT some animal studies show regeneration of cord
What is the spinal cord tolerance affected by?
- hyperfractionation (reduced by 10-15%)
- patient age
- neurotoxic chemotherapy agents (such as platinum-based drugs)
- pre-existing damage (whiplash/cord damage)
Brainstem - QUANTEC
The entire brainstem may be treated to 54Gy using conventional fractionation with limited risk of severe or permanent neurological effects. Smaller volumes of the brainstem (1-10cc) may be irradiated to maximum doses of 59Gy for dose fractions < 2Gy. The risk appears to increase markedly at doses > 64Gy. However, there is insufficient information to determine whether there is a further volume effect.
Dmax < 54Gy
Optic apparatus - QUANTEC
Dmax of 50Gy is close to a “near zero” incidence.
The incidence of radiation induced optic neuropathy (RION) is unusual for a Dmax <55Gy, particularly for fraction sizes <2Gy.
The risk increases (3-7%) in the region of 55-60Gy and becomes more substantial (>7-20%) for doses >60Gy when fractionations of 1.8-2.0Gy are used.
Larynx and Pharynx - QUANTEC
From the published data, it seems reasonable to suggest the mean non-involved larynx dose to 40-45Gy and limiting the maximum dose to <63-66Gy if possible, according to the tumour extent to reduce risk of laryngeal oedema and vocal dysfunction.
The limited available data have suggested that minimising the volume of the pharyngeal constrictors receiving 60Gy and reducing, when possible, the volume receiving 50Gy is associated with reduced dysphagia and aspiration.
A separate question is whether such sparing is safe clinically, taking into account the uncertainties in target delineation
Salivary Glands - QUANTEC
Severe xerostomia (long-term salivary function <25% at baseline) can usually be avoided if at least one parotid gland has been spared to a mean dose of less than 20Gy or if both glands have been spared to a mean dose of less than 25Gy.
When it can be deemed oncologically safe, submandibular gland sparing to modest mean doses (<35Gy to see any effect) might reduce xerostomia symptoms.
The mean dose to the oral cavity (containing minor salivary glands) has been found to be an independent risk factor in some data sets but not others, probably because of technique differences.
Larynx and Pharynx
Larynx:
V50 < 27%, mean dose <44Gy and Dmax <66Gy
Pharynx:
Pharyngeal constrictors: Mean dose <50Gy
Cochlea - QUANTEC
For conventionally fractionated RT, to minimise the risk for sensorineural hearing loss (SNHL), the mean dose to the cochlea should be limited to <45Gy (or more conservatively <35Gy). Because a threshold for SNHL cannot be determined for the present data, to prevent SNHL the dose to the cochlea should be kept as low as possible.
SNHL means that there is damage to either the neural pathways from the inner ear to the brain or to the hair cells in the inner ear. Patients who experience SNHL state that they can hear speech but cannot understand it, particularly in the presence of background noise.
Almost all DVCs for cochlea is Dmean<35Gy for patients on cisplatin and RT together.
Skin and Lips
Skin/lips as critical structures.
- skin dose is influenced by immobilisation mask, oblique incidence of beams, high MU/segment, plan optimisation trying to influence photon fluence to the build-up region to achieve PTV prescription dose.
- skin should be contoured if distance between PTV and skin is less than 1cm
Eye and Lacrimal Gland
Lens:
- Cataract Formation (Dmax <6-10Gy, otherwise 2/3 years to cataract)
Lacrimal Gland:
- Starts with ‘dry eye syndrome’
- opacification (cloudy vision), ulceration, perforation of cornea
- predisposition to bacterial infection
- Millon et al: Starts at Dmax 30Gy, doses exceeding Dmax 55-60Gy, all patients affected
Mandible
Dose to mandible should not exceed a Dmax of 70Gy
RT creates a hypoxic environment resulting in devascularisation of the mandible
supply of nutrients to repair the cellular damage and breakdown of collage formation within the irradiated bone is then compromised
this can lead to osteoradionecrosis (ORN) of the mandible
Hair Follicles
Permanent alopecia (persisting for >12 months post RT)
for H&N cancers, exit dose is an issue, particularly for nasopharyngeal cancers (right at the occiput)
Lawenda et al found that radiation dose only correlated with permanent alopecia in cranial irradiation
The D50, the follicle dose at which 50% of the patients developed permanent alopecia, was estimated to be 43Gy (95% confidence interval, 33Gy-52Gy)
Dmax <46Gy for hair follicles
Pervious history of alopecia or chemotherapy use were approaching statistical significance
Age, gender, family history of baldness, beam energy, smoking pack years and diabetes had no effect on permanent alopecia in this multivariate analysis
Positioning and Immobilisation H&N
- Precise positioning and reproducibility
- comfort
- stabilisation
- restraint to prevent motion
- Neutral head position - majority of cases
- forehead and chin lie in the same plane
- head elevation required to achieve this, varies from patient to patient and greatly depends on chest separation
- Extension - e.g. parotid, larynx
- Immobilisation device e.g. thermoplastic mask
- reproducible head position
- restrict motion
- placement of set-up marks
- if possible, cut out if unwanted bolus effect
- head supports / neck rest
- bite block / dental impression
- reduce volume of oral mucosa in field
