OAR Delineation in Head and Neck Cancers

Mayur Mayank

25.05.2015

ICRU 50

Organs at Risk : These are normal tissues whose radiation sensitivity may significantly influence the treatment planning and/or prescribed dose.

Divided into 3 classes :

1. Class I : Radiation lesions are fatal or result in severe morbidity.

2. Class II : Radiation lesions result in mild to moderate morbidity.

3. Class III : Radiation lesions are mild, transient, and reversible, or result in no significant morbidity.

Brainstem

Temporal lobe

Eyes and lens

Optic Nerves and Optic Chiasm

Pituitary

Temporomandibular Joint

Inner Ear

Middle Ear

Mandible

Parotids

Submandibular glands

Spinal cord

Pharyngeal Constrictors

Brachial Plexus

Cranial Nerves IX-XII

Oesophagus

Thyroid

Good Planning CT Good Immobilization setup

Contrast imaging

3mm slice thickness or smaller

MRI fusion if required

Optimal CT window settings [Centre (HU) and width (HU) values] used to delineate the OARs Brain: C35, W100

Bone: C450, W1,600

H&N: C35, W350

Parotid: C840 , W370

RTOG Contouring guidelines Cranial Nerves IX-XII

Brachial Plexus William H. Hall et al. ; International Journal of Radiation Oncology*Biology*Physics, Volume 72,

Issue 5, 1 December 2008, Pages 1362-1367

Salivary Glands Van de Water et al. ; Radiotherapy and Oncology, Volume 93, Issue 3, December 2009, Pages 545-

552

Swallowing Apparatus Piet Dirix et al. ; International Journal of Radiation Oncology*Biology*Physics, Volume 75, Issue 2,

October 2009, Pages 385-392

Optic Nerves and Chiasm Charles Mayo et al. ; International Journal of Radiation Oncology*Biology*Physics, Volume 76, Issue

3, Supplement, 1 March 2010, Pages S28-S35

Temporal lobe and Ear

Ying Sun et al. ; Radiotherapy and Oncology, Volume 110, Issue 3, March 2014, Pages 390-397

Identify and contour C5, T1, and T2.

Identify and contour the subclavian and axillary neurovascular bundle.

Identify and contour anterior and middle scalene muscles from C5 to insertion onto the first rib.

To contour the brachial plexus OAR use a 5-mm diameter paint tool.

Start at the neural foramina from C5 to T1; this should extend from the lateral aspect of the spinal canal to the small space between the anterior and middle scalene muscles.

For CT slices, where no neural foramen is present, contour only the space between the anterior and middle scalene muscles.

Continue to contour the space between the anterior and middle scalene muscles; eventually the middle scalene will end in the region of the subclavian neurovascular bundle.

Contour the brachial plexus as the posterior aspect of the neurovascular bundle inferiorly and laterally to one to two CT slices below the clavicular head.

The first and second ribs serve as the medial limit of the OAR contour.

IJROBP Vol 72, Dec 2008

Parotid Gland

Lateral : Hypodense area corresponding to subcutaneous fat and more caudally by the platysma.

Medial : Posterior belly of the digastric muscle, the styloid process and the parapharyngeal space.

Cranial : Related to the external auditory canal and mastoid process.

Caudal : Protrudes into the posterior submandibular space inferior to the mandibular angle.

Anterior : Masseter muscle, the posterior border of the mandibular bone and the medial and lateral part of the pterygoid muscle.

Posterior : Anterior belly of the sternocleidomastoid muscle and the lateral side of the posterior belly of the digastric muscle.

The external carotid artery, the retromandibular vein and the extracranial facial nerve are prescribed to be enclosed in the parotid gland

Radiotherapy and Oncology Vol 93, Dec 2009

Radiotherapy and Oncology Vol 110, March 2014

Submandibular Gland

Cranial : Medial pterygoid muscle and the mylohyoid muscle

Caudal : Fatty tissue

Anterior : Lateral surface of the mylohyoid muscle and the hyoglossus muscle

Posterior : Parapharyngeal space and the sternocleidomastoid muscle

Lateral : Medial surface of the medial pterygoid muscle, the medial surface of the mandibular bone and the platysma.

Medial : Lateral surface of the mylohydoid muscle, the hyoglossus muscle, the superior and middle pharyngeal constrictor muscle and the anterior belly of the digastric muscle.

Radiotherapy and Oncology Vol 93, Dec 2009


IJROBP Vol 75, Oct 2009

IJROBP Vol 75, Oct 2009

Should be contoured on the Brain window

The lateral boundary of the temporal lobe should be delineated on the soft tissue window

Should include the hippocampus, parahippocampal gyrus and uncus

The basal ganglia and insula are located anteriorly and superiorly to the hippocampus and parahippocampal gyrus and should be excluded

Delineation is better when fused with MRI


Middle ear : The tympanic cavity and bony part of the Eustachian Tube (ET) should be contoured individually

The tympanic cavity is delineated

Laterally by the tympanic membrane, defined by the ligature between the two bony structures with an increased density along the anterior and posterior walls of the most medial aspect of the outer air canal

The sharp narrow region connected anteriorly to the ET, and the interface between the temporal bone and air at all other walls

Inner ear : Delineation of the cochlea and Internal Auditory Canal (IAC) should be done individually

The cochlea is located anteriorly to the IAC


1: Cochlea (basal turn)

2: Tensor tympani

muscle

3: Manubrium of

malleus

4: Facial nerve canal

5: Stapedius muscle

6: Round window


RTOG Contouring atlas

Cranial Nerves IX-XII : http://www.rtog.org/CoreLab/ContouringAtlases/HNAtlases.aspx

http://www.rtog.org/CoreLab/ContouringAtlases/HNAtlases.aspx









Health & Medicine

OAR Delineation in Head and Neck Cancers