RT225 Special Procedures pt 1

• Stereotactic external beam irradiation (SEBI)

• Total body irradiation (TBI)

• Total skin electron irradiation (TSEI)

• Intraoperative radiotherapy (IORT)

• Endorectal irradiation (Endocavitary rectal irradiation)

• Conformal radiotherapy

• Intensity modulated radiotherapy (IMRT)

• Image guided radiotherapy (IGRT)

Special dose delivery techniques

• Stereotaxy

• Image guided radiotherapy (IGRT)

• Respiratory gated radiotherapy

• Adaptive radiotherapy (ART)

• PET/CT/MRI/US fusion

Special target localization techniques in radiotherapy

Focal irradiation

Stereotactic irradiation comprises ___ techniques that use multiple, non-coplanar photon radiation beams and deliver a prescribed dose of ionizing radiation to pre-selected and stereotactically localized lesions

Brain

Lesions are primarily in the ___

1960s and 1970s

Time when stereotactic irradiation was considered an obscure irradiation technique

• Through a stereotactic implantation of radioactive sources (stereotactic brachytherapy)

• With one or several external radiation sources (stereotactic external beam irradiation)

Dose in stereotactic irradiation may be delivered:

• Stereotactic radiosurgery

• Stereotactic radiotherapy

With regard to dose fractionation SEBI is divided into:

Stereotactic Radiosurgery

In which the total dose is delivered in a single treatment session

Stereotactic Radiotherapy

In which the total dose is delivered in multiple fractions, similarly to standard radiotherapy

10-50 Gy

Total prescribed doses are of the order of __ - __ Gy

1cm³ to 35cm³

Planning targets are small, with typical volumes ranging from __ to __

±1mm and ±5%

Requirements for positional and numerical accuracy in dose delivery are __ and __, respectively

• Cobalt-60 gamma rays

• Megavoltage x rays

• Proton and heavy charged particle beams

• Neutron beams

Useful radiation beams for external beam radiotherapy

• Accurate determination of the target volume and its location with stereotactic techniques

• Calculation of 3D dose distributions inside and outside the target

• Calculation of dose-volume histograms (DVHs) for the target and specific sensitive organs surrounding the target

• Dose distributions that conform to target shape and give a sharp dose fall-off outside the target volume

• Direct superposition of isodose distributions on diagnostic images showing the anatomical location of the target

Physical requirements for radiosurgery

• Accurate knowledge of the total dose and fractionation scheme required for treatment of a particular disease

• Accurate positional (within ±1mm) delivery of dose to the predetermined target

• Accurate numerical (within ±5%) delivery of dose to the predetermined target

• Low skin dose (to avoid epilation) and low eye lens dose (to avoid cataract formation)

• Low or negligible scatter and leakage dose to radiosensitive organs (to avoid subsequent somatic and genetic effects)

Clinical requirements for radiosurgery

• Functional disorders

• Vascular lesions

• Primary benign tumours

• Primary malignant tumours

• Metastatic tumours

Five categories of diseases treated with stereotactic irradiation

Arterio-venous malformation (AVM)

A mass of abnormal blood vessels in the brain consisting of a “nidus” through which the arteries connect directly to veins instead of through capillaries

• Surgery

• Embolization

• Stereotactic radiosurgery

Treatment options for Arteriovenous malformation (AVM)

• Stereotactic Frame

• Imaging Equipment (CT, MRI, and DSA)

• Target localization software

• Treatment planning system

• Appropriate radiation source and radiosurgical treatment technique

Equipment for stereotactic radiosurgery

Stereotactic Frame

Defines a fixed coordinate system for an accurate localization and irradiation of the planning target volume (PTV)

Imaging Equipment

With which the structures, lesions, and PTVs are visualized, defined, and localized

Target Localization Software

Used in conjunction with the stereotactic frame system and imaging equipment to determine the coordinates of the target in the stereotactic reference system

Treatment planning system

Calculates the 3D dose distribution and superimposes it onto the patient’s anatomical information

Mussen, 1918

The first human stereotactic frame was designed by __ and built around __

Lars Leksell, 1951

Combined use of stereotaxy and irradiation was introduced by ___ in __ in Stockholm, Sweden

Radiosurgery

Leksell also coined the term ___ to describe the technique of stereotactic irradiation with a high, single dose of radiation

• Orthovoltage x-rays from x-ray machines

• Protons and heavier ions from cyclotrons and synchotrons

• Gamma rays from the Gamma Knife (201 gamma ray beams)

• Megavoltage x-rays from linacs (isocentric linacs and CyberKnife)

• Neutron beams from cyclotrons

Radiotherapy ionizing radiation beams that were also found useful in radiosurgery

Gamma Knife, 1968

Leksell also designed and developed the ___ in ___ and the machine is still available commercially today

2005, 100

In ___, there were over ___ Gamma Knife machines in clinical operation around the world

Isocentric Linacs, 1980s

Megavoltage x-ray beams from ___ are used in radiosurgery since the mid ___

• 200 kVp orthovoltage x-rays

• Protons from cyclotron

• Gamma Knife (179 cobalt-60 sources)

• Megavoltage x-rays from linear accelerators

Combined use of stereotaxy and irradiation:

• Multiple convergic arcs

• Dynamic rotation

• Conical rotation

• Cyberknife (miniature linac on robotic arm)

• Tomotherapy (miniature linac on CT gantry)

Linac based stereotactic radiosurgery:

Gamma Knife, isocentric linacs and Cyberknife machines

Contermporary radiosurgery is carried out mainly with Gamma Knife machines, but a significant number of procedures is also carried out with modified ___ and ___

Robotic Arm

CyberKnife incorporates a miniature linac mounted on a ___

1990s, 2005, 50

Cyberknife is in clinical operation since the mid ___ and in ____ there were over __ of these machines in clinical operation around the world

Gamma Knife (Gamma unit)

A radiosurgical device that has been associated with, and dedicated to, radiosurgery for the past four decades

201 cobalt-60 sources, 1.1 TBq (30Ci)

Gamma unit incorporates ___, each source with an activity of ___

201, 40cm

Gamma Knife sources produce __ circular gamma ray beams directed to a single focal spot at an SAD of __

• Source core

• 201 cobalt-60 sources

• Shutter mechanism

• Helmet and secondary collimators

• Treatment couch

Main components of the Gamma Knife:

• 4mm

• 8mm

• 14mm

• 18mm

Collimator helmets are available producing circular fields with diameters of: