L7- Principles of Isodose Planning (Treatment Planning)

Treatment Planning

This process involves the radiation oncologist, medical physicist/dosimetrist.

Treatment Planning

will draw/contour the treatment fields

Treatment Planning

Involves designing of the field of radiation therapy treatment

Treatment Plans

are the blue print for treatment delivery.

Treatment Planning System (TPS)

is the software used in radiation therapy to design, calculate, and optimize how radiation dose is delivered to a patient.

Treatment Planning System (TPS)

ensures treatment quality. A great machine is technically useless if the plans are not great and acceptable

Forward Planning

this treatment planning system is used in 2D, 3DCRT

Inverse Planning

this treatment planning system is used in IMRT, VMAT

Inverse Planning

Planner sets goals → system optimizes

Forward Planning

Planner manually adjusts beams

Source-Axis-Distance

The distance from the source of radiation to axis of rotation of the treatment unit

Source-Axis-Distance

It involves isocentric technique(FixedSADtechnique)

Source-Axis-Distance

Source-Skin-Distance

2 Methods of Radiotherapy Planning Setup

Source-Skin-Distance

The distance from the source of radiation to the patient’s skin.

Source-Skin-Distance

It involves non-isocentric technique (SSD technique).

Fixed SAD technique

Also called isocentric technique

Fixed SAD technique

the axis of machine rotation is place on the target volume

Fixed SAD technique

Gantry of the machine can be rotated to any angle while target remains within the field boundaries.

Fixed SAD technique

Can make a machine rotate round the tumor in complete circle and partial circle

partial circle (arch therapy– 180 degrees)

treat multiple stationary fields directed at the target from any angle

rotation therapy- 360 degrees

complete circle

arch therapy– 180 degrees

partial circle

Fixed SAD technique

the patient (lying on the patient table) is move to adjust SSD

skin mark (tattoo)

the only reference in Fixed SAD technique

Fixed SAD technique

use in single field technique

Fixed SAD technique

The distance from the source surface of the patient is kept constant for all beams.

Single field treatment

Treatment through a single photon field is rarely acceptable except for superficial targets such as the internal mammary and supraclavicular nodes or shallow tumors in an extremity

Single field treatment

Only used in cases where tumor is approximately less than 5 10cm deep from the skin surface.

single posterior field technique

Tumors in and near the spinal cord are often treated through a

reasonably uniform

Single Treatment Field

Criteria of Acceptability:

Dose distribution within the tumor volume should be ___

excessive

Single Treatment Field

Criteria of Acceptability:

The maximum dose to the tissue in the beam should not be ____

near or beyond tolerance

Single Treatment Field

Criteria of Acceptability:

Normal critical structures in the beam should not receive doses ____

parallel opposed

refers to two identical beams aimed toward each other from exactly opposite direction

Parallel opposed field treatment

These are probably most used field arrangement. They are most often used in metastatic disease in various sites and are also frequently employed in treating large fields

Parallel opposed field treatment

This field arrangement result in uniform dose

Parallel opposed field treatment

Best for head, neck, andlunglesions

Parallel opposed field treatment

what treatment is used when the target is uncertain

Parallel opposed field treatment

what treatment is used when the target volume extends throughout the area to be treated

Parallel opposed field treatment

what treatment is used when multiple fields are impossible to set-up

Parallel opposed field treatment

Advantages

1. The arrangement is simple to set-up and more reproducible

2. The risks of a tumor miss are reduced, particularly in uncooperative patients

Beam arrangement

is the incidental irradiation of large volumes of normal tissues situated within the fields, between the target and the skin surface. Therefore, the entrance/exit point of the two beams can be quite high.

Multiple-field treatment

It was clear that the dose in the tissues near the entrance/exit point of the two beams can be quite high. These high-dose areas can be avoided by using a multiple field arrangement in which all beams encompass the target but include different areas of surrounding normal tissues.

Multiple-field treatment

As the number of field increases, the dose in any given area of normal tissue decreases

Multiple-field treatment

Includes various techniques such as Four-field technique and Wedge Pair technique, rotation therapy

Four-field technique

One commonly used technique is two sets of opposed fields at right angles

Four-field technique

This is often referred to as a box technique- the name pertains to the shape of the resulting high-dose area

high dose box shaped region.

A technique of four beams(two opposing pairs at right angles) producing a relatively ___

Four-field technique

This arrangement is used most often for treatments in the pelvis, where most lesions are central (e.g. prostate, bladder and uterus)

diamond-shaped

As an alternative to the four-field box technique, two sets of opposing fields can be angles and high-dose area becomes

Diamond shaped field technique

is not very useful when centrally located prostrated or gynecologic tumors are treated, because a larger volume of bladder and rectum, is also within the high dose of area

wedge filters

are commonly used to improve dose uniformity toward the target volume

physical wedge

is usually constructed from a high-density material, such as lead or steel, which attenuates the beamprogressively across the entire field.

Wedges

were originally designed to be used in the treatment of small, shallow tumors where only two fields, separated by less than 180 degrees are used

Rotational technique

It produce a relatively concentrated region of high dose near the isocenter but can also irradiate a greater amount of normal tissue to lower doses.

Rotational technique

Beam continuously moves around the patient.

Rotational technique

Best suited for small deep- seated tumors

SRS frame

refers to an immobilization and registration device physically attached, usually by pointed screws, to the patient's cranium.

Small target, narrow beams

High dose is focused to where beams intersect over the target

Large Target, Broad Beams

Increased beam overlap beyond target boundary