L8- Principles of Isodose Planning (Treatment Planning 2)

CRU Reports50/62

recommendations for target delineation in which the target volume is separated into three distinct regions:

Gross tumor volume(GTV)

denotes the demonstrable tumor

Clinical Target volume (CTV)

denotes the GTV and subclinical disease (region to account for uncertainties in microscopic tumor spread)

Planning Target Volume (PTV)

denotes the CTV and includes margins for geometric / position uncertainties. Usually, 1.5 cm physical margin are set around the CTV

Treated volume

is the volume of tissue enclosed by an isodose surface, selected and specified by the radiation oncologists as being appropriate to achieve the purpose of treatment.

Treated volume

is always larger than the PTV and usually has a simpler shape.

Irradiated volume

is the volume of tissue that receives a dose considered significant in relation to tissue tolerance.

Organs at Risk (OAR)

are the healthy tissues/organs placed near the clinical target volume (CTV) whose irradiation could cause damage that would make changes to the radiation therapy treatment plan.

Dose Constraints

Tolerance to ionizing radiation from organs at risk, dependent on radiosensitivity and volume, is one of the main factors limiting the choice of radiation therapy dose.

2DCRT(Two-Dimensional Conventional Radiation Therapy)

refers to the old techniques of radiation therapy where treatments would be planned by defining a limited number of beams with the boundaries delineated on orthogonal x-rays of the patient

2DCRT(Two-Dimensional Conventional Radiation Therapy)

It has been largely replaced by other highly conformal external beam radiation therapies, which use CT images to plan the treatment.

2DCRT(Two-Dimensional Conventional Radiation Therapy)

Beam shaping was limited, and typically simple square or rectangular beams were used. A typical beam arrangement is the four-field box. Due to the low conformity of these treatments, adjacent tissues/organs often fall into the high dose region resulting in treatment side effects. Also, the amount of radiation delivered to the targeted tumor is usually not adequate resulting in less effective treatment

3DCRT(Three-Dimensional Conformal Radiation Therapy)

is a cancer treatment that shapes the radiation beams to match the shape of the tumor.

height and width of the tumor

➢In the past, radiation beams only matched the ____ - exposing healthy tissue to radiation

3DCRT(Three-Dimensional Conformal Radiation Therapy)

uses the targeting information to focus precisely on the tumor, while avoiding the healthy surrounding tissue

3DCRT(Three-Dimensional Conformal Radiation Therapy)

This exact targeting makes it possible to use higher levels of radiation in treatment. More radiation is more effective in shrinking and killing tumors.

CT (computed tomography) scan,

MRI (magnetic resonance imaging)

PET (positron emission tomography) scan

PET-CT scan

The radiologist will take a 3D image of your tumor, often using one of the following imaging methods

IMRT(Intensity-modulated radiation therapy)

➢It is an advanced mode of high-precision radiotherapy that uses computer- controlled linear accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor

IMRT(Intensity-modulated radiation therapy)

allows for the radiation dose to conform more precisely to the three- dimensional (3-D) shape of the tumor by modulating—or controlling—the intensity of the radiation beam in multiple small volumes.

IMRT(Intensity-modulated radiation therapy)

also allows higher radiation doses to be focused on the tumor while minimizing the dose to surrounding normal critical structures

IMRT(Intensity-modulated radiation therapy)

Treatment is carefully planned by using 3-D computed tomography (CT) or magnetic resonance (MRI) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape.

IMRT(Intensity-modulated radiation therapy)

Typically, combinations of multiple intensity-modulated fields coming from different beam directions produce a customized radiation dose that maximizes tumor dose while also minimizing the dose to adjacent normal tissues

IMRT(Intensity-modulated radiation therapy)

Due to its complexity, ___ does require slightly longer daily treatment times and additional planning and safety checks before the patient can start the treatment when compared with conventional radiotherapy.

IMRT(Intensity-modulated radiation therapy)

also has the potential to reduce treatment toxicity, even when doses are not increased.

IGRT(Image guided radiation therapy)

is the use of imaging during radiation therapy to improve the precision and accuracy of treatment delivery

IGRT(Image guided radiation therapy)

patient's position and/or the radiation beams may be adjusted to more precisely target the radiation dose to the tumor.

It is a novel radiation therapy technique that delivers the radiation dose continuously as the treatment machine rotates

VMAT(Volumetric arc radiotherapy)

this technique accurately shapes the radiation dose to the tumour while minimizing the dose to the organs surrounding the tumour

VMAT(Volumetric arc radiotherapy)

works similarly to intensity-modulated radiation therapy (IMRT) in the way the radiation dose is varied throughout treatment

Helical Radiotherapy(Volumetric arc radiotherapy)

IMRT Treatment that combines the principles of CT Scan. Fan beam is used instead of volumetric beams to deliver doses slice by slice. Couch is continuously moving during treatment delivery

Fractionation and Protraction

are the two ways to reduce patient exposure

Fractionation

the total dose to deliver is divided between several sessions

Fractionation

It is characterized by the dose per session and the number of sessions. High dose, with breaks in-between doses

Protraction

The dose is delivered continuously but at a lower dose rate until all of the dose is given

less

✓If the dose is administered over a long time rather than quickly, the effects of that dose will be

same effect

if the time of irradiation is lengthened, a higher dose is required to produce the

intracellular repair and tissue recovery

Dose protraction and fractionation cause a less effect allowing time for

Radiation therapy

is most effective when a tumor is contained, easily accessible, and located away from major organs of the body

Radiosensitive

The decision to treat a tumor with radiation is based on the location of the primary tumor and whether the tumor cells are

Radiocurability

means that the normal tissue-tumor relationship is such that curative doses of radiation can be used without excessively damaging the normal tissue.

Radiocurative tumors

include carcinoma of the cervix, larynx, breast, and prostate. Radiation may be the only therapy necessary for ___

Radiation

only therapy necessary for radiocurative tumors

Palliative Radiotherapy

Offers a quick, inexpensive, and effective way of reducing many of the focal symptoms of advanced, incurable cancer, whether these arise from the primary tumour or from metastatic deposits

Palliative Radiotherapy

It can improve quality of life while being associated with limited treatment burden in terms of both hospitalattendances and side effects

Palliative Radiotherapy

Re-treatment may be possible for recurrent symptoms, but side effects may be greater

Palliative Radiotherapy

a. bone metastases(in up to 70% of patients with advanced cancer)

b. advanced thoracic cancer

c. Malignant spinal cord compression(occurs when vertebral disease compresses the cord, either directly or as a result of vertebral collapse)

d. Brain metastases (occur in 20-40% of individuals with systemic cancer)

Curative Radiotherapy

• Patients with locally advanced head and neck cancer

• Locally advanced pelvic cancers

• Bleeding, pain, and malodor due to skin cancer

Adjuvant Therapy

In order to achieve the most effective cancer curative results, radiation treatment is frequently used as ___ to other treatments.

Pre-operative technique

Sometimes, pre-surgery radiation treatment is administered to shrink the tumor so that it can be surgically removed more easily or make the operation less radical, thereby preserving more normal tissue

Post-operative technique

can be administered to destroy microscopic residual cancer cells left after surgery

Increases

As the energy of the beam increases the depth where the maximum dose occur also ___

Surface (decreases)

As the field size increases the depth where the maximum dose occur shift towards the ____

Build-up region

The distance between the surface and the d_m.

Skin-sparing effect

Because of electron build-up, the skin is spared from receiving the maximum dose

Percentage Depth Dose (PDD)

The ratio expressed as a percentage of the dose at any depth(Dd) along the central axis of the beam to the dose at a reference point (Dmax).

Percentage Depth Dose (PDD)

Applicable for SSD set-up

Tissue-Air Ratio (TAR)

The ratio of the absorbed dose at depth din the phantom (Dd) and the dose in free space at the same point in air (Dfs).

Tissue Phantom Ratio (TPR)

The ratio of the dose at a given point in phantom to the dose at the same point (same SAD) at a fixed reference depth in a phantom

Backscatter Factor (BSF)

he ratio of the exposure rate at the phantom surface (Xo) to the exposure rate in air (X) at the same point with the phantom removed

Backscatter Factor (BSF)

The phantom serves as the scattering medium

Backscatter Factor (BSF)

It is applicable for energies 400kV and below.

Peak Scatter Factor (PSF)

Ratio of the absorbed dose rate (Dmax ) at Dm to the absorbed dose rate in free space (Dfs ) at the same point.

Peak Scatter Factor (PSF)

t is applicable for megavoltage radiation