radiotherapy planning

Question 1

what does 26:05:01 mean

Answer 1

25Gy in five fractions in one week

Question 2

what is the I.C.R.U?

Answer 2

provides universal recommendations for qualities and units of radiotherapy and radioactivity

Question 3

define gross tumour volume G.T.V

Answer 3

“The gross palpable or visible/demonstration extent and location of the malignant growth”
* This involves the actual tumour that can be seen through imaging or surgery.

Question 4

Define clinical target volume CTV

Answer 4

“Tissue volume that contains the G.T.V. and/or sub-clinical microscopic malignant disease”.
* Mirrors the shape of the GTV and is an area surrounding the GTV where there is the risk of metastatic spread which cannot be visibly demonstrated.

Question 5

define planning target volume PTV

Answer 5

“A geographical concept, defined to select appropriate beam sizes and beam arrangements to ensure the prescribed dose is delivered to the GTV”.
* If we can make the PTV conformal it will reduce risk to nearby organs/tissues – Alara.

Ideally, the PTV should be homogenous as heterogeneity can lead to underdosing and overdosing. Therefore, dose heterogeneity should be kept at +7% and -5%

A limitation of the CTV and GTV is that soft tissue will move therefore the PTV accounts for this.

Question 6

define organs at risk (OAR)

Answer 6

“Normal tissues whose radiation sensitivity may significantly influence treatment planning or prescribed dose”.