Lecture 23 - B&ST Contouring

ONCOL 306 - Imaging. University of Alberta

what 5 factors result in an increased risk of local recurrence for sarcomas?

1. surgical margins

2. grade

3. tumor size

4. anatomic location

5. histopathologic subtype

What is the major and most consistent factor to predict local recurrence of sarcomas?

resection margin

what three factors are considered when determining the role for radiation therapy

1. consequence of recurrence

2. effect on functional outcome

3. morbidity of surgical salvage

the addition of RT to surgery reduces the risk of local recurrence compared to …

surgery alone

Low grade, superficial sarcomas less than 5 cm in size can be managed with _____ if wide margins of ____ cm can be acheived

surgery alone, margins of 1 cm

tumors > 5 cm, deep or high grade require _______ prior to surgery

radiation

is preoperative or postoperative radiation preferred for sarcomas, and why?

pre-operative radiation is preferred as there is a trial showing less long term toxicity

how long after RT should we wait before surgery

4-6 weeks: you get more bleeding and complications if you wait less than 4 weeks.

what is the most important modality for treating soft tissue sarcomas?

surgery with a good resection margin

what is the D/F for pre-operative RT?

5000 cGy / 25 f

what is the D/F for post-operative RT

6600 cGy / 25 f

• we have 1600 cGy boost to where tumor bed was

describe a general set-up for a STS in the upper extremity

custom set-up as per mould room OR akimbo in vac bag on 6 cm headrest, knee rest

is there any prep required for STS in extremeities

no

what does the pilot scan for STS of extremity include

5 cm above and below tumor / scar, and one joint must be included

is a mock set-up done? who is present and why is it done

yes: dosimetrist, medical physicst, RO, therapist are involved

• the positioning of the patient is highly complex so the plan needs to be evaluated that it is feasibly possible

how many tattoos are there in an STS upper extremity? where is it placed

one

• AP tattoo on arm

the lateral reference on the shell/vac bag is matching _____ level

contour level

the AP straightening line on the shell / vac bag is in line with ____

the tattoo

what is included in an STS GTV? What image is it contoured on?

visible tumor volume

• contour on T1 sequence with gadolinium contrast

what is the formula for the CTV for an STS? what do we crop out?

GTV + 4 cm margin sup/inf and 1 cm radially

• crop out bone and 5 mm inside the body contour to avoid treating circumference resulting in lymphedema

what image is the STS CTV contoured on?

T2 to show the edema

what is the formula for the STS PTV? do we crop the structure?

PTV = CTV + 1 cm margin isotropically

• do not crop structure

what is the formula for STS PTV_OPT? do we crop?

PTV_OPT = CTV + 1 cm margin isotropically

• crop inside of body with 5 mm margin!

what are the two EBRT techniques to treat an STS extremity

• 3D-CRT (AP/PA etc): if we don’t want to elevate/move contralateral extremity out of way

• VMAT: will need to elevate/move contralateral extremity out of way

list two acute side effects of EBRT in STS

Radiation dermatitis – erythema, dry or moist desquamation of the skin in the treated limb.

Edema (limb swelling) – inflammation and fluid accumulation in the treated extremity during treatment.

Fatigue

list two chronic toxicities of EBRT in STS

Fibrosis – stiffening and thickening of soft tissues, which can limit limb mobility.

Lymphedema – long-term swelling of the extremity due to damage to lymphatic drainage.

Radiation induce malignancy

low grade localized / superficial STS is managed with …

surgery alone

all other localized STS are managed with …

RT (often pre-op) and surgery

what is the goal for treatment for STS patients

cure