Superficial lesions with >2 cm margin (6)

• infiltrative
• large (>6 cm)
• high histologic grade
• recurrent
• indistinct margins
• sclerosing BCC or merkle cell

Sup/Post = clear skin

Inf = C2

Ant = 10 mm beyond the most anterior aspect of the brain

Sup: iso @ 20 cm from cranial field (C2); 40 L

Inf: ends at S2

Lat: encompass vertebral bodies

wider inferiorly to encompass neural foramina

MATCH @ anterior edge of the spinal cord

Prostate field margins

(from CTV to PTV)

ANT/SUP/LAT: 1 cm

POST: 0.5 cm

(overall all the smallest margin from GTV)

INF: 0 cm

ISL = [VSD/(VSD +/- difference*)]²

*stand in = subtract

stand off = add

SAD = 100cm (height + margin)

             ----------------------------

            40 cm (max. opening)

• patient factors
• treatment factors
• tumour factors

d = sq. root [SAD² + OAR²]

ISL = (SAD/d)²

Thickness = tissue deficit x  thickness ratio

---------------------------------

density of compensator

1. correct distance
2. attenuation of scatter
3. immobilisation
4. visualisation of the field

Increasing fall off with:

decreasing energy, SSD and FS

Sup: 60 - 150 kV, 10 - 30 SSD, 2-5 mm

Ortho: 150 - 500 kV, 50 SSD, <2cm

LD: lesion diametre, outline of the lesion

FD: the GTV, the LD + the margin

Given Dose: the dose that would be prescribed at 100%

What are the two methods of calculating MU for sup/ortho treatments?

#1: MU = D/ DR(cone, cutout)

#2: MU = D/(DR x BSF ratio)

*BSF ratio = cutout/cone

18/1

35/5

42.5/10

47.5/15

50/20

What are the 2 methods of creating the "dispersed" electron beam?

Scattering foil: high atomic numbers, thin, photon contamination

Scanning: magnetic fields to scan, dosimetry problems, expensive

1. tail (flat lines, higher with higher energies, photon contamination)
2. dose fall off (increases at lower energies)
3. surface dose (increases with energy)
4. build up depth (increases with energy)

• longer plateau at higher energies

6 - 12 MeV 

* too low = bulging

* too high = similar to photons, constriction of 80%

1. oblique surfaces
2. steep changes in contours (stand ins = hot spot out)
3. inhomogeneities (increased photoelectric effect)
4. matching fields (bulging/constrict)

• skin/lip
• post-mastectomy
• mesothelioma
• post. neck nodes
• TSEB (MF patients)

• longer time to treat with the extra MUs needed
• slower fall off (higher PDD) at a further distance - treating areas beyond treatment depth

• feathering
• beam spoiler

autologous: self donor

allogenic: outside donor (usually a relative)

• over disease
• critical structure

• dosimetric
• geometric
• half beam block
• adjacent
• orthogonal

1. motion (breathing)
2. misreading details
3. table movement

1000 cGy

50 cGy/min

1000 - 1200 cGy

50 - 180 cGy/min

*6 hour minimum between fractions

High (treatments such as leaukemia with cancer in the skin)

Achieved: high SSD (= low Dmax), perspex door, other bolus

• sitting (weak, arms shield the lungs)
• standing
• lying (children/infants)

• half-body irradiation
• dispersed bone mets
• single fraction
• helps to increase QoL

• Testing dose distribution in a water tank
• Using TLDs placed on the patient

IR: image fusion

Seg: contouring

Dose Volume histogram

Doesn't show the distribution and location of the dose.

Tumor Control Probability (want it to be low)

Normal Tissue Complication Probability (want it to be high)

X = dose, Y = TCP/NTCP

*want the curves to be as far apart as possible

Conformal Radiation Therapy: a method of treatment often using multiple beams to delivered a very conformed dose distribution

defined by its distribution NOT the technique

(requires 3D viewing)

GTV

CTV (GTV + microscopic spread)

PTV (CTV + IM + setup margin)

EUD = equivalent uniform dose

objective function = penalty given for not reaching EUD objectives

EUD

maximum/minimum dose

DVO = dose volume optimizer: used to optimise fluence when meeting objectives

LMC = leaf motion calculator: used to calculate motion of MLCs (either sliding or static)

1. label the contour overlap section
2. label the PTV ring
3. treat aggressive, spare lightly
4. segment limits (area, number, MU)

• beam number = more conformal (& dose)
• modulation = more conformal (& MU)
• area = lower resolution (& dose gradient and intra-fx motion)

• segment number = more conformal (& tx. time & max. dose)

step: ~700 MU

slide: ~1200 MU

manual hot loading

manual after-loading

remote after-loading

HDR: >12 Gy/hr

LDR: 0.4 - 2.0 Gy/hr

Pd-103

17 days, 5 mCi

DR = [(|''''')(f_med)(A)]/r²  x *

*B(r) or T(r,E)

decrease (ISL, attenuation (source capsule and tissue))

increase (build-up scatter) 

mgm (A,d)

x by dose and / tx. time

x radium equivalent  (rad/iso)

= mCi

1800 cGy/ 3fx

vagina (for recurrence)

long distribution

2600 cGy/4 fx

vaginal fornices, cervix, endometrium

pear shaped (tandem+ring and 2 ovoids)

from the cervical os

A: 2 cm sup, 2cm lat = uterine vessels/ureters

B: 2 cm sup, 3 cm lat = lymph nodes

Esophageal: 1400 cGy/ 3fx 

Lung: 2100 cGy/ 3fx 

(may have multiple sites, obstructive)

*both 1 cm radial to catheter

HDR: 21 Gy/3 fx OR 20 Gy/2 fx

*CT taken after 1st tx., planned on grid

LDR: 14.4 Gy

*planned with US or fluro, <50 cc

Structure

• Staffing (ratios, roles + responsibilities + education)
• Equipment
• Facility

Process (policy and procedures)

Outcome (review past problems, severity and frequency)

Systematic - solve through procedure/staff

Random - can not minimise

Interfx - between fx

Intrafx - during tx.

Human - caused by human mistake

Technical Variance Report

nature of variance

location of variance

treatment site

causative factors

level of variance

I: tx. not affected

II: tx. affected by correctable

III: tx affected but not correctable

geographic miss

human error

Sx: 1 - 5 fractions, ONLY necrosis

Th: multiple fractions, necrosis + apoptosis

1. < 4cm
2. in-operable
3. recurrent
4. too weak for surgery

• intensity modulated stereotactic rad. therapy
• stereotactic body radiation
• intensity modulated rad. therapy
• volumetric modulated arc therapy
• intra-operative rad. therapy

CT (1 mm)   [1-1.25 slices]

MRI/PET (2 - 3 mm) [distortion]

Angiography (0.6 mm)

A measure of the conformity of the 95% to the PTV

(CI = volume of PTV/ volume of 95%)