Treatment and Room Design, Patient Safety, Data Transfer, Professionalism

Emami Paper

presented a dose for different treatment sites at which 5% of patients would suffer a complication.

• did not consider concurrent chemo

• did no use rx or calcs with heterogeneity calcs

• mostly 3D

QUANTEC Constraint and Endpoint: Brain

1. Endpoint: Necrosis (death of tissue)

2. 3D-CRT: Dmax < 60 Gy (<3% complication rate)

3. SRS (Single Fraction): V12 (volume receiving 12 Gy) < 10 cc (<20% complication rate)

QUANTEC Constraint and Endpoint: Brainstem

1. Endpoint: Necrosis or neuropathy (damage to a nerve resulting in loss of associated function)

2. 3D-CRT: Dmax < 54 Gy (<5% complication rate)

3. SRS (Single Fraction): Dmax < 12.5 Gy (<5% complication rate)

QUANTEC Constraint and Endpoint: Optics/BrainChiasm

1. Endpoint: neuropathy (optic to be precise)

2. 3D-CRT: Dmax < 55 Gy (<3% complication rate)

3. SRS (Single Fraction): Dmax < 12 Gy (<10% complication rate)

QUANTEC Constraint and Endpoint: Spinal Cord

1. Endpoint: myelopathy (spinal cord dysfunction)

2. 3D-CRT: Dmax = 50 Gy (0.2% complication rate)

3. SRS (Single Fraction): 13 Gy (1% complication rate)

4. SRS (Hypofractionation): 20 Gy (1% complication rate)

QUANTEC Constraint and Endpoint: Chochlea

1. Endpoint: sensory hearing loss

2. 3D-CRT: Mean Dose < 45 Gy (<30% complication rate)

3. SRS (Single Fraction): prescription dose < 14 Gy (<25% complication rate)

QUANTEC Constraint and Endpoint: Parotids

1. Endpoint: loss of parotid salivary function

2. 3D-CRT: Mean Dose < 25 Gy (<20% complication rate)

QUANTEC Constraint and Endpoint: Lungs

1. Endpoint: pneumonitis

2. 3D-CRT:V20 < 30% (<20% complication rate)

QUANTEC Constraint and Endpoint: Esophagus

1. Endpoint: esophagitis

2. 3D-CRT: Mean Dose < 34 Gy (5-20% complication rate)

QUANTEC Constraint and Endpoint: Heart

1. Endpoint: pericarditis (inflammation of the pericardium)

2. 3D-CRT: V25 < 10% (<1% complication rate)

QUANTEC Constraint and Endpoint: Liver

1. Endpoint: Hepatitis and RILD (Radiation Induced Lung Disease - can involve pneumonitis and fibrosis.  Note: this is for the right lung for a whole liver GTV)

2. 3D-CRT: Mean Dose < 30 Gy (<5% complication rate)

3. SRS (Hypofractionation): Mean Dose < 13 Gy (<5% complication rate)

QUANTEC Constraint and Endpoint: Kidneys

1. Endpoint: renal dysfunction

2. 3D-CRT: V20 < 32% (<5% complication rate)

QUANTEC Constraint and Endpoint: Small Bowel

1. Endpoint: bowel toxicity diarrhea

2. 3D-CRT: V15 < 120 cc (<10% complication rate)

QUANTEC Constraint and Endpoint: rectum

1. Endpoint: rectal toxicity (fistulas)

2. 3D-CRT: V50 < 50% (<15% complication rate)

QUANTEC Constraint and Endpoint: bladder

1. Endpoint: toxicity (loss of urinary control)

2. 3D-CRT: V65 < 50%

QUANTEC Constraint and Endpoint: penile bulb

1. Endpoint: erectile dysfunction

2. 3D-CRT: V50 < 90% (<35% complication rate)

 

ACR-ASTRO definition of SRS

radiation therapy delivered via stereotactic guidance with approximately 1 mm targeting accuracy to intracranial targets in 1-5 fractions.”

ACR-ASTRO definition of SBRT

radiation therapy delivered via stereotactic guidance with high levels of targeting accuracy to extracranial targets.”  Furthermore, “SBRT is typically a complete course of therapy delivered in 1 to 5 [fractions].”

Dose Delivery Accuracy Requirement: for SRT

3%

size of tumor common requirements for SRS/SBRT

normally confined to being less than 4-5 cm in diameter

QMP responsibilities for SBRT as outlined in MPPG9

1. QMP must be available for consult from start (simulation) to finish (treatment delivery) (taken from ACR-ASTRO).

2. QMP must provide or oversee acceptance testing and commissioning including:

   1. TPS validation,

   2. Small field dosimetry,

   3. Heterogeneity calculations (if applicable),

   4. IGRT/localization evaluation, and

   5. E2E testing.

3. Develop an ongoing QA program.

4. Develop and collaborate for the composition of standard operating procedures (SOPs).

5. Develop safety checklists.

6. Incorporate an incident learning system (for example, the Radiation Oncology Incident Learning System, RO-ILS).

7. Supervise or perform treatment planning (if performing, adequate secondary plan evaluation must be in place).

8. Initial and final plan review (if performing the planning, adequate secondary/independent plan evaluation must be in place).

9. Provide appropriate plan-specific QA (including dosimetric and “dry run” verifications).

10. TG-100 and MPPG 9 both explicitly recommend that the QMP provide personal supervision (defined above) for the entirety of the first fraction.  Following that, MPPG 9 states that subsequent fractions can minimally be under direct supervision (defined above) by the QMP.

CT sim slice thickness for SRS and SBRT

1. For SBRT: slice thickness of 1-3 mm.

2. For SRS: no greater than 1.25 mm.

PDDs and beam profile measurements for SRT QA

you should use your smallest chamber available (needs to have a diameter < 1mm.

ICRU conformity index and common value for SRS

ratio of the volume enclosed by the prescription isodose surface and the planning target volume.

• between 1 and 1.6 for SRS

Paddick conformity index

• does not distinguish between over-coverage and under-coverage.  The value will always be less than or equal to 1.0 but greater than or equal to 0.0 by mechanism of the formula

• TV_PIV is target volume covered by rx isodose volume

CI50

• used to assess intermediate dose falloff

• This value is the ratio of the volume receiving 50% of the prescription dose to the volume of the PTV.

• A general target goal for CI50 for lung SBRT plans should be less than 5-6.

Gradient Index

• unitless value

• ratio of volumes of half he rx isodose to entire rx dose

• should be less than 5 (ideally 3-4)

Homogeneity Index

the inverse of the prescription isodose line and is a general indicator of the uniformity (or, conversely, non-uniformity) of the dose across the target volume.  In equation form, it is equal to the maximum dose divided by the prescription dose.

• should be greater than 1 and can approach 2

Heterogeneity Index

Ratio of highest dose received by 5% of PTV to the lowest dose received by 95% of PTV.

Other SBRT common important metrics

V12 in the brain

V20 in lung

D2cm lung

what guidelines/TG reports handle SRS/SBRT

1. MPPG 9: SRS-SBRT

2. TG-135: Quality assurance for robotic radiosurgery

3. TG-42: Stereotactic radiosurgery

4. TG-101: Stereotactic body radiation therapy

CSI LINAC 3D setup

1. LINAC-based (patient is setup prone).

   A pair of lateral fields are used to treat the brain and upper cervical spine.

2. For adults, 2 PA fields are used to treat the spinal column due to the length.

   This necessitates a junction on the spinal cord which is usually matched at the anterior of the cord (for a cold match).

3. For pediatric cases, the entire spinal column can usually fit within a single field.

4. Both the cranial and spinal junctions are moved every few fractions to ensure that any hot and cold spots are distributed and not concentrated in one area.

Number of junctions needed in CSI tx

Junction # = tumor dose/(tolerance-dose)

Field matching with CSI: what needs to be matched and by how much

The cranial field has to be matched in 2 places: at upper spine and at cranial themselves

• to do so rotate the collimator for spine field

• can do half beam block or kick couch for cranials

when using 2 spine fields in 3D CSI how do we match them

cold match safest - vary the junction

need to know the depth of cord

TSE: areas that commonly need to be boosted

1. The soles of the feet

2. The palms of the hand

3. The top of the scalp

   1. The perineum and anal area

TSE: commonly shielded areas

• top of scalp

• eyes

• nails

How are upper and lower fields used for TSE

upper and lower fields are used separated by about 20 degrees.  The air and plexiglass degrader function to scatter the electrons into a uniform field within (+/- 8% vertical and +/- 4% horizontal).

1. There is another added benefit to the angled fields in that most of the x-ray contamination is concentrated around the central axis.  Having two angled fields then directs this above and below the patient (x-ray contamination above 4% is considered unacceptable

what is the function of the plexiglass spoiler for TSE

• degrades and lowers the energy so electrons do not penetrate as far

• scatters electrons to produce a more uniform field

Ideally what should the dose uniformity be for a TBI

1. Dose uniformity should be within +/-10% over the whole body.

What nodes are commonly looked at for involvement in breast cancer and potentially treated

1. Level 1 nodes (Axillary Nodes)

2. Level 2 nodes (Axillary Nodes)

3. Level 3 nodes

4. Supraclavicular nodes

5. Internal mammary nodes

Breast treatment fields setup for a 2 field plan

1. 6x is usually used to keep the skin dose high, but for large patients, a mix of 6x and 18x may be used to reduce hot spots.

2. The posterior border of the fields is usually matched to remove divergence reducing dose to the lung and heart.

3. The collimator is turned (about 8 degrees) to match the angle of the chest wall and fields extend about 1-2 cm into the lung.

4. The fields should cover all the palpable breast tissue plus a 2 cm margin on all sides.

5. Care should be taken to not cross the midline and expose contralateral breast tissue to unnecessary radiation (induces secondary cancers).

6. Wedges or field-in-field planning may be performed to reduce hot spots.

1. Note that a conventional hard wedge produces significant scatter and will increase dose to the contralateral breast by about 2.5%.

2. FiF planning is essentially a step and shoot IMRT plan that uses a forward optimization process. That is the planner designs the MLC movements.

Breast 3 field plan field design

1. The patient's head is normally turned away (to keep the chin out of the field) from the field which is then angled 10 degrees to reduce cervical spine dose and the cord is blocked using MLCs.

2. The most important facet of these plans is matching the tangents and the supraclav field (SCV field).

1. If the plan uses separate isocenters for the tangents and SCV fields, then the couch can be kicked for the tangents to have matched upper borders.  MLCs are then used to collimate the tangents to match the SCV field.

2. Another option is to use the same isocenter for the SCV and tangent fields which would then be half beam blocked by definition removing the divergence and thereby simplifying the matching.

breast 4 field plan

3 field with higher dose to the sclav field (4th post field)

breast 5 field plan

boost to the IMNs

Different breast “balloon” options

• mammosite: balloon with central channel

  • filled with saline and contrast

  • have a new multilumen with 4 channels

• Contura

  • 5 channels

  • vacuum to help with removing air and seroma

• SAVI

  • no balloon just struts

how does contrast in the breast balloon affect the dose

lower the dose compared to TG-43 by up to 5% (but limiting the Iodine contrast agent concentration to 10% reduces the dose discrepancy to below 3%)

Breast balloon dose constraints

1. Skin must be kept below 425 cGy (the minimum acceptable skin distance is usually about 5-7 mm).

2. Rib must be kept below 425 cGy (or risk fractures).

Draw and label the different treatment fields for hodgkins

Heterotopic ossification RT

1. delivery must come within hours of the operation associated with the trauma surgery.

2. It is for this reason that these patients must be treated emergently. 

3. 700-800 Gy

4. most common in hips

I-131 ablation therapy

1. The thyroid is the only organ in the body that requires iodine, and therefore any administered I-131 accumulates in the thyroid in great quantities.

2. The amount of I-131 that is delivered varies and depends on the following:

   1. 30-150 mCi is administered for primary tumors following resection.

   2. 150-250 mCi is administered for metastases or recurrences.

   3. more precise way is to look at uptake with I-124 PET

I-131 isotope properties

beta emitter (606 and 334 keV) decaying to a metastable state of xenon which emits high energy gammas (364 and 636 keV).

I-131 release criteria

1. Release of the patient based on activity.  For I-131, you can release the patient if the activity is no greater than 33 mCi.  Or,

2. Release of the patient based on measured dose rate.  You can release the patient, even if they received an activity greater than 33 mCi, provided that the dose rate at one meter from the patient is no greater than 0.07 mSv/hr (specific to I-131).  Or,

3. Release of the patient based on patient-specific dose calculations.  For these criteria, one has to perform patient-specific dose calculations to demonstrate that no dose to an individual is likely to be greater than 5 mSv.  Furthermore, clear instructions should be provided to the patient to help them keep to that goal (for example, with instructions for how long to sleep in a separate bed from a spouse).  The details of this calculation are provided in the cited NUREG regulatory document.

If the I-131 patient cannot be released what considerations need to be made for their hospital stay

1. Dose to patients in adjacent rooms is of concern and shielding the treatment room will likely be required.

2. The entire room must be covered in plastic sheeting that will be disposed of after patient discharge, as I-131 will be coming out of every pore on the patient.

3. Any nursing staff must wear dosimeters along with any visitors.

4. All staff involved with care and cleanup for the treatment must undergo a bioassay to assess the amount of radioactive iodine their thyroids took up.

5. Once dose rate readings fall below 0.07 mSv/hr at 1 meter the patient may be released with instructions to minimize dose to others (NUREG 1556).

6. The overarching goal when releasing any brachytherapy patient is to keep the dose to the maximally exposed individual below 5 mSv.

Hippocampal sparing WBRT dose constraints

1. Greater than 98% of the PTV (brain) receiving 25 Gy

2. Less than 2% of the PTV (brain) receiving 37.5 Gy.

3. Hippocampus max dose of 16 Gy.

4. 100% of the Hippocampus receiving less than 9 Gy.

5. Optic Nerves and chiasm receiving less than 37.5 Gy.

storing radioactive material from patient waste and cite source

10 half lives

10CFR35

Photon beams spectrum:

• max E

• average E

max: designated energy

avg: 1/3

PDD for 10×10 10cm depth

• Co

• 6

• 10

• 18

1. Co-60 = 55%

2. 6X = 65%

3. 10X = 75%

4. 18X = 80%

TMR 10cm depth

• 6

• 10

• 18

1. 6X = 0.78

2. 10X = 0.85

3. 18X = 0.90

attenuation per cm 6/10/18

1. 6X = 3% per cm

2. 10X = 2.5% per cm

3. 18X = 2% per cm

dmax for 10×10

• Co

• 6

• 10

• 18

1. Co-60 = 0.5 cm

2. 6X = 1.5 cm

3. 10X = 2.4 cm

4. 18X = 3.3 cm

surface doses

• Co

• 6

• 10

• 18

1. Co-60 = 50%

2. 6X = 25%

3. 10X = 23%

4. 18X = 20%

neutron contamination 18 x beam

1. 0.5% on the central axis

2. 0.15% outside of the beam

neutron head leakage 6/10/18

1. 6X = none

2. 10X = 0.01%

3. 18X = 0.15%

Scatter at 1 meter from a phantom

1/1000 primary beam

Lateral Scatter has a maximum energy

511 keV

backscattered radiation

255 keV

Photon interaction proportionalities per unit mass

1. Compton scattering - Z independent, proportional to electron-density.

2. Photoelectric interactions - proportional Z³.

3. Pair production - proportional to Z.

Conversion factor for Roentgens to cGy (f-factor)

• air (MV)

• tissue (MV)

• tissue I-125

air: 0.876 cGy/R.

tissue: 0.97

tissue I125: 0.886

SRS treat to for linac and gamma knife

1. LINAC based therapy is prescribed to about the 80% isodose line.

2. Gamma Knife therapy is prescribed to the 50% isodose line.

scatter contributions of physical and dynamic wedges

1. Physical wedges - scatter about 2.5% the central axis dose.

2. Dynamic wedges - scatter about 1.0% the central axis dose.

extending perpendicular beam at dmax, magnitude at 10/30 cm

1. 10 cm away receives approximately 1% of the central axis dose at d_max.

2. 30 cm away receives approximately 0.2% of the central axis dose at d_max.

electron depth max dose

 

electron 80% depth

E/3

electron range in water

Rp = E/2

depth of 50% isodose line

E/2.4

depth max dose for 10×10 FS common electron E

1. 6E = 1.2 cm

2. 9E = 1.9 cm

3. 12E = 2.1 cm

4. 20E = 2.5 cm

electron surface dose: 6/12/20

1. 6E = 80%

2. 12E = 90%

3. 20E = 95%

electron xray contamination: 6/12/20

1. 6E = 1%

2. 12E = 2%

3. 20E = 5%

Amount of lead shielding needed in millimeters to stop an electron beam

E₀(MeV) / 2.

occupation and public limits and avg worker exposure

1. Occupational limit = 50 mSv/year (5 mSv if pregnant).

2. Public limit = 1 mSv/year.

3. The average worker in the USA receives 2 mSv/yr from occupational exposures.

Neutrons produced in photonuclear reactions energy

about 2 MeV

concrete TVL for 6/18x

1. 6X - 37 cm

2. 18X - 45 cm

amount of lead in centimeters necessary to shield an electron beam (to less than 5%)

divide the practical range by 10.

avg exposure per year for average person

1. Radon - 1.0 mSv/yr

2. Ingested isotopes - 0.4 mSv/yr

3. Isotopes occurring naturally - 0.4 mSv/yr

4. Cosmic rays - 0.4 mSv/yr

5. Medical exposures - 2.0 mSv/yr

adding up to about 4-5 mSv per year for the average person:

k edge of lead and iodine

lead is 88 keV and Iodine’s is 33 keV.

Increase in mortality risk due to an acute and chronic radiation exposure

acute: 8% per Sv

chronic: 4% per Sv

radiation syndrome dose levels

1. Hematopoietic syndrome - 2 Sv

2. GI syndrome - 10 Sv

3. CNS syndrome - 30 Sv

Radiation skin effects dose levels (acute exposures):

1. Erythema - 6 Sv

2. Wet Desquamation - 25 Sv

3. Radionecrosis - 50 Sv

Radiation weighting factors:

1. Photons = 1

2. Electrons = 1

3. Protons = 5 (some discrepancy here with a range of 2-10 quoted with the NRC quoting 10 via 10CFR20)

4. Neutrons = 5-20 (10 for unknown energy)

5. Alpha = 20

Package Shipping Labels

1. White 1: <0.5 mrem/hr at surface

2. Yellow 2: <50 mrem/hr at surface, <1 mrem/hr at 1 m

3. Yellow 3: <200 mrem/hr at surface, <10 mrem/hr at 1 m

Package receiving wipe test action limits (for a 300 cm² area):

1. Alpha - 22 dpm/cm²

2. Beta/gamma - 220 dpm/cm²

ALARA levels

1. ALARA level 1: 10% the allowed limit per quarter

2. ALARA level 2: 30% the allowed limit per quarter

sealed source leak test limits

more than 185 Bq of leakage then it must be removed from service (remember sealed sources must be checked at least every 6 months)

Patient exposure release levels

• I-125

• Pd-103

• I-131

1. I-125: <1 mR/hr at 1 meter

2. Pd-103: <3 mR/hr at 1 meter

3. I-131: <7 mR/hr at 1 meter

brachy medical events

1. Wrong patient, site or nuclide

2. Total dose differs by 20%

3. Single fraction differs by 50%

teletherapy medical events

1. Wrong patient or site

2. Total dose differs by 20% (for treatments >3fx)

3. Total dose differs by 10% (for treatments 

   < 3fx)

Co-60 Energy, gamma, half life, HVL lead

1250 keV

13.07

5.3 years

1 cm

Ra-226 Energy, gamma, half life, HVL lead

830

8.25

1600 years

0.7 cm

Cs-137 Energy, gamma, half life, HVL lead

660 keV

3.26

30.2 years

0.55 cm