Test 3: Beam Shaping & Modifying Devices, Treatment Tech, R & V, Imaging in RT, Endocrine Cancers, and Bone Cancers
Ewing's Sarcoma: Field Borders
-2 cm margin around soft tissue -exclude 2 epiphyseal center -treat entire surgical scar -shape field to maintain lymph drainage
Stereoscopic Imaging
-2 images from different angles on the same point -ex. orthogonal films
Cone-Beam CT (CBCT)
-3D image -can be preformed on a linac with a KV source and flat-panel detector
Verification Imaging: Types
-EPID -port films using cassettes -in room CT scanner -KV cone-beam -MV cone-beam -Ultrasound
POP
-Hinge angle of 180 degrees -enter patient from 2 directions [AP/PA, Laterals, Obliques]
Pituitary Cancer: Critical Structures
-Lens: 10 Gy - cataract -Lacrimal gland: 26 Gy - dry eye -optic chiasm: 50 Gy - blindness -optic nerve: 50 Gy - blindness -brain stem: 50 Gy - necrosis -temporal lobe: 47 Gy - necrosis -spinal cord: 47 Gy - myelitis -ear: 30 Gy - acute serous otitis -ear: 55 Gy - chronic serous otitis
Backup System:
-MU -Time
Types of Treatment Techniques
-POP -Tangentials -4 Field/Box Technique -Wedge-Pair Technique -Arc Therapy
Emergency Procedures
-all departments will have an emergency plan to follow in case of machine malfunction or fire -always turn "beam-off" and get patient off the table [don't leave them there]
Conformal Therapy (IMRT)
-applies 3 dimensional localization of the tumor volume -6 or more fields -couch and gantry rotations
Beam Modifiers Examples
-bolus -wedges -virtual wedge -compensation filters -transmission filters
MLC Disadvantages
-can break easily -not as accurate for shaping of irregular fields
Advantages of EPID
-can verify the isocenter position and location of treatment field prior to treating -images can be viewed immediately online
Interlocks:
-closing doors -placement of proper beam modifiers -machine opération requirements -MU (with R&V) -Energy (with R&V) -pendant
Compensating Filter
-compensate for a sloped surface -(mostly for lung treatment) -[is the thing with little metal blocks of varying heights]
Wedges are used for:
-compensation for lack of tissue -eliminate hot and cold spots -create a more homogenous dose distribution -(Toe is smaller side, and Heel is larger end)
Room Prep before patient arrives
-confirm setup, F.S., gantry, collimator, and table positions -make sure lasers are visible -make sure table and accessories are cleaned after each patient, and new linens
Wedges
-cut at different angles -made of aluminum, lead, or plastic -labeled with machine, angle, and max field potential -computer coded for machine (will tell you if you put it in the wrong way)
R&V
-defines and records the patient's complete course of therapy
Beam Modifiers
-devices that change the shape of the treatment field or distribution of the radiation depth -modify the radiation dose across the treatment field
Custom Blocks Advantages
-divergent -more accurate -setup speed is faster (lighter)
Metastatic Bone Cancers: Field Borders
-encompass all involved areas -if patient had surgery, include ALL of fixation device
Pituitary Cancer: Field Borders
-encompass tumor and avoid critical structures -typically 5x5 or 6x6 field size
Totally Body Irradiation (TBI)
-entire body of the patient is treated -treated with arms down to lower the dose to the lungs -patient usually in fetal position -gantry at 90 or 270 degrees -treated POP -lead shield is placed to block critical structures in the head -TLDs used to check patient's midline doses
Application of bolus
-entire treatment area -over scars -superficial modes -areas of concern
Frequency of films
-films are taken in the first day of treatment and every 5th treatment to verify the actual treatment portal -if patient loses marks, film must be taken
Verification Imaging: Disadvantages
-films taken with linac usually have poor contrast, making landmarks hard to see -films are checked after treatment are given so no chance to correct that treatment -if films are taken and check before treatment, have to worry about patient movement while processing the film
Settings with tolerances
-gantry -collimator -table angle -MU -aperture settings -beam modifers -arc versus fixed treatment
Superficial
-goes no deeper than .5 cm -lead cut-outs used to treat superficial treatment ports -can be treated with electrons
Room Prep when patient arrives
-greets patient -identifies patient -verify site -have open communication -evaluate condition of the patient
Thyroid Cancer: Special Instructions
-head should be extended to avoid oral cavity -use immobilization for reproducibility -CT for treatment planning
Soft Tissue Sarcoma (STS): commonly met to
-hematogenous -lung (most common) -liver -other abdominal organs
Disadvantages of EPID
-high imaging dose (1-5 cGy) -low quality of image due to high energy (poor contrast, and bony anatomy hard to see)
Wedge Pair Technique
-hinge angle between 2 ports is decreased, which makes the dose increased -wedge added to improve the dose distribution
"Beam-Off"
-if treatment needs to be interrupted, turn off beam -emergency pendant (in gantry stand) may be needed to lower patient in the event the machine has been "shut down"
Thyroid Cancer: Field Borders
-include entire thyroid gland -neck -superior mediastinum
Pituitary Cancer: when to use Post-Op therapy
-incomplete resected invasive tumor -tumors demonstrating suprasellar extension with an associated visual field defect -large tumors in which the risk of attempted removal is relatively high -persistent hormal elevation after surgery
When Thyroid Cancer would be treated with XRT
-inoperable lesion -patient is physically unfit for surgery -superior vena cava syndrome -skeletal mets -residual disease involving trachea, larynx, or esophagus
Pituitary Cancer: Commonly Mets to
-invade sella turcia -neoplasms can invade sinuses, brain and 3rd ventricle -can met via CSF or vascular pathways [rare]
Pituitary Cancer: Special Instructions
-lead markers on canthus of eye -spare orbits by tucking chin
Bone Cancers: Other Information
-leave 1-3 cm strip of skin to avoid fibrosis and edema -spare joint farthest away from tumor
Multileaf Collimation (MLC)
-leaves of lead that close in on a field -made of tungsten -each leaf can be positioned independently -computer controlled
Chondrosarcoma
-low grade, doesn't tend to met -surgical resection is most common treatment (has radio-resistant qualities) -RT used when total resection cannot be made
Osteosarcoma: commonly met to
-lung -bone -liver -brain
Thyroid Cancer: Commonly Mets to
-lung -bone -liver -brain
Types of Beam Shaping Devices
-machine collimators (jaws) -custom blocks -standard blocks -multileaf collimation (MLCs)
Electronic Portal Imaging Device (EPID)
-method of improving treatment field accuracy and verification -used to check internal structures during entire treatment process
Arc Therapy
-multiple field technique -radiation is delivered as the gantry moves through its arc of rotation
Image-Guided Radiation Therapy (IGRT)
-newest technology -tracks changes in patient positioning due to variations -image patient every day
Brain-Lab ExacTrac
-not attached to linac -in the floor and ceiling -images are analyzed and couch corrections calculated
Fibrosarcoma
-not highly radio-sensitive -RT used for palliation
Custom Blocks Disadvantages
-not readily available -if wrong, you have to make a whole new one -expensive
Steps for Electron Block Cutting
-obtain DRR -template is used to form a mold -mold is made from cutting styrofoam -cerrobend is poured into the styrofoam -cerrobend hardens, and styrofoam is taken away
Metastatic Bone Cancers Cause
-pain -pathologic fractures -spinal cord compression -neurologic deficits -immobility -decrease in quality of life
EPID used to detect:
-patient movement during treatment -organ movement -patient positioning for breast and abdomen setups
Positioning of port films:
-perpendicular to the beam -maximize the SFD -radiopaque marker indicate the position of the port and central ray -graticule is used
Thyroid Cancer: CT Sim
-position patient supine -take diameter -position patient in head rest (head perfectly straight, extended neck) -construct thermoplastic mask -mark 3 reference points -but BBs on marks (for scan) -scan from apex of skull through mid-abdomen (including lungs) -after placement of reference points couch parameters, scanning limits and length scout are recorded -record all set up information
Thyroid Cancer: Conventional Sim
-position patient supine -take diameter -positition patient in registered head rest (perfectly straight, extended neck) -construct thermoplastic mask -set border according to physician -film both AP and lateral fields -mark 3 point setup -record ODI for all fields -take contour through CA if required
R&V: Electronic Medical Records
-prescribe treatments -create and edit plans -track doses -review reference images -record/monitor and evaluate patients health through out their course of tx -perform chart audits -scheduling -charging
Types of Bone Cancers
-primary -metastatic (more common in clinic)
Common sites of mets
-prostate -breast -lung (most common) -kidney -thyroid
MLC Advantages
-provides more flexibility than blocks -increases safety for patient and therapists
IGRT can track:
-respiratory motion -body movement -internal structure movement -weight loss -radiation-induced changes (tumor shrinkage)
Treatment Delivery
-review patient chart -prepare room -check patient ID, verify site -explain procedure -assist patient onto table, locate patient markings -raise couch, set appropriate SSD -align patient with lasers -set gantry and collimator angles -position blocks and conform with field light -position other beam modifying devices -inform patient you are leaving the room, but that you can see and hear them -monitor patient -set machine parameters and verify with R&V system -initiate "beam-on" -assist patient off table -complete patient's treatment chart -prepare room for next patient
Room Preparation
-room engineered around an isocenter -lasers projected from 3-4 points -standard and dim lighting is required in room
IMRT forms
-segmental MLC (SMLC) -dynamic MLC IMRT
Verification Imaging
-setup and portal verification imaging necessary -documents the actual treatment given by providing a visual confirmation of the planned treatment -identifying anatomy is vital for comparing on-board images with the DRR
Multiple Myeloma: common sites
-skull -vertebrae -ribs -pelvis
Dynamic MLC IMRT
-sliding window technique -leaves move through one beam on/off sequence -field-in-field technique: changed the beam shape during "beam-on" -commonly used for head and neck
Multiple Myeloma
-slow growing tumor -treatment: chemo and RT -RT for palliation of pain
Segmental MLC (SMLC)
-step and shoot -1st beam is delivered, then turned out and leaves are moved to a new position, and 2nd beam is delivered. this continues until all field are treated
Soft Tissue Sarcoma (STS) Treatments
-surgery -chemo -RT (pre-op or post-op)
Ewing's Sarcoma: Treatment
-surgery (main option) -RT -chemo (chemo-sensitive) -combo is most effective
Pituitary Cancer: Immobilization
-thermoplastic mask -bite block -intraoral stents
4 Field/Box Technique
-treat deep seated tumors (pelvis, abdomen) -usually arranged 90 degrees from each other -usually requires blocks for shaping fields
Giant Cell Tumor
-treated locally, doesn't tend to metastasize -surgery is common
Sterotatic Radiation Therapy (SRT)
-use of high-energy photon beam with multiple ports of entry convergent on the target volume -designed to deliver a high dose of radiation to the target utilizing either a single dose of small number of fx (as many as 5)
Treating with Electrons
-used to treat superficial areas -provides rapid dose build up followed by rapid fall-out -collimation is needed to decreases the scatter from the electrons
Tangentials
-used to treat superficial volumes (breast and ribs) -can be POP
Record and Verify Systems
-verify actual treatment being delivered -computer assisted set-up -records patient date -allows for data transfer from sim and treatment planning -assist in quality assurance
Lead Standard Block Advantages
-very dense -absorbs radiation
Lead Standard Block Disadvantages
-very high melting point -high boiling point -toxic and a carcinogen
Thyroid Cancer: Critical Structures
-vocal chords: 45 Gy -thyroid: 45 Gy -esophagus: 55 Gy -spinal cord: 45-47 Gy
Metastatic Bone Cancers
-what will see most of -not curable -treatment is for palliation
Patient Transfers
-wheelchair? stretcher? -O2 tubes, catheters -use proper body mechanics
Double exposed port film
1st part: -set F.S. -put blocks in our engage MLCs -expose film -take blocks out 2nd part: -open field size -make another exposure with the field size opened [No blocks]
Pituitary Cancer: Alignment
3 point set up
Thyroid Cancer: Alignment
3 point set up
Metastatic Bone Cancers: Dose
30 Gy in 10 fx
Multiple Myeloma: Doses
30 Gy in 10/15 treatments
Chondrosarcoma: Doses
40-55 Gy up to 70 Gy (for unresectable tumors)
Giant Cell Tumor: Doses
45-55 Gy for 5/6 weeks
Ewing's Sarcoma: Doses
55-60 Gy
Thyroid Cancer: Dose
6000-7000 cGy [180-200 cGy per fx]
Fibrosarcoma: Doses
66-70 Gy with shrinking field technique
Thyroid Cancer: Beam Arrangement
AP/PA to 45 Gy Obliques to 65 Gy
Malignant Fibrous Histiocytoma (MFH): Doses
EBRT: 46-66 Gy IORT single fx: 15-30 Gy
Malfunctions or Discrepancies in treatment must be recorded and reported
Malfunctions or Discrepancies in treatment must be recorded and reported
Standard Blocks
NOT divergent
Osteosarcoma: Doses
Preop: 35 Gy in 10 fx; 46 Gy in 23 fx (POP fields) Postop: -64-68 Gy for high risk areas -70 Gy for un-resectable tumors
Soft Tissue Sarcoma (STS): Dose
Preop: 50 Gy, with boost -Brachy: 12-20 Gy [3 days are resection] -IORT: 10-16 Gy [immediately after tumor removal] Postop: 45 Gy [negative margins] -EBRT & Brachy: 16-20 Gy [positive margins]
Pituitary Cancer: Beam Arrangement
RT/LT lateral with vertex field (couch at 90 degrees, beam is directed superiorly from top of the head), arc, IMRT, IGRT
Most Common Endocrine Cancer
Thyroid
Radioactive Iodine
Used to treat: -inoperable primary tumors -thyroid capsular invasion -thyroid ablation -post-op residual disease -cervical or mediastinal nodes -mets
Bolus: Skin Sparing-Effect
bolus thickness equal to the dmax dose of the energy being used will eliminate the skin-sparing effect of the mega-voltage beams
Malignant Fibrous Histiocytoma (MFH)
complete local excision is best chance for relapse-fete survival
Bone Cancers: Critical Structures
dependent on where the cancer is in the body
Pituitary Cancer: Dose
depends on department
Responsiveness of Thyroid Cancers
depends on histology
Transmission Filters
designed to allow the transmission of a predetermined percentage of the treatment beam to a portion of a treatment field and may be used throughout the course of treatment
Wedges:
designed to change the able of the isodose curve relative to the beam at a specified depth
Beam Shaping Devices
devices that produce the shape of the beam
Common sites for bone sarcomas
growth plates -distal femur and proximal tibia most common because they have large growth plates
KV Imaging
has more info about soft tissue and bony anatomy -on linac at right angles to the treatment beam (on board imaging)
Metastatic Spine: Field Borders
include 1 vertebrae above infected vertebrae, and 1 vertebrae below
Pituitary Gland
lies in sella turcica
Custom Blocks
made of lead of cerrobend
Thyroid Cancer: Lymph Drainage
mets to regional lymph nodes through lymphatic channels
Thyroid: Types and Treatment
radioactive iodine is used to treat papillary, mixed papillary-follicuclar and follicular cancers
Pituitary Cancer: Treatment Position
supine chin tucked
Thyroid Cancer: Treatment Position
supine, arms by side or with arm stretcher
Osteosarcoma Treatments
surgery and chemo -are chemo-sensitive and radio-resistant -RT used in patients that cannot have surgery
Pituitary Cancer: treatment techniques
surgery plays a significant role in treatment and controls 70-90% of tumors
Osteosarcoma: Field Borders
surgical scar must be included in field
Half Value Layer (thickness) [HVL]
the amount of material required to reduce the intensity of a beam by 50% -cannot have more than 5% transmission through a block
Monitor Units
the time the treatment machine is on in order to deliver a prescribed dose -effected by beam energy, distance from source of radiation, field size
Thyroid Cancer: Immobilization
thermoplastic mask with head rest to extend chin
Bolus
tissue equivalent material that conforms to the treatment surface without air gaps
Metastatic Bone Cancers: Treatment
treat to improve quality of life -relieving pain -decrease need for narcotic meds -maintaining ambulation
Virtual Wedges
use a moving straight edged collimator to create the same isodose curves as that produced using a physical wedge -delivers a range of dose over the treatment field
IGRT
used to image the patient right before treatment
Metastatic Bone Cancers: Beam Arrangement
varies depending on area, typically AP/PA