TBI and TSET
What energy is utilized for TSET?
6 MeV beam that becomes 2-3 MeV at patient
Describe to me AP/PA method? What do you need?
AP/PA method is utilized to achieve more homogeneous dose distribution 1. Treat at 400 SSD (two purposes treat with single field and reduce dose rate to 10 cGy/min to reduce pneumonitis) 2. Patient is on platform with bicycle seat 3. Spoiler is utilized to give more superficial dose (2 cm thick acrylic) 4. Lungs are protected by lung blocks - need to deliver dose to superficial region of lung area with electron boosts 5. 6 MV beam 6. 45 collimator angle, 40x40 field, gantry 90 7. Measurements taken at umbilicus, knee, calfs, and skull What do you need? - Patient thickness at umbilicus (prescribed at midline) - measure distance to lung and lung depth (to help determine dose of lung) (and determine blocking) -kidney blocks - determine electron boost energy - PDD/TMR data to perform hand calc
What are benefits to bilateral treatment vs AP/PA for TBI? Disadvantages?
Bilateral Advantages - inherent blocking of lung, patient comfort (lying down) Disadvantages - compensators, dose heterogeneity AP/PA Advantages - easy to block lung, dose homogeneity Disadvantages - patient is almost standing up, boost lung are with electrons
Describe a TSET setup?
In my experience - Utilize stanford technique - 12 fields utilized for 6 positions (gantry kick to reduce bremstrahlung - 15 degree rotation) - 6 MeV HDTSET - high dose rate - Multiple point of measurements with OSLD giving superficial reading - AP, RPO and LPO day 1 - then PA, RAO, LAO on day 2 - distance of 400 cm - scatter plate of 1 cm is utilized - for more scatter - Boost with electrons for sole of feet and perineum
How do you increase dose homogeneity for TBI?
Increase SSD - Inverse square has less affect at larger distances Treat AP/PA vs bilateral Use higher energies - can underdose skin though
TBI is the treatment for what?
Preparatory regimen for bone marrow transplant for patients with leukemia and non-hodgkins lymphoma
What are you treating with TSET and what is the dose prescription?
Treating cutaneous T-cell lymphoma - mycosis fungoides - treat to 5 mm depth to 1 cm Two dose levels Conventional - 30 Gy in 15 fx Low dose - 12 Gy in 6 fx Giving 1 Gy per session - (three dual fields)
What is the major issue with TBI?
Treatment with a dose uniformity of plus/minus 10% across patients body
Dose homogeneity trying to achieve with TSET?
Vertical plus/minus 8% Horizontal plus/minus 4% in-vivo dosimetry with OSLD
TSET shielding? What do you shield with TSET?
-Lens of eye with shield placed between eyes and eyelid -Fingernails and toenails with lead
What is the dose for TBI?
12 Gy in 6 fractions over 3 days - BID - seperate 6 hours Also low dose TBI of 2 Gy in 1 fraction Lung is dose limiting organ of 10 Gy
