ANNOUNCEMENT: May’s Vitamins and Minerals

Beginning May 1st, we will be posting a Vitamins and Minerals pages that will be composed of “new” information that should be added to the arsenal.  No one knows what may be on the exam, so a broad knowledge base is required.  Here is how you take your Vitamins and Minerals.  Vitamins are notes and Minerals are 5-10 question quizzes.

May 1:	Vitamin 1 Posted
May 2:	Vitamin 2 Posted Mineral 1 Posted
May 3:	Vitamin 3 Posted Mineral 2 Posted

Take all Vitamins and Minerals.  This information is to supplement the book.

Cheers.

Brent

Vitamin 1:  May 1

Topic:  Radiation Shielding for Linac Rooms

1. Walls or barriers need to be shielded for:
   1. Primary Radiation
   2. Secondary Radiation (Scatter)
   3. Leakage Radiation
2. Primary Walls require 6 TVLs of Shielding.  (96 inches of concrete)
3. Scatter and Leakage Walls require 3 TVLs of Shielding.  (48 inches of concrete)
4. TVL = 16 inches concrete, 4 inches steel, 2 inches Lead.
5. Leakage is considered to be 0.1% or 1/1000th of the Primary dose.
6. Use factors for all scatter barriers = 1.00.  Note, regardless of which way the beam points (primary), there is always scatter bouncing around in the room.
7. For IMRT, the workload for primary barriers is the same (note, it is the same dose to patient).
8. For IMRT, the workload for secondary barriers Leakage may increase by 3 –5 times.  This is due to the machine being on longer.  This does not imply that the shielding thickness is increased by 3-5, it only notes that the current Leakage barriers should be evaluated.
9. Neutrons are produced at 10MV X-ray.
10. Neutrons are not a problem until 15MV X-ray.
11. A 18X beam has 4 times the number of neutrons as a 15X beam.
12. Neutrons come from interactions in the linac head.  Principally the target, flattening filter, and collimators.  Most neutrons come from the target.
13. Neutrons have an average energy of 2 MeV (fast neutrons).
14. Neutron energy at the door (room with maze) is about 100-200 keV.
15. Linac doors have borated polyethylene in the door.  It is located on the linac side of the door.  Lead is located on the outer part of door.  The reason for this order is that a neutron interaction in the Borated Polyethylene may lead to a 2.2 MeV gamma.  The Pb then could shield this gamma.

Mineral 1:  May 2

Topic:  Radiation Shielding for Linac Rooms

1. If the Primary Workload is 50,000 cGy per week, the Leakage Workload is:
2. Why are most vaults shielded with concrete?
3. The TVLs for 6X and 18X are 14 inches and 16 inches of concrete respectively.  Why are the TVLs so close although the energy is much higher.
4. A vault does not have a maze.  A pocket door is used.  The pocket door should be located where?
5. A clinic only treats 3D.  The primary walls are 96 inches of concrete.  The clinic now treats 30% of the patients with IMRT.  What is the new thickness of concrete required for the primary.

Answers:

• 0.1% of 50,000 cGy / wk or 50 cGy /wk.
• Concrete is much cheaper than lead or steel.
• 18X has more PP interactions.  This tends to soften the beam.
• Pocket door should not be located in the primary beam.  It should be placed at point easy for entry and in one of the corners of the vault furthest from the beam.  Distance is your friend.
• Primary barrier does not change.  Dose to patient does not change.  Walls remain at 96 inches.

Vitamin 2:  May 2

Topic:  HDR

1. HDR sources are exchanged quarterly.
2. HDR sources exhibit anisotropy.  This may be an issue with vaginal cylinder cases if not considered.
3. HDR calibration accuracy should be 5%.
4. HDR calibrations should be performed quarterly upon receipt of a new source.  Note, if you put monthly in the State or NRC license, then it must be done monthly.
5. HDR positional accuracy should be 1mm.
6. A survey using a meter (ion chamber), should be done BEFORE and AFTER the HDR treatment.  Historically, the survey was performed only after the procedure.  The pre treatment survey is needed to establish background levels and check to see if the patient exposure is indeed background (note, the patient may have had a Nuc Med study and still have a radioactive material in their body).
7. The patient ID should be verified prior to treatment.
8. On a linear plan, example esophageal case, the end dwell positions will have the highest dwell times.
9. HDR emergency procedures would involve getting the source out of the patient ASAP….via interrupt button, emergency off button, manually retracting the source, withdrawing the applicator (with source inside) from the patient (then placing it in a Pb pig).
10. HDR sources are received in a drum with a Yellow II label.
11. HDR double checks prior to each fraction would include:
    1. Source Activity
    2. Source Dwell Positions
    3. Source Dwell increment
    4. Souce Dwell Times
    5. Patient ID
    6. Fraction Number and Dose per Fraction
    7. Note:  Fraction 1 (Act X Time) = Fraction N (Act X Time)……..The activity will go down and the treatment time goes.  The product will be the same.

Mineral 2:  May 3

Topic:  HDR

1. A HDR source is loaded.  The stated Activity is 10.0 Ci.  When measured, the source activity should fall between what?
2. A plan with a 10Ci source requires 100 seconds.  What is the treatment time when the source activity is 5Ci to deliver the same dose.
3. The pre-treatment patient survey measures 0.010 mR/hr.  The post-treatment patient survey measures 0.020 mR/hr.  Is the source still in the patient?
4. HDR units use what isotope?
5. Security of HDR units is become of paramount importance.  Why?

Answer:

1. +/- 5%, thus the calibration should fall between 9.5 Ci – 10.5 Ci.
2. The activity is ½ so the treatment time is doubled.  200 seconds.
3. No.  0.020 mR/hr is still in the background range.  If the source were in the patient, the survey would read R/hr.
4. Ir-192
5. Since 911, radioactive material security is very important.  Ir-192 sources could be used in the fabrication of a “dirty” bomb.

 

GENERAL INFORMATION

Thank you for expressing an interest in the review courses conducted by ARC, Advanced Radiotherapy Consulting. I will attempt in this cover letter to explain the philosophy and modality in which these courses are conducted. Included in this mailing are an application, course schedule, and general course outline. The outline is subject to change consistent with the changing test criteria of the AAMD, ABR, and ABMP.

The demands placed on the medical dosimetrists and medical physicists today are ever increasing; diverse yet specialized at the same time. With the managed health care environment not allowing most institutions to operate at adequate staffing, the ability to find ample study time becomes more and more challenging. The intent of ARC is to fill this void by providing no-nonsense intense instruction with accompanying study guides. In a sense, ARC will have done the homework for you. Several schools have put on review board courses and have failed to provide the necessary focus to ensure students are adequately prepared to PASS their boards. ARC’s philosophy for preparing students adequately is based on:

• Organized Study Notes
• Connecting the Physics to the Clinical Application
• Thoroughness
• Test Rehearsals

The distinction of certification is most definitely a discriminator. The American College of Radiology recognizes competent dosimetrists or physicists as those who are Board Certified. We both know that experience is equally if not more important, however, certification does have several advantages. Physicists / Dosimetrists that are board certified are paid on the average in order of $5,000 to $10,000 more annually. Although some may view the ARC courses are premium priced, the payback could be less than one year. ARC courses are premium priced. Why take the exam more than once or attend several other review courses that have not worked for you in the past? Time is money. Let ARC do the work for you. In many cases, your institute would pay for the course or a portion thereof. Administrators and Physicians need to be aware of the importance of certification. If you would like me to write or talk to these individuals for you, do not hesitate to call me. I look forward to working with you in the future.


Brent D. Murphy, MS, DABR
Certified Medical Physicist