Medical Event Criteria in Prostate Seed Implant / Prostate Brachytherapy

September 15, 2009 · Written by MDPhysics.com · mdphysicsblog@gmail.com

Prostate brachytherapy implant is not going to be perfect all the time. The routine way to check the accuracy of an implant is to obtain a CT scan of the prostate after the implant, then run a post-treatment plan and compare it with the pre-treatment plan. Discrepancy in the delivered dose to the prostate (as well as to the surrounding organs) between the post and pre-plans could create a medical event or misadministration if one or both of the following NRC rules are not met:

10 CFR Part 35.3045 (a)(1)(i): The target (prostate, in this case) receives a dose that was less than 80 percent of the prescribed dose.

10 CFR Part 35.3045 (a)(3): Other organs or tissue other than the target (prostate) receive doses above 0.5 Sv and 50 percent more than the expected dose to the organ or tissue.

As a result of the recent prostate brachytherapy misadministrations and the subsequent NRC inspection, the Philadelphia Veteran Affairs Medical Center (PVAMC) adopted the following criteria to determine whether or not a prostate brachytherapy implant results in a medical event. Every prostate seed implant program should include a similar criteria in their quality management program.

10 CFR Part 35.3045 (a)(1)(i)
The first condition fails if the calculated D90 from the post-treatment plan is less than 80 percent of the prescribed dose.

10 CFR Part 35.3045 (a)(3)
The PVAMC established the following guidelines to determine if the rectum or bladder receives a dose above 0.5 Sv and 50 percent more than the expected dose.

Rectum: Dose to 1.33 cubic centimeter volume exceeded 150 percent of the pre-treatment plan dose.

The D1.33 was selected because it is the volume of the VariSeed treatment planning program used to identify high dose volume during the pre-treatment planning. D1.33 is also found in the literature: “Defining the Risk of Developing Grade 2 Proctitis following I-125 Prostate Brachytherapy Using a Rectal Dose-Volume Histogram Analysis”

Bladder: 3 or more seeds located in the bladder wall.

This criteria was selected based on the review of a patient’s post-treatment plan which identified that two seeds in the bladder contributed to less than 60 Gy (equivalent to 60 Sv) to the bladder wall. The dose to the bladder wall with the seeds in the wall was compared to the dose to the bladder wall with the seeds removed. This criteria was well below the bladder tolerance dose.

References:
http://adamswebsearch.nrc.gov/idmws/ViewDocByAccession.asp?AccessionNumber=ML090900382
10 CFR Part 35.3045 defines reporting and notification of a medical event using by product material
NRC Inspection Report No 030-34325/08-029 (DNMS) on the medical event which occurred at Philadelphia Veteran Affairs Medical Center

Posted in: Misadministration ·Tags: no tags

Replies

One Response to “Medical Event Criteria in Prostate Seed Implant / Prostate Brachytherapy”

  1. Ronald Scala on March 16th, 2010 11:37 am

    I do not agree with many criteria listed above.
    The D90 criteria sounds rational but you must keep in mind that the pre-implant plan can never be exactly duplicated at implant. Hence the possibility that irreversible seed placement could be such that the dose is outside this criteria. I do not feel that this is a ME if the physician has done his/her best to comply with the plan. The 0.5Sv and 50% criteria are also problematic. Radiation therapy cannot be delivered w/o dose to adjacent tissues. The skin receives more than 0.5Sv in Ext Beam but is not considered a ME. This criteria is only intended for dose delivery mistakes that cause organ irradiation to 0.5Sv above what is expected or otherwise unavoidable. Likewise with the 50% criteria. Seed placement is cannot be exact enough to ensure a “tissue” will not receive 50% more than the pretreatment plan showed. Last, three seeds in the bladder wall is in no way a meaningful criteria since seed dislodging is not a always or often the result of incorrect seed placement.

    R Scala, MS

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