The purpose of the study is to assist someone who is establishing a new quality assurance program or revising one already in place into adhere to the recently issued Nuclear Regulatory Commision (NRC) regulations and the guidelines from the American Association of Physicists in Medicine (AAPM). In my opinion this paper is one of the important reading material for all the medical physicists worldwide because it serves as a guide to ensure that the patient will benefit in a radiation treatment more than getting the risk out of it.
The discovery of Radium-226 by the Curies paved a way for brachytherapy as form of cancer treatment modality. After a century that this radioisotope is abandoned, the ability to produce high specific activity Iridium-192 sources combined with developments in computer controlled after loader technology has led to widespread adaptation of high dose rate (HDR) techniques (Wilkinson, 2004). Thus the paper showed the advantages of HDR treatments (e.g. greater ease and comfort for the patient, more precise dose delivery, easier dose shaping, and less exposure to medical personnel). However, because of the dangers of using a source with very high activity, I agree with the author that it is of utmost importance to have proper quality assurance (QA) procedures. This is in place along with the required dosimetric and planning equipment, and appropriately trained staff in a brachytherapy facility. Thus the author is persuaded to make a guide on QA procedures and the training for the staff.
I agree with the paper that part of the duty of the medical physicist is to establish a quality management program to satisfy the regulations that apply in the country. In this regard, I made a brachytherapy QA program in the facility where I am working at the time. Since the author is working in Cleveland Clinic Foundation (CCF), which is situated in the United States, the study focused in the regulations of the US NRC, which in our case is PNRI, and the recommendations made by the AAPM, which in our case is IAEA. The recommendations by the AAPM and IAEA for the medical physicists are intended to provide a proper guidance to ensure that brachytherapy procedures are carried out safely and with due attention to these rules. CCF used two AAPM task group (TG) that are relevant to HDR QA at the time of completing this guide. One of those is TG 56 - Code of practice for brachytherapy physics and the other is TG 59 - HDR brachytherapy treatment delivery. Furthermore, this paper promised to provide the details about HDR QA as it is performed in their radiation therapy department and how the QA program is related to the NRC regulations and the TG recommendations.
The paper stated that prior to initial use of a new (or replacement) applicator, it is necessary to verify that the source dwell positions correspond to the radiographic marker positions used in simulation and treatment planning. TG 56 recommends that coincidence of dummy/dwell and radioactive sources be checked annually. In this aspect, CCF used autoradiography to verify the coincidence of dwell position and radiographic markers. As far as I'm concerned, this technique is already in practice of HDR facilities in our country especially those who are using the same Treatment Planning System (TPS). The author described clearly how to secure the applicator to a sealed film envelope, with the use of the actual images, and stated that the HDR after loader is programmed to send the source to a few chosen dwell positions for less than 1 second. Next, the film with the applicator is transferred to a simulator. The dummy source markers are then placed in the applicator and the film is exposed and developed. TG recommends coincidence of dummy and active sources are within 2 mm while the NRC regulations call for +/- 1 mm.
NRC required a periodic spot-check of each HDR unit prior to the first use on any given day that the after loader is in operation and after each new source installation. This paper mentioned that these spot-checks may be done by the other trained staff in the facility, but the Medical Physicist must review the results and notify the licensee in writing of the findings. There is a mandated spot checks that must be performed given by the NRC regulations but to make things easier for the clinic they made their own checklist to implement and record the above QA. Important spot check such as the source activity comparison can be made using a source decay table, generated by the CCF medical physicist, and the printout from the HDR control console. The agreement should be within 1% tolerances. In our case and since PNRI has no specific limit for this, we used the tolerance limit indicated in the manufacturer's manual.
The paper presented a “full calibration” which is mandated for several different circumstances such as before first medical use, any major repair, etc. Quarterly QA testing of HDR after loaders is recommended in TG 56. In this context, CCF used an excel spreadsheet that allows convenient calculations of source activity and positioning as well as timer accuracy and linearity. We also used this kind of excel spreadsheet to calculate these aspects. The activity of the source is then measured using a well chamber and electrometer. The source is programmed to go to a series of positions within the well chamber and the maximum current reading is used to calculate the activity in air kerma units. The value obtained is compared to the manufacturer’s stated activity. NRC regulations allow a 5% deviation but the CCF results usually fall within 2%. Positioning accuracy is measured using a special ruler with 1 mm tolerance. It is suggested that some care must be taken to ensure that the transfer tube is reasonably straight and horizontal to attain the tolerance level.
TREATMENT PLANNING QUALITY ASSURANCE
For brachytherapy, the independent check is desirable but there is no specific accepted method nowadays. TG 59 addresses this issue and lists several approaches that have appeared in the literature (Kubo, 1992). Typically, the dose is calculated at representative points by the treatment planning system and then compared to the results from the second independent system. In CCF, the method has been used is a product of a plot of treatment time and source activity divided by dose versus the global parameter of treatment volume for various applicator types. Results are used for checking new patient plans to ensure consistency. This aspect also applied in my previous facility, since there is no accepted method to check the consistency of the treatment plans in the Philippines as well.
TRAINING OF PERSONNEL
The paper itemized the personnel involved in the program which include the radiation oncologist, authorized medical physicist, radiation safety officer, dosimetrist, nurse and radiation therapy technologist. In the US, the physician and physicist should be certified by the appropriate medical specialties board and had special training in brachytherapy. In case of the Philippines, the brachytherapy physicist should have masters degree in medical physics and at least have 1 year working experience. This is due to the fact that medical physicist board examination is not implemented yet in the country. For radiation oncologists, they are required to get a certification from the Philippine Regulatory Commission. Of prime importance is the radiation safety training that all personnel involved in HDR treatments should undergo. At CCF, annual training to review and discuss in detail what each member of the brachytherapy team would do in various emergency situations. I agree with CCF with their practice and I suggest that it should be implemented in all brachytherapy facilities in our country although PNRI conducts training and exam in radiation protection.
1. Wilkinson DA, Clouser E, Fleming PA. A method for checking HDR
brachytherapy treatment plans. Radiother Oncol 2004; 71 (supp 2):S47.
2. Kubo HD, Chin RB. Simple mathematical formulas for quick checking of singlecatheter
HDR brachytherapy treatment plans. Endocurietherapy/Hyperthermia
I'm very thankful to the author of this article because his paper really served as a guide for me when I was just starting in HDR brachytherapy.