Although the underlying radiobiological mechanisms have not been understood completely yet and the target cells and/or target structures have not been clearly identified, there is a general consensus on the definition of the target volume:
• The target volume of IVB is the entire vessel wall in the section of the vessel injured by the interventional procedures plus a safety margin on both sides. Furthermore, the target vol-ume is significantly longer than the length of the lesion of the stenosis.
• The safety margin is a length of at least 5 mm for the use in coronary arteries and of at least 10 mm in peripheral vessels.
• Caution: It has to be considered that on both ends of uniformly active line, cylinder or vol-ume sources only 50% of the dose which is present at a uniform radial distance from the middle plane of the source will be applied.
• For the treatment of long target volumes sufficiently long sources or sufficiently long travel-ling distances for stepping point sources should be used. For typical length of stenosis of 15-20 mm the associated injured length may amount to 30 to 40 mm. Longer intracoronary lea-sons, treated interventionelly may have a length up to 90 mm.
For multisegmental irradiation performed by lining up individual irradiations using line, cyl-inder or volume sources - as a transitional solution, cf. 9., until appropriately long sources are available - it should be ensured that within the injured section there will be no underdosage between segments which might lead to irradiation-induced neointimal hyperplasia.
8. Documentation
The requirements of the standards DIN 6827-2 and 6827-3 in regard to recording the relevant parameters for intravascular brachytherapy should be observed, cf. sample in Attachments 12.3 and 12.4. For each intravascular radiotherapy treatment a prescription, a treatment plan and a treatment record must be created and signed and dated by the personnel responsible for the planning and performance of the irradiation (radiotherapist/nuclear medical personnel, medical physicist, cardiologist/angiologist) (cf. sample for recording in Attachments 12.3 and 12.4).
The prescription, treatment plan and treatment record must be stored for 30 years.
8.1 Radiotherapeutic prescription
8.1.1 Relevant parameters for reporting intravascular brachytherapy
The following relevant parameters of intravascular brachytherapy should be determined and their values reported - even if the protocoll of a clinical trial requests different data:
Relevant parameters of intravascular brachytherapy are:
• The target volume, which has to be localized and recorded: Vessel and vessel section, radial extension and longitudinal extension of the target volume. Additionally, the reference di-ameter of the vessel and the minimal lumen didi-ameter (MLD) should be stated.
• The spatial distribution of the absorbed dose: the absorbed dose to water at the calibration reference point PRef , the dose volume histogram (DVH) or the mean dose and the dose variation (minimum and maximum dose) in the target volume (or in partial target structures and structures at risk).
To allow for international comparisons, and to be in accordance with the AAPM TG60 rec-ommendations, in the radiotherapeutic prescription, the absorbed dose prescribed should be specified at the system-related calibration reference point:
at PRef = 2 mm for all radiation sources used for intracoronary brachytherapy and
at PRef = 5 mm for all radiation sources used for brachytherapy in peripheral vessels.
In the radiotherapeutic treatment report the applied absorbed dose to water should be re-corded in a system-related way (cf. above), and also at the target volume-related dose speci-fication point:
at a mean tissue depth of z = 1 mm for intracoronary brachytherapy and
at a mean tissue depth of z = 2 mm for brachytherapy of peripheral vessels.
It has to be considered that the tissue depth should be determined from the luminal surface, not from the surface of the balloon used, as the balloon diameter is selected according to the minimal lumen diameter.
• The temporal distribution of dose: the absorbed dose rate in water at the system-related and at the target volume-related reference dose point as well as the effective irradiation time (in-cluding interruptions e.g. because of ischemia) should be reported.
• For a transition period – until appropriate standards are established for the representation and transfer of the quantity absorbed dose to water (cf. 9.) – for intravascular brachytherapy using gamma sources (a, b) there should be additional documentation of the nominal air kerma rate at a distance of 1 m from the center of gravity of the source (according to national and international recommendations: DIN 6814-8, DIN 6809-2, DIN 6827-3, DGMP-Bericht Nr. 13, Leitlinie in der Radioonkologie P3, ICRU 38, ICRU 58, AAPM TG 43, AAPM TG 60). For line sources, the length-related nominal air kerma rate should be recorded, too. In addition, the total nominal air kerma, i.e. the sum of the products of the nominal air kerma rates and the respective irradiation times should be documented.
• For brachytherapy with permanently implanted sources, the biologically as well as the physically relevant parameters should be documented. Biologically relevant parameters in-clude: the maximum dose rate and the dose which is achieved in a biologically relevant pe-riod of time, e.g. in 48 h at the radial calibration reference point at a distance of 2 mm. From a physical aspect, the dose which will be achieved in e.g. 28 days is of interest (AAPM TG 60). The physically relevant irradiation time should be specified (e.g. with three radioactive half life values).
8.1.2 Irradiation treatment plan
For the local application of sealed radioactive sources in therapy the standard DIN 6827-3 lays down the extent and form of the recordings. These recommendations should be transferred ac-cordingly to the recording of intravascular brachytherapy with all kinds of irradiation procedures (a-f, h) and sources. This should include those procedures which use liquid or gaseous radioac-tive materials for filling balloon catheters (f) or which use balloon catheters with a radioacradioac-tive layer in its wall (e).
General information to be recorded:
• Identification of patient, indication,
• radiotherapy prescription
type and purpose of treatment,
target volume,
• treatment plan:
planning documents
dose prescription,
application type and technique, specifications of the sources used, specifications of the source geometry,
information on the spatial distribution of dose,
rated values for the temoral distribution of dose (application time, maximum dose rate at PRef ).
• information on personnel involved, signatures, date, time.
8.2 Treatment record
For the treatment record of the intravascular brachytherapy, the values which were actually achieved should be documented:
• Identification of patient, indication,
• type and purpose of treatment, target volume,
• specification of dose delivered,
• information on interruptions,
• information on additional measures,
• actual values for the time-related dose distribution (application time, dose rate at PRef ),
• for radioactive stents (h): maximum dose rate at PRef ,
• specifications of dose rate equivalent of patient,
• information on personnel involved, signatures, date, time.
For intravascular radionuclide irradiation therapy using unsealed radioactive material (g) according to the standard DIN 6827-2 the following should be recorded in addition:
• Radioactive material: designation, radionuclide, origin,
• activity, date of delivery,
• purity of radionuclide(s),
• chemical purity (as a radiopharmaceutical),
• information on application: date and time, type of application,
• specification of the required data for the dose measurement,
• information on the dose measurement in emergencies (e.g. radiotoxicity, retained activity, effective half-life),
• information on the patient: date and time of discharge, specification of dose rate equivalent.
8.3 Treatment list, operating logbook, and device logbook
All patient-related treatment data should be recorded chronologically in the treatment list.
An operating logbook and a device logbook must be maintained. Beside the date, time and name of the responsible user, all observations of failures and countermeasures taken as well as quality controls and sealing checks must be recorded.
The treatment list must be signed by the specialized physician, the operating logbook must be signed by the specialized medical physicist on the day of the application.
The treatment list, the operating logbook and the device logbook must be retained for 30 years.