Quality control in interstitial brachytherapy of the breast using pulsed dose rate: treatment planning and dose delivery with an Ir-192 afterloading system.
OBJECTIVE
In the Radiotherapy Department of Leuven, about 20% of all breast cancer patients treated with breast conserving surgery and external radiotherapy receive an additional boost with pulsed dose rate (PDR) Ir-192 brachytherapy. An investigation was performed to assess the accuracy of the delivered PDR brachytherapy treatment. Secondly, the feasibility of in vivo measurements during PDR dose delivery was investigated.


METHODS
Two phantoms are manufactured to mimic a breast, one for thermoluminescent dosimetry (TLD) measurements, and one for dosimetry using radiochromic films. The TLD phantom allows measurements at 34 dose points in three planes including the basal dose points. The film phantom is designed in such a way that films can be positioned in a plane parallel and orthogonal to the needles.


RESULTS
The dose distributions calculated with the TPS are in good agreement with both TLD and radiochromic film measurements (average deviations of point doses <+/-5%). However, close to the interface tissue-air the dose is overestimated by the TPS since it neglects the finite size of a breast and the associated lack of backscatter (average deviations of point doses -14%).


CONCLUSIONS
Most deviations between measured and calculated doses, are in the order of magnitude of the uncertainty associated with the source strength specification, except for the point doses measured close to the skin. In vivo dosimetry during PDR brachytherapy treatment was found to be a valuable procedure to detect large errors, e.g. errors caused by an incorrect data transfer.
Mangold
C A
CA
Department of Oncology, Section of Radiation Physics, University Hospital Leuven, Herestraat 49, 3000, Leuven, Belgium.
Rijnders
A
A
Georg
D
D
Van Limbergen
E
E
Pötter
R
R
Huyskens
D
D
D001918:Brachytherapy / Q000379:methods* / Q000592:standards; D001943:Breast Neoplasms / Q000532:radiotherapy*; D002138:Calibration; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005373:Film Dosimetry / Q000379:methods; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D019047:Phantoms, Imaging; D011786:Quality Control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D013819:Thermoluminescent Dosimetry / Q000379:methods
D007496:Iridium Radioisotopes