Postimplant dosimetry using a Monte Carlo dose calculation engine: a new clinical standard.
OBJECTIVE
To use the Monte Carlo (MC) method as a dose calculation engine for postimplant dosimetry. To compare the results with clinically approved data for a sample of 28 patients. Two effects not taken into account by the clinical calculation, interseed attenuation and tissue composition, are being specifically investigated.


METHODS
An automated MC program was developed. The dose distributions were calculated for the target volume and organs at risk (OAR) for 28 patients. Additional MC techniques were developed to focus specifically on the interseed attenuation and tissue effects.


RESULTS
For the clinical target volume (CTV) D(90) parameter, the mean difference between the clinical technique and the complete MC method is 10.7 Gy, with cases reaching up to 17 Gy. For all cases, the clinical technique overestimates the deposited dose in the CTV. This overestimation is mainly from a combination of two effects: the interseed attenuation (average, 6.8 Gy) and tissue composition (average, 4.1 Gy). The deposited dose in the OARs is also overestimated in the clinical calculation.


CONCLUSIONS
The clinical technique systematically overestimates the deposited dose in the prostate and in the OARs. To reduce this systematic inaccuracy, the MC method should be considered in establishing a new standard for clinical postimplant dosimetry and dose-outcome studies in a near future.
Carrier
Jean-François
JF
Département de Radio-Oncologie, et Centre de Recherche du CHUM, Hôpital Notre-Dame du CHUM, 1560 rue Sherbrooke Est, Montréal, Québec, Canada. jean-francois.carrier.chum@ssss.gouv.qc.ca
D'Amours
Michel
M
Verhaegen
Frank
F
Reniers
Brigitte
B
Martin
André-Guy
AG
Vigneault
Eric
E
Beaulieu
Luc
L
D001918:Brachytherapy / Q000379:methods* / Q000592:standards; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D009010:Monte Carlo Method; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage / Q000592:standards; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D014521:Urethra / Q000528:radiation effects
D007457:Iodine Radioisotopes