Dosimetric impact of the variation of the prostate volume and shape between pretreatment planning and treatment procedure.
OBJECTIVE
The goal of this study is to evaluate the dosimetric impact on a pretreatment planning of prostatic volume and shape variations occurring between the moment of the volume study (preplanning) and just before a transperineal permanent seed implant procedure. Such variations could be an obvious source of misplacement of the seeds relative to the prostate gland and organs at risk. Other sources of dosimetric uncertainties, such as misplacement due to the procedure itself or edema, are eliminated by looking at these variations before the implant procedure.


METHODS
For 35 clinical cases, prostate contours were taken at preplanning time as well as in the operating room (OR) minutes before the procedure. Comparison of shape and volume between the two sets was made. The impact on V100 was evaluated by placing the seeds in their planned positions in the new volume (clinical situation) and also by performing a new plan with the second set of contours to simulate an intraoperative approach.


RESULTS
The volume taken in the OR remained unchanged compared to the pretreatment planning volume in only 37% of the cases. While on average the dose coverage loss from pretreatment planning due to a combination of variations of volume and shape was small at 5.7%, a V100 degradation of up to 20.9% was observed in extreme cases. Even in cases in which no changes in volume were observed, changes in shape occurred and strongly affected implant dosimetry.


CONCLUSIONS
Variations of volume and shape between pretreatment planning and the implant procedure can have a strong impact on the dosimetry if the planning and the implant procedure are not performed on the same day. This is an argument in favor of performing implant dosimetry in the OR.
Beaulieu
Luc
L
Department of Radiation Oncology and Centre de Recherche en Cancérologie de l'Université Laval, Hôtel-Dieu de Québec, Centre Hospitalier Universitaire de Québec (CHUQ), 11 Cote du Palais, Québec G1R 2J6, Canada. beaulieu@phy.ulaval.ca
Aubin
Sylviane
S
Taschereau
Richard
R
Pouliot
Jean
J
Vigneault
Eric
E
D001918:Brachytherapy; D006801:Humans; D008297:Male; D055585:Physical Phenomena; D010825:Physics; D011467:Prostate / Q000473:pathology*; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage