Dose-volume histogram evaluation of prone and supine patient position in external beam radiotherapy for cervical and endometrial cancer.
OBJECTIVE
To evaluate the influence of patient positioning on dose-volume histograms of organs at risk in external beam radiotherapy for cervical and endometrial cancer.


METHODS
In 20 patients scheduled for definitive (7) or postoperative (13) external beam radiotherapy of the pelvis treatment planning CT scans were performed in supine and prone (belly board) positions. After volume definition of target and organs at risk treatment plans were calculated applying the four-field box technique. The dose-volume histograms of organs at risk were compared.


RESULTS
Radiotherapy in prone position causes a reduction of the bladder portion (mean 15%, p<0.001) and an increase of the rectum portion (mean 11%, p<0.001) within the 90% isodose. A reduction of the bowel portion could only be observed in postoperatively treated patients (mean 13%, p<0.001). In definitive radiotherapy the target volume increases in supine position (mean 7%, p=0.02) due to an anterior tumour/uterus movement, so that bowel portions within the 90% isodose are similar. The bladder filling correlates with a reduction of bladder and bowel (postoperatively treated patients) dose.


CONCLUSIONS
External beam radiotherapy of the pelvis should be performed in prone position in postoperative patients because of best bowel protection. Considering the additional HDR brachytherapy rectum protection takes the highest priority in definitive treatment-the requirements are best met in supine position. An adequate bladder filling is important to reduce the irradiated bladder and bowel volumes.
Pinkawa
Michael
M
Klinik für Strahlentherapie, Universitätsklinikum der RWTH Aachen, Pauwelsstr. 30, Aachen 52057, Germany.
Gagel
Bernd
B
Demirel
Cengiz
C
Schmachtenberg
Axel
A
Asadpour
Branka
B
Eble
Michael J
MJ
D016889:Endometrial Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007422:Intestines / Q000528:radiation effects; D016684:Prone Position; D011832:Radiation Injuries; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000528:radiation effects; D016683:Supine Position; D001743:Urinary Bladder / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*