Influence of volumes of prostate, rectum, and bladder on treatment planning CT on interfraction prostate shifts during ultrasound image-guided IMRT.
OBJECTIVE
The purpose of this study was to analyze the relationship between prostate, bladder, and rectum volumes on treatment planning CT day and prostate shifts in the XYZ directions on treatment days.


METHODS
Prostate, seminal vesicles, bladder, and rectum were contoured on CT images obtained in supine position. Intensity modulated radiation therapy plans was prepared. Contours were exported to BAT-ultrasound imaging system. Patients were positioned on the couch using skin marks. An ultrasound probe was used to obtain ultrasound images of prostate, bladder, and rectum, which were aligned with CT images. Couch shifts in the XYZ directions as recommended by BAT system were made and recorded. 4698 couch shifts for 42 patients were analyzed to study the correlations between interfraction prostate shifts vs bladder, rectum, and prostate volumes on planning CT.


RESULTS
Mean and range of volumes (cc): Bladder: 179 (42-582), rectum: 108 (28-223), and prostate: 55 (21-154). Mean systematic prostate shifts were (cm, +/-SD) right and left lateral: -0.047 +/- 0.16 (-0.361-0.251), anterior and posterior: 0.14 0.3 (-0.466-0.669), and superior and inferior: 0.19 +/- 0.26 (-0.342-0.633). Bladder volume was not correlated with lateral, anterior/posterior, and superior/inferior prostate shifts (P > 0.2). Rectal volume was correlated with anterior/posterior (P < 0.001) but not with lateral and superior/inferior prostate shifts (P > 0.2). The smaller the rectal volume or cross sectional area, the larger was the prostate shift anteriorly and vice versa (P < 0.001). Prostate volume was correlated with superior/inferior (P < 0.05) but not with lateral and anterior/posterior prostate shifts (P > 0.2). The smaller the prostate volume, the larger was prostate shift superiorly and vice versa (P < 0.05).


CONCLUSIONS
Prostate and rectal volumes, but not bladder volumes, on treatment planning CT influenced prostate position on treatment fractions. Daily image-guided adoptive radiotherapy would be required for patients with distended or empty rectum on planning CT to reduce rectal toxicity in the case of empty rectum and to minimize geometric miss of prostate.
Reddy
Nandanuri M S
NM
Department of Radiation Oncology, New York Hospital Queens, Flushing, New York 11355, USA. nmr9001@nyp.org
Nori
Dattatreyudu
D
Sartin
William
W
Maiorano
Samuel
S
Modena
Jennifer
J
Mazur
Andrej
A
Osian
Adrian
A
Sood
Brijmohan
B
Ravi
Akkamma
A
Sampath
Seshadri
S
Lange
Christopher S
CS
D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D009068:Movement; D009929:Organ Size; D011467:Prostate / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D012007:Rectum / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D001743:Urinary Bladder / Q000033:anatomy & histology* / Q000000981:diagnostic imaging