1004 Clinical assessment of CT-MRI image fusion software in localization of the prostate for 3D conformal radiation therapy

Bulb of penis as a marker for prostatic apex in external beam radiotherapy of prostate cancer

PURPOSE

To investigate the relationship between the bulb of the penis and the peak of the urethrogram, and to compare this measurement with the ischial tuberosities (ITs) to peak distance.

METHODS AND MATERIALS

Pelvic CT scans from 50 consecutive patients with localized prostate cancer were analyzed to identify the penile bulb. Each patient was required to undergo retrograde urethrography during CT-based treatment planning with 3-mm slices. The peak of the urethrogram was defined as the last CT slice in which the contrast dye in the urethra could be visualized. Measurements were taken from the slice containing the most superior aspect of the penile bulb to the last slice of the urethrogram peak. The superior aspect of the penile bulb was defined as the CT slice nearest the peak that contained a bulbous structure at the base of the penis. This distance was defined as the bulb-peak distance. Similarly, the IT-peak distance was recorded for comparison.

RESULTS

The mean bulb-peak and IT-peak distances were calculated for 47 of 50 patients. The peak of the urethrogram was unable to be evaluated in 3 patients. The mean, median, and range bulb-peak distance was 2.4 mm (SD 1.8), 3 mm, and 0-6 mm, respectively. The mean, median, and range IT-peak distance was 20.1 mm (SD 6.6), 21 mm, and 6-33 mm, respectively. No patient had the bulb located above the apex of the urethrogram.

CONCLUSION

The bulb of the penis is a relatively consistent soft-tissue landmark compared with the ITs and is located an average of 3 mm below the peak of the urethrogram. Therefore, the bulb of the penis is another landmark for the identification of the prostatic apex and is less invasive than retrograde urethrography.

Trans-rectal ultrasonography (TRUS) with lipiodol injection for localization of the prostatic apex before radiotherapy planning

PURPOSE

To evaluate reliability of Trans-rectal ultra-sonography (TRUS) guidance with lipiodol injection for prostate localization before radiotherapy planning.

MATERIAL AND METHODS

From October 1997 to March 2000, 31 patients with prostatic adenocarcinoma and six patients with anastomotic recurrence after radical prostatectomy had TRUS-guided injection of lipiodol. Two milliliters of lipiodol were injected into each side of the prostate and 1 ml into both seminal vesicles with a 22 Gauge CHIBA needle and US probe guide before radiotherapy planning. We had established a contrast quality index (0 for no prostate enhancement to 5 for efficient pacification without any diffusion). On simulation films, we had performed anatomic measurements for comparison with other anatomic studies.

RESULTS

For all 37 patients, TRUS-guided injection was well tolerated. Among 31 patients with the prostate in situ, three had no apex opacification and 15 had no vesicle enhancement or peri-vesicle space diffusion. However, in 19 patients there was good contrast quality with an index score of > or =3. The majority of patients had prostatic apex between 1.5 and 3.5 cm from ischial tuberosities ligne (27 from 28 evaluable for apex). Among 19 evaluable patients, 15 had seminal vesicles 2-4 cm above the top of pubis. For six patients with anastomotic recurrence after radical prostatectomy, lipiodol was precious aid to locate it. We had only one failure because of a precocious bladder absorption relating to a delay which is too long between rectal probe locating and portal films.

CONCLUSION

TRUS injection of lipiodol is a simple, inexpensive, relatively safe technique for localization of prostatic apex, but not appropriate for seminal vesicles enhancement. This is also an interesting method to locate anastomotic recurrence.

Imaging and radiotherapy of the prostate

Prostate cancer is the most common malignancy diagnosed in men. Over the past 10 to 20 years, advances in screening and diagnostic and management paradigms have led to improved treatment outcomes. This article offers an overview of the evolution of the role and nature of diagnostic imaging techniques in the management of prostate cancer.

The role of retrograde urethrography in the planning of prostate cancer radiotherapy

This analysis was performed to examine the role of retrograde urethrography in the planning of prostate cancer irradiation. Retrograde urethrograms were performed in 91 patients at the time of simulation. The abrupt narrowing of the contrast column in the urethra was visualized in each case. The distance between the abrupt narrowing of the contrast column and a line connecting the lower poles of the ischial tuberosities was measured in each patient. This distance ranged from 2 to 33 mm with a mean and median of 14 mm. A review of the literature revealed that the abrupt narrowing of the contrast column lies between 5-13 mm inferior to the prostate apex as determined by computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonography. The prostate apex will be adequately covered by placing the inferior edge of the treatment field 15 mm below the abrupt narrowing of the contrast column. This technique will result in at least 20 mm between the prostate apex and the inferior field edge. Performing a retrograde urethrogram at the time of simulation can help prevent geographic misses of the prostate gland when delivering radiation for prostate cancer.

Localization of the prostatic apex for radiotherapy treatment planning using urethroscopy

PURPOSE

To assess the ability of computed tomography (CT) scans and retrograde urethrograms to accurately define the prostatic apex in the craniocaudad dimension, using urethroscopy as a reference.

METHODS AND MATERIALS

Plain film radiographs of the pelvis were obtained in 15 patients with early-stage adenocarcinoma of the prostate, with the tip of a urethroscope held in place at the external sphincter, which most closely approximates the prostatic apex. The scope was then withdrawn, and a retrograde urethrogram was performed. Immediately afterwards, a CT scan of the pelvis was obtained. Because differential filling of the bladder and rectum affects the position of the prostatic apex, patients voided prior to rather than in between the three consecutive studies.

RESULTS

The urethroscopy-defined prostatic apex was located 4 +/- 8 mm (mean +/- SD) superior to the CT-defined apex, 13 +/- 3 mm (mean +/- SD) superior to the urethrogram tip and 30 +/- 7 mm (mean +/- SD) superior to the ischial tuberosities. There was significant interobserver variability in the location of the prostatic apex as determined by CT scans. Placement of the inferior border of the radiation portals at the ischial tuberosities would have resulted in irradiation of > or = 20 mm bulbar urethra, as defined by the dye column of the retrograde urethrogram, in 6 out of 15 (40%) of the patients and irradiation of < 10 mm bulbar urethra in 2 out of 15 (13%) of the patients.

CONCLUSION

Because the prostate blends inferiorly with the urogenital diaphragm, CT scans do not allow one to precisely localize the prostatic apex. Due to anatomic variability, the ischial tuberosities do not allow one to accurately localize the prostatic apex. Retrograde urethrograms provide helpful supplemental information regarding the position of the prostatic apex for radiotherapy treatment planning.