Pelvic Radiation Therapy: Implications for the Small Bowel

Hani Ashamalla, MD, FCCP, and David Silver, MD, Radiation Oncology Department, New York Methodist Hospital, Brooklyn, NY (HA), and the Urologic Oncology Service, Maimonides Medical Center, Brooklyn, NY (DS)

November 27, 2001

Case Description

A 66-year-old man, with two prior transurethral prostate surgeries for prostatism, presented with gross painless hematuria. Digital rectal examination (DRE) revealed a markedly enlarged prostate without induration or nodularity, and serum prostate-specific antigen (PSA) was 22 ng/mL. Urothelial evaluation was unremarkable. Transrectal sextant prostate needle core biopsies showed prostatic adenocarcinoma, Gleason's score 3 + 4 = 7/10. Radionuclide bone scan showed no evidence of osseous metastasis. The patient elected radiotherapy with neoadjuvant androgen deprivation. After four months of total androgen blockade, serum PSA was undetectable. At the time of computed tomography (CT) scan planning for conformal radiotherapy, multiple small bowel loops were noted in the pelvis, as well as a large prostatic volume (Figs 1-2).

Which of the following answers is most appropriate?

  1. The patient is not a candidate for radiotherapy and should be referred for radical prostatectomy.

  2. The patient is not a candidate for radiotherapy or surgery, and hormonal ablation therapy only should be continued.

  3. The patient is not a candidate for external radiotherapy, so interstitial implantation (brachytherapy) should be administered.

  4. The patient can be treated with conformal radiation therapy in a prone position so that the small bowel may be outside the field.

View the correct answer.

The tolerance (TD 5/5) of the small bowel to radiation therapy is in the range of 45 to 50 Gy.[1] Radiation-induced small bowel injury may vary from Radiation Therapy Oncology Group (RTOG) grade 1 (abdominal cramps occur) to grade 4 (surgical intervention is warranted). Table 1 illustrates the various small bowel toxicities within the RTOG grading system. Repositioning of the small bowel in the pelvis after abdominopelvic surgery is not uncommon and can be largely prevented by intraoperative placement of surgical mesh or the creation of an omental sling (Table 2).[2] Additionally, several nonsurgical strategies may be used to reduce the volume of the small bowel within the planned postoperative field. These include the use of multiple fields technique, full bladder, prone positioning and "false tabletop" (Table 3).[2]

Our patient had no prior history of abdominal surgery, and no abdominal scars were observed. Surprisingly, CT scan study revealed a large volume of the small bowel in the pelvis overlapping the seminal vesicles (Figs 1-2), which would result in predictable morbidity with the delivery of the planned doses of close to 70 Gy. Repeat CT planning done in the prone position with a full bladder showed that at least 90% of the small bowel previously visualized in the pelvis was displaced outside the target classically covered for prostate cancer (Figs 3-4). Sagittal and coronal films also demonstrated the marked change of the small bowel volume in this prone position (Figs 5-6).

Although radical prostatectomy is not an option for this patient, the markedly elevated serum PSA of 22 ng/mL predicts lymph node involvement in approximately 22% of cases, according to Roach's formula.[3] In this setting, with a predicted cure rate of less than 80%, few patients are willing to incur the potential morbidity of prostatectomy (partial incontinence or impotence)[4] merely to achieve local control. Conversely, hormonal ablation therapy alone is not the standard of care for disease that is clinically localized. Given the history of multiple prior transurethral prostate surgeries, dose delivery is unreliable with interstitial implantation alone.

Our patient was treated with external radiation therapy. A dose of 45 Gy was delivered to the true pelvis, followed by a boost to the prostate and periprostate tissues using conformal radiation therapy to a total dose of 70.20 Gy in seven weeks.