H. Lee Moffitt Cancer Center & Research Institute

Imaging in Oncology

(ANSWER)

Answer:

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

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
Table 1. — RTOG Gastrointestinal Morbidity Scoring System
Grade 0 Grade 1 Grade 2 Grade 3 Grade 4
None Mild diarrhea Moderate diarrhea and colic Obstruction or bleeding requiring surgery Necrosis
  Mild cramping     Perforation
  Bowel movement 5 times daily Bowel movement >5 times daily   Fistula
  Slight rectaldischarge or bleeding Excessive rectal mucus or intermittent bleeding    

 

Table 2. — Surgical Techniques to Minimize Toxic Effects in the Small Bowel From Pelvic Radiation Therapy
Reconstruct pelvis to exclude small bowel from pelvis
Reperitonealize pelvic floor
Retrovert the uterus
Construct omental sling
Insert absorbable mesh
Place clips to delineate high-risk areas
Data adapted from Cohen.2

 

Table 3. — Radiation Therapy Techniques to Minimize Toxic Effects
in the Small Bowel From
Pelvic Radiation Therapy
During Planning:
Use small bowel radiographs during simulation
Consider the liberal use of other diagnostic tools (eg, CT, ultrasound, or magnetic resonance imaging) to delineate tumor-small bowel relationship
Place the patient in prone position
Use multiple fields for pelvic treatment, with judicious blocking
Use carefully planned boost fields
During Treatment:
Distend bladder (with patient prone)
Use external compression
Use "false tabletop"
Use small doses per fraction (18 Gy) or hyperfractionation (bid)
Regulate patient’s diet
Potential:
Use of radioprotectors
Data adapted from Cohen et al.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).

Fig 3. — Axial CT scan image in a prone position (figure is reversed) in the same anatomical slice of Fig 1. This image demonstrates lack of the small bowel in the pelvis.

 


Fig 4. — Axial CT scan image in a prone position taken at the same anatomical slice of Fig 2. This image shows complete displacement of the small bowel from this region.

 


Fig 5. — Sagittal reconstruction CT scan demonstrating displacement of the small bowel contrast outside the pelvis (arrow).

 


Fig 6. — Coronal reconstruction CT scan demonstrating displacement of the small bowel contrast outside the pelvis (arrow).

 

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.

References

1. Rubin P. The law and order of radiation sensitivity, absolute vs relative. In: Vaeth JM, Meyer JL, eds. Radiation Tolerance of Normal Tissues, Frontiers of Radiation Therapy and Oncology. 23rd Annual San Francisco Cancer Symposium, San Francisco, Calif, March 4-5, 1988. Basel, Switzerland: Karger; 1989:7-40.

2. Cohen A, Minsky B, Friedman M. Colorectal cancer. In: DeVita VT Jr, Hellman S, Rosenberg S, eds. Cancer: Principles and Practice of Oncology. 5th ed. Philadelphia, Pa: Lippincott Raven; 1997:1144-1184.

3. Roach M 3rd, Marquez C, Yuo HS, et al. Predicting the risk of lymph node involvement using the pre-treatment prostate specific antigen and Gleason score in men with clinically localized prostate cancer. Int J Radiat Oncol Biol Phys. 1994;28:33-37.

4. Murphy GP, Mettlin C, Menck H, et al. National patterns of prostate cancer treatment by radical prostatectomy: results of a survey by the American College of Surgeons Commission on Cancer. J Urol. 1994;152:1817-1819.
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