Comparison of different external beam treatment techniques to deliver high-dose irradiation to local recurrent rectal carcinoma

Aims and background: Treatment of local-regional recurrent rectal carcinoma is a challenging problem, and local control may be dose dependent; doses should probably exceed 60 Gy. Our aim was to verify the possibility to deliver 66 Gy to the target, but less than 35 Gy to the small bowel, comparing different 3D irradiation techniques, in a selected group of patients. Methods: Five patients with local recurrent rectal carcinoma were selected as representative of different presentations of the disease. Gross tumor volume and clinical target volume were defined [by RS]. Tumors ranged between 182 and 540 cc, and small bowel volumes between 748 and 1050 cc. A three-field technique, coplanar multiple fields, noncoplanar fields and a proton beam were compared using dose volume histograms. A positive result was scored when ≥90% of the target received the prescribed dose with no more than 5% of the small bowel receiving more than 35 Gy. Doses were escalated in steps of 2 Gy from 60 to 66 Gy. Results: The number of plans fitting the constraints were 7/19, 11/19, 18/19 for doses of 66 Gy, 64 Gy and 62 Gy, respectively. The stage of the tumor did not seem to correlate with the possibility to homogeneously cover the target with the prescribed dose. Conclusions: Simple coplanar and complex coplanar techniques (up to six fields), positioning the patient in a prone position with dislocation of the bowel, seem to be the best solutions to treat almost all of the patients with doses of 64 Gy. Where higher doses are concerned, it is not possible to suggest a "standard" solution. More personalized techniques have to be tested to define the best option.