Purpose: Standard treatment of anal cancer is a protocol of combined chemotherapy and percutaneous radiotherapy. We developed a new endosonography-based radiation target simulation method, because endoanal sonography gives the best opportunity to stage the tumor accurately. Based on this method, an afterloading needle application procedure could be performed to optimize the radiation target geometry and to control the application of afterloading needles. In a prospective study, this new method was evaluated, with special regard for complications and tumor recurrence.
Methods: Anal cancer was restaged endosonographically six weeks after external beam radiation with 45 Gy. A computer-generated three-dimensional reconstruction of the tumor and radiation target simulation was performed based on endoanal sonographic imaging. By using a new type of applicator, which is permeable to ultrasound waves, the transperineal implantation procedure of afterloading needles could be controlled. Application needles were inserted into the target area according to the endoanal sonography-based dosimetry planing. The dose of the (high-dose rate) brachytherapy boost was started with two 6-Gy fractions, each within eight days. The fraction dose was reduced to 4 Gy to minimize side effects. Lymph node-positive tumors got additional chemotherapy (5-fluorouracil and mitomycin C).
Results: From January 1992 until August 1996, we performed 42 endosonography-guided afterloading procedures in 18 patients. One patient underwent percutaneous radiation two years before and was treated only by afterloading radiation. In every patient, we found complete tumor remission at the end of radiotherapy. Three patients with a high-dose rate of 2 x 6 Gy developed radiogenic proctitis, and two patients developed ulceration, which lead to reduction of the dose. After reduction to 4 Gy per fraction, no more side effects could be seen. In follow-up (median, 24 (range, 1-56) months), we detected two anal cancer recurrences (2/18 patients).
Conclusion: The radiation target field can be optimized by individual endosonography-based three-dimensional tumor reconstruction and radiotherapy simulation. Endosonography-guided transperineal implantation of afterloading needles can be performed according to the computer-generated simulation by using a new type of applicator. We could achieve total primary tumor remission in every patient. After reduction of the afterloading dose to 2 x 4 Gy, no brachytherapy-related side effects could be seen.