A simple technique for irradiation of recto-anal cancers with electrons using an internal anal shield

A method of treating the primary site of recto-anal cancers using an en face electron beam in combination with an internal lead shield in the anus has been developed. Dose measurements using lithium fluoride thermoluminescent dosimetry indicate that the internal anal shield reduces the dose to the uninvolved anal wall by up to a factor of two while leaving the dose to the primary tumor site unaffected. Because the internal anal shield is placed in the anus during treatment, this system leads to a more precise daily positioning of the shield compared to the setup using an external shield alone. This technique has been used to treat two patients with anal cancer who tolerated the treatment well with no acute side effects. Both patients are now disease free, more than 30 months after their radiation treatment, without any treatment-related sequelae.