Reirradiation for De novo Anorectal Cancers in Patients with a History of Prostate Radiation Therapy: Dosimetric Considerations and Practical Radiation Planning Techniques

This case report examines the treatment planning approach for patients receiving anorectal radiotherapy with a history of prostate radiotherapy. Three cases are presented: two of these patients received prior 50.4 Gy in 28 fractions via external beam radiation therapy, where one proceeded to obtain a cone-down of 30.6 Gy in 17 fractions, while the other received 100 Gy of low-dose-rate brachytherapy; the third patient only received prior low-dose-rate brachytherapy to an unknown dose due to absent prior planning records. This paper explores the unique challenges this reirradiation setting poses, outlines treatment planning strategies to overcome these obstacles, and reviews retreatment dose constraints from the literature.