The role of particle therapy in the treatment of locally recurrent rectal cancer: a systematic review.

Colorectal cancer is a common malignancy. Advancements in multimodality treatment have improved outcomes. About 2-10% of patients will have a local recurrence even after optimal treatment. Salvage surgical treatment is the treatment of choice, however, in posterior and lateral recurrences, surgery is linked to a high rate of treatment-related morbidity. Some recurrences remain unresectable even after neoadjuvant treatment. A systematic literature review was performed to search for studies on curative-intent radiation therapy (RT) with photons, stereotactic body radiation therapy (SBRT) and particle beam therapy. The aim of the literature search was to define the role of particle therapy in the treatment of patients with unresectable or inoperable local recurrences of rectal cancer where neoadjuvant treatment is unlikely to result in downstaging, leaving patients with RT as the only curative treatment option. 32 studies which fulfil the criteria were identified. In general, SBRT and particle beam therapy permitted the application of significantly higher doses to the target without a concomitant increase in treatment-related toxicities. For unresectable and inoperable locally recurrent rectal cancer ablative radiotherapy techniques such as SBRT and particle beam therapy offer a curative treatment approach as an alternative to surgery. SBRT can be offered for small local and nodal recurrences, while particle beam therapy can be offered for larger recurrences and complex shapes spanning several anatomical compartments as well. Further research is needed to stratify patients according to their need and eligibility for the different possible modalities of curative-intent RT.