Evaluation of Dosimetric Robustness of Carbon Ion Boost Therapy for Anal Carcinoma

Abstract

Purpose: The radiation therapy treatment outcome of human papillomavirus–negative anal carcinoma may be improved by the biological effectiveness of carbon ions. However, abdominal tissue motion can compromise the precision of carbon ion therapy. This work aims to evaluate the dosimetric feasibility of carbon ion boost (CIB) therapy for anal carcinoma. Materials and Methods: An algorithm to generate computed tomographies based on daily magnetic resonance imaging data and deformable image registration was developed. By means of this algorithm, fractional computed tomography data for 54 treatment fractions for 3 different patients with anal carcinoma were derived. The dose for a sequential CIB (CIBseq) treatment plan was recalculated on the fractional computed tomography data and accumulated over the number of fractions. The resulting dose distributions were compared to standard intensity-modulated radiation therapy treatment with an integrated photon boost. Results: For the investigated patient cases, similar dosimetric results for CIBseq treatment and for intensity-modulated radiation therapy with an integrated photon boost were found. For CIBseq treatment, bladder-filling variation had the strongest influence on the dose distribution. However, the detrimental effects on the mean target dose remained below 1 Gy (RBE) as compared to photon therapy. Conclusion: This study shows the dosimetric feasibility of CIB therapy for anal carcinoma for the first time and gives reason for clinical exploitation of the enhanced biological effect of carbon ions for patients with human papillomavirus–negative anal cancer.

The Emerging Potential of Multi-Ion Radiotherapy

“…Seeking adequate base dose with strategically deployed high-LET irradiation led to initial combination studies, specifically modern CIRT-boost treatments ( 45 ) (p). Boost treatments typically combine CIRT or the lower-LET proton beam with intensity-modulated [photon] radiation therapy (IMRT), tomotherapy, or other forms of conventional radiotherapy ( 26 , 53 – 59 ). Schulz-Ertner and colleagues in 2005 deployed carbon-boosted photon on adenoid cystic carcinoma to achieve three times the locoregional control of photon at 4 years ( 60 ).…”