IMRT, RapidArc® and conformal radiotherapy in the treatment of tumours of the anal canal

Purpose: To compare dosimetric results of the use of RapidArc® with simultaneous integrated boost, sliding window intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost, and conformal radiotherapy with sequential boost in the management of anal canal cancer. Methods: Two patients with squamous cell cancer of the anal canal with compromised inguinal nodes were included. The simulation was performed in the supine position with a customized Vac-Lok™ immobilizer. Treatment volumes and organs at risk were defined in accordance with international recommendations. Dosimetric comparisons were made in the target volume by means of tumour conformity, coverage, and homogeneity indexes; in healthy organs, integral doses were compared. Results: A similar planning target volume coverage was achieved with the three techniques. The two IMRT techniques demonstrated benefits in doses received by healthy organs compared to the conformal radiotherapy. RapidArc® showed reduction in the execution time and monitor units required for treatment compared with sliding window IMRT. Conclusions: The IMRT showed coverage and tumour conformity indexes similar to those of conformal radiotherapy with better dosimetric results in the organs at risk, which should translate into a better toxicity profile. RapidArc® demonstrated benefits over the sliding window IMRT, which makes treatment more comfortable for the patient with less uncertainty about intrafraction motion and a reduced potential for radiation-induced tumours.