[Intensity-modulated radiation therapy for anal carcinoma]

[Recommendations for the management of cancers of the anal canal]

Anal canal carcinomas remain rare, but their management has improved recently. The PET-CT is now used as a standard at the first diagnosis and after relapses. The introduction of intensity-modulated irradiation techniques makes it possible to better conform the pelviperineal and inguinal volumes, improving the homogeneity of the irradiation while sparing some pelvic structures, thus reducing acute and late effects. Nevertheless, the conversion from 3D to intensity-modulated radiotherapy needs a specific and careful approach, mainly for the management of the perineal region, where relapses and complications occur. Last but not least, new chemotherapy associations are studied for metastatic disease.

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.

[Strategy for technical evaluation in radiation oncology: methodological and ethical aspects, the French society for radiation oncology's opinion]

Evidence-based medicine is a paradigm founded on a hierarchy of research design, accepted as a dogma. Applied to radiation oncology, and specifically to radiotherapy technical comparisons, evidence-based medicine implies methodological and ethical problems. The concept of "incremental" evolution and the dosimetric evidence are proposed as an acceptable alternative to comparative clinical trials if total dose, time, fractionation, and target volumes are not modified. For other situations, either randomized comparative trials or observational studies are needed. When randomized comparative trials are not possible, observational studies, whose validity can be enhanced by appropriate methodology, must be considered as a valid method.

[Image guidance for the evaluation of setup accuracy]

Information obtained by different methods of image-guided radiotherapy now allows us to reposition the target volume. This evolution causes a change in practice and positioning control. In order to control positioning errors, a systematic control during the first three to five sessions is required. Random repositioning errors and clinical target volume motions can be mastered only by performing a daily imaging. Finally, image-guided radiotherapy allows assessing anatomical changes occurring during treatment, and opens the field of adaptive radiotherapy.