Prospects for proton therapy in carcinoma of the cervix.

Carcinoma of the cervix remains a serious problem worldwide. The results of radiation therapy varies from institution to institution, with actuarial 5-year survival rates for Stage IIIB disease of between 28 and 60%. The inferior survival figures can be ascribed to poor local control due to inadequate dosage, partly due to the non-use of intracavitary therapy. Results from the literature were reviewed to assess the optimal dose required to sterilize the primary, para-metrial and nodal disease within the pelvis. The aim of this study is to assess whether the target volume could be reduced to allow an increased dose to be delivered. Protons, in view of their physical characteristics, would aid this objective. From CT scans the minimal target volume was determined, and treatment plans for a 200 MeV proton beam were evaluated. It appears that a volume reduction of up to 60% in the target volume may be achieved with proton therapy when compared to the usual target volume achievable with photon therapy, and thus a 20% dose increment may be reasonable. This increased dose may translate to a 40% improvement in the local control rate without an expected increase in complications. An improved local control rate may lead to improved survival. A compatible technique of well-fractionated high dose rate intracavitary therapy (ICT) based on an indwelling intra-uterine tube is offered that will allow up to 10 fractions of ICT with only a single anaesthetic, to be integrated with a similar number of fractions of proton therapy.