Comparison of Tomotherapy Versus Intensity-modulated Step-and-shoot and Conventional Radiation Treatment Plans for Patients With Locally-advanced Squamous Cell Carcinoma of the Cervix

Background Information:

The addition of concurrent chemotherapy to radiotherapy (RT) for locally-advanced cervix cancer has improved patient outcomes, but treatments are associated with significant rates of radiotherapy (RT)-related toxicities. Plus, the disease-free and overall survival benefits conferred by concurrent chemotherapy appear to be most prominent in patients with earlier stage disease. Limits to RT for cervix cancer which can impact patient outcomes are overall treatment time and RT dose. Attempts to overcome these limits have been made in trials using altered RT fractionation schemes. Promising rates of local control reported in these trials are offset by excessive rates of acute and late RT-related toxicities.

Intensity-modulated radiotherapy (IMRT) is innovative RT planning and delivery technology with the ability to vary the intensity of radiation across a beam, allowing for increased conformity of RT dose around target volumes along with decreased dose delivered to normal structures. Tomotherapy uses an intensity-modulated beam which rotates around the patient as the patient is being translated longitudinally through the gantry and features the ability to acquire megavoltage CT (MVCT) images of target structures at each treatment. It is thought that Tomotherapy can plan and deliver more conformal RT with the added advantage of daily assessment of target and critical structure position via MVCT imaging.

Experience with using IMRT for cervix cancer is sparse. Reports of treating pelvic nodal targets in small numbers of selected cervix cancer patients with IMRT suggests that the treatments are tolerable and associated with decreased incidences of acute and late RT-related toxicities compared with a similar patient cohort treated with conventional RT technologies. Currently, there is no published report of using Tomotherapy to plan or deliver RT using conventional or altered fractionation for cervix cancer patients.

The limitations of overall treatment time and the maximal dose of RT that can be safely delivered to the pelvis targets make cervical carcinoma a tumor in which Tomotherapy can potentially improve the therapeutic ratio. Tomotherapy's ability to deliver more conformal RT to target structures and minimize dose to normal structures may allow for delivery of altered fractionation radiation plans for cervix cancer with acceptable rates of RT-related toxicities. Tomotherapy allows for delivery of differential daily doses of RT to target volumes that lie within larger target volumes which in effect delivers a simultaneous integrated boost (SIB) to areas of gross disease which lie within a larger volume at risk for harbouring micrometastases. Delivery of the boost dose of radiation in a simultaneous as opposed to sequential fashion decreases the overall RT treatment time which theoretically reduces the effects of accelerated tumor cell repopulation. Delivering higher doses per fraction to areas of gross disease would theoretically increase the radiobiologic enhancement effects of concurrent cisplatin chemotherapy.