Megavoltage CT (MVCT) Imaging for Intracavitary Radiation Treatment in Cervix Cancer

Megavoltage CT Imaging for Intracavitary Radiation Treatment in Cervix Cancer

Proposal

To assess the feasibility of performing CT imaging using a megavoltage CT scanner on five patients where remote afterloading intracavitary applicators have been inserted for the purpose of delivering intracavitary radiotherapy in the treatment of cervix cancer.

Rationale

While there has been recent improvements in the treatment of more advanced stages of cervix cancer by combining radical radiation treatment with concurrent cisplatin based chemotherapy, there is room for further improvements in local regional control. One approach to achieving this is to increase the dose of therapeutic radiation to the clinical target volume without exceeding the tolerance of the adjacent normal tissues. Modern radiotherapy techniques allow for better conformation of the high dose radiation volume to the clinical target volume by using external beam techniques (conformal radiation treatment and intensity modulated radiation treatment) and the use of tomotherapy is likely to be particularly advantageous in this regard. The mainstay of cervix cancer radiotherapy has always been and will likely remain the use of brachytherapy. Future improvements in the outcome of cervix cancer treated by radiotherapy are therefore likely to necessitate accurately combining intracavitary radiation treatment with intensity modulated external beam radiation treatment and particularly with the use of tomotherapy techniques.

The ability to accurately reconstruct the three-dimensional dosimetry achieved by the combined use of intracavitary radiation treatment and helical tomotherapy will be pivotal in the success of this strategy. Conventional CT imaging of patients receiving intracavitary radiation treatment is hampered by distortion artifacts from the metallic applicators. The opportunity to gain improved images using megavoltage CT scanning using the same equipment and same patient set-up that will ultimately by used for the delivery of tomotherapy offers some unique potential advantages and solutions to the problem.

By imaging patients with the remote afterloading applications in situ, the researchers should be able to generate accurate isodose distributions in three dimensions for the intracavitary component of the cervix cancer treatment. By contouring the clinical target volume, which includes the primary cancer, local routes of spread and regional pelvic lymph nodes, the researchers can explore the feasibility of generating combined helical tomotherapy and intracavitary radiation treatment plans.

Patients and Methods

Patients who are to receive intracavitary brachytherapy on the low dose rate selectron at the Cross Cancer Institute will be approached to participate in this pilot study. An informed consent will be obtained from five patients for this study. Following the insertion of the remote afterloading applicators in the operating room, patients are normally transferred from the operating room to Simulator C for orthogonal simulator films and then to Station 30 where treatment is started approximately two hours later after dosimetry calculations have been performed and treatment has been prescribed.

For the patients consenting to this study, they will proceed from Simulator C to Station 30 via the tomotherapy unit in CBIAR where megavoltage CT scans will be taken. Patients will be accompanied by a brachytherapy radiation therapist. The megavoltage CT scans will take approximately one hour to perform, but this will not result in any treatment delay for the patient.

Isodose volumes from the prescribed intracavitary brachytherapy will be reconstructed on the megavoltage images. The feasibility of defining the clinical target volume on the megavoltage scans will be explored. This may require fusion with conventional CT images that will already have been taken for diagnostic and external beam treatment planning purposes. Megavoltage and/or fused images will be used to pilot the integration of tomotherapy intensity modulated radiation therapy treatment plans with intracavitary brachytherapy dosimetry.

The current study will have no influence on individual patient treatments but is a prelude to a potential dose escalation study using tomotherapy for patients with cervix cancer.