Dean Paterson
Wellington Blood and Cancer Centre
Radiation Therapist

Shelley Pearson
Radiation Therapist
Wellington Blood and Cancer Centre

Andrew Neil Wilson
Radiation Oncologist
Wellington Blood and Cancer Centre

Background and Purpose:

A custom balloon applicator was created to deliver HDR brachytherapy to a patient with a superficial vaginal carcinoma at the vaginal vault. The patient was unable to be treated with a conventional intracavitary technique, due to an extremely narrow introitus which prevented the introduction of a vaginal cylinder. Ovoids were not appropriate due to the limited treatment length they provide.

Methods:

The custom applicator was created by inserting a straight titanium tandem applicator (Mick Radio-Nuclear Instruments, NY, USA) through a Foley catheter balloon (C. R. Bard Inc, GA, USA). The tandem was inserted so the tip of the tandem was flush with the top of the balloon. The balloon inserted to the top of the vaginal vault and inflated with 45mL of contrast solution. CT (Phillips Healthcare, Netherlands) and MRI (Philips Healthcare, Netherlands) imaging was performed with the applicator in-situ prior to the first treatment insertion to determine the feasibility of the technique. CT imaging was then performed at each treatment fraction for delineation of the applicator and organs at risk. The MRI was used to evaluate tumour response to EBRT and for delineation of a clinical target volume. Individual balloon eccentricities resulted in small radial tandem offsets within the balloon for some insertions. This situation was exploited by orientating the offset in the direction of the target volume. Each plan was optimised to deliver 100% of the prescribed dose to a 5cm long reference line, placed 0.5cm from the balloon surface on the patient’s left (tumour location).

Results:

Three brachytherapy treatments were delivered using this technique. Balloon dimensions were consistent with an inter-fraction deviation of 0.1cm for length and 0.2cm for diameter. The balloon length was adequate for a treatment length of 5cm. The tandem was central in the balloon for fraction one. Radial offsets of the tandem position within the balloon, up to 3.5mm, were present for fractions two and three. Table 1 provides a summary of dosimetric quantifiers for each brachytherapy plan and for the total treatment course.

Conclusions:

The custom applicator was a viable solution that resulted in an acceptable dose distribution and was well tolerated by the patient.


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