Shelley Pearson
Wellington Blood and Cancer Centre
Radiation Therapist

Eeva Boman
Medical Physicist (PhD)
Wellington Blood and Cancer Centre

Dean Paterson
Radiation Therapist (Hons)
Wellington Blood and Cancer Centre

Junou Huang
Radiation Therapist
Wellington Blood and Cancer Centre

Carol Johnson
Radiation Oncologist (FFRadT(SA), FRANZCR)
Wellington Blood and Cancer Centre

Background: In 2016 our institution implemented a pilot project treating a small cohort of patients with high-dose-rate multi-catheter interstitial breast brachytherapy in order to collect data, so that the long-term feasibility of the technique at our department could be assessed. In concordance with the International Commission on Radiological Protection (ICRP) recommendations total internal applicator length measurements were conducted prior to each fraction (1). Our institutions initial experience of internal applicator length measurements for breast brachytherapy has shown that the nylon 6/6 treatment catheters used in our center appear to stretch over a patients 5-8 day treatment course.

Purpose: Nylon 6/6 interstitial breast brachytherapy catheters may stretch when exposed to moisture, mechanical tension, and body temperature. The purpose of this study is to evaluate the magnitude of catheter stretch during a course of multi-catheter interstitial breast brachytherapy for nylon 6/6 treatment catheters, and to assess the impact this has on treatment plan dosimetry.

Methods: Catheters were exposed to water at 37˚C for six days and the internal catheter length change (ΔL_W) was measured daily. Additionally, the measured internal catheter length change (ΔL_P), performed prior to each treatment fraction, for seven interstitial breast brachytherapy patients (total of 76 catheters) were retrospectively analysed. The maximum length change seen in ΔL_P and ΔL_W were introduced as a source positional error to retrospective treatment plans, and treatment plan dosimetry was analysed.

Results: ΔL_W and ΔL_P were on average +4.0% and +1.6% of the catheter lengths in water or tissue after 48 hours. Weak correlation was seen between the average ΔL_P per catheter and both the catheter length within tissue (ρ = 0.36, p = 0.0007), and the mid-catheter depth in tissue (ρ = 0.42, p < 0.0001). The D90CTV decreased 1.5% (p < 0.05) and 8.2% (p < 0.05) when the ΔL_P and ΔL_W were introduced to the initial plans.

Conclusions: Nylon 6/6 catheters stretch during a course of multi-catheter interstitial breast brachytherapy treatment. The observed stretch may affect treatment plan dosimetry if the catheter internal length is only measured immediately after the insertion. Additional catheter length checks are recommended to verify the actual catheter internal length during the treatment.

References: (1) Valentin J; International Commission on Radiation Protection.Prevention of high-dose-rate brachytherapy accidents. ICRP Publication 97. Ann ICRP 2005; 35: 1-51.


← Back to all abstracts