The impact of body mass index on organs at risk in breast axillarynodal radiotherapy (2016)

Type of publication:
Conference abstract

*Pettit L., *Welsh A., *Puzey-Kibble C., *Williams M., *Santos J., *Wardle G., *Khanduri S.

Radiotherapy and Oncology, April 2016, vol./is. 119/(S558)

Purpose or Objective: There has been recent move within the U.K. to contour the nodal CTV for patients receiving adjuvant radiotherapy for breast cancer. Axillary radiotherapy (ART) following a positive sentinel lymph node biopsy is becoming more common for certain groups of patients. Organs at risk (OAR) should be delineated and considered during the planning process. Body mass index (BMI) has been shown to impact upon spinal cord and brachial plexus doses in irradiation of the supraclavicular fossa. The impact upon the OAR in the axilla has not yet been well documented. Material and Methods: Patients undergoing ART between 01/04/15-01/10/15 were identified. Non – contrast radiotherapy planning CT scans were taken. External beam radiotherapy was planned with extended tangents using a field in field approach with an additional low weighted anterior oblique field if deemed appropriate for adequate dose coverage. Dose delivered was 40.05 Gy in 15 fractions. BMI was calculated by: weight(kg)/height (m)2. CTV’s were contoured in accordance with the RTOG contouring atlas. OAR including ipsilateral lung, humeral head and brachial plexus were delineated. Results: Fifteen patients were identified. Six patients had a BMI between 20-25, 3 between 25-30, 5 between 30-40 and 1 BMI>40. Mean ipsilateral lung V12 was 10.44% (range 2.3%- 14.33%). Mean V12 did not vary with BMI (BMI 20-25;mean V12=9.33%, BMI 25-30; mean V12=8.52%, BMI 30-40;mean V12=9.51%, BMI>40 mean V12=6.38%, p=0.55 Chi-Squared). The mean humeral head maximum dose was 35.2 Gy (range 1.2-41.5 Gy). Mean humeral head maximum dose did not vary with BMI (BMI 20-25; mean=34.2Gy, BMI 25-30;mean=27.8Gy, BMI 30-40; mean=40.3Gy, BMI>40; mean=38.2Gy, p=0.49 ttest). The ipsilateral brachial plexus D2 mean was15.6Gy (range 1.2-37.4 Gy). Mean ipsilateral brachial plexus D2 dose did not vary with BMI(p=0.21 t-test). Conclusion: BMI did not significantly impact upon OAR dosage although this series is limited by a small sample size. Ipsilateral lung and brachial plexus were comfortably within departmental tolerance. A planning risk volume of 10 mm around the humeral head has now been adopted within the department. It is recognised that intravenous contrast provides better quality images for delineating OAR in particular for the brachial plexus. However, this impacts upon resources in terms of radiographer scanning time. Adequate time needs to be allocated in consultant and physics teams job plans to enable high quality delineation and subsequent radiotherapy plans to be produced.

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