ABSTRACT
Breast with supraclavicular fossa (Br+SCF) radiotherapy treatments can utilise a monoisocentric
technique to concurrently treat the breast area (tangent fields) and supraclavicular
area (opposing fields). The region where these treatment areas adjoin is known as
the junction region, field junction, or match line. Dose variations that may occur
about the junction region, due to geometrical inaccuracies, are typically feathered
out in patient free-breathing treatments. However, there is limited information on
how dose at the junction is influenced in deep inspiration breath hold (DIBH) treatments.
This study aims to investigate dose variation at the field junction for a patient
population undertaking a DIBH Br+SCF treatment course. GAFChromic EBT3 film was used
to record the dose across the junction at skin surface for approximately one third
of the 25 fraction treatment course for 11 patients undergoing DIBH Br+SCF treatment.
Single fraction and summated fraction profiles for each patient were compared to profiles
in the treatment planning system and assessed the: (1) local dose variations, (2)
position of the 50% dose gradient, and (3) relative dose at the nominal junction.
Local dose variations of 10% or greater, position displacement of the junction greater
than 5 mm, and relative dose differences at the match line greater than 10% can be
found within single fraction dose profiles. When these single fractions are summed
over the treatment course, the position variations reduce to 2 mm and dose variations
reduced to within 10% for 10 of the 11 patients. Only one of 11 patients recorded
a summed dose difference greater than ±10% over their treatment, recording 76% ± 8%
of the planned dose in this region. This was due to a small overall position displacement
of 1.8 ± 1.6 mm from the nominal junction. A feathering of the dose at the junction
is present for DIBH Br+SCF patient treatments. The feathering effect is sufficient,
in the majority of cases studied, to reduce any differences in dose and displacement
present in single fractions. This work also demonstrates that there may be exceptions
from this observed behavior that should be considered. Further study in this area
using a larger patient cohort is recommended.
Keywords
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Article info
Publication history
Published online: May 03, 2022
Accepted:
March 18,
2022
Received in revised form:
March 3,
2022
Received:
October 9,
2021
Identification
Copyright
© 2022 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
