Abstract
PurposeThe aim of this study was to assess the feasibility and advantages of a patient-specific breast bolus made using a 3D printer technique.MethodsWe used the anthropomorphic female phantom with breast attachments, which volumes are 200, 300, 400, 500 and 650 cc. We simulated the treatment for a right breast patient using parallel opposed tangential fields. Treatment plans were used to investigate the effect of unwanted air gaps under bolus on the dose distribution of the whole breast. The commercial Super-Flex bolus and 3D-printed polylactic acid (PLA) bolus were applied to investigate the skin dose of the breast with the MOSFET measurement. Two boluses of 3 and 5 mm thicknesses were selected.ResultsThere was a good agreement between the dose distribution for a virtual bolus generated by the TPS and PLA bolus. The difference in dose distribution between the virtual bolus and Super-Flex bolus was significant within the bolus and breast due to unwanted air gaps. The average differences between calculated and measured doses in a 200 and 300 cc with PLA bolus were not significant, which were -0.7% and -0.6% for 3mm, and -1.1% and -1.1% for 5 mm, respectively. With the Super-Flex bolus, however, significant dose differences were observed (-5.1% and -3.2% for 3mm, and -6.3% and -4.2% for 5 mm).ConclusionThe 3D-printed solid bolus can reduce the uncertainty of the daily setup and help to overcome the dose discrepancy by unwanted air gaps in the breast cancer radiation therapy.
Highlights
High energy photon beams for radiation therapy exhibit penetration, beam uniformity, and skin-sparing properties [1, 2]
There was a good agreement between the dose distribution for a virtual bolus generated by the treatment planning system (TPS) and polylactic acid (PLA) bolus
Normal organs including lung and heart could be protected because bolus brings isodose lines toward the surface and it was demonstrated that the use of bolus in the postmastectomy radiotherapy reduced the normal tissue complication probabilities (NTCPs) of the ipsilateral lung [7]
Summary
High energy photon beams for radiation therapy exhibit penetration, beam uniformity, and skin-sparing properties [1, 2]. This skin sparing near the surface inside a patient is caused by a dose build-up effect of megavoltage photon beam. The ability to spare the skin is very useful for many different types of cancer, there is a problem with the treatment of superficial lesions near the skin surface. A build-up material (bolus) is placed in direct contact with the patient’s skin surface in order to increase the superficial dose and improve dose uniformity by compensating for missing tissue [4,5,6]. In case of the irregular surface region of a patient, unwanted air gaps under bolus might occur between the bolus and patient skin due to the malleability of bolus material
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