Design and production of 3D printed bolus for electron radiation therapy

Abstract

This is a proof‐of‐concept study demonstrating the capacity for modulated electron radiation therapy (MERT) dose distributions using 3D printed bolus. Previous reports have involved bolus design using an electron pencil beam model and fabrication using a milling machine. In this study, an in‐house algorithm is presented that optimizes the dose distribution with regard to dose coverage, conformity, and homogeneity within the planning target volume (PTV). The algorithm takes advantage of a commercial electron Monte Carlo dose calculation and uses the calculated result as input. Distances along ray lines from the distal side of 90% isodose line to distal surface of the PTV are used to estimate the bolus thickness. Inhomogeneities within the calculation volume are accounted for using the coefficient of equivalent thickness method. Several regional modulation operators are applied to improve the dose coverage and uniformity. The process is iterated (usually twice) until an acceptable MERT plan is realized, and the final bolus is printed using solid polylactic acid. The method is evaluated with regular geometric phantoms, anthropomorphic phantoms, and a clinical rhabdomyosarcoma pediatric case. In all cases the dose conformity are improved compared to that with uniform bolus. For geometric phantoms with air or bone inhomogeneities, the dose homogeneity is markedly improved. The actual printed boluses conform well to the surface of complex anthropomorphic phantoms. The correspondence of the dose distribution between the calculated synthetic bolus and the actual manufactured bolus is shown. For the rhabdomyosarcoma patient, the MERT plan yields a reduction of mean dose by 38.2% in left kidney relative to uniform bolus. MERT using 3D printed bolus appears to be a practical, low‐cost approach to generating optimized bolus for electron therapy. The method is effective in improving conformity of the prescription isodose surface and in sparing immediately adjacent normal tissues.PACS number: 81.40.Wx

Use of a 3D printer to create a bolus for patients undergoing tele-radiotherapy

“…This paper showed that a 3D printed bolus represented a precise reproduction of the designed model bolus at relatively low cost. This precision increased the certainty that the dose distribution in the target area would be consistent with the planned dose distribution and results a substantial reduction of the volume of normal tissues being irradiated, which agrees with the results of Su et al (10) . The 3D printed bolus displayed a better it to the planned model and greater material uniformity compared to the classical paraf in bolus.…”

“…Using 3D printed bolus could help to overcome the problem with air cavities and improve the quality of realized treatment, by reproducibility of daily setup conditions on irregular surfaces, which was con irmed by Shin -Wook et al (11) . Additionally, a 3D printer can be easily installed in the cancer center and offer practical advantages -neither patient nor staff needs to be present all the time during the bolus production, which was con irmed by Su et al (10) .…”

“…The use of 3D printing technology to recreate a bolus designed in a treatment planning system can increase the quality of teleradiotherapy (10) . This paper showed that a 3D printed bolus represented a precise reproduction of the designed model bolus at relatively low cost.…”

“…Although recently there have been several reports describing the possibility to implementation of the threedimensional printing technology to produce bolus in radiotherapy, this is still a new ansd very rarely used method (10)(11) . Presumably, boluses printed in this technology are nowhere routinely used in radiation therapy.…”

Introduction to passive electron intensity modulation

“…Clinical sites for which bolus ECT is useful are well documented in the literature, e.g. posterior wall sarcomas 25 , postmastectomy chest wall 26–28 , head and neck 29,30 , and extremities 31 , and on the .decimal web site.…”