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Title: SU-E-T-19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses

Abstract

Purpose: We compared the dosimetric effects of brass mesh (Whiting and Davis, Attleboro Falls, MA) and Superflab (CNMC, Nashville, TN) boluses to verify equivalence between the two. Brass mesh bolus may be a convenient alternative to traditional bolus as it better conforms to the skin surface. Methods: Measurements were taken using a 6MV 10×10cm field produced by an Infinity linear accelerator (Elekta, Stockholm, Sweden) in a solid water phantom using a parallel plate ion chamber (Model 96035, Keithley Instruments, Cleveland, OH). Measurements compared 0.5cm and 1cm of Superflab to one to six layers of brass bolus mesh. Measurements were performed at depths from 0cm (‘skin’) to 10cm. Oblique beams were not studied. Results: Four layers of brass mesh were equivalent to 0.5cm Superflab within 5% at all depths. Six layers of brass compares most favorably with 0.5cm Superflab, with doses at all depths within 3%. Six layers of brass were not fully equivalent to 1cm Superflab, although the agreement was within 5% for depths greater than 3mm. Surface dose was 12% lower than 1cm Superflab. Surface dose can be up to 34% different between Superflab and brass mesh, but is less than 5% different with 4–6 layers of brass whenmore » compared to 0.5cm Superflab. To achieve surface dose agreement better than 5% compared to 1cm Superflab, more than 6 layers would be needed. The attenuation at depth was a maximum of 0.17cm per layer. Conclusion: Between four and six layers of brass mesh can be equivalent to 0.5cm Superflab, depending on the level of agreement desired. Equivalence within 5% at all depths to 1cm Superflab was not achieved even with six layers. This data agrees with measurements taken by Utsunomiya et al. (2010). More point measurements at shallower depths should be taken prior to clinical implementation of brass bolus mesh.« less

Authors:
; ;  [1]
  1. Vassar Brothers Hospital, Poughkeepsie, NY (United States)
Publication Date:
OSTI Identifier:
22545154
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; BRASS; DEPTH; DOSIMETRY; IONIZATION CHAMBERS; LINEAR ACCELERATORS; PHANTOMS; RADIATION DOSES; SKIN

Citation Formats

Irwin, JS, Gong, J, and Pavord, D. SU-E-T-19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses. United States: N. p., 2015. Web. doi:10.1118/1.4924380.
Irwin, JS, Gong, J, & Pavord, D. SU-E-T-19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses. United States. doi:10.1118/1.4924380.
Irwin, JS, Gong, J, and Pavord, D. Mon . "SU-E-T-19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses". United States. doi:10.1118/1.4924380.
@article{osti_22545154,
title = {SU-E-T-19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses},
author = {Irwin, JS and Gong, J and Pavord, D},
abstractNote = {Purpose: We compared the dosimetric effects of brass mesh (Whiting and Davis, Attleboro Falls, MA) and Superflab (CNMC, Nashville, TN) boluses to verify equivalence between the two. Brass mesh bolus may be a convenient alternative to traditional bolus as it better conforms to the skin surface. Methods: Measurements were taken using a 6MV 10×10cm field produced by an Infinity linear accelerator (Elekta, Stockholm, Sweden) in a solid water phantom using a parallel plate ion chamber (Model 96035, Keithley Instruments, Cleveland, OH). Measurements compared 0.5cm and 1cm of Superflab to one to six layers of brass bolus mesh. Measurements were performed at depths from 0cm (‘skin’) to 10cm. Oblique beams were not studied. Results: Four layers of brass mesh were equivalent to 0.5cm Superflab within 5% at all depths. Six layers of brass compares most favorably with 0.5cm Superflab, with doses at all depths within 3%. Six layers of brass were not fully equivalent to 1cm Superflab, although the agreement was within 5% for depths greater than 3mm. Surface dose was 12% lower than 1cm Superflab. Surface dose can be up to 34% different between Superflab and brass mesh, but is less than 5% different with 4–6 layers of brass when compared to 0.5cm Superflab. To achieve surface dose agreement better than 5% compared to 1cm Superflab, more than 6 layers would be needed. The attenuation at depth was a maximum of 0.17cm per layer. Conclusion: Between four and six layers of brass mesh can be equivalent to 0.5cm Superflab, depending on the level of agreement desired. Equivalence within 5% at all depths to 1cm Superflab was not achieved even with six layers. This data agrees with measurements taken by Utsunomiya et al. (2010). More point measurements at shallower depths should be taken prior to clinical implementation of brass bolus mesh.},
doi = {10.1118/1.4924380},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: It has been suggested that the use of a brass mesh bolus for chest wall irradiation sufficiently increases surface dose while having little effect on the dose at depth. This work quantified the increase in surface dose when using a brass mesh bolus in postmastectomy chest wall radiotherapy compared to tissue-equivalent bolus and assessed its effect on dose at depth. Methods: Percent depth doses with brass bolus, 5mm tissue-equivalent bolus, and no bolus were determined for a 6 MV photon beam in a solid water phantom using a parallel plate ionization chamber. Gafchromic film was used to determine themore » surface dose for the same three experimental setups. For comparison to a realistic treatment setup, gafchromic film and OSLDs were used to determine the surface dose over the irradiated area of a 6 MV chest wall plan with tangential beams delivered to a heterogeneous thorax phantom. The plan was generated using a CT of the phantom and delivered using brass mesh bolus, 5mm tissue-equivalent bolus, and no bolus. Results: For the en face beam, the central surface dose increased to 90% of maximum with the tissue-equivalent bolus, but to only 62% of maximum with the brass mesh. Using tangential beams on the thorax phantom, the surface dose increased from 40–72% to 75–110% of prescribed dose, with the brass mesh, and to 85–109% with the tissue-equivalent bolus. At depths beyond dmax in the plastic water phantom, the dose with and without brass mesh bolus differed by less than 0.5%. Conclusion: A brass mesh may be considered as a substitute for tissue-equivalent bolus to increase the superficial dose of 6 MV chest wall tangent plans. The brass mesh does not significantly change the dose at depth, so a non-bolus plan could be used for bolus and non-bolus treatments.« less
  • Purpose: Increasingly, brass mesh bolus is used to insure dosimetric coverage of the skin for patients treated post-mastectomy for breast cancer. Contribution of photoelectrons from interactions between the bolus and the primary beam increases dose superficially without affecting dose at greater depths. We present our experience using brass mesh bolus – including patients for whom the bolus was dosimetrically inadequate – along with analysis of relevant patient-specific parameters. Methods: Optically-stimulated luminescent dosimeters (OSLDs) were used to determine the effect of the bolus for 15 patients. They were positioned beneath the bolus within the tangent fields at three positions: 1.5–3cm insidemore » the medial and lateral field edges, and midway between the two. All OSLDs were midfield in the cranial-caudal direction. The measurements were compared with patient-specific parameters including separation, chest wall/breast tissue thickness, beam angle incidence, and planned surface dose. Results: The average OSLD measurement at the medial field edge, midfield, and lateral field edge position was 86.8%, 101.8%, and 92.8% of the prescription dose, respectively. A measurement for one patient was low enough (77.0%) to warrant a switch to an alternative type of bolus. Anatomic parameters were analyzed to investigate the low dose in this case, not observed in the planning system. The patient was observed to have a thin chest wall and very oblique beam angles. A second patient was also switched to an alternative type of bolus due to her being high risk and treated with an electron patch that extended onto the breast. Conclusion: Brass mesh bolus increases dose superficially while leaving dose at greater depths unaffected. However, our results suggest that this effect may be insufficient in patients with a thin chest wall or very oblique beam angles. More data and analysis is necessary to proactively identify patients for whom brass mesh bolus is effective.« less
  • Purpose: Brass mesh bolus has been shown to be an acceptable substitute for tissue equivalent bolus to increase superficial dose for 6 MV chest wall tangent plans. It may be advantageous to deliver a portion of the treatment using higher energy beams to decrease dose heterogeneity. The purpose of this study is to investigate the photoneutron production and activation of brass mesh bolus by high energy x-ray beams. Methods: MCNPX was used to determine brass mesh photoneutron energy spectrum and PDDs for 15 MV and 24 MV beams. PDD and photoneutron spectra were determined with and without photoneutron production tomore » assess the contribution of photoneutrons to CAX dose. Brass mesh was placed on a solid water slab phantom and irradiated with 500 MU of 15 MV photons at 100cm SSD. A Geiger-Mueller counter was used to record counts in 10-second intervals for 30 minutes. A survey meter was used to estimate dose on contact immediately following irradiation. Results: The thickness of brass mesh bolus for MCNPX simulation was 0.4 mm. The PDDs with and without photoneutron production were statistically equivalent (i.e. the increase in neutron dose at the central axis is insignificant). Using ICRP 103 dose conversion coefficients, the increase in effective dose from en-face delivery of 300 MU was 0.047 mSv for 15 MV and 0.525 mSV for 24 MV. The dose rate on contact after the 500 MU irradiation was 0.4 mrem/hr. The effective half-life was estimated to approximately 6 minutes. Conclusion: The use of brass mesh bolus with high energy beams does not significantly affect central axis PDD. The use of a 24 MV beam with brass bolus results in nearly 10 times the increase in effective dose as with 15 MV. The activation products produced by brass bolus have an effective half-life of approximately 6 minutes.« less
  • Purpose: To evaluate dosimetric differences of copper compared to conventional lead-alloy apertures for electron beam therapy. Methods: Copper apertures were manufactured by .decimal, Inc. and matching lead-alloy, Cerrobend, apertures were constructed for 32 square field sizes (2×2 – 20×20 cm{sup 2}) for five applicator sizes (6×6–25×25 cm{sup 2}). Percent depth-dose and off-axis-dose profiles were measured using an electron diode in water with copper and Cerrobend apertures for a subset of aperture sizes (6×6, 10×10, 25×25 cm{sup 2}) and energies (6, 12, 20 MeV). Dose outputs were measured for all field size-aperture combinations and available energies (6–20 MeV). Measurements were takenmore » at 100 and 110 cm SSDs. Using this data, 2D planar absolute dose distributions were constructed and compared. Passing criteria were ±2% of maximum dose or 1-mm distance-to-agreement for 99% of points. Results: A gamma analysis of the beam dosimetry showed 93 of 96 aperture size, applicator, energy, and SSD combinations passed the 2%/1mm criteria. Failures were found for small field size-large applicator combinations at 20 MeV and 100-cm SSD. Copper apertures showed a decrease in bremsstrahlung production due to copper's lower atomic number compared to Cerrobend (greatest difference was 2.5% at 20 MeV). This effect was most prominent at the highest energies with large amounts of shielding material present (small field size-large applicator). Also, an increase in electrons scattered from the collimator edge of copper compared to Cerrobend resulted in an increased dose at the field edge for copper at shallow depths (greatest increase was 1% at 20 MeV). Conclusion: Apertures for field sizes ≥6×6 cm{sup 2} at any energy, or for small fields (≤4×4 cm{sup 2}) at energies <20 MeV, showed dosimetric differences less than 2%/1mm for more than 99% of points. All field size-applicator size-energy combinations passed 3%/1mm criteria for 100% of points. Work partially funded by .decimal, Inc. (Sanford, FL)« less
  • Purpose: The study compared the dosimetry plans of Stereotatic Body Radiotherapy (SBRT) prostate cancer patients using the M6 Cyberknife with Multi-leaf Collimation (MLC) compared with the plans using G4 Cyberknife with circular collimators. Methods: Eight previously treated prostate cancer patients' SBRT plans using circular collimators, designed with Multiplan v3.5.3, were used as a benchmark. The CT, contours and the optimization scripts were imported into Multiplan v5.0 system and replanned with MLC. The same planning objectives were used: more than 95% of PTV received 36.25Gy, 90% of prostate received 40Gy and maximum dose <45Gy, in five fractions. For organs at risk,more » less than 1cc of rectum received 36Gy and less than 10cc of bladder received 37Gy. Plans were evaluated on parameters derived from dose volume. The beam number, MU and delivery time were recorded to compare the treatment efficiency. Results: The mean CTV volume was 41.3cc (27.5∼57.6cc) and mean PTV volume was 76.77cc (59.1∼99.7cc). The mean PTV coverage was comparable between MLC (98.87%) and cone (98.74%). MLC plans had a slightly more favorable homogeneity index (1.22) and conformity index (1.17), than the cone (1.24 and 1.15). The mean rectum volume of 36 Gy (0.52cc) of MLC plans was slightly larger than cone (0.38cc) and the mean bladder volume of 37 Gy was smaller in MLC (1.82cc) than in cone plans (3.09cc). The mean number of nodes and beams were 65.9 and 80.5 in MLC vs 65.9 and 203.6 in cone. The mean MUs were significantly less for MLC plans (24,228MUs) than cone (32,347MUs). The total delivery time (which included 5 minutes for setup) was less, 29.6min (26∼32min) for MLC vs 45min (35∼55min) for cone. Conclusion: While the differences in the dosimetry between the MLC and circular collimator plans were rather minor, the MLC plans were much more efficient and required significantly less treatment time.« less