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Title: SU-F-T-317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri-Co-60 MR-IGRT System

Abstract

Purpose: To investigate exposure outside the treatment field when treating breast cancer with tri-Co-60 magnetic resonance (MR) image guided radiation therapy (IGRT) system. Methods: A total of 7 patients who treated with accelerated partial breast irradiation (APBI) technique were selected prospectively for this study (prescription dose = 38.5 Gy in 10 fractions). Every patient treated with two plans, one was an initial plan and the other was an adaptive plan generated after finishing 5 fractions (a total of 14 plans). Every plan was calculated with and without magnetic field in the treatment planning system. The EBT3 films were attached on the front and the back of 1 cm bolus, and then it was placed on the patient body vertically to cover patient’s jaw and shoulder. After measurements, the maximum point dose and the mean dose of whole area of EBT3 film were acquired. Results: In the treatment plan with magnetic field, low dose stream outside the patient body was observed, almost reaching the patient’s jaw or shoulder, while it was not observed without magnetic field. The average values of the measured maximum and mean doses at the front of bolus were 30.1 ± 11.1 cGy (7.8% of the daily dose)more » and 14.7 ± 3.3 cGy (3.8%), respectively. At the back of bolus, those values were 6.0 ± 1.9 cGy (1.6%) and 5.1 ± 1.6 cGy (1.3%), respectively. The largest maximum dose at the front was 54.2 cGy (14.1%) while it was 20.7 cGy (5.4%) at the back. The average decrease of the maximum dose by the bolus was 24.0 ± 11.0 cGy. Conclusion: Due to magnetic field, dose stream outside the patient body can be generated during breast cancer treatment with the tri-Co-60 MR-IGRT system. Since this dose stream irradiated skin outside the treatment field, it should be shielded. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1C1A1A01054192).« less

Authors:
; ;  [1];  [2];  [3]
  1. Seoul National University Hospital, Seoul (Korea, Republic of)
  2. Nuclear Safety and Security Commission, Seoul (Korea, Republic of)
  3. Seoul National University College of Medicine, Seoul (Korea, Republic of)
Publication Date:
OSTI Identifier:
22648923
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 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; MAGNETIC FIELDS; MAMMARY GLANDS; NEOPLASMS; PATIENTS; PLANNING; RADIOTHERAPY; SKIN

Citation Formats

Park, J, Kim, J, Park, S, Kim, S, and Shin, K. SU-F-T-317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri-Co-60 MR-IGRT System. United States: N. p., 2016. Web. doi:10.1118/1.4956502.
Park, J, Kim, J, Park, S, Kim, S, & Shin, K. SU-F-T-317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri-Co-60 MR-IGRT System. United States. doi:10.1118/1.4956502.
Park, J, Kim, J, Park, S, Kim, S, and Shin, K. Wed . "SU-F-T-317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri-Co-60 MR-IGRT System". United States. doi:10.1118/1.4956502.
@article{osti_22648923,
title = {SU-F-T-317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri-Co-60 MR-IGRT System},
author = {Park, J and Kim, J and Park, S and Kim, S and Shin, K},
abstractNote = {Purpose: To investigate exposure outside the treatment field when treating breast cancer with tri-Co-60 magnetic resonance (MR) image guided radiation therapy (IGRT) system. Methods: A total of 7 patients who treated with accelerated partial breast irradiation (APBI) technique were selected prospectively for this study (prescription dose = 38.5 Gy in 10 fractions). Every patient treated with two plans, one was an initial plan and the other was an adaptive plan generated after finishing 5 fractions (a total of 14 plans). Every plan was calculated with and without magnetic field in the treatment planning system. The EBT3 films were attached on the front and the back of 1 cm bolus, and then it was placed on the patient body vertically to cover patient’s jaw and shoulder. After measurements, the maximum point dose and the mean dose of whole area of EBT3 film were acquired. Results: In the treatment plan with magnetic field, low dose stream outside the patient body was observed, almost reaching the patient’s jaw or shoulder, while it was not observed without magnetic field. The average values of the measured maximum and mean doses at the front of bolus were 30.1 ± 11.1 cGy (7.8% of the daily dose) and 14.7 ± 3.3 cGy (3.8%), respectively. At the back of bolus, those values were 6.0 ± 1.9 cGy (1.6%) and 5.1 ± 1.6 cGy (1.3%), respectively. The largest maximum dose at the front was 54.2 cGy (14.1%) while it was 20.7 cGy (5.4%) at the back. The average decrease of the maximum dose by the bolus was 24.0 ± 11.0 cGy. Conclusion: Due to magnetic field, dose stream outside the patient body can be generated during breast cancer treatment with the tri-Co-60 MR-IGRT system. Since this dose stream irradiated skin outside the treatment field, it should be shielded. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1C1A1A01054192).},
doi = {10.1118/1.4956502},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}
  • Purpose: To evaluate the possibility of utilizing the BEBIG HDR 60Co remote after-loading system for malignant skin surface treatment using Monte Carlo (MC) simulation technique. Methods: First TG-43 parameters of BEBIG-Co-60 and Nucletron Ir-192-mHDR-V2 brachytherapy sources were simulated using MCNP6 code to benchmark the sources against the literature. Second a conical tungsten-alloy with 3-cm diameter of Planning-Target-Volume (PTV) at surface for use with a single stepping HDR source is designed. The HDR source is modeled parallel to treatment plane at the center of the conical applicator with a source surface distance (SSD) of 1.5-cm and a removable plastic end-cap withmore » a 1-mm thickness. Third, MC calculated dose distributions from HDR Co-60 for conical surface applicator were compared with the simulated data using HDR Ir-192 source. The initial calculations were made with the same conical surface applicator (standard-applicator) dimensions as the ones used with the Ir-192 system. Fourth, the applicator wall-thickness for the Co-60 system was increased (doubled) to diminish leakage dose to levels received when using the Ir-192 system. With this geometry, percentage depth dose (PDD), and relative 2D-dose profiles in transverse/coronal planes were normalized at 3-mm prescription-depth evaluated along the central axis. Results: PDD for Ir-192 and Co-60 were similar with standard and thick-walled applicator. 2D-relative dose distribution of Co-60, inside the standard-conical-applicator, generated higher penumbra (7.6%). For thick-walled applicator, it created smaller penumbra (<4%) compared to Ir-192 source in the standard-conicalapplicator. Dose leakage outside of thick-walled applicator with Co-60 source was approximately equal (≤3%) with standard applicator using Ir-192 source. Conclusion: Skin cancer treatment with equal quality can be performed with Co-60 source and thick-walled conical applicators instead of Ir-192 with standard applicators. These conical surface applicator must be used with a protective plastic end-cap to eliminate electron contamination and over-dosage of the skin.« less
  • Purpose: To characterize magnetic field effects on Optically Stimulated Luminescence Detectors (OSLDs) for use as an in-vivo dosimeter in an MRIGRT machine. Methods: Landauer OSLD nano-dots and the MicroStar II reader were used to measure and record OSLDs exposed in and on a solid water phantom in a 10.5 × 10.5 cm{sup 2} field, Co-60, 0.32-Tesla MR-IGRT machine - with and without the presence of the magnetic field. Two orthogonal gantry angles were considered to assess orientation effects on the OSLDs with respect to the incident angle of the radiation beam and magnetic field. The same OSLDs were then usedmore » (after readout and bleaching) when the magnetic field was restored. Results: The measured surface dose decreased by 14.1 ± 1.8% when magnetic field was ’on’ due to contamination electrons being swept away by the field. Doses at both 0.5 cm and 5 cm depth increased by 6.5 ± 0.9% and 8.8 ± 0.5% respectively when the magnetic field was present and the OSLDs oriented with their long axis parallel with the incident beam. This contrasts with an increased dose of 2.7 ± 1.1% when the magnetic field was present and the OSLDs were oriented with their long axis perpendicular to the incident beam. Conclusion: Previous works have shown that OSLDs have a dependence on beam incidence angle. Our current work suggests an additional dependence on the presence of the magnetic field when the beam is not perpendicular to the plane of the detector and this effect needs to be considered. Furthermore, the use of an in-vivo dosimeter was shown to have no effect on image quality during the use of MR guidance. Future work will focus on the use of an electromagnet with a linear accelerator to further characterize these effects.« less
  • Purpose: To validate absolute dose measurements for a MR-IGRT system without presence of the magnetic field. Methods: The standard method (AAPM’s TG-51) of absolute dose measurement with ionization chambers was tested with and without the presence of the magnetic field for a clinical 0.32-T Co-60 MR-IGRT system. Two ionization chambers were used - the Standard Imaging (Madison, WI) A18 (0.123 cc) and the PTW (Freiburg, Germany). A previously reported Monte Carlo simulation suggested a difference on the order of 0.5% for dose measured with and without the presence of the magnetic field, but testing this was not possible until anmore » engineering solution to allow the radiation system to be used without the nominal magnetic field was found. A previously identified effect of orientation in the magnetic field was also tested by placing the chamber either parallel or perpendicular to the field and irradiating from two opposing angles (90 and 270). Finally, the Imaging and Radiation Oncology Core provided OSLD detectors for five irradiations each with and without the field - with two heads at both 0 and 90 degrees, and one head at 90 degrees only as it doesn’t reach 0 (IEC convention). Results: For the TG-51 comparison, expected dose was obtained by decaying values measured at the time of source installation. The average measured difference was 0.4%±0.12% for A18 and 0.06%±0.15% for Farmer chamber. There was minimal (0.3%) orientation dependence without the magnetic field for the A18 chamber, while previous measurements with the magnetic field had a deviation of 3.2% with chamber perpendicular to magnetic field. Results reported by IROC for the OSLDs with and without the field had a maximum difference of 2%. Conclusion: Accurate absolute dosimetry was verified by measurement under the same conditions with and without the magnetic field for both ionization chambers and independently-verifiable OSLDs.« less
  • Purpose: To determine if a MOSFET based in-vivo dosimetry system can be used for patients undergoing MR-IGRT. Methods: Standard and high sensitivity MOSFET detectors were used for in-field and out-of-field measurements respectively. The systems were benchmarked and calibrated against a calibrated ionization chamber on a standard 6 MV linear accelerator, and then on the MR-IGRT system. Known doses were delivered to a water phantom with the MOSFETs placed between the top of the phantom and underneath a layer of bolus and water equivalent plastic, using a 6 MV beam and a {sup 6} {sup 0}Co MR-IGRT beam. The latter wasmore » performed with and without real-time MRI-guidance during the beam delivery (MRIGRT). Results: The in-field dosimeter response was linear from 50-500 cGy with little evidence of energy dependence or change in response due to the permanent static magnetic field of the MR-IGRT system. The detector response varied by < 2% between 6 MV and {sup 6} {sup 0}Co without image guided delivery. The out-of-field dosimeter response was linear from 1-50 cGy; however the detectors did display dose rate and energy dependence as the response varied by > 20% depending on distance from isocenter used during calibration. Therefore, to use the dosimeters for out-of-field measurements they must be calibrated out-of-field. Regardless of the detector orientation in the coronal plan, the response of the MOSFETs during MRI-guided delivery increased by 5% due to induced currents from the dynamic magnetic field present with image guidance. During the MRI-guided delivery, some loss in image quality was seen when the MOSFETs were present in the imaging plane. This was mitigated by using a handheld reader without a transmitting wireless receiver. Conclusion: A MOSFET-based in-vivo dosimetry system can be used for patients receiving MR-IGRT; however the change in detector response due to the dynamic magnetic field requires a special calibration.« less
  • Purpose: To measure the skin dose and compare it with the calculated dose from a treatment planning system (TPS) for breast cancer treatment using scanning proton beam therapy (SPBT). Methods: A single en-face-beam SPBT plan was generated by a commercial TPS for two breast cancer patients. The treatment volumes were the entire breasts (218 cc and 1500 cc) prescribed to 50.4 Gy (RBE) in 28 fractions. A range shifter of 5 cm water equivalent thickness was used. The organ at risk (skin) was defined to be 5 mm thick from the surface. The skin doses were measured in water withmore » an ADCL calibrated parallel plate (PP) chamber. The measured data were compared with the values calculated in the TPS. Skin dose calculations can be subject to uncertainties created by the definition of the external contour and the limitations of the correction based algorithms, such as proton convolution superposition. Hence, the external contours were expanded by 0, 3 mm and 1 cm to include additional pixels for dose calculation. In addition, to examine the effects of the cloth gown on the skin dose, the skin dose measurements were conducted with and without gown. Results: On average the measured skin dose was 4% higher than the calculated values. At deeper depths, the measured and calculated doses were in better agreement (< 2%). Large discrepancy occur for the dose calculated without external expansion due to volume averaging. The addition of the gown only increased the measured skin dose by 0.4%. Conclusion: The implemented TPS underestimated the skin dose for breast treatments. Superficial dose calculation without external expansion would result in large errors for SPBT for breast cancer.« less