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Title: SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator

Abstract

Purpose: The feasibility of dose measurement using new generation EBT3 film was explored in a water phantom for a ring and tandem HDR applicator for measurements tracking mucosal dose during cervical brachytherapy. Methods: An experimental fixture was assembled to position the applicator in a water phantom. Prior to measurement, calibration curves for EBT3 film in water and in solidwater were verified. EBT3 film was placed at different known locations around the applicator in the water tank. A CT scan of the phantom with applicator was performed using clinical protocol. A typical cervical cancer treatment plan was then generated by Oncentra brachytherapy planning system. A dose of 500 cGy was prescribed to point A (2 cm, 2 cm). Locations measured by film included the outer surface of the ring, measurement point A-m (2.2 cm, 2.2 cm), and profiles extending from point A-m parallel to the tandem. Three independent measurements were conducted. The doses recorded by film were carefully analyzed and compared with values calculated by the treatment planning system. Results: Assessment of the EBT3 films indicate that the dose at point A matches the values predicted by the planning system. Dose to the point A-m was 411.5 cGy, and the outermore » circumferential surface dose of the ring was between 500 and 1150 cGy. It was found that from the point A-m, the dose drops 60% within 4.5 cm on the line parallel to the tandem. The measurement doses agree with the treatment planning system. Conclusion: Use of EBT3 film is feasible for in-water measurements for brachytherapy. A carefully machined apparatus will likely improve measurement accuracy. In a typical plan, our study found that the ring surface dose can be 2.5 times larger than the point A prescription dose. EBT3 film can be used to monitor mucosal dose in brachytherapy treatments.« less

Authors:
; ; ; ; ; ;  [1]
  1. Northwestern Memorial Hospital, Chicago, IL (United States)
Publication Date:
OSTI Identifier:
22642258
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; ACCURACY; BRACHYTHERAPY; CALIBRATION; COMPUTERIZED TOMOGRAPHY; FILM DOSIMETRY; IMAGE PROCESSING; NEOPLASMS; PHANTOMS; RADIATION DOSES

Citation Formats

Lee, B, Grelewicz, Z, Kang, Z, Cutright, D, Gopalakrishnan, M, Sathiaseelan, V, and Zhang, H. SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator. United States: N. p., 2016. Web. doi:10.1118/1.4956142.
Lee, B, Grelewicz, Z, Kang, Z, Cutright, D, Gopalakrishnan, M, Sathiaseelan, V, & Zhang, H. SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator. United States. doi:10.1118/1.4956142.
Lee, B, Grelewicz, Z, Kang, Z, Cutright, D, Gopalakrishnan, M, Sathiaseelan, V, and Zhang, H. Wed . "SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator". United States. doi:10.1118/1.4956142.
@article{osti_22642258,
title = {SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator},
author = {Lee, B and Grelewicz, Z and Kang, Z and Cutright, D and Gopalakrishnan, M and Sathiaseelan, V and Zhang, H},
abstractNote = {Purpose: The feasibility of dose measurement using new generation EBT3 film was explored in a water phantom for a ring and tandem HDR applicator for measurements tracking mucosal dose during cervical brachytherapy. Methods: An experimental fixture was assembled to position the applicator in a water phantom. Prior to measurement, calibration curves for EBT3 film in water and in solidwater were verified. EBT3 film was placed at different known locations around the applicator in the water tank. A CT scan of the phantom with applicator was performed using clinical protocol. A typical cervical cancer treatment plan was then generated by Oncentra brachytherapy planning system. A dose of 500 cGy was prescribed to point A (2 cm, 2 cm). Locations measured by film included the outer surface of the ring, measurement point A-m (2.2 cm, 2.2 cm), and profiles extending from point A-m parallel to the tandem. Three independent measurements were conducted. The doses recorded by film were carefully analyzed and compared with values calculated by the treatment planning system. Results: Assessment of the EBT3 films indicate that the dose at point A matches the values predicted by the planning system. Dose to the point A-m was 411.5 cGy, and the outer circumferential surface dose of the ring was between 500 and 1150 cGy. It was found that from the point A-m, the dose drops 60% within 4.5 cm on the line parallel to the tandem. The measurement doses agree with the treatment planning system. Conclusion: Use of EBT3 film is feasible for in-water measurements for brachytherapy. A carefully machined apparatus will likely improve measurement accuracy. In a typical plan, our study found that the ring surface dose can be 2.5 times larger than the point A prescription dose. EBT3 film can be used to monitor mucosal dose in brachytherapy treatments.},
doi = {10.1118/1.4956142},
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 maximize the dose to HRCTV while minimizing dose to the OARs, the combination of two HDR brachytherapy sources, 192-Ir and 169-Yb, used in combination with the recently-proposed novel direction modulated brachytherapy (DMBT) tandem applicator were examined. Methods: The DMBT tandem, made from nonmagnetic tungsten-alloy rod, with diameter of 5.4mm, has 6 symmetric peripheral holes of 1.3mm diameter. The 0.3mm thick bio-compatible plastic tubing wraps the tandem. MCNPX v.2.6 was used to simulate the mHDR 192-Ir V2 and 4140 HDR 169-Yb sources inside the DMBT applicator. Thought was by combining the higher energy 192-Ir (380keV) and lower energy 169-Ybmore » (92.7keV) sources could create unprecedented level of dose conformality when combined with the high-degree intensity modulation capable DMBT tandem applicator. 3D dose matrices, with 1 mm3 resolution, were imported into an in-house-coded inverse optimization planning system to evaluate plan quality of 19 clinical patient cases. Prescription dose was 15Gy. All plans were normalized to receive the same HRCTV D90. Results: Generally, the use of dual sources produced better plans than using either of the sources alone, with significantly better performance in some patients. The mean D2cc for bladder, rectum, and sigmoid were 11.65±2.30Gy, 7.47±3.05Gy, and 9.84±2.48Gy for 192-Ir-only, respectively. For 169 -Yb-only, they were 11.67±2.26Gy, 7.44±3.02Gy, and 9.83±2.38Gy, respectively. The corresponding data for the dual sources were 11.51±2.24Gy, 7.30±3.00Gy, and 9.68 ±2.39Gy, respectively. The HRCTV D98 and V100 were 16.37±1.86Gy and 97.37±1.92Gy for Ir-192-only, respectively. For 169-Yb-only, they were 16.43±1.86Gy, and 97.51±1.91Gy, respectively. For the dual source, they were 16.42±1.87Gy and 97.47±1.93Gy, respectively. Conclusion: The plan quality improves, in some cases quite significantly, for when dual 192-Ir and 169-Yb sources are used in combination with highly intensity modulation capable DMBT tandem applicator for image guided cervical cancer brachytherapy.« less
  • Purpose: To investigate differences in: (i) relative location of the tandem and the ring compared to a rigid standard applicator model; and (ii) relative loading and changes in loading pattern between standard and image-guided planning. Methods: All T and R insertions performed in 2013 in our institution under CT- or MR-guidance were analyzed. Standard plans were generated using library applicator models with a fixed relationship between ring and tandem, standardized uniform dwell loading and normalization to point A. The graphic plans and the associated standard-plan dwell configurations were compared: the rings were rigidly registered, and the residual tandem shift, rotationmore » and maximum distance between plan tandem dwell and corresponding model tandem dwell were calculated. The normalization ratio (NR = the ratio of graphic versus standard-plan total reference air kerma [TRAK]), the general loading difference (GLD = the difference between graphic and standard ratios of the tandem versus the ring TRAK), and the percent standard deviation (SD% = SD/mean) of the tandem and the ring TRAK for the graphic plan (all standard-plans SD% = 0) were calculated. Results: 71 T and R were analyzed. Residual tandem shift, rotation and maximum corresponding dwell distance were 1.2±0.8mm (0.4±0.4mm lateral, 0.9±0.8mm craniocaudal, 0.4±0.3mm anterior-posterior), 2.3±1.9deg and 3.4±2.3mm. NR was 0.86±0.11 indicating a lower overall loading of the graphic compared to the standard plans. GLD was -0.12±0.16 indicating a modest increased ring loading relative to the tandem in the graphic plans. SD% was 2.1±1.6% for tandem and 2.8±1.9% for ring, indicating small deviations from uniform loading. Conclusion: Variability in the relative locations of the tandem and the ring necessitates the independent registration of each component model for accurate digitization. Our clinical experience suggests that graphically planned T and R results on average in a lower total dose to the patient, and in an increased relative loading of the ring component.« less
  • Purpose: A novel tungsten alloy shielded, MRI-compatible, direction modulated brachytherapy (DMBT) concept tandem applicator, which enables unprecedented intensity modulation, was used to evaluate treatment plan quality improvement over a conventional tandem. The utility of the 192-Ir and 169-Yb HDR sources, for use with the DMBT applicator, was evaluated. Methods: The total diameter of the DMBT tandem applicator is 6.0 mm, which consists of 5.4-mm diameter tungsten alloy and 0.3 mm thick plastic sheath. The tandem has 6 symmetric peripheral 1.3-mm diameter grooves for the source to travel. MCNPX v.2.6 was used to simulate the 192-Ir and 169-Yb sources inside themore » DMBT applicator. First, TG-43 source parameters were evaluated. Second, 3D dose matrix with 1 mm3 resolution were imported into an in-house-coded inverse optimization treatment planning program to obtain optimal plans for 19 clinical cases. All plans were compared with the standard tandem and ring plans. Prescription dose was 15.0 Gy. All plans were normalized to receive the same HRCTV D90. Results: Generally, the DMBT tandem (and ring) plans were better than the conventional tandem and ring plans for 192-Ir and 169-Yb HDR sources. The mean data of D2cc for bladder, rectum, and sigmoid were 11.65±2.30 Gy, 7.47±3.05 Gy, and 9.84±2.48 Gy for Ir-192 DMBT tandem, respectively. These data for Yb-169 were 11.67±2.26 Gy, 7.44±3.02 Gy, and 9.83±2.38 Gy, respectively. The HR-CTV D98 and V100 were 16.37±1.86 Gy and 97.37 ± 1.92 Gy for Ir-192 DMBT, respectively. The corresponding values for Yb-169 were 16.43±1.86 Gy, and 97.51 ± 1.91 Gy. Plans with the 169-Yb source generally produced more favorable results where V100 increased by 13.65% while D2cc across all OARs reduced by 0.54% compared with the 192-Ir plans. Conclusion: For the DMBT tandem applicator, 169-Yb source seems to produce more directional beams resulting in increased intensity modulation capacity, thus resulting in more conformal plans.« less
  • Purpose: To evaluate volumetric coverage of a Mick Radionuclear titanium Split-Ring applicator (SRA) with/without interstitial needle compared to an intracavitary Vienna applicator (VA), interstitial-intracavitary VA, and intracavitary ring and tandem applicator (RTA). Methods: A 57 year-old female with FIGO stage IIB cervical carcinoma was treated following chemoradiotherapy (45Gy pelvic and 5.4Gy parametrial boost) with highdose- rate (HDR) brachytherapy to 30Gy in 5 fractions using a SRA. A single interstitial needle was placed using the Ellis Interstitial Cap for the final three fractions to increase coverage of left-sided gross residual disease identified on 3T-MRI. High-risk (HR) clinical target volume (CTV) andmore » intermediate-risk (IR) CTV were defined using axial T2-weighted 2D and 3D MRI sequences (Philips PET/MRI unit). Organs-at-risks (OARs) were delineated on CT. Oncentra planning system was used for treatment optimization satisfying GEC-ESTRO guidelines for target coverage and OAR constraints. Retrospectively, treatment plans (additional 20 plans) were simulated using intracavitary SRA (without needle), intracavitary VA (without needle), interstitial-intracavitary VA, and intracavitary RTA with this same patient case. Plans were optimized for each fraction to maintain coverage to HR-CTV. Results: Interstitial-intracavitary SRA achieved the following combined coverage for external radiation and brachytherapy (EQD2): D90 HR-CTV =94.6Gy; Bladder-2cc =88.9Gy; Rectum-2cc =65.1Gy; Sigmoid-2cc =48.9Gy; Left vaginal wall (VW) =103Gy, Right VW =99.2Gy. Interstitial-intracavitary VA was able to achieve identical D90 HR-CTV =94.6Gy, yet Bladder-2cc =91.9Gy (exceeding GEC-ESTRO recommendations of 2cc<90Gy) and Left VW =120.8Gy and Right VW =115.5Gy. Neither the SRA nor VA without interstitial needle could cover HR-CTV adequately without exceeding dose to Bladder-2cc. Conventional RTA was unable to achieve target coverage for the HR-CTV >80Gy without severely overdosing OARs. Conclusion: The Ellis Interstitial Cap for the SRA offered superior dosimetric coverage as compared to the interstitialintracavitary VA. This represents the first reported use for this devise, and further investigation is warranted.« less
  • Purpose: We propose the use of a HDR X-ray source collimator to apply a conformal, relatively small, radiation suitable for a single fraction with short delivery time. In addition, this technique can be applied using a radioactive source. Methods: We have built a stainless steel 1.5 mm thick applicator, to accommodate the needle applicator of the Intra-Beam X-ray source. Additional cavity is created in the applicator to allow the hosting/nesting/positioning of a LED diode. This LED is allowing a pre-irradiation beam marking on the tissue. The visible light emitted from the opening of the collimated applicator will delineate/verify the aperturemore » of the kV beam to be applied, as well as serve as distance indicator and will assist in the determination of dose to be delivered. For the evaluation of the collimated spatial dose distribution we have performed water tank measurements using (IBA Dosimetry) with a 0.4 cc ion chamber (IBA Dosimetry). We have scanned a two dimensional array with 1mm pitch in depth and 0.3 mm step size laterally. Additional verifications were conducted using Gaf-Chromic film for PDD measurements and Optical Stimulated Luminescence Dosimetry (OSLD, Landauer inc.) for absolute dosimetry. Results: The collimated applicator enables a conformal irradiated cross-section of about 3 mm square at the applicator surface was used in this study. A 180 seconds of 50 kVp delivery yielded 29 Gy, 20.6 Gy and 14.5 Gy at 5, 10 and 15 mm depths respectively. These results are in good agreement with the needle applicator depth dose curve published data. Conclusion: We have demonstrated the feasibility of focal HDR brachytherapy for conjunctival and ocular tumors, using the Intra-Beam needle applicator with in-house developed collimator. The delivery time was found to be several minutes- suitable for an intra-operative procedure and will allow dose fractionation deliveries.« less