Quality management for Breast Brachytherapy.

Transcription

1 Quality management for Breast Brachytherapy. DORIN TODOR, Ph.D. Medical College of Virginia Campus Department of Radiation Oncology New England AAPM Chapter 2012 Summer Meeting, Providence, RI

2 Quality management: objectives The aim of quality management in brachytherapy is to ensure that each individual radioactive source treatment of the intended target is: administered accurately consistent with the written directive within the scope of the institution s license for radioactive material safe for the patient, staff and others who may be exposed to radiation during the course of treatment.

3 The other equally important part of the brachytherapy quality management program is the procedure specific quality assurance defined as the set of actions selected to ensure that each important step leading to delivery of a brachytherapy procedure is correctly carried out While one can recommend QA forms, they really have to be specific to the way a treatment procedure is implemented and carried out in a particular center.

4 Present setting at MCVH Operating Room Imaging Suite Treatment Room

5 The most well established modality in APBI Multi-catheter Interstitial Breast implants

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7 The Virginia technique

8 Planning: catheter identification

9 Planning: identification and measurement of catheters

10 Planning: identification and measurement of catheters

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12 Planning: contouring of structures

13 Planning: definition of applicators

14 Planning: modifying dose

15 Planning: dose optimization geometry based

16 Planning: dose optimization DVH-based

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22 Final QA. Treatment Delivery

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26 Courtesy of Rupak Das, Ph.D.

27 Quantitative Analysis of Interstitial Implants Dose Homogeneity Index (DHI) DHI = V 100 V 100 V 150 Ideal: DHI = 1.0

28 Balloons- A bit of History MammoSite The treatment planning is based on orthogonal Xray films, but the 3D CT based planning system was used retrospectively to do a detailed analysis of the dosimetry. The paper describes the treatment planning consisting primarily of identifying the treatment radius and using of a precalculated table linking radii to treatment times. Dosimetric characteristics of the MammoSite RTS, a new breast brachytherapy applicator. Edmundson GK, Vicini FA, Chen PY, Mitchell C, Martinez AA, Int J Radiat Oncol Biol Phys Mar 15;52(4):

29 Variably Inflatable Balloon Contura MLB Depth Markers 5 Radiation Lumens Vacuum Ports Inflation Lumen Vacuum Lumen Stiffening Stylet Available balloon sizes 4-5cm variable 33cc to 58cc fill volume 5-6cm variable 66cc to 108cc fill volume Shaft diameter 8 mm, Shaft length 16cm to hub Orientation line on shaft Lumen #1

30 Side by Side

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35 How close to the tip should the first dwell position be? It depends on how your afterloader is adjusted, the length and diameter of transfer tubes, etc. Particularly challenging for Accuboost and Ring applicators, not an applicator issue for APBI A safe distance is probably cm Experiment and find out the minimum value for which your machine will not produce an obstruction fault.

36 Varian

37 Central lumen vs MLB: some issues disappear Dose to skin - previously limited to 145% PD and coupled to both skinto-balloon distance and coverage. By decoupling the dose to skin from the balloon-to-skin distance and from the coverage, one can maximize dosimetric coverage while minimizing dose to skin (and/or chest wall). Balloon Asymmetry...some issues gain emphasis: Planning: CT-based only DVH-based Optimization Pre-Treatment QA

38 What is improved: Shaping the dose Pushing the dose asymmetrically Making dose more conformal Better sparing of adjacent structures: skin and chest wall Better dosimetric indices

39 Planning for MLB. What to do and what not to do? Creating appropriate planning and optimization structures Use a template plan from template library Using an inverse DVH-Based optimization Imposing adequate constraints Do not use the manual dose shaping tools Do not entertain the idea that the radiation oncologist can improve an optimized plan

40 On optimization Get to know (and understand) your optimizer. If optimization doesn t create optimal plans, something is wrong! Use of pseudo-structures Constraints (typically Dose-Volume) Experiment!

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48 V95> 95% V150=25.5cc V200=9.3cc Max Dose to Skin=167.2% Treat. Time=430.9s

49 V95> 95% V150=20.1cc V200=4.2cc Max Dose to Skin=149.0% Treat. Time=380.4s

50 V95> 95% V150=18.2cc V200=4.6cc Max Dose to Skin=109.0% Treat. Time=257.1s

51 Pre-treatment Balloon QA One of the fastest and easiest methods uses an ultrasound scanner with a breast probe. In the next two slides, ultrasound images of the Contura balloon are shown, along with measurement of the balloon diameter. These measurements are consistent with the previously measured values, based on CBCT measurements.

52 Ultrasound Image of Contura Central lumen Contained in the Transducer s Imaging plane

53 Ultrasound Image of Contura Central lumen Perpendicular on the Transducer s Imaging plane

54 Balloon diameter verification A diameter is obtained from the treatment planning system

55 And compared with an ultrasound based measurement. If a difference of more than 1mm is identified, balloon is refilled to the nominal diameter (or replaced).a new CT can be ordered to check the consistency of the volume prior to treatment.

56 Rotation. How to estimate its dosimetric impact? Part of the QA procedures preceding the initiation of each treatment delivery is the verification of the balloon s rotation.

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60 Conclusions Significant potential for extending the Central Lumen Balloon treatment paradigm, in both definition of the target and the dosimetric constraints. The image datasets made available for the dry run can be used by the early investigators to test and experiment the potential and limits of the Contura MLB.

61 SAVI (Strut-Adjusted Volume Implant) It is a single entry hybrid catheter for APBI Manufactured by Cianna Medical, Aliso Viejo, CA) More aggressive dose shaping to the PTV, larger V200 and poor DHI

62 Number of struts varies from 6 to 10.

63 workflow It is inserted collapsed into the lumpectomy cavity. Once in place, rotation of the expansion tool deploys the catheters (struts) conforming the device to the size of the cavity. It is recommended that imaging takes place at least 24h after insertion, to allow for the settling of the device, especially strut splay. Also at the imaging time, one should record the patient positioning and measure the skin to hub distance. AP and lateral CT scout films (or radiographs) will be used for identifying inter-fraction device motion.

64 workflow Treatment planning more time consuming than for balloon-devices as multiple struts need to be digitized/outlined. Target outlining starts with lumpectomy cavity identification after which 1cm margin is applied to create a PTV, similar with the balloon. Once dwell positions are identified along each catheter and anatomic and planning structures are created, one can optimize the dosimetry by imposing constraints for both PTV dose coverage as well as on the dose-limiting structures. If you need to touch up or use graphical optimization, your inverse optimization is not really working.

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67 Major QA issues Factors that could potentially alter the dose modulation from beneficial to detrimental: Device rotation & rotational stability, Change in the geometry of the device (strut symmetry), Change in cavity conformance. APBI Brachytherapy Device Stability and the Importance of Pre-fraction Device QA D. Scanderbeg, T. Pawlicki, and C. Yashar, Department of Radiation Oncology, University of California San Diego, La Jolla, CA 92093, Presented at ASTRO in 2009

68 APBI Brachytherapy Device Stability and the Importance of Pre-fraction Device QA D. Scanderbeg, T. Pawlicki, and C. Yashar, Department of Radiation Oncology, University of California San Diego, La Jolla, CA 92093, Presented at ASTRO in 2009

69 Clinical implementation of a new HDR brachytherapy device for partial breast irradiation Daniel J. Scanderbeg, Catheryn Yashar, Roger Rice, Todd Pawlicki Radiotherapy and Oncology 90 (2009) 36 42

70 Recommendations for QA Wait 24h after insertion to start planning Patient positioning is key to identify inter-fraction device motion Get AP and lateral radiographs at imaging time and before each fraction. Worry about device deployment in a patient with a small cavity, close to the skin and if struts were splayed on the anterior side higher risk for rotation Measure the distance between maximally displaced peripheral struts on radiographs prior to each fraction Measure and check skin to hub distance Measure total applicator length with the transfer tubes connected. If a QuickConnect connector is used, don t forget to substract 1.4cm!

71 More recommendations For safety: Prior to connection of the HDR machine to the device, the expansion tool should be inserted over the central device strut. This assures that if the source would dislodge from the wire and were to be left in one of the struts, the device could be quickly collapsed, removed from the patient and placed in a lead storage container. The transfer tubes from the machine can be mistakenly connected to the device so it is extremely important that second checks are in place to make sure that the guide tubes are connected to the proper device strut. Two people should connect and independently check each connection. Post-treatment procedures include the survey of the patient to assure that the source has been completely removed from the patient. The machine transfer tubes are then disconnected from the device, expansion tool removed and the patient is bandaged, returning later for their next treatment. Finally, the transfer tubes are cleaned at the device connection end with an isopropyl alcohol-based disinfectant wipe between each use.

72 Thank you.