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K. Van Tilburg



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    P1.08 - Poster Session 1 - Radiotherapy (ID 195)

    • Event: WCLC 2013
    • Type: Poster Session
    • Track: Radiation Oncology + Radiotherapy
    • Presentations: 1
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      P1.08-004 - Australian Implementation of VMAT for stereotactic body radiotherapy in early lung cancer lung: Comparing VMAT with Coplanar and Non-coplanar Intensity Modulated Radiotherapy and 3D-Conformal Radiotherapy. (ID 2119)

      09:30 - 16:30  |  Author(s): K. Van Tilburg

      • Abstract

      Background
      Stereotactic ablative body radiotherapy is being implemented in Australia on a wider scale. Significant differences exist between protocols, particularly in the constraint of dose wash. To achieve a high level of dose conformality large numbers of beams, and non-coplanar techniques may be used, resulting in long treatment times. We report on a study comparing volumetric modulated arc therapy (VMAT) to coplanar (CP) and non-coplanar (NCP) conformal radiotherapy (3D-CRT) and intensity modulated radiation therapy (IMRT), and assess whether plans meet RTOG 0915 and TROG CHISEL criteria.

      Methods
      Eight Pinnacle VMAT, and CP and NCP 3D-CRT and IMRT plans for delivery on Elekta Linacs were assessed for: target coverage (coverage with the prescribed dose), dose conformality (100% and 50% conformity indices, D2cm and high dose outside the PTV) and V20 (volume of lung receiving 20 Gy). Plans aimed to deliver the prescription dose to at least 98% of the volume, with a V20 ≤ 8% . All VMAT plans were single arc with 4° spacing, and all IMRT and 3D-CRT plans used identical beam angles with 10-12 beams. Treatment time was measured by delivering the plans to a phantom. All patients had peripheral tumours and received 48 Gy in 4 fractions.

      Results
      VMAT achieved equivalent radiotherapy target coverage to 3D-CRT and IMRT (>98.2%). However, 3D-CRT plans had a large volume of surrounding normal tissue receiving a high dose (24.0% and 21.3% of the PTV volume for CP and NCP ) when compared to VMAT and IMRT plans (3.9% and 4-5% of PTV volume). 100% conformity indices were lowest for VMAT and NCP IMRT (1.1 for both) and highest for 3D-CRT (1.5 and 1.4 for CP and NCP). D2cm was also lowest for VMAT and NCP IMRT (26.1 Gy and 25.3 Gy) and highest for 3D-CRT plans (29.4 Gy and 28.7 Gy for CP and NCP). V20 was between 4.4 and 6.1% for all plans. VMAT plans were three times as fast to deliver as NCP IMRT (6min and 6s vs. 19 min 34s) and twice as fast as NCP 3D-CRT plans (12min 35s) . TROG CHISEL criteria: one CP-3D-CRT plan had a major violation on spinal cord. There were no other violations. RTOG 0915 criteria: no major violations were recorded for VMAT plans. CP IMRT plans had 2 major violations and NCP IMRT had 1 major violation. All violations were in the D2cm and 50% CI constraints. Seven CP 3D-CRT had major violations in 50% CI, D2cm and high dose spill, and 4 NCP-3DCRT plans had major violations in high dose spill and 100% CI.

      Conclusion
      VMAT plans are similar in quality to NCP IMRT, but are faster to deliver due to reduced gantry and couch movements. 3D-CRT plans were unable to deliver equivalent dose conformality, and a larger region of normal tissue was exposed to a high dose when equivalent PTV coverage was achieved. CP 3D-CRT plans do not meet RTOG criteria due to the inability to meet low dose wash constraints, and more complex planning is beneficial in these cases.

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    P2.08 - Poster Session 2 - Radiotherapy (ID 198)

    • Event: WCLC 2013
    • Type: Poster Session
    • Track: Radiation Oncology + Radiotherapy
    • Presentations: 2
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      P2.08-021 - Comparison of Two Radiotherapy Planning Techniques for Stage IIIA and IIIB NSCLC: Volumetric Modulated Arc Therapy (VMAT) vs 3D Conformal Radiotherapy (3DCRT) (ID 2506)

      09:30 - 16:30  |  Author(s): K. Van Tilburg

      • Abstract

      Background
      Introduction: The treatment of locally advanced lung cancer with radiation therapy has traditionally utilised multiple beam conformal plans. On occasions, the curative intent is compromised due to excessive normal tissue dose, especially to healthy lung tissue. This necessitates a reduction in total delivered dose to a more palliative regimen. With the advent of Volumetric Modulated Arc Therapy (VMAT) at Nepean Cancer Care Centre (NCCC), the question arises of whether VMAT plans can be utilised in these circumstances in order to deliver curative tumour dose, whilst still delivering acceptable normal tissue doses. This study shows a planning comparison of the VMAT and traditional 3D Conformal Radiotherapy (3DCRT) planning techniques. Hypothesis: It is expected that VMAT plans will produce equivalent target volume coverage, whilst resulting in lower toxicities to surrounding healthy tissue, when compared to 3DCRT plans.

      Methods
      Method: This study was conducted retrospectively on three patients who had previously been treated with 3DCRT for stage IIIA or IIIB Non-Small Cell Lung Cancer at NCCC, and had undesirably high healthy lung doses when prescribed 60Gray (Gy) in 30 fractions. The original treatment volumes (planning target volume (PTV), clinical target volume/gross tumour volume) and total prescribed dose for each planning method was left unchanged for this study. The original 3DCRT plans utilised, on average, 4 static beams with 8mm field margins. Angles, wedges, weighting and energy were selected as a best fit to treat the target volume and avoid spinal cord irradiation and healthy lung tissue. Each VMAT replan comprised of one 352° arc, with 89 control points, delivered over a maximum of 90 seconds, with all radiotherapy dose delivered through this dynamic arc. This study compared the two planning methods based on PTV coverage, Conformity Index (CI), V20 (volume of normal lung receiving 20Gy) <30% and V30 (volume of normal lung receiving 30Gy) <20% of the combined healthy lung volume and mean lung dose.

      Results
      Results: Improved coverage of the PTV by 60Gy is achieved with VMAT, with an average of 92.5%, whilst 3DCRT plans achieved an average of 77.7% 60Gy PTV coverage. VMAT combined lung doses were reduced when compared to 3DCRT, with an average V20 of 29.9% for VMAT plans compared to 34.1% for conformal plans, and V30 of 18.4% for VMAT plans, compared to 27% for 3DCRT plans. Combined mean lung dose was also lower for VMAT plans, with an average reduction of 2Gy, with average mean lung dose of 18.01Gy for VMAT plans compared to 20.09Gy for 3DCRT plans. The CI of the D95% was improved in all three cases, with an average 100% CI of 1.01 for VMAT plans, and an average CI of 1.2 for 3DCRT plans.

      Conclusion
      Conclusion: VMAT is a viable planning method to achieve radical treatment intent to 60Gy in 30 fractions, adequate PTV coverage by D95% and improved healthy lung doses for patients with stage IIIA and IIIB NSCLC.

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      P2.08-027 - Atlas segmentation for lung stereotactic ablative radiotherapy (ID 3195)

      09:30 - 16:30  |  Author(s): K. Van Tilburg

      • Abstract

      Background
      With the high radiation dose used in stereotactic ablative body radiotherapy (SABR), it is vital to accurately delineate radiosensitive normal tissues in the planning process such that the dose distributions can be optimised to avoid these regions. This can become a time consuming process. It is also well understood that there is variation in how these volumes are delineated and this has influence on the plan and follow-up data. This work aims to determine if the use of automatic atlas segmentation can help to quickly and accurately delineate CT volumes for SABR planning - saving time, reducing complexity and improving the uniformity of process between patients.

      Methods
      From a retrospective sample of 5 patients delineated by an oncologist, each patient’s CT scan and contours was used as an atlas for a deformable image registration to map volumes to the other patients. A range of quantitative metrics (based on both overlap and distance) were used to evaluate the agreement between the expert contours and the atlas contours for each.

      Results
      The Dice similarity co-efficient showed overlap varied depending on the structure – lungs and heart performed well with a mean of 90% (range 71 – 99%) while the airway structures (trachea, oesophagus, proximal bronchi) performed poorer, with a mean of 52% (range 17 – 99%). This indicates while some structures are well suited to atlas segmentation, some are not. The mean Hausdorff distance, indicated that contours requiring editing after applying the atlas, had mean Hausdorff distances on the order of 1 mm. Typically, atlases that did not perform acceptably had a mean Hausdorff distance > 3 mm indicating it was better to start again with manual delineation. From the sample of 5 atlases, none performed significantly better than the others across all cases.

      Conclusion
      The use of atlases could potentially encourage consistency in delineation and could reduce the laborious task of delineation for lung SBRT treatment planning, however editing of contours is still required. Larger structures performed well, however they could also be easily delineated with threshold-based automatic segmentation. Further investigation to develop a bank of representative atlases may improve performance.

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    P3.08 - Poster Session 3 - Radiotherapy (ID 199)

    • Event: WCLC 2013
    • Type: Poster Session
    • Track: Radiation Oncology + Radiotherapy
    • Presentations: 1
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      P3.08-020 - Comparison of two Radiotherapy Planning Techniques for Stage IIIA and IIIB NSCLC: Hybrid Volumetric Modulated Arc Therapy (VMAT) vs 3D Conformal Radiotherapy (3D CRT) (ID 2515)

      09:30 - 16:30  |  Author(s): K. Van Tilburg

      • Abstract

      Background
      Aim/Objective: Radiotherapy for Stage IIIA and B non-small cell lung cancer at Nepean Cancer Care Centre (NCCC) consists of a 3D conformal radiotherapy (3D CRT) plan dosed to 60Gy in 30 fractions. However, due to the size and location of many stage IIIA and B NSCLC lesions radical radiotherapy is not always clinically deliverable, with the limiting factor often being healthy lung toxicity. In these cases the prescribed dose may be reduced to 50Gy, or the treatment intent altered to palliation. One solution to achieve treating these lesions with a radical intent at NCCC is a hybrid (Volumetric Modulated Arc Therapy) VMAT planning technique. We present a comparison planning study of the Hybrid Volumetric Modulated Arc Therapy (VMAT) vs. 3D Conformal Radiotherapy (3D CRT). Hypothesis: It is expected that the hybrid VMAT technique will achieve better coverage of the Planning Target Volume (PTV) by 95% (57Gy) of the prescribed dose (PD) in addition to reducing the combined lung V20 (volume of lung receiving 20 Gy) and V30 (volume of lung receiving 30 Gy) doses when compared to 3D CRT technique.

      Methods
      Method: This study was conducted retrospectively on 3 patients diagnosed with NSCLC lesions staged IIIA or B previously treated at NCCC. The original 3D CRT plans were used for comparison. Gross Tumour Volume/ Clinical Target Volume (GTV/CTV and PTV) contours have remained unchanged. Original 3D CRT utilised on average 4 static beams, 8mm field margins, and dosed 60Gy in 30 fractions. The hybrid VMAT technique consists of AP/PA static beams, 8mm field margin only dosed to a portion of the prescribed dose, the remaining dose delivered using a partial VMAT arc. The two techniques were compared using PTV coverage, V20 < 30% and V30 <20% of the combined lung volume and mean lung doses.

      Results
      Results: Average results from the first two planning comparisons show coverage of the PTV by D95% is achieved with both hybrid VMAT (96.6%), and 3D CRT (99.2%). However improvements in coverage by D100% are seen using the hybrid VMAT technique compared to 3D CRT (88.7% vs. 79.5%). Hybrid VMAT combined lung doses were reduced, average results V30 = 19.5% and V20 = 24.8% compared to 3DCRT 23.9% and 30% respectively. Mean lung doses using the hybrid technique were also lower in comparison to 3D CRT, 15.6Gy vs. 18.5Gy, reduced on average by 2.9Gy. Average contralateral mean lung dose also followed this trend with hybrid VMAT 7.3Gy vs. 3D CRT with 9.4Gy average reduction by 2.01Gy.

      Conclusion
      Conclusion: Hybrid VMAT is a viable treatment option to achieve radical treatment intent to 60Gy in 30 fractions, adequate PTV coverage by D95% whilst obtaining acceptable V20 and V30 lung doses for patients with stage IIIA and B NSCLC.