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<ul><li><p>1</p><p>Inverse Planning Techniques for IMRT</p><p>Ping Xia, Ph.D.</p><p>University of California-San Francisco</p><p>AAPM 2004, course TH-A-BRA CE</p><p>Forward vs. Inverse Planning</p><p> Conventional forward planning mostly depends on geometric relationship between the tumor and nearby sensitive structures.</p><p> Inverse planning is less dependent on the geometric parameters but more on specification of volumes of tumor targets &amp; sensitive structures, as well as their dose constraints.</p><p>Inverse Planning Is Less Forgiving</p><p> Only treat contoured tumor targets.</p><p> Only spare contoured sensitive structures.</p><p>70 Gy, 59.4 Gy, 54.0 Gy, 45 Gy</p><p>Adding Artificial Structure</p></li><li><p>2</p><p>Volume Delineation</p><p>Volume Delineations </p><p> How to define target volumes? How to contour sensitive structures? How many sensitive structures should </p><p>be contoured?</p><p>Sensitive Structure Delineation</p><p> About 24 sensitive structures need to be contoured</p><p> Lt &amp; Rt parotid, optic nerves, eyes, lens, inner ears, TMJ ( 12).</p><p> Spinal cord, brain stem, chiasm, brain, temporal lobes, larynx, mandible, tongue, airway, apex lung, neck skin, thyroid (12) </p><p>What are Serial and Parallel Organs ?</p><p> A Serial organ is damaged if one of its sub-volumes is damaged.</p><p> A parallel organ loses its functionality only if all sub-volumes of the organ are damaged.</p></li><li><p>3</p><p>R T L T</p><p>2 9</p><p>3 0</p><p>3 1</p><p>3 2</p><p>3 3</p><p>3 4</p><p>3 5</p><p>3 6</p><p>3 7</p><p>3 8</p><p>Dose</p><p>(Gy)</p><p>ABCDE</p><p>Differences in Mean Dose to Parotid Glands</p><p>Tumor Margin vs Beam Margin</p><p> Tumor margin: position uncertaintieslocalization uncertainties</p><p> Beam margin: Beam penumbra</p><p>1.5 cm block margin = 0.8 cm tumor margin + 0.7 cm beam margin</p><p>3 mm superior</p><p>3D Tumor Margin or 2D Tumor Margin</p></li><li><p>4</p><p>Dose Constraints</p><p>Dose Constraints Inverse planning requires us to specify dose constraints </p><p>to all structures.</p><p> Inverse IMRT planning becomes a trial-error process in searching for a proper dose constraint specification.</p><p> Improperly specified dose constraints will result in inferior plans</p><p>Tell Me Your Dream</p><p> Full dose to the tumor target Zero dose to sensitive structures </p><p>Impossible !!!!</p><p>Treatment GoalsRx doses:</p><p>95 % GTV &gt; 70 Gy at 2.12 Gy95 % PTV &gt; 59.4 Gy at 1.8 Gy</p><p>Tolerance doses:Spinal Cord: Max &lt; 45 Gy,Brain Stem: Max &lt; 55 Gy,Parotid glands: mean dose &lt; 26 Gy,Optic structures: Max &lt; 54 Gy, </p></li><li><p>5</p><p>Realty and Physics Limitations</p><p> Single beam penumbra ~ 7-8 mm, from 90% - 20% iso-dose lines 10%/mm</p><p> IMRT iso-dose lines are also limited by this radiation physics.</p><p> Scatter dose from multiple beams makes the beam penumbra shallower.</p><p>15 Gantry angles</p><p>60, 50, 42, 34 Gy</p><p>70%</p><p>40%</p><p>Systematic Trial-and-Error</p><p>Everything Equally Important</p></li><li><p>6</p><p>See What We Get</p><p> Rx 70% to 66 Gy7% of GTV underdose, 10% of CTV underdose,</p><p> Max-dose RT-eye = 64 Gy, LT-eye =61RT-OPN = 56 Gy, LT-OPN = 57 GyBrain Stem = 46 GyChiasm = 54 Gy</p><p>Everything Equally Important</p><p>Tumor Important</p><p> Rx 84% to 66 Gy4 % of GTV underdose, 5% CTV underdose,</p><p> Max-dose to critical structures RT-eye = 71 Gy, LT-eye =64 GyRT-OPN = 66 Gy, LT-OPN = 69 GyBrain Stem = 48 GyChiasm = 59 Gy</p><p>Tumor Important</p></li><li><p>7</p><p>What We Can Get Critical Structures Important</p><p>See What We GetCritical Structures Important</p><p> Rx 75% to 66 Gy6 % of GTV underdose, 7% CTV underdose,</p><p> Max-dose to critical structures RT-eye = 63 Gy, LT-eye =64 GyRT-OPN = 51 Gy, LT-OPN = 51 GyBrain Stem = 42 GyChiasm = 51 Gy</p></li><li><p>8</p><p>Compromise Solution Final Solution</p><p>Final Solution</p><p> Rx 80% to 66 Gy6% of GTV underdose, 8% CTV underdose,</p><p> Max-dose to critical structures RT-eye = 60 Gy, LT-eye =62 GyRT-OPN = 55 Gy, LT-OPN = 56 GyBrain Stem = 46 GyChiasm = 54 Gy</p><p>70 Gy, 60 Gy, 54 Gy, 45 Gy</p><p>Equal important</p><p>Critical structure</p><p>Tumor important</p><p>Compromised</p></li><li><p>9</p><p>Beam Angle Selection</p><p>Beam Selections</p><p> Are more beams better than fewer beams? </p><p> Equal spaced beam angles? Non-coplanar beam angles?</p><p>Not necessarily</p><p>Non-coplanar Beam Angles</p><p> Rx 80% to 66 Gy5% of GTV underdose, 8% CTV underdose,</p><p> Max-dose to critical structures RT-eye = 62 Gy, LT-eye =63 GyRT-OPN = 49 Gy, LT-OPN = 51 GyBrain Stem = 39 GyChiasm = 53 Gy</p><p>15 Beam Angles</p><p> Rx 82% to 66 Gy4 % of GTV underdose, 4% CTV underdose,</p><p> Max-dose to critical structures RT-eye = 63 Gy, LT-eye =62 GyRT-OPN = 53 Gy, LT-OPN = 56 GyBrain Stem = 33 GyChiasm = 56 Gy</p></li><li><p>10</p><p>15 beam angles 9 beam angles</p><p>Non-coplanar beam angles</p><p>70 Gy, 60 Gy, 54 Gy, 45 Gy</p><p>Plan Refinement</p><p>Plan 1</p><p>Plan 2</p><p>Plan 1</p></li><li><p>11</p><p>Plan 2</p><p>Plan 1 Plan 2</p><p>70 Gy, 59.4 Gy, 52 Gy</p><p>Plan Evaluation</p><p>Evaluation of IMRT Plans</p><p> Define endpoints Dose volume histogram (DVH) Dose distributions on every CT slice </p><p>(Rx, hot spot, cold spot)</p></li><li><p>12</p><p>Plan Acceptance Criteria</p><p>Head and Neck Tumor:</p><p>&gt; 80% isodose line to the GTV</p><p>70 Gy &gt; 95% of GTV (2.12 Gy/day)59.4 Gy &gt; 95% of CTV (1.8 Gy/day)54 GY &gt; 95% of CTV2 (1.64 Gy/day)</p><p> Sensitive Structures:Serial Structures: Maximum dose</p><p>Cord &lt; 45 Gy, 1cc &lt; 40 GyStem &lt; 54 Gy, 1 cc &lt; 54 GyOptic structures &lt; 54 GyMandible &lt; 70 GyTemporal lobe &lt; 70 Gy</p><p>Plan Acceptance Criteria</p><p> Parallel Structures: Mean doseParotid &lt; 26 Gy~ 30 Gy</p><p>Inner ear &lt; 50 Gy</p><p>Other Structures: as low as possibleOral cavitysub-mandibular glandLarynx</p><p>Plan Acceptance Criteria</p><p>Isodose Distributions</p></li><li><p>13</p><p>Cold spot</p><p>70 Gy,59.4 Gy,45 Gy</p><p>Hot-spot</p><p>70.0 Gy,59.4 Gy,54 Gy</p><p>6 mm superior</p><p>Three Dimensional Examination</p><p>70 Gy60 Gy</p><p>70 Gy60 Gy</p><p>Class Solutions</p></li><li><p>14</p><p>Review Old Plans Review previous clinically accepted plans </p><p>9 plans for T1-2 Nasopharyngeal patients.16 plans for T3-4 Nasopharyngeal patients.</p><p>24 plans for oropharyngeal patients.</p><p>(Xia, P et. al, IJROBP, in press)</p><p>31.338.3 41.4 Mid./Inner Ear</p><p>26.7 30.5 33.8 T-M joint17.9 25.1 26.8 </p><p>Parotid Gland </p><p>Dose to 80% Vol. (Gy)</p><p>Dose to 50% Vol. (Gy)</p><p>Mean Dose (Gy)</p><p>9.8 13.5 25Eye18.8 22.2 23.7 Optic Nerve37.6 40.4 50.9 Brain Stem25.8 30.6 38.3 Spinal Cord 19.7 21.5 27.5 Chiasm</p><p>Dose to 10% Vol. (Gy)</p><p>Dose to 5% Vol. (Gy)</p><p>Max. Dose (Gy)Structures</p><p>T1-2 Nasopharyngeal Cancer</p><p>42.249.8 49.6Middle/Inner Ear </p><p>31.5 36.7 38T-M joint18.7 24.6 27.8Parotid Gland </p><p>Dose to 80% Vol. (Gy)</p><p>Dose to 50% Vol. (Gy)Mean Dose (Gy)</p><p>19.6 21.9 32.8 Eye31.634.4 41.6 Optic Nerve40.0 43.1 55.3 Brain Stem26.7 33.0 42.2Spinal Cord 34.236.442.7Chiasm</p><p>Dose to 10% Vol. (Gy)</p><p>Dose to 5% Vol. (Gy)Max Dose (Gy)Structures</p><p>T3-4 Nasopharyngeal Cancer PTV70PTV70</p><p>PTV70</p><p>PTV60</p><p>PTV60</p><p>PTV60</p><p>Cord</p><p>Lt Parotid</p><p>Rt Parotid</p><p>Brainstem</p><p>AntiPTV</p><p>Parotids</p><p>Q block</p></li><li><p>15</p><p>79.2, 70.0, 59.4, 54.0, 45.0 GyArtificial structure</p><p>airway</p><p>Neck skin</p><p>79.2, 70.0, 59.4, 54.0, 45.0 Gy</p><p>cord</p><p>stem</p><p>Parotids</p><p>GTV</p><p>PTV</p><p>PTV2</p><p>Nasopharynx Tumor Target Oropharyngeal Cancer</p><p>9.0 4.8</p><p>80.8 2.0</p><p>60.6 2.7</p><p>54.3 4.7</p><p>690.4 274.1</p><p>PTV-60</p><p>0.1 0.1</p><p>80.2 2.6</p><p>71.2 1.5</p><p>69.3 1.4</p><p>76.7 47.3</p><p>PTV-70</p><p>V93% (cc)</p><p>D1cc (Gy)</p><p>D95% (Gy)</p><p>D99% (Gy)</p><p>Vol. (cc)</p><p>Rx IDL 85.8% 2.0%</p></li><li><p>16</p><p>Sensitive Structures Oropharyngeal Cancer</p><p>26.2 7.5</p><p>26.9 7.6</p><p>TMJ67.7 3.0</p><p>71.6 2.9</p><p>Mandible</p><p>23.3 8.9</p><p>24.2 8.6</p><p>Ear40.1 10.1</p><p>43.5 9.8</p><p>Brain Stem</p><p>23.5 3.5</p><p>26.1 3.2</p><p>Parotid40.2 3.8</p><p>42.6 3.5</p><p>Spinal Cord</p><p>Median (Gy)</p><p>Mean (Gy)</p><p>D1% (Gy)</p><p>D1cc (Gy)</p><p>78.2 Gy70.0 Gy59.4 Gy54.0 Gy45.0 Gy</p><p>Oropharynx</p><p>Oropharynx</p><p>78.2 Gy, 70.0 Gy, 59.4 Gy, 54.0 Gy, 45 Gy</p><p>GTV</p><p>PTV</p><p>Brain stem</p><p>cord</p><p>Parotids</p><p>Oropharynx</p></li><li><p>17</p><p>Class Solutions Class solutions can be applied to patients with </p><p>same or similar types of cancer Streamline treatment planning can significantly </p><p>improve planning efficiency. Planning turn around time has been reduced from </p><p>one week to two days. Actual planning time for a typical head and neck </p><p>case is about 4-8 hours, including contouring , printing, waiting, coffee break</p><p>Simplify IMRT Plans</p><p>Seeking Simple IMRT Plans</p><p> Five oropharyngeal cases were planned using five different beam angle arrangements.</p><p> The criteria for plan acceptance are based on RTOG protocols (RTOG-0022)</p><p> Five patients were not limited to early stage as in RTOG protocol.</p><p>Submitted to Int. J. Radiat. Oncol. Biol. Phys </p><p>Tumor Target Oropharyngeal Cancer</p><p>9.0 4.8</p><p>80.8 2.0</p><p>60.6 2.7</p><p>54.3 4.7</p><p>690.4 274.1</p><p>PTV-60</p><p>0.1 0.1</p><p>80.2 2.6</p><p>71.2 1.5</p><p>69.3 1.4</p><p>76.7 47.3</p><p>PTV-70</p><p>V93% (cc)</p><p>D1cc (Gy)</p><p>D95% (Gy)</p><p>D99% (Gy)</p><p>Vol. (cc)</p><p>Rx IDL 85.8% 2.0%</p></li><li><p>18</p><p>Sensitive Structures Oropharyngeal Cancer</p><p>26.2 7.5</p><p>26.9 7.6</p><p>TMJ67.7 3.0</p><p>71.6 2.9</p><p>Mandible</p><p>23.3 8.9</p><p>24.2 8.6</p><p>Ear40.1 10.1</p><p>43.5 9.8</p><p>Brain Stem</p><p>23.5 3.5</p><p>26.1 3.2</p><p>Parotid40.2 3.8</p><p>42.6 3.5</p><p>Spinal Cord</p><p>Median (Gy)</p><p>Mean (Gy)</p><p>D1% (Gy)</p><p>D1cc (Gy)</p><p>9 Equally Spaced 8 selected angles</p><p>0O</p><p>200O 160O</p><p>240O</p><p>320O</p><p>120O</p><p>40O</p><p>80O</p><p>0O</p><p>30O340O</p><p>290O</p><p>230O</p><p>90O</p><p>130O</p><p>280O</p><p>260O</p><p>7 selected anglesForward plan</p><p>7 angles fromMSKCC </p><p>210O</p><p>270O</p><p>150O</p><p>90O</p><p>180O</p><p>120O240O</p><p>0O</p><p>210O 150O</p><p>60O</p><p>90O270O</p><p>300O</p><p>Five beam angles</p><p>230O</p><p>65O</p><p>0O</p><p>130O</p><p>295O</p></li><li><p>19</p><p>PTV70</p><p>PTV70</p><p>PTV70</p><p>PTV60</p><p>PTV60</p><p>PTV60</p><p>Cord</p><p>Lt Parotid</p><p>Rt Parotid</p><p>Brainstem</p><p>AntiPTV</p><p>Parotids</p><p>Q block</p><p>Isodose line covering 95% of GTV</p><p>0.84</p><p>0.85</p><p>0.86</p><p>0.87</p><p>0.88</p><p>0.89</p><p>9 angles 8 angles 7 angles 7 angles(MSKCC)</p><p>5 angles FPMS</p><p>isod</p><p>ose</p><p>line</p><p>(%)</p><p>Target Volume Coverages (V70/V59.4)</p><p>90.00</p><p>92.00</p><p>94.00</p><p>96.00</p><p>98.00</p><p>100.00</p><p>9 angles 8 angles 7 angles 7 angles(MSKCC)</p><p>5 angles FPMS</p><p>Volu</p><p>me</p><p>(%)</p><p>GTV/CTV</p><p>Endpoint doses to sensitive structures</p><p>2000.00</p><p>2500.00</p><p>3000.00</p><p>3500.00</p><p>4000.00</p><p>4500.00</p><p>9 angles 8 angles 7 angles 7 angles(MSKCC)</p><p>5 angles FPMS</p><p>Dose</p><p>(cG</p><p>y)</p><p>Mean dose to parotid Max dose to 1 cc of cord</p></li><li><p>20</p><p>Treatment delivery time</p><p>0.00</p><p>5.00</p><p>10.00</p><p>15.00</p><p>20.00</p><p>25.00</p><p>9 angles 8 angles 7 angles 7 angles(MSKCC)</p><p>5 angles</p><p>Tim</p><p>e(m</p><p>in)</p><p>7000 cGy6000 cGy4500 cGy2500 cGy</p><p>7000 cGy6000 cGy4500 cGy2500 cGy</p><p>Seeking Simple IMRT Plans</p><p> For simple H&amp;N cases (oropharyngeal),5-6 beam angles with 60-80 segments~ 15-20 minutes.</p><p> For complex H&amp;N cases (naso, sinus), 7-8 beam angles with 100-130 segments ~ 20 30 minutes.</p><p>Submitted to Int. J. Radiat. Oncol. Biol. Phys </p></li><li><p>21</p><p>Special Clinical Problems-Skin Dose Problem</p><p>Patient with marked skin reaction </p><p>Patient Skin Dose Problem Multiple tangential beams decrease skin sparing.</p><p> Bolus effect, due to the use of the head-shoulder mask, increases skin dose about 15%.</p><p> In order to cover superficial nodes, the inverse planning system increases beam intensity onthe neck skin.</p><p> Neck skin may be contoured as a sensitive structure to avoid high dose on the neck skin.</p><p>Lee, N, et. al. IJROBP, 2002.</p><p>38.7047.5441.1050.3454.6460.1043.1250.63Ave. Total dose (Gy)</p><p>1.17 +0.10</p><p>1.44 +0.12</p><p>1.25 +0.17</p><p>1.53 +0.16</p><p>1.66 + 0.15</p><p>1.82 +0.13</p><p>1.31 + 0.31 </p><p>1.53 + 0.39</p><p>Ave. Daily dose (Gy)</p><p>w/o mask</p><p>w/ mask</p><p>w/o mask</p><p>w/mask</p><p>w/o mask</p><p>w/mask</p><p>w/o mask</p><p>w/mask</p><p>IMRT w/skin excluded + skin </p><p>spare</p><p>IMRT w /skin excluded</p><p>IMRT w/ skin included</p><p>Opp. Lateral</p><p>Skin Dose Investigation</p></li><li><p>22</p><p>807060504030201000</p><p>20</p><p>40</p><p>60</p><p>80</p><p>100</p><p>Non-Skin Sparing PlanSkin Sparing Plan</p><p>Dose (Gy)</p><p>Volu</p><p>me</p><p>(%)</p><p>Patient neck skin sparing</p><p>Take Home Messages Inverse planning is not intuitive but easy to establish </p><p>class solution for a specific cancer. Know the realistic goals, find the upper limit and lower </p><p>limits for both dose conformity and uniformity. Systematically research for compromise solution</p><p> Find a proper dose constraints while </p><p>starting with 9 11 beam angles Find a optimal beam angles while </p><p>keeping the same dose constraints</p><p>Take Home Messages</p><p> Once you know the upper and lower limits, simplify IMRT plan as much as possible to reduce treatment time, unnecessary radiation</p><p> Develop your own class solutions</p></li></ul>

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