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Clinical Site specific IMRT Bulent Aydogan, PhD

Clinical Site specific IMRT Bulent Aydogan, PhD. Department of Radiation and Cellular Oncology University of Chicago. Nov 2007 Antalya, Turkiye.

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Clinical Site specific IMRT Bulent Aydogan, PhD

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  1. Clinical Site specific IMRTBulent Aydogan, PhD Department of Radiation and Cellular Oncology University of Chicago Nov 2007 Antalya, Turkiye

  2. You can download the full-blown version of this talk which has site specific clinical IMRT info for H&N, Prostate and GYN from ASTRO website under the refresher courses. • You can email me @ baydogan@radonc.uchicago.edu

  3. Target Audience Everybody New to treating with IMRT Planning to treat a new site Learn from others mistakes!

  4. IMRT • IMRT is a method of treatment planning and delivery that conforms the high dose region to the shape of the target volume while sparing surrounding critical organs

  5. IMRT in numbers • In US • 80% are using • 80% started in the last 3-4 yrs • 90% non-user are planning to use. • Outside of USA • Turkiye!

  6. IMRT ALARMING RPC STATISTICS • Dose accuracy • Recommended 3% dose and 3mm • RPC IMRT validation experience (ASTRO 2006 Abstract, A. Molineau et. al.) • 155 inst. 196 irradiations • 7% dose and 4mm DTA • 54 failure ~>1/3 failed (33 on dose)

  7. IMRT

  8. Purpose • To illustrate how various aspects of the IMRT planning process can influence the resultant treatment plan and delivery • To provide an update of IMRT planning techniques for gynecologic malignancies AND H&N, prostate • How IGRT influence IMRT process

  9. Summary • IMRT treatment planning is a multi-step process • Careful consideration throughout the entire process is necessary to ensure that an optimal plan is achieved • Decisions made at the time of simulation, target and tissue delineation, planning and the delivery/verification process itself impact the overall plan

  10. Treatment Planning Process Simulation – Prone vs. Supine; Type of immobilization  Target and Tissue Delineation – Multiple imaging modalities  Treatment Planning/Optimization – Number of beams/orientation  Plan Evaluation – High conformity vs. dose homogeneity  Quality Assurance – Verification of calculated dose  Treatment Delivery/Verification – Verification scheme

  11. SUMMARY • IGRT • Changing the way we do IMRT • Margins • Biological targeting • Intrafraction vs. interfraction • Organ motion management • Gating , IID • Adaptation • Requires more resources and careful planning

  12. PTV Margin and IGRT Litzenberg DW, IJROB, 65(2), 2006

  13. General issues In Treatment Planning • Dose distribution depends • Treatment planning system / optimization • Dose calculation method • PBC, Superposition Convolution, MC • User experience • Realistic expectations (e.g., dose constraints) • Beam configuration, Energy?

  14. 3 – Field 7 – Field Number of Beams • More beams = Better plan? • Generally Yes • But improvement can be marginal over 7 beams • Degree of improvement depends on tumor shape and proximity to critical structures

  15. Beam Angles and Energies • Nearly all studies report using 6 MV • Generally use 6-9 co-planar beams • Avoid parallel opposed beams • Beams are equidistant but may not be uniformly distributed • Non-uniform beam distribution may be used for special sites

  16. Beam configuration 9 Field 8 Field

  17. User Dependency Can you guess which plan is done by a experienced user?

  18. Realistic expectation

  19. Managing Hot Spots“Tuning” Structures • Occasionally “hot” spots or unwanted dose in surrounding unspecified tissue • Adding an additional (“tuning”) structure can reduce these “hot” spots and improve dose conformity around the PTV • However, improved conformity may reduce dose homogeneity within the target

  20. Use of “Tuning” Structure to Improve Dose Conformity Pawlicki T et al. Plan Evaluation. IMRT: A Clinical Perspective 2005

  21. Optimizing with Base Plan Aydogan et al, TCRT, 2006

  22. Fluence editing • It is very handy • Needs experience • Exercise caution when using • Works better for smaller hot spots

  23. IMRT forGynecologic Malignancies

  24. GYN IMRT • Rationale • Reduce volume of small bowel, bladder and rectum irradiated • Decrease volume of pelvic bone marrow irradiated in patients receiving CRT • Potentially useful in delivering higher than conventional doses • Alternative boost technique for patient who are not amenable to BC

  25. Immobilization • Patient in supine position • Immobilized using alpha cradles indexed to the treatment table Univ of Chicago

  26. Immobilization (Prone) Univ of Colorado • Others favor the prone position • Data from the U Iowa suggest ↑dosimetric benefits to the prone position (Adli et al. Int J Radiat Oncol Biol Phys 2003;57:230-238) Schefter T, Kavanagh B. Cervical Cancer: Case Study IMRT: A Clinical Perspective 2005

  27. Planning CT Scan • Scan extent: L3 vertebral body to 3 cm below ischial tuberosities • Typically use 3 mm slice thickness • Larger volumes used only if treating extended field whole abdomen or pelvic-inguinal IMRT

  28. Contrast Administration • Oral, IV and rectal contrast are commonly used • IV contrast is important to delineate vessels which serve as surrogates for lymph nodes • Generally bladder contrast is not needed

  29. Normal Tissues • Normal tissues delineated depends on the clinical case: In most cases, include: Small bowel, rectum, bladder may be femoral heads • In patients receiving concomitant or sequential chemotherapy, include the bone marrow (experimental) • Kidneys and liver included only if treating more comprehensive fields

  30. PTV Considerations • Organ motion in the inferior portion of the CTV due to differential filling of the bladder and rectum • Set-up uncertainty • Appropriate expansion remains unclear; various reports ranging from 1 – 1.5 cm • At Univ of Chicago, we use a 1 cm expansion • Less is known about normal tissues • Other centers (e.g., MD Anderson) routinely expand normal tissues

  31. Set-up Uncertainties • Dependent on type of immobilization • Therapist • University of Chicago immobilization: Alpha cradle under legs and upper body with arms above head* sLR = 3.2 mm sSI = 3.7 mm sAP = 4.1 mm * Haslam JJ et al. Med Dosim. 2005 Spring;30(1):36-42

  32. Treatment Planning • 7-9 co-axial beam angles (equally spaced) • Most centers use 6 MV • Comparative plans of 6 vs. 18 MV show little or no difference • However, 18 MV associated with higher total body doses

  33. Treatment Planning • Prescription dose: 45-50.4 Gy • 45 Gy in pts receiving vaginal brachytherapy • 45-50.4 Gy if external beam alone • 1.8 Gy daily fractions • Avoids hot spots > 2 Gy • “Dose painting” (concomitant boost) remains experimental • Potentially useful in pts with high risk factors (positive nodes and/or margins)

  34. INPUT DVH Small bowel input DVH based on NTCP data

  35. NTCP Analysis GYN IMRT PatientsVolume receiving 45 Gy Probability of Moderate to Severe Acute GI Toxicity Conventional Pelvic RT IMRT Roeske et al : IJROB

  36. IMRT Isodose Distribution PTV 100% 70%

  37. Plan Evaluation Acceptable Unacceptable Conformity Good Poor PTV Coverage > 98% < 96% Hot Spots Location Within CTV Edge of PTV Preferably within GTV Rectal or bladder walls in ICB region Magnitude <10% (110% dose) >20% (110% dose) <2% (115% dose) >2% (115% dose) Cold Spots Location Edge of PTV Within CTV or GTV Magnitude <1% of the total dose none

  38. Organ Motion • A concern in the region of the vaginal cuff • Two approaches are being studied at our institution to address this: • IGRT (CBCT) • Vaginal immobilization • Now we simply avoid tight CTV volumes and use a 1 cm CTV→PTV expansion • Produces very generous volumes around the vaginal cuff

  39. “Integrated Target Volume” • A creative solution to the organ motion problem developed at MDAH • Two planning scans: one with a full and one with an empty bladder • Scans are then fused • An integrated target volume (ITV) is drawn on the full bladder scan (encompassing the cuff and parametria on both scans) • ITV is expanded by 0.5 cm → PTVITV

  40. Illustration of ITV Integrated Target Volume (ITV) Small Bowel Bladder PTVNodes Rectum MD Anderson

  41. Vaginal Immobilization Device • Cervical and Endometrial cancer pts treated with IM-PRT and vaginal (cylinder) HDR • Goal: Use vaginal cylinder-type immobilization device and IGRT IID adjustment and indexing Treatment table mount and indexing B Aydogan, PhD – Univ of Chicago, Patent pending

  42. Adaptive approach in Gynecologic IMRT • Many cervical tumors rapidly shrink during RT (especially with concomitant chemotherapy) • Tight margins (CTV-to-PTV expansions) early on may be too large by the end of treatment

  43. 14 cervical cancer pts MRI before RT and after 30 Gy 46% ↓GTV Impact of Tumor Regression in Cervical Cancer Patients Van de Bunt et al. Int J Radiat Oncol Biol Phys 64(1):189-96, 2006.

  44. Tumors Shrink Plan Adapts Bladder Bladder Tumor Tumor Rectum Rectum Prescription Isodose Week 1 Week 3

  45. IMRT <> ICB ? • IMRT has been used to reduce volume of normal tissues irradiated • In selective sites (e.g., head and neck, prostate), IMRT has been used to deliver higher than conventional doses • Can the same paradigm be applied to cervical cancer?

  46. Approaches • SRS Boost • Molla et al. Int J Radiat Oncol Biol Phys 62: 118-24, 2005. • Vaginal Immobilization Device • Aydogan B. Int J Radiat Oncol Biol Phys 65:266-73, 2006. • SIB • Guerrero M, et al. Int J Radiat Oncol Biol Phys 62(3):933-39, 2005.

  47. HDR vs. IMRTin early and recurrent endometrial cancer HDR IMRT Aydogan B. Int J Radiat Oncol Biol Phys 65:266-73, 2006.

  48. IMRT-SIB Planning Approach 60 Gy 25 x 2.4 Gy 20 Gy 45 Gy 25 x 1.8 Gy X. Allen Li, PhD – Med Col of Wisconsin

  49. BMS-IMRT • Rationale • CRT Improved tumor control and survival • Increased toxicity in particular HT • Acute grade >2 HT is up to 50% more • Acute grade >3 HT is up to 35% more • BMS-IMRT may reduce HT Aydogan et al: IJROB, under review ASTRO 2007 ARRO Poster # 2353

  50. Dose comparison

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