A Comparison of IMRT and VMAT Technique for the Treatment of Rectal Cancer

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1 A Comparison of IMRT and VMAT Technique for the Treatment of Rectal Cancer Tony Kin Ming Lam Radiation Planner Dr Patricia Lindsay, Radiation Physicist Dr John Kim, Radiation Oncologist Dr Kim Ann Ung, Radiation Oncology Fellow American Association of Medical Dosimetrists 39 th Annual Meeting June 5, 2014

2 Princess Margaret Cancer Centre Toronto, Canada

3 Princess Margaret Cancer Centre Radiation Medicine Program 1) 16 Linear Accelerators 2) 1 Superficial / Orthovoltage Machine 3) 4 CT Scanners 4) 2 MR Scanners 5) Brachytherapy Suite 6) 1 Gamma Knife Perfexion unit 7) 1 Magnetic Resonance Image Guided Radiotherapy unit ( can be used clinically soon) 8) 55 Pinnacle planning stations 9) 40 Planners

4 Background Role of adjuvant radiation (RT) in addition to surgery in the management of locally advanced rectal cancer Reduce the risk of local recurrence Radiation can be given pre or post operatively

5 Background Recently, there has been significant progress in the pelvic RT technique from conventional RT to a more conformal approach using IMRT and VMAT 115 patients with rectal cancer treated with RT in our cancer center within the year 2013

6 Objectives 1) Describe Princess Margaret Cancer Centre s RT technique in rectal cancer 2) Compare the planning parameters and dosimetry distribution for these RT techniques: 1) 3 field conventional RT 2) Intensity modulated RT (IMRT) 3) Volumeric modulated RT (VMAT) 3) Physics QA measurement in IMRT and VMAT

7 Methods Retrospective study: 1) Five pre existing IMRT pelvic RT plans were randomly selected 2) A VMAT plan was generated for each dataset to achieve the same level of planning target volume (PTV) dose coverage 3) Both IMRT and VMAT plans were generated by using inverse planning algorithm in a treatment planning system 4) Dose prescription = 50 Gy in 25 fractions

8 Methods 1) IMRT: 7 co planer 6 MV beams 2) VMAT: 2 full 360 arcs (6 MV) 3) IMRT and VMAT plan quality comparison: Measuring the conformity index (CI) of PTV Dose volume statistics of the organ at risk (eg. small bowel, femur and genital) Definition of CI = ratio of PTV volume receiving at least 95% of the prescribed dose divided by the PTV volume

9 Workflow for Rectum RT

10 Treatment Protocol Clinical indications for pre operative RT in rectal cancer: Adenocarcinoma Locally advanced Stage T1 2 N1 2, T3 4 N0 2

11 Contour Delineation Gross Tumor Volume Primary GTV Primary rectal tumour from physical exam, endoscopy, diagnostic imaging and CT/MRI simulation Gross lymph nodes Any gross or suspicious lymph nodes

12 Contour Delineation Clinical Target Volume Primary CTV 1 cm circumferential expansion on GTV + 1 cm radial margin on rectum at the level of GTV and 2 cm above and below CTV of gross lymph nodes 1 cm circumferential expansion on gross lymph nodes mctv 1 cm circumferential expansion around the contoured mesorectum

13 Contour Delineation Clinical Target Volume LCTV and RCTV 1.5 cm expansion around left & right internal iliac vessels Superior S1/S2 junction Inferior pelvic floor defined by the upper surface of the levator muscle Anterior approx. mid portion of femoral heads Planning Target Volume (PTV) 7 mm circumferential expansion on all CTVs

14 Contour Delineation Organ at Risk By oncologist: Anal Mesorectum Rectum Rectosigmoid Large bowel: to top of L5 or minimum 2 cm above PTV Small bowel: to top of L5 or minimum 2 cm above PTV Bladder By the planner: Right & left femur

15 CT and MRI Simulation 1) Prone position 2) Comfortably full bladder for planning & treatment Voiding and drinking 500 ml of water 1 hour before simulation & treatment 3) IV contrast facilitate identification of blood vessels 4) Oral contrast facilitate identification of small bowel 5) MR simulation fused with the planning CT scan (bone match)

16 Advancements in RT Technique 3 field technique Wedge Segments IMRT VMAT

17 3 field Rectum with Segments Beam Orientation

18 3 field RT technique DRR Posterior field Lateral field

19 Posterior Field Segments 3 field Rectum Technique

20 Lateral Field Segments 3 field Rectum Technique

21 3 Field Dose Distribution

22 Advantages of Using Segmentations (Without Wedge) 1. Save treatment time Therapists do not need to go into the room to insert wedge 2. Reduce error using incorrect wedge 3. Move one step forwards to IMRT practice

23 IMRT Rectum Prone position Seven 6 MV co planer beams Beam angles: 0, 40, 85, 160, 200, 275, 315

24 3 field RT vs. IMRT 3 field technique IMRT IMRT rectum: Enables 50 Gy to be delivered (compared to 45 Gy with 3 field technique) PTV overlapping with small bowel receives at least 45 Gy but not more than 47.5 Gy (95% prescribed dose) Anterior pelvis can be spared (receiving <50% isodose level, similar to 3 field technique)

25 Planning criteria for VMAT 1) Meet dose constraints for OARs 2) Cover PTV by 95% prescription dose. To achieve PTV D99= 95% prescription dose 3) To keep hot spot within 108% prescription dose

26 VMAT Rectum Planning Process Prone position Two 360 arcs (6 MV) Clockwise Counter clockwise Gantry spacing = 3 Collimator angle=0, 15 to minimize fields overlapping to reduce tongue & groove effect

27 VMAT Dose Avoidance Volumes VMAT VMAT As VMAT rectum uses two 360 arcs, 2 dose avoidance volumes are created to limit dose to lateral & anterior pelvis Lateral locations (green) Anterior location (blue)

28 VMAT Dose Avoidance Volumes VMAT The anterior dose avoidance volume is divided into 2 sections with different dose constraints: Superior (blue) higher dose constraint Inferior (pink) lower dose constraint

29 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Transverse CT Cyan = 50% isodose line

30 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Sagittal CT Cyan = 50% isodose line

31 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Coronal CT Cyan = 50% isodose line

32 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Transverse CT Pink = 20% isodose line

33 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Sagittal CT Pink = 20% isodose line

34 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #1 Coronal CT Pink = 20% isodose line

35 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #3 Transverse CT Genital dose sparing

36 Dose Distribution IMRT vs. VMAT IMRT VMAT Case #3 Sagittal CT Genital dose sparing

37 Conformity Index PTV (CI) CASE # IMRT VMAT # # # # # Range Mean Dose CI of PTV = V95 / PTV volume

38 Maximum dose to 0.5 cc Small Bowel (Gy) CASE # IMRT VMAT # # # # # Range Mean Dose

39 Maximum dose to 0.5 cc Right Femur (Gy) CASE # IMRT VMAT # # # # # Average max dose

40 Maximum Dose to 0.5 cc Left Femur (Gy) CASE # IMRT VMAT # # # # # Average max dose

41 Maximum dose to 0.5 cc Genitals (Gy) CASE # IMRT VMAT # # # # # Average maxdose

42 50% Isodose Volume (cc) CASE # IMRT VMAT % difference respect to VMAT # # # # # Average % difference 2.6% 50% isodose volume VMAT < IMRT (slight)

43 Low Isodose Volume 20% isodose (cc) CASE # IMRT VMAT % difference respect to VMAT # # # # # Average % difference +8.2 Low isodose volume (20% isodose) VMAT > IMRT

44 Total Monitor Units (MUs) CASE # IMRT VMAT # # # # # Range Mean Dose

45 Planning and Treatment Time 3 field RT IMRT VMAT Optimization time Treatment time 10 min 30 min 90 min 15 min 20 min 15 min Treatment time includes: Patient set up, cone beam CT verification, treatment delivery

46 IMRT vs. VMAT Comparison Summary Conformity index of PTV 0.5 cc max small bowel dose similar similar 0.5 cc max femur dose VMAT < IMRT 0.5 cc max genital dose VMAT > IMRT 50% isodose volume VMAT < IMRT 20% isodose volume VMAT > IMRT Total monitor units VMAT < IMRT Optimization time VMAT > IMRT Treatment time VMAT < IMRT

47 IMRT vs. VMAT Simulation process, patient set up and image verification with CBCT = same for IMRT and VMAT

48 Image Verification CBCT IMRT/VMAT rectum with daily pre treatment CBCT verification bone match

49 Physics Measurement QA IMRT Fluences (EPID or film) We compare the measured vs. computed results qualitatively (visual inspection) Simple QA test that the beams are being correctly delivered MapCheck 2 D array of diodes Quantitative comparison of planned vs. measured fluences Only used if fluence measurements show potential discrepancies

50 IMRT Example Fluence Computed Fluence Measured Fluence (EPID) Visual comparison of fluence pattern Check for leaf leakage Check for tongue & groove effect

51 Physics Measurement QA VMAT ArcCheck A 3D array of 1386 diode detectors Arranged in a spiral pattern 10 mm spacing We compare the results between measured and computed doses based on a 3%/2mm criteria Cannot use for prone orientation treatments Delta diodes detectors Arranged in a matrix along two orthogonal planes 5 mm spacing We compare the results between measured and computed doses based on a 2%/2mm criteria Can use for either prone or supine orientations

52 VMAT Measurement Devices ArcCheck Delta4

53 VMAT Example ArcCheck Measurement Treatment Plan

54 VMAT Example Delta4

55 Physics Measurement QA Summary Time for QA Measurements IMRT < VMAT IMRT simple, visual comparison VMAT complex, quantitative

56 Conclusions Both IMRT and VMAT plans offer better PTV conformity and normal tissue sparing compared with 3 field technique Similar PTV conformity and normal tissue sparing can be achieved with IMRT and VMAT plans Advantages of VMAT: Reduces treatment delivery times Reduces monitor units 50% isodose volume slightly better than IMRT Disadvantages of VMAT: Low isodose volume (20% isodose) more than IMRT Increases optimization time Future improvements in treatment planning hardware & software can hopefully reduce planning time

57 Future Direction patients treated so far with VMAT it is time to review dosimetry quality on those 15 plans, especially, low dose region and genital dose Still have rooms for improvement in dosimetry quality 2. Follow up analysis of patients treatment toxicity to IMRT and VMAT

58 Acknowledgements Princess Margaret Cancer Centre GI site group Planners Physicists Oncologists