Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy Planning

DOSE COMPARISON OF RIVAL PLANS FOR CRANIO-SPINAL IRRADIATION

USING HELICAL TOMOTHERAPY

G.Guidi1, M.Amadori2, G.Tolento2, P.Antognoni2, E.Cenacchi1, A.E.Francia1, L.Morini1, C.Danielli1, F.Bertoni2, T.Costi1

1 Struttura Complessa di Fisica Sanitaria2 U.O. Radioterapia OncologicaAzienda Ospedaliero - Universitaria di Modena - Policlinico

diapositiva 2G.Guidi, M.Amadori, G.Tolento et.al.

Simulation and comparison : PAEDIATRIC (CRANIO-SPINAL)

Old Standard Treatment @ Modena

1. Linac 6MV2. Prone Position3. Multiple field junction4. 3 Split-beam (1cm each day)5. No-Coplanar Beam6. Multiple Isocenter (No SSD=100cm)7. PTV Margin 1cm8. Conformal field9. Portal verification of each junction

10.Procedure time 45-60 min

DVH Results1. PTVTx=PTV+1cm2. PTVTx: 90% dose prescription (Dp) @

95%Vol3. PTVTx: Max 115% Dp4. PTV: 95%Dp @ 95%Vol5. Lens < 5-10Gy6. Kidneys V20<20% Vol7. Lung V20<20% and V30<20%8. Abdominal dose in Field : 70% Dp

PTV=CTV=GTV


Simulation using Tomotherapy: PAEDIATRIC (CRANIO-SPINAL)

Tomotherapy Simulation1. Tomotherapy2. Prone Position3. No Multiple field junction4. No Split-beam 5. No-Coplanar Beam6. No Multiple Isocenter 7. PTV Evaluation

i. Margin 1cmii. Margin 0cm

8. High Conformal9. MVCT verification and adjustment10. Procedure time 20-30min

Tomotherapy vs. Linac•Lung, Hearth, Liver, Eyes, and Kidneys less dose/volume; for Hearth and Liver decrease the DMax•Optical Nerve : same Dmax but less dose/volume•Lens: decrease the Dmax Dose (Using Complete Block Option)•PTVTx shows that may be an extra margin to the GTV=PTV could help in case of misalignments

Clinical Implementation : Phase2/3• Supine position• Immobilization device• Target and Margin definition• Dummy Definition• OAR objective• Optimize verification time• Optimize treatment time• Analyze dosimetric accuracy• Treat patients

DVH Results1. PTVTx=PTV+1cm2. PTVTx: 99% dose prescription (Dp) @

100%Vol3. PTVTx: Max 105-107% Dp4. PTV: 100%Dp @ 100%Vol5. Lens < 5-7Gy6. Kidneys V20<20-25% Vol7. Lung V20<10% and V30<2%8. Abdominal dose in Field : 20% Dp


Multiple Plan Comparison and Integral Doses: PAEDIATRIC (CRANIO-SPINAL)

Competitive Plan Comparison (PTV vs PTVTx)• Same plan prescription and constrains using Tomotherapy• Same number of iterations• Export Doses Matrix• Comparing using Focal• Evaluate the differences of the dose matrixes

Homogeneity and Integral Doses must be investigated• Using Prone position and LINAC Beams, the integral doses

seems to be less (Using Tomo 5Gy at 70% of the Vol)• It is possible to appreciate an increase of the low doses some

treatment regions (Lung, Kidney, etc…)• Dedicate studies is been activated across Europe and

Tomotherapy centers to confirm or demonstrate no implication of the low doses delivered with IMRT and Helical IMRT within secondary tumors


Comparison and results : PAEDIATRIC (CRANIO-SPINAL)

Comparison1. 2 rivals plan

i. Plan 1: PTV=GTVii. Plan 2: PTVTx=GTV+1cm

2. Develop (“Adjust”) a software comparison using 3rd software (Focal/Xio)3. Dose subtraction between plans4. Plan on GTV+1cm guaranties adequate target coverage in cases of <1cm of mismatch during the setup5. Plan on GTV+0cm does not give adequate target coverage in cases of <1cm of mismatch during the setup

i. Without any PTV margin the dose difference could be significant decreased (mean 10%):i. 20%Dose @100% of the GTVii. 10% of Dose @ 90% of the GTViii. 5% of Dose @ 80 of the GTV Volume


Comparison of competitive plans : PAEDIATRIC (CRANIO-SPINAL)

Comparison1. OAR analysis

i. Heart & Liver : 20% of the volume savingsii. Lung : 20-40% of the volume savings


Comparison and Considerations : PAEDIATRIC (CRANIO-SPINAL)

Comparisoni. Kidneys : 10-20% of the volume savings

Tomotherapy Simulation for Cranio - Spinal1. Dose accuracy estimation must be

investigated and validated, especially into the non homogeneity interface and grids

2. Tomotherapy calculate on 256x256 matrix (eyes and small volume could be calculate not accurately as we are supposing)

3. Use a fine grid could be a trick, but the batch beamlets and optimization estimation is very higher to believe to do the plans in a days

4. We will try move to 512x512 matrix and verify if there are any differences

5. Patients QA procedure are very long and complicate for long patients and volumes, but is possible in any position (Head, Lung and Cauda)

6. Roll, Pitch and Yaw are not corrected and could change the patient dosimetry (Also TLI, TMI and TBI could have same problems)

7. Using a completion procedure during the treatment could be helpful to align and setup correctly the patients during the treatment in each part of the body, but doses overlap could create problems

8. For sure Tomotherapy improve patients comfort (supine and fast procedures) and the quality of the treatments, but without a deep analysis of the process, bias on the treatment could appear.

9. Less risk using Tomotherapy comparing with multiple split field junctions using Linac in case of hot spots

10. Machine Down could be a problem and a solution with a Linac must be provided (Not all center have 2 Tomotherapy) with the opportunity to sum 3DCRT plans with any Tomotherapy Plan


Today

ADVANTAGES AND DISADVANTAGES

• Supine• Faster• Comfortable• Safety (No beam junctions or couch

rotation and film exposition)• Accurate setup using MVCT but an

extra doses to consider• Accurate dose calculations (Lens

seems calculates not accurately relatively to the images down sampling)

• Procedures time: 20-30 Min• Integral dose must be evaluate

accurately, especially for paediatric patients

• Lateral Dummy ROI with directional block option activate can help to control the doses, but the DVH not shows real volumes and could get in trouble the doctors (New release will resolve the problems)

• In-homogeneity to the Target is bigger using lateral dummy at the arms, but decrease the integral doses

• Lung and Kidney sparing is evident• Lens has similar same problems

during calculation• Abdominal doses is comparable

with the Linac techniques using the dummy ROI

.... NOT ANYMORE NIGHTMARE FOR PHYSICIST AND DOCTORS THINKING TO THE JUNCTION...


Conclusion

• Cranio-Spinal using Tomotherapy provide better comfort and safety procedures compared with the Linac Junctions techniques

• Tomotherapy has some disadvantages associated with integral doses that must be carefully analyzed especially for Paediatric treatment.

• Using lateral Dummy ROI can be introduced some tricks to optimize better the plan, but should be evaluated carefully the OARs volume

• A better PTV coverage and OARs sparing and dose uniformity distribution is indisputable using Tomotherapy

• Anyway, Tomotherapy allows to treat patients in less time and with a better setup verification• No multiple junction and split beams can guaranties an improve of the safety procedures• A 3th part software analysis (Using Focal) has showed the opportunity to compare multiple

Plans and define the better margin expansion and the best plan for the patients, based on quantitative analysis, but also has shows some limitation referable to the images down sampling (e.g. Lens dose and volume calculation)

• Unexpected machine down or maintenance could be create some problem if there isn’t a Tomotherapy backup machine. Must be investigate the opportunity to create a 3DCRT plan using a different TPS and sum the doses with the previous treatment delivered by Tomotherapy

Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy Planning

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