Pre-clinical commissioning of plans with an aperture based IMRT treatment planning system.

Transcription

1 Pre-clinical commissioning of plans with an aperture based treatment planning system. Misleidy Nápoles Morales, M, R.O,Yaima Yanes López, BSc, RTT,Yudy Ascención Ybarra, Eng., Med. Phys.,RodolfoAlfonso Laguardia, Ph,Carlos Calderón Marín, MSc, Med. Phys. *Institute of Oncology & Radiobiology (INOR), Havana, Cuba. Introduction. The incremental benefits in the transition from conventional radiotherapy to 3- CRT are substantially greater than those achieved in the transition from 3- CRT to. The highly conformal dose distribution produced by potentially allows for dose escalation while preserving, or even decreasing, the toxicity rate. After completion of essential milestones for transition from 3-CRT to, and previous to clinical implementation of this technique, a procedure has been developed at INOR, in order to commission the treatment planning techniques with test cases based on real patient image sets. The main objective of this study is then to validate the rationale of this transition from dosimetric and radiobiological perspectives. Material and Methods. Ten patients were included in the study. The 3-CRT and plans were obtained with Elekta s PrecisePlan RTPS and the computed VHs were used for dosimetric qualitative comparison of each patient s plan pair. For radiobiological estimation of potential treatment outputs, the VHs were used as input to compute the Equivalent Uniform ose (EU) of targets and organs at risk (OAR), as well as for determination of Tumor Control Probability () and Normal Tissue Complication Probability () in each plan. Software Albireo Target version was employed for this purpose. This software allows us to compare two planifications of the same patient and decide which of these is superior by determining the tumour control probability without complications based on the dose volume histograms of the CTV and the OARs which form the input of the software. This way a radio biological verification of the treatment plans is obtained. Aperture based plans performed with Elekta s PrecisePlan RTPS. Typical 9 fields per plan, 5-7 segments per field.

2 Typical 9 fields per plan, 5-7 segments per field.

3 Results and discussion. osimetric evaluation of results showed a mean OAR dose (parotid) of 5725 cgy for 3- CRT plans, averaged for the 10 studied patients, compared with 4213 cgy for plans. For cervical spinal cord, the averaged reduction was from 4282 cgy to 3187 cgy. For PTVs, the mean dose differences are not as significant as for OARs. According to this results, the calculated EUs for OARs were significantly lower for plans, so their s. EU-based objective functions are very sensitive to selected organ penalties; nevertheless in all cases the results indicated a rational advantage for the plans. Further studies are in progress to establish more evidence-based parameters. (Poisson s model), (Lyman s model, EU (generalized formula, Nimierko 1999) are calculated from VHs. Relative deviations (/3) were calculated for tumors and OARs: VH and dosimetric indexes

4 osimetric Quality Indexes for parotid glands based on: o Mean parotid dose= 1.38 QI OAR mean = 3CRT mean mean o Mean cord dose= 1.22 o 2/3-volume tolerance parotid= 1.56 QI 60 % = 3CRT 60% 60% Radiobiology Quality Indexes based on: EU-based and /-based RBQI 3 3CRT = RBQI CRT = Similar results were observed for /-based objective functions. is globally improved by in comparison with conformal 3; EU for OARs is also minor for. The mean values for and EU in tumor trends to be increased for.

5 3-CRT OAR Mean Relative ev. = % TUMOR Mean Relative ev. = 7.22% Equivalent Uniform ose (EU) [Gy] 3-CRT Mean Relative ev. = % Mean Relative ev. = 0.43% Probability

6 Conclusion. This pre-clinical experience is expected to create the basis for further clinical implementation of randomized studies that demonstrate the superiority of the vs 3CRT in our environment. The study has demonstrated that yields better treatment output than 3-CRT in H&N patients using aperture based planning. Radiobiology quality indexes used are adequate for estimation of expected treatment outcome. It is recommended to start a gradual inclusion of actual patients in an randomized study in order to confirm our results. References. 1. INTERNATIONAL ATOMIC ENERGY AGENCY, esign and implementation of a radiotherapy programme: clinical, medical physics and safety aspects, IAEA-TECOC- 1040, IAEA, Vienna, (1998). 2. INTERNATIONAL ATOMIC ENERGY AGENCY,Transition from 2- Radiotherapy to 3- Conformal and Intensity Modulated Radiotherapy, IAEA-TECOC-1588,IAEA, Vienna,(2008). 3. INTENSITY MOULATE RAIATION THERAPY COLLABORATIVE WORKING GROUP. Intensity-modulated radiotherapy: Current status and issues of interest. Int. J. Radiat. Oncol. Biol. Phys 51: (2001). 4. EZZELL, GA., GALVIN, JM., LOW,., et al., Guidance document on delivery, treatment planning, and clinical implementation of : Report of the Subcommittee of the AAPM Radiation Therapy Committee. Med. Phys. 30: (2003) 5. Arno J. Mundt,M; Jhon C Roeske, Ph. Intensity Modulated Radiation Therapy; Macías J, Wals A. Programa Albireo 1.0 Versión Cygnus X1.

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