scripting automation and biomechanical modeling for ...

SCRIPTING AUTOMATION AND BIOMECHANICAL MODELING FOR ADAPTIVE RADIATION THERAPY C.VECCHI, G.GUIDI, N.MAFFEI, G.BALDAZZI Physics Department, University of Bologna, via Irnerio 40 40138 Bologna, Italy [email protected],[email protected]

G. GUIDI, A.CIARMATORI, T. COSTI Medical Physics Department,University Hospital”Policlinico”, Modena Italy , via del Pozzo 71 40121 Modena, Italy [email protected]

Scripting automation offers the possibility to reduce involved resources in order to apply Adaptive Radiation Therapy (ART) in the clinical day routine. We used a Treatment Planning System (TPS) to achieve the goal of ART and speed up the whole process by script development. Nowadays, due to automation we could follow biomechanical organ motion and reduce time consuming. We presented the time gain and advantages between scripting automation and user interface approach. Using python scripting approach, we collected statistical volume-dose data of 51 patients (Head and neck, Prostate, SBRT Lung) treated by Tomotherapy. As novel biomechanical approach in radiation oncology, we focused on H&N results and we used script to analyze parotids organ variations of 23 patients during the course of therapy. We evaluated properties and motion of parotids system and we quantified the displacement of those glands during the treatment sessions compared to clinical aspects. Keywords: script automation; biomechanics; radiotherapy. 1.

Introduction

Adaptive Radiation Therapy (ART) technique begin to be a new standard for advanced radiotherapy treatment because offers the possibility to personalize and adapt the patient treatment plan based on anatomical organs deformation due to diagnostic imaging. This technique needs to be investigated and automatized in order to apply it, in the clinical routine [1], limiting the request of resources. Our study is based on Treatment Planning System (TPS) that it allows the application of ART and the development of IronPython script (IS) in order to automatize and speed the inner operations of ART process [2]. The automatized approach has allowed collecting and evaluating statistical dose-volume data of 51 patients from Tomotherapy treatments. As well as ART, biomechanics aspect in radiotherapy have grown in importance in the last decades. The major step was to focus on H&N pathology, which have such a critical aspects in clinical routine, caused by typical motion of the glands (e.g. parotids) during the therapy treatments [3]. We evaluated and analyzed the variations and displacement of parotids compared to the first treatment session, laying the foundation for an important research in the field of radiation therapy in the future also applicable to other diseases.

2.

Materials and methods 2.1. Scripting automation in ART process

A mix of 23 H&N, 20 prostate and 8 Lung SBRT cases, amounting to1340 MVCT were imported and post processed using TPS and python scripting. Each H&N patients received an MVCT (Mega-Voltage CT) for setup purpose. The course of treatment consists in 30 daily fractions (equivalent to 30 CT studies). Performing Adaptive RT workflow such import DicomRT studies, make rigid registration, copy ROI (Region Of Interest) from CTn to CT1, perform deformable image registration (DIR), mapping ROI and extract the statistical data of the deformable doses and ROIs volume it is possible to follow the mechanical motion of the glands during therapy. We compare time consuming to perform both manual and automatic ART operations. We create a large patients database with the improvement effort by the scripting. 2.2. Scripting automation in biomechanics During H&N treatments, parotids could have important quantitative variations in both dimension and position. Using scripts development, we analyzed the distance variations between these organs from therapy session to session.

Fig. 1 – At left side: hybrid deformation of parotids and mandible for H&N patient. Right side: parotids problem modelized.

The script is launched in each patient after the deformation process occurs and it creates in automatic way a point of interest (POI) in the planning image (kVCT) exactly in the absolute coordinates point (0,0,0). The origin and points are to the other images (MVCT) but in different coordinates, based on the deformable grids. POIs are useful as a reference point in order to simulate the real system as a triangulation problem (e.g. See Fig. 1) and to calculate variables of system. 3.

Results and Discussion 3.1. Script: time comparison between manual and automatic approach

Time consumption is related to HW and code optimization. Using IS, human tasks can completed in nighttime, when the consoles are out of service, so to provide operators with important partial results and warning indicators during morning. ART results for each pathology are reported here as mean time for each operation groups.

H&N A (min) M (min)

Prostate

SBRT Lung

Time Time Time A (min) M (min) A (min) M (min) gain (%) gain (%) gain (%)

CT/MVCT import Rigid registration

30

50

40

43

55

22

7

10

30

CopyROI – Hybrid deformation – Mapping ROI

180

240

25

140

240

42

15

50

70

Statistical data extraction

60

350

83

60

360

83

3

70

96

Total time

270

640

148%

243

655

147%

25

130

196%

Table 1 – Time for ART in comparison.

The average time gain for the 3 pathology analyzed: H&N, Prostate and SBRT Lung is respectively of 370, 412 and 105 minutes. In terms of percentage, the time gain stands almost at 164%, equivalent to 5 hours for each patient processing. 3.2. Biomechanics: evaluation of parotids motion : Average difference between parotid-parotid distance in the nth session and the same distance in the first day of treatment. This quantity could give us information about the displacement of the system “Left Parotid” and “Right parotid”. A negative value means that parotids in the nth session have decrease distance from the first session and vice versa. : Average difference between the semi side of one parotid in the n th session and the same parotid semi side but in the first session. gives information about the displacement of one parotid independently to other parotid, because it is an asymmetric system.

Fig. 2 – Left side: ∆semiside average trend for right parotid (red) and left parotid (green) Vs session numbers. Right side: ∆d12 trend Vs session numbers.

4.

Conclusions

ART automation involves in 3 main advantages: 1. Time reduction for patient and treatment post-process. 2. Limited user operation (only the dose warping operation are not automatized). 3. Saving labor costs and possible human errors during the manual approach. The improvement in terms of time was significantly high, though some tasks need to be checked out by user. We report some critical aspects:  Rigid transform matrix with rotation > 5 degrees need to be revised, due to abnormal ROIs and doses deformation.  Copy ROIs operation sometimes failed and ROIs are copied outside the external body of the patient. The above errors are detectable through some script for checking results.  If DIR is carried out in studies with cranio–caudal slices < 6cm in width, results are affected by errors (e.g. due to limited CT study used during the rigid registration).  Limited MVCT FOV (Field-Of-View) for large patients can introduce errors during mapping ROI and dose warping (DW) for lateral structures.  Prosthesis implants can produce artifacts both in DIR and DW. The biomechanical results are: parotids have an asymmetric trend through sessions. The right parotid have a larger displacement than left one, and may be this need to be investigated if is imputable to the clock-wise rotation of the Tomotherapy and to some reconstruction algorithms. The average distance between left / right parotid is decreasing with sessions number due the efficacy of radiotherapy treatment and because patients, usually, lose weight during treatments. This biomechanical analysis can help to understand the motion of the glands during course of therapy. Many tumor tissues decrease during the treatment and are replaced by the healthy tissue and organs that appear in motion. 5.

Acknowledges

The research is partially co-funded by the MoH (GR-2010-2318757) and Tecnologie Avanzate S.r.l.(Italy) 6.

References

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