Theme
Medical Physics
INSTITUTION
Advanced Medical and Dental Institute, Universiti Sains Malaysia, Penang, Malaysia
Radiotherapy and Oncology, Pantai Hospital Sungai Petani, Kedah, Malaysia
Each radiotherapy centre should have a site-specific PTV margin and IGRT correction protocol to compensate for the geometric error that can occur during the treatement.
However, the software for calculation of the PTV margin and correction for offline IGRT protocols is not available on the IGRT system.
This work developes a Matlab algorithm for automated calculation of these parameters from CBCT-based IGRT.
The algorithm was tested on 25 head and neck cancer (HNC) patients that were treated using IG-IMRT.
Fig. 5 and 6 show the results of the population error and PTV margin from the HNC patients
Fig. 5: Population systematic and random error
Fig. 6: PTV margin for NAL and eNAL offline protocols
The algorithm provides an automated method for optimisation of offline correction protocols and further reduction of PTV margin for CBCT-based IG-IMRT.
1. An algorithm for automated calculation of PTV margins and correction for offline protocols is now developed.
2. Reduction in PTV margin could be achieved using NAL and eNAL IGRT protocols.
3. eNAL allow tigher PTV margin compared to NAL protocol.
[1] de Boer H C, van Sörnsen de Koste J R, Creutzberg C L, Visser A G, Levendag P C and Heijmen B J 2001 Electronic portal image assisted reduction of systematic set-up errors in head and neck irradiation. Radiother. Oncol. 61 299–308
[2] de Boer H C J and Heijmen B J M 2007 eNAL: An Extension of the NAL Setup Correction Protocol for Effective Use of Weekly Follow-up Measurements Int. J. Radiat. Oncol. Biol. Phys. 67 1586–95
[3] van Herk M, Remeijer P, Rasch C and Lebesque J V 2000 The probability of correct target dosage: dose-population histograms for deriving treatment margins in radiotherapy. Int. J. Radiat. Oncol. Biol. Phys. 47 1121
This work was funded by Prototype Research Grant Scheme (FRGS), Ministry of Education Malaysia, with the project code of 203/CIPPT/6740047. We also acknowledge the support from Tertiary education trust fund (TETFUND), Nigeria.
Contact Person: DR HAFIZ M ZIN, Advanced Medical and Dental Institute (AMDI), Universiti Sains Malaysia, MALAYSIA. Email: hafiz.zin@physics.org
CBCT based IGRT is used to check and correct a setup error and subsquently store the error data in XVI text file during each treatment session (Fig. 1).
Fig. 1: IGRT system for identification and correction of setup errors
A MATLAB algorithm (Fig. 2) was developed to extract the setup errors in three translational directions (x, y and z) that were logged by the IGRT system during the treatment delivery and calculates the correction for NAL and eNAL protocols [1,2].
The algorithm also calculates the resulted population setup error and PTV margin (Fig. 3) based on van Herk margin recipe [3], and subsequently estimates their respective values for NAL and eNAL offline protocols (Fig. 4).
Fig. 2: MATLAB algorithm for automated calculation of PTV magin and offline correction
Fig. 3: Sample of XVI text file and PTV margin calculation process
Fig. 4: Flow chart for NAL and eNAL offline IGRT protocols
Post your comments
Send Email