• Phd

MANAGING PATIENT DOSE WITH DAILY IMAGE GUIDED RADIOTHERAPY

 

MANAGING PATIENT DOSE WITH DAILY IMAGE GUIDED RADIOTHERAPY

 

 ABSTRACT

 

Kilovoltage cone beam CT (kV-CBCT) based on flat panel technology is primarily used for patient positioning. It can also be used for dosimetric verification in adaptive radiotherapy by validating the accuracy of CBCT image based treatment planning. This study evaluates the accuracy of dose calculation based on the patients’ CBCT images.

The Hounsfield unit – electron density calibration curves for head and pelvis region were obtained using ROI mapping method and these were compared with the planning CT-EU curve. The isodose distributions of IMRT fields were compared between the CT and CBCT image based dose calculation. Simulated identical organs at risks were delineated in the CT and CBCT images for IMRT plans comparisons. The percentage dose differences and DVHs were compared between CT and CBCT based plans. It is found that the CBCT values were highly influenced by the CBCT image acquisition parameters tube voltage, filtering and collimation and patient geometry.

This suggests that a single HU-D table will not be applicable to different imaging presets and different patient geometry. The isodose distributions and DVH computed based on CBCT and CT for for IMRT organ and risk doses, the dose difference was as high as ± 3%. From this study, it can be thus concluded that the CBCT image can be used for the dose calculation. For the CBCT imaging dose measurements, a metal oxide semiconductor field effect transistor (MOSFET) and an ion chamber were employed to measure the CBDIvol in CT phantom. The CBDIvol of the head scanning protocol were found to be 0.92 mGy and 1.0 mGy for chamber and MOSFET measurements respectively. The CBDIvol of the pelvis scanning protocol were found to be 16 mGy and 20 mGy for chamber and MOSFET measurements respectively. The maximum effective dose (ED) was found to be 1.0 mSv for the head and 6.99 mSV for the pelvis scanning protocols.    

Hence, when setting up CBCT scanning protocol and should try to reduce the high voltage usage and reduce mAs setting. Reduction in both parameters can reduce radiation dose to the patient, especially for pediatric patients. Care should be given to the long-term follow up of patients under image guided radiation therapy, while the indications for its use in certain cases should be reconsidered.

 

PENGURUSAN DOS PESAKIT MENGGUNAKAN RADIOTERAPI BERPANDUKAN IMEJ HARIAN

 

 ABSTRAK

 

 Kilovoltage kon rasuk CT (kV-CBCT) berasaskan teknologi panel rata digunakan terutamanya untuk kedudukan pesakit. Ia juga boleh digunakan untuk pengesahan dosimetri dalam radioterapi penyesuaian dengan mengesahkan ketepatan perancangan rawatan berasaskan CBCT imej. Kajian ini menilai ketepatan pengiraan dos berdasarkan imej CBCT pesakit.

 

Unit Hounsfield - ketumpatan elektron keluk penentukuran bagi rantau kepala dan pelvis telah diperolehi dengan menggunakan kaedah pemetaan ROI dan ini berbanding dengan perancangan keluk CT-EU. Pengagihan isodose bidang IMRT dibandingkan antara CT dan CBCT pengiraan dos berasaskan imej. Organ-organ risiko yang sama ditandakan pada CT dan CBCT imej untuk rancangan IMRT perbandingan. Perbezaan dos peratusan dan DVHs dibandingkan antara CT dan pelan berasaskan CBCT. Ia didapati bahawa nilai CBCT sangat dipengaruhi oleh imej CBCT pemerolehan parameter voltan tiub, penapisan dan collimation dan pesakit geometri. Ini menunjukkan bahawa jadual HU-D tunggal tidak akan terpakai bagi pratetap pengimejan yang berbeza dan geometri pesakit yang berbeza. Pengagihan isodose dan DVH dikira berdasarkan CBCT dan CT untuk untuk IMRT organ dan dos risiko, perbezaan dos adalah setinggi ± 3%.

 

Daripada kajian ini , ia boleh dengan itu membuat kesimpulan bahawa imej CBCT boleh digunakan untuk pengiraan dos. Bagi CBCT ukuran dos pengimejan, logam oksida semikonduktor transistor kesan medan ( MOSFET ) dan ruang ion telah digunakan untuk mengukur CBDIvol dalam CT phantom. The CBDIvol protokol kepala imbasan didapati 0.92 mGy dan 1.0 mGy untuk ruang ion dan ukuran MOSFET masing-masing . CBDIvol protokol pelvis imbasan didapati 16mGy dan 20mGy masing-masing untuk ukuran MOSFET . Dos maksimum yang berkesan (ED) didapati 1.0 mSv untuk kepala dan 6.99 mSv untuk pelvis imbasan protokol.

 

Oleh itu, apabila menubuhkan protokol imbasan CBCT kita harus cuba mengurangkan penggunaan voltan tinggi dan mengurangkan setting mAs . Pengurangan dalam kedua-dua parameter boleh mengurangkan dos sinaran kepada pesakit, terutama bagi pesakit pediatrik. Penjagaan perlu diberikan kepada jangka panjang susulan pesakit di bawah imej terapi radiasi berpandu, manakala tanda-tanda untuk digunakan dalam kes-kes tertentu perlu dipertimbangkan semula .