Year : 2013 | Volume
: 38 | Issue : 2 | Page : 109--110
Review of PhD thesis "Study on Dosimetric Methods of Intensity Modulated Radiotherapy"
Faculty of Paramedical Sciences, S.M.S. Medical College, Jaipur, India
Faculty of Paramedical Sciences, S.M.S. Medical College, Jaipur
|How to cite this article:|
Chougule A. Review of PhD thesis "Study on Dosimetric Methods of Intensity Modulated Radiotherapy".J Med Phys 2013;38:109-110
|How to cite this URL:|
Chougule A. Review of PhD thesis "Study on Dosimetric Methods of Intensity Modulated Radiotherapy". J Med Phys [serial online] 2013 [cited 2021 Dec 3 ];38:109-110
Available from: https://www.jmp.org.in/text.asp?2013/38/2/109/111337
The thesis by Dr. Rajesh Kinhikar is based on the work carried out at the Tata Memorial hospital, Mumbai on dosimetric verification of Intensity Modulated Radiotherapy (IMRT). The guide was Dr. D. S. Dhote of Dept. of Electronics, Brijlal Biyani Science College, Amravati and the PhD degree for physics was awarded by Sant Gadge Baba Amravati University (India). Dr. Kinhikar designed and fabricated a phantom for IMRT verification with adaptors for various detectors. This appears to be a unique phantom which has several advantages over the commercial phantom. The author did perform validation of these adaptors for IMRT.
The phantom developed in this study has solid water phantom slabs of various thicknesses. It has provisions for inserting different ion chambers, namely FC 65G, CC01, CC13, CC01, A1SL and PTW 0.6 CC, and diode (IsoRAD). Also, it has a provision for placing thermolumenescence dosimeters (TLDs) in a matrix and a groove for placing MOSFET. Films could also be sandwiched in the phantom for film dosimetry. The developed phantom is handy and portable.
All IMRT patients in this study were planned with a sliding window technique on Eclipse (v 7.3.10) using Helios inverse planning software. Treatment planning was also done with TomoPlan. The phantom was scanned in a computed tomography scanner and images were transferred to Eclipse and also in TomoPlan. The IM fluence from individual patient was transferred to this phantom and mean central axis dose and off-axis doses were calculated at a depth. The calculated IM fluence in a phantom from coronal section was then, exported to a film dosimetry system (Scanditronix Wellhofer, Germany) for comparison with the actual delivered and measured fluence. All measurements were performed with a 6MV photon beam from a Varian Novalis Tx LINAC equipped with a high definition MLC and on Tomotherapy system.
The author measured absolute central axis point dose for cumulative fields and compared with the TPS-calculated mean dose. The doses were also measured at off-axis distance (+1 cm and +2) and compared with the calculated off-axis doses. All the dose measurements were additionally carried out by using TLDs (LiF: Mg, Ti chips of dimensions 0.32 × 0.32 × 0.09 cm 3 ). The TLD chips were irradiated in a polystyrene (Polystrol 495F, BASF, Germany) phantom slabs (density = 1.04 g/cm 3 ) at a depth with a target to axis distance (TAD) of 100 cm.
MOSFET One Dose (Thomson and Nielson, Ottawa, Canada) detectors were also used to measure the dose of each patient. These detectors were pre-calibrated by against established X and gamma ray doses from high energy X-rays and of 60 Co gamma rays. The MOSFET detectors were used for all cumulative fields at clinically relevant depth in a polystyrene phantom along the central axis and the absolute doses were measured.
EDR2 (Eastman Kodak Company, Rochester, NY, USA) films and Gafchromic films were used to measure doses at coronal plane. For each patient, a set of film was exposed to known doses (44, 87, 130, 175, 218, 262, 350 and 437 cGy) at 5 cm depth in a polystyrene phantom to create a characteristic curve to convert optical density to dose. Film measurements were made perpendicular to the central axis (TAD = 100 cm) at 5-cm depth in IMRT phantom for a fixed gantry, collimator and couch angle of 0° . Gamma and DTA were evaluated to verify quantitatively. Finally, the coefficient of correlation was evaluated.
The results of dosimetry with each detector were within the acceptance criteria (less than 3%). The inserts of each detector was accurately designed and fabricated by the author. The ion chambers, TLD, Diode and MOSFET are demonstrated to be useful for IMRT dosimetry and the films were found useful for 2D planar verification of the IMRT fluence.
The evaluation of various detectors for IMRT dosimetry was a benchmark for the clinical implementation as the dosimetry of IMRT is complex and needs systematic approach. The virtual water phantom developed by the author is unique to be used for IMRT dosimetry with any detector. The use of various volumes of the ion chambers gave an optimal ion chamber to be used with IMRT. The evaluation of MOSFET was very useful due to their high spatial resolution. TLDs were much helpful since it is a benchmark dosimeter. Films gave us a planar distribution and the dosimetry was very well interpreted in the high dose gradient regions where the finite size of the other detectors is the main constraint.
This work would contribute significantly towards the improvement of accuracy in IMRT dose delivery. The author claims that it helped to establish an accredited protocol for the dosimetry of advanced treatment modality like IGRT as well. In fact, many important aspects have been addressed and useful recommendations have been made. Evidently, this study on dosimetric methods would prove to be a valuable contribution to IMRT.