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Fulltext A single institutional audit of setup errors for 3DCRT rectal cancers

Chew, Wei Zhuen, Jong,Wei Loong, Zulaikha Jamaluddin, Haiza Fasha Zakaraiah, Atiqah Kadri, Mohamad Afandi Azman, et al.

JUMMEC, 2020;23(1):6-10.
MyJurnal

Background: Set-up errors are errors which are inevitable in radiotherapy. However, they should be kept to a minimum to achieve the maximum radiation dose to a tumour as to maximise treatment efficacy. This study aims to quantify those errors and assess if they remain within the tolerance limit of 5 mm in all directions. This study will also determine the adequacy of the margins for set up error for 3DCRT of rectal cancers at University of Malaya Medical Centre (UMMC).
Methods: A total of 20 rectal cancer patients (July 2018 to May 2019) who were treated with radiotherapy amounting to a total of 119 CBCT images were included in the study. Population systematic errors and random setup errors were calculated.
Results: Population systematic errors and random setup errors in the vertical, longitudinal and lateral direction were tabulated in Table 1. There is a large deviation (>5 mm) noted in some patients’ setup between the first 3 days and the next successive day of imaging. Clinical target volume (CTV) to planning target volume (PTV) margin were calculated using Van Herk’s margin recipe (M=2.5Σ+0.7σ). The margins were 5.0 mm, 6.2 mm, and 4.0 mm for vertical, longitudinal and lateral directions, respectively. The systematic error for the population was 1.1 mm, 0.9 mm, 0.9 mm in the vertical, longitudinal and lateral directions respectively, while the random error is 3.2 mm, 5.7 mm and 2.5 mm in the vertical, longitudinal and lateral directions respectively.
Conclusion: All of the patients involved in the study were within tolerance limits at some point in their treatment. The results demonstrated that a larger margin is needed in the longitudinal direction. Weekly CBCT is also necessary after the initial 3-day imaging to ensure that patients are kept within the tolerance limits.
Fulltext Evaluation of X-Ray Beam Quality Based on Measurements and Estimations Using SpekCalc and Ipem78 Models

Chen SC, Jong WL, Harun AZ

Malays J Med Sci, 2012 Jul;19(3):22-8.
PMID: 23610546 MyJurnal

Different computational methods have been used for the prediction of X-ray spectra and beam quality in diagnostic radiology. The purpose of this study was to compare X-ray beam qualities based on half-value layers (HVLs) determined through measurements and computational model estimations.
Evaluation of Imaging Dose From Different Image Guided Systems During Head and Neck Radiotherapy: A Phantom Study

Cheng CS, Jong WL, Ung NM, Wong JHD

Radiat Prot Dosimetry, 2017 Jul 01;175(3):357-362.
PMID: 27940494 DOI: 10.1093/rpd/ncw357

This work evaluated and compared the absorbed doses to selected organs in the head and neck region from the three image guided radiotherapy systems: cone-beam computed tomography (CBCT) and kilovoltage (kV) planar imaging using the On-board Imager® (OBI) as well as the ExacTrac® X-ray system, all available on the Varian Novalis TX linear accelerator. The head and neck region of an anthropomorphic phantom was used to simulate patients' head within the imaging field. Nanodots optically stimulated luminescent dosemeters were positioned at selected sites to measure the absorbed doses. CBCT was found to be delivering the highest dose to internal organs while OBI-2D gave the highest doses to the eye lenses. The setting of half-rotation in CBCT effectively reduces the dose to the eye lenses. Daily high-quality CBCT verification was found to increase the secondary cancer risk by 0.79%.
"Edge-on" MOSkin detector for stereotactic beam measurement and verification

Jong WL, Ung NM, Vannyat A, Jamalludin Z, Rosenfeld A, Wong JH

Phys Med, 2017 Jan;33:127-135.
PMID: 28089106 DOI: 10.1016/j.ejmp.2016.12.020

Dosimetry in small radiation field is challenging and complicated because of dose volume averaging and beam perturbations in a detector. We evaluated the suitability of the "Edge-on" MOSkin (MOSFET) detector in small radiation field measurement. We also tested the feasibility for dosimetric verification in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). "Edge-on" MOSkin detector was calibrated and the reproducibility and linearity were determined. Lateral dose profiles and output factors were measured using the "Edge-on" MOSkin detector, ionization chamber, SRS diode and EBT2 film. Dosimetric verification was carried out on two SRS and five SRT plans. In dose profile measurements, the "Edge-on" MOSkin measurements concurred with EBT2 film measurements. It showed full width at half maximum of the dose profile with average difference of 0.11mm and penumbral width with difference of ±0.2mm for all SRS cones as compared to EBT2 film measurement. For output factor measurements, a 1.1% difference was observed between the "Edge-on" MOSkin detector and EBT2 film for 4mm SRS cone. The "Edge-on" MOSkin detector provided reproducible measurements for dose verification in real-time. The measured doses concurred with the calculated dose for SRS (within 1%) and SRT (within 3%). A set of output correction factors for the "Edge-on" MOSkin detector for small radiation fields were derived from EBT2 film measurement and presented. This study showed that the "Edge-on" MOSkin detector is a suitable tool for dose verification in small radiation field.
Influence of exposure and geometric parameters on absorbed doses associated with common neuro-interventional procedures

Safari MJ, Wong JHD, Jong WL, Thorpe N, Cutajar D, Rosenfeld A, et al.

Phys Med, 2017 Mar;35:66-72.
PMID: 28256398 DOI: 10.1016/j.ejmp.2017.02.002

PURPOSE: The purpose of this study was to investigate the effects of routine exposure parameters on patient's dose during neuro-interventional radiology procedures.
METHODS: We scrutinized the routine radiological exposure parameters during 58 clinical neuro-interventional procedures such as, exposure direction, magnification, frame rate, and distance between image receptor to patient's body and evaluate their effects on patient's dose using an anthropomorphic phantom. Radiation dose received by the occipital region, ears and eyes of the phantom were measured using MOSkin detectors.
RESULTS: DSA imaging technique is a major contributor to patient's dose (80.9%) even though they are used sparingly (5.3% of total frame number). The occipital region of the brain received high dose largely from the frontal tube constantly placed under couch (73.7% of the total KAP). When rotating the frontal tube away from under the couch, the radiation dose to the occipital reduced by 40%. The use of magnification modes could increase radiation dose by 94%. Changing the image receptor to the phantom surface distance from 10 to 40cm doubled the radiation dose received by the patient's skin at the occipital region.
CONCLUSION: Our findings provided important insights into the contribution of selected fluoroscopic exposure parameters and their impact on patient's dose during neuro-interventional radiology procedures. This study showed that the DSA imaging technique contributed to the highest patient's dose and judicial use of exposure parameters might assist interventional radiologists in effective skin and eye lens dose reduction for patients undergoing neuro-interventional procedures.
Characterization of MOSkin detector for in vivo dose verification during Cobalt-60 high dose-rate intracavitary brachytherapy

Jamalludin Z, Jong WL, Abdul Malik R, Rosenfeld A, Ung NM

Phys Med, 2019 Feb;58:1-7.
PMID: 30824140 DOI: 10.1016/j.ejmp.2019.01.010

In vivo dosimetry in high dose-rate (HDR) intracavitary brachytherapy (ICBT) is important for assessing the true dose received by surrounding organs at risk during treatment. It also serves as part of the treatment delivery quality assurance and verification program with the use of a suitable dosimeter. Such a dosimeter should be characterized under brachytherapy conditions before clinical application to ensure the accuracy of in vivo measurement. In this study, a MOSFET-based detector, MOSkin, was calibrated and characterized under HDR Cobalt-60 (Co-60) brachytherapy source. MOSkin possessed the major advantages of having small physical and dosimetric sizes of 4.8 × 10-6 mm3 with the ability to provide real-time measurements. Using solid water and polymethyl methacrylate (PMMA) phantom, the detectors' reproducibility, linearity, angular and distance dependency was tested for its suitability as an in vivo detector. Correction factors to account for differences in depth measurements were determined. The MOSkin detector showed a reliable response when tested under Co-60 brachytherapy range of doses with an excellent linearity of R2 = 0.9997 and acceptable reproducibility. A phantom verification study was also conducted to verify the differences between MOSkin responses and treatment planning (TPS) calculated doses. By taking into account several correction factors, deviations ranging between 0.01 and 0.4 Gy were found between MOSkin measured and TPS doses at measurement distance of 20-55 mm. The use of MOSkin as the dosimeter of choice for in vivo dosimetry under Co-60 brachytherapy condition is feasible.
Evaluation of treatment plan quality for head and neck IMRT: a multicenter study

Hizam DA, Jong WL, Zin HM, Ng KH, Ung NM

Med Dosim, 2021 04 08;46(3):310-317.
PMID: 33838998 DOI: 10.1016/j.meddos.2021.03.003

Intensity-modulated radiotherapy (IMRT) treatment planning for head and neck cancer is challenging and complex due to many organs at risk (OAR) in this region. The experience and skills of planners may result in substantial variability of treatment plan quality. This study assessed the performance of IMRT planning in Malaysia and observed plan quality variation among participating centers. The computed tomography dataset containing contoured target volumes and OAR was provided to participating centers. This is to control variations in contouring the target volumes and OARs by oncologists. The planner at each center was instructed to complete the treatment plan based on clinical practice with a given prescription, and the plan was analyzed against the planning goals provided. The quality of completed treatment plans was analyzed using the plan quality index (PQI), in which a score of 0 indicated that all dose objectives and constraints were achieved. A total of 23 plans were received from all participating centers comprising 14 VMAT, 7 IMRT, and 2 tomotherapy plans. The PQI indexes of these plans ranged from 0 to 0.65, indicating a wide variation of plan quality nationwide. Results also reported 5 out of 21 plans achieved all dose objectives and constraints showing more professional training is needed for planners in Malaysia. Understanding of treatment planning system and computational physics could also help in improving the quality of treatment plans for IMRT delivery.
Fulltext On the Use of Optically Stimulated Luminescent Dosimeter for Surface Dose Measurement during Radiotherapy

Yusof FH, Ung NM, Wong JH, Jong WL, Ath V, Phua VC, et al.

PLoS One, 2015;10(6):e0128544.
PMID: 26052690 DOI: 10.1371/journal.pone.0128544

This study was carried out to investigate the suitability of using the optically stimulated luminescence dosimeter (OSLD) in measuring surface dose during radiotherapy. The water equivalent depth (WED) of the OSLD was first determined by comparing the surface dose measured using the OSLD with the percentage depth dose at the buildup region measured using a Markus ionization chamber. Surface doses were measured on a solid water phantom using the OSLD and compared against the Markus ionization chamber and Gafchromic EBT3 film measurements. The effect of incident beam angles on surface dose was also studied. The OSLD was subsequently used to measure surface dose during tangential breast radiotherapy treatments in a phantom study and in the clinical measurement of 10 patients. Surface dose to the treated breast or chest wall, and on the contralateral breast were measured. The WED of the OSLD was found to be at 0.4 mm. For surface dose measurement on a solid water phantom, the Markus ionization chamber measured 15.95% for 6 MV photon beam and 12.64% for 10 MV photon beam followed by EBT3 film (23.79% and 17.14%) and OSLD (37.77% and 25.38%). Surface dose increased with the increase of the incident beam angle. For phantom and patient breast surface dose measurement, the response of the OSLD was higher than EBT3 film. The in-vivo measurements were also compared with the treatment planning system predicted dose. The OSLD measured higher dose values compared to dose at the surface (Hp(0.0)) by a factor of 2.37 for 6 MV and 2.01 for 10 MV photon beams, respectively. The measurement of absorbed dose at the skin depth of 0.4 mm by the OSLD can still be a useful tool to assess radiation effects on the skin dermis layer. This knowledge can be used to prevent and manage potential acute skin reaction and late skin toxicity from radiotherapy treatments.
Fulltext Characterization of MOSkin detector for in vivo skin dose measurement during megavoltage radiotherapy

Jong WL, Wong JH, Ung NM, Ng KH, Ho GF, Cutajar DL, et al.

J Appl Clin Med Phys, 2014 Sep 08;15(5):4869.
PMID: 25207573 DOI: 10.1120/jacmp.v15i5.4869

In vivo dosimetry is important during radiotherapy to ensure the accuracy of the dose delivered to the treatment volume. A dosimeter should be characterized based on its application before it is used for in vivo dosimetry. In this study, we characterize a new MOSFET-based detector, the MOSkin detector, on surface for in vivo skin dosimetry. The advantages of the MOSkin detector are its water equivalent depth of measurement of 0.07 mm, small physical size with submicron dosimetric volume, and the ability to provide real-time readout. A MOSkin detector was calibrated and the reproducibility, linearity, and response over a large dose range to different threshold voltages were determined. Surface dose on solid water phantom was measured using MOSkin detector and compared with Markus ionization chamber and GAFCHROMIC EBT2 film measurements. Dependence in the response of the MOSkin detector on the surface of solid water phantom was also tested for different (i) source to surface distances (SSDs); (ii) field sizes; (iii) surface dose; (iv) radiation incident angles; and (v) wedges. The MOSkin detector showed excellent reproducibility and linearity for dose range of 50 cGy to 300 cGy. The MOSkin detector showed reliable response to different SSDs, field sizes, surface, radiation incident angles, and wedges. The MOSkin detector is suitable for in vivo skin dosimetry.
Medical physics aspects of Intensity-Modulated Radiotherapy practice in Malaysia

Hizam NDA, Ung NM, Jong WL, Zin HM, Rahman ATA, Loh JPY, et al.

Phys Med, 2019 Nov;67:34-39.
PMID: 31655398 DOI: 10.1016/j.ejmp.2019.10.023

PURPOSE: Intensity Modulated Radiotherapy (IMRT) has changed the practice of radiotherapy since its implementation in the 1990s. The purpose of this study is to review current practice of IMRT in Malaysia.
METHODS: A survey on medical physics aspects of IMRT is conducted on radiotherapy departments across Malaysia to assess the usage, experience and QA in IMRT, which is done for the first time in this country. A set of questionnaires was designed and sent to the physicist in charge for their responses. The questionnaire consisted of four sections; (i) Experience and qualification of medical physicists, (ii) CT simulation techniques (iii) Treatment planning and treatment unit, (iv) IMRT process, delivery and QA procedure.
RESULTS: A total of 26 responses were collected, representing 26 departments out of 33 radiotherapy departments in operation across Malaysia (79% response rate). Results showed that the medical physics aspects of IMRT practice in Malaysia are homogenous, with some variations in certain areas of practices. Thirteen centres (52%) performed measurement-based QA using 2D array detector and analysed using gamma index criteria of 3%, 3 mm with variation confidence range. In relation to the IMRT delivery, 44% of Malaysia's physicist takes more than 8 h to plan a head and neck case compared to the UK study possibly due to the lack of professional training.
CONCLUSIONS: This survey provides a picture of medical physics aspects of IMRT in Malaysia where the results/data can be used by radiotherapy departments to benchmark their local policies and practice.

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