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22nd International Conference on Medical Physics 2016, Bangkok, Thailand; Medical physics propelling global health

Tsapaki V, Ibbott G, Krisanachinda A, Ng KH, Suh TS, Tabakov S, et al.

Phys Med, 2017 Dec;44:196-198.
PMID: 29221890 DOI: 10.1016/j.ejmp.2017.11.022

As medical technology evolves and patient needs increase, the need for well-trained and highly professional medical physicists (MPs) becomes even more urgent. The roles and responsibilities of MPs in various departments within the hospital are diverse and demanding. It is obvious that training, continuing education and professional development of MPs have become essential. One of the ways for an MP to advance his or her knowledge is to participate in conferences and congresses. Last year, the 22nd International Conference of Medical Physics (ICMP 2016) took place in Bangkok, Thailand. The event attracted 584 delegates with most of the participants coming from Asia. It attracted also delegates from 42 countries. The largest delegations were from Thailand, Japan and South Korea. ICMP 2016 included 367 oral presentations and e-posters, most of these being in the fields of Radiation Therapy, Medical Imaging and Radiation Safety. All abstracts were published as an e-book of Abstracts in a supplement to the official IOMP Journal. Many companies had exhibition stands at ICMP2016, thus allowing the participants to see the latest developments in the medical physics-related industry. The conference included 42 mini-symposia, part of the first "IOMP School" activity, covering various topics of importance for the profession and this special issue follows from the success of the conference.

Matched MeSH terms: Neoplasms/radiotherapy
Fulltext A Randomized Controlled Trial of Novel Treatment for Hemorrhagic Radiation Proctitis

Pui WC, Chieng TH, Siow SL, Nik Abdullah NA, Sagap I

Asian Pac J Cancer Prev, 2020 Oct 01;21(10):2927-2934.
PMID: 33112550 DOI: 10.31557/APJCP.2020.21.10.2927

BACKGROUND: Various methods have been used for treatment of hemorrhagic radiation proctitis (HRP) with variable results. Currently, the preferred treatment is formalin application or endoscopic therapy with argon plasma coagulation. Recently, a novel therapy with colonic water irrigation and oral antibiotics showed promising results and more effective compared to 4% formalin application for HRP. The study objective is to compare the effect of water irrigation and oral antibiotics versus 4% formalin application in improving per rectal bleeding due to HRP and related symptoms such as diarrhoea, tenesmus, stool frequency, stool urgency and endoscopic findings.
METHODS: We conducted a study on 34 patients with HRP and randomly assigned the patients to two treatment arm groups (n=17). The formalin group underwent 4% formalin dab and another session 4 weeks later. The irrigation group self-administered daily rectal irrigation at home for 8 weeks and consumed oral metronidazole and ciprofloxacin during the first one week. We measured the patients' symptoms and endoscopic findings before and after total of 8 weeks of treatment in both groups.
RESULTS: Our study showed that HRP patients had reduced per rectal bleeding (p = 0.003) in formalin group, whereas irrigation group showed reduced diarrhoea (p=0.018) and tenesmus (p=0.024) symptoms. The comparison between the two treatment arms showed that irrigation technique was better than formalin technique for tenesmus (p=0.043) symptom only.
CONCLUSION: This novel treatment showed benefit in treating HRP. It could be a new treatment option which is safe and conveniently self-administered at home or used as a combination with other therapies to improve the treatment outcome for HRP.
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Matched MeSH terms: Pelvic Neoplasms/radiotherapy; Radiotherapy/adverse effects*
A computational model to investigate the influence of electrode lengths on the single probe bipolar radiofrequency ablation of the liver

Cheong JKK, Yap S, Ooi ET, Ooi EH

Comput Methods Programs Biomed, 2019 Jul;176:17-32.
PMID: 31200904 DOI: 10.1016/j.cmpb.2019.04.028

BACKGROUND AND OBJECTIVES: Recently, there have been calls for RFA to be implemented in the bipolar mode for cancer treatment due to the benefits it offers over the monopolar mode. These include the ability to prevent skin burns at the grounding pad and to avoid tumour track seeding. The usage of bipolar RFA in clinical practice remains uncommon however, as not many research studies have been carried out on bipolar RFA. As such, there is still uncertainty in understanding the effects of the different RF probe configurations on the treatment outcome of RFA. This paper demonstrates that the electrode lengths have a strong influence on the mechanics of bipolar RFA. The information obtained here may lead to further optimization of the system for subsequent uses in the hospitals.
METHODS: A 2D model in the axisymmetric coordinates was developed to simulate the electro-thermophysiological responses of the tissue during a single probe bipolar RFA. Two different probe configurations were considered, namely the configuration where the active electrode is longer than the ground and the configuration where the ground electrode is longer than the active. The mathematical model was first verified with an existing experimental study found in the literature.
RESULTS: Results from the simulations showed that heating is confined only to the region around the shorter electrode, regardless of whether the shorter electrode is the active or the ground. Consequently, thermal coagulation also occurs in the region surrounding the shorter electrode. This opened up the possibility for a better customized treatment through the development of RF probes with adjustable electrode lengths.
CONCLUSIONS: The electrode length was found to play a significant role on the outcome of single probe bipolar RFA. In particular, the length of the shorter electrode becomes the limiting factor that influences the mechanics of single probe bipolar RFA. Results from this study can be used to further develop and optimize bipolar RFA as an effective and reliable cancer treatment technique.

Matched MeSH terms: Liver Neoplasms/radiotherapy
Fulltext A custom made phantom for dosimetric audit and quality assurance of three-dimensional conformal radiotherapy

Radaideh, K.M., Matalqah, L.M., Tajuddin, A.A., Lee Luen, F.W., Bauk, S., Abdel Munem, E.M.E

Jurnal Sains Nuklear Malaysia, 2012;24(1):0-0.
MyJurnal

The ultimate check of the actual dose delivered to a patient in radiotherapy can be achieved by using dosimetric measurements. The aims of this study were to develop and evaluate a custom handmade head and neck phantom for evaluation of Three-Dimensional Conformal Radiation Therapy (3D-CRT) dose planning and delivery. A phantom of head and neck region of a medium built male patient with nasopharyngeal cancer was constructed from Perspex material. Primary and secondary Planning Target Volume (PTV) and twelve Organs at Risk (OAR) were delineated using Treatment Planning System (TPS) guided by computed tomography printout transverse images. One hundred and seven (107) holes distributed among the organs were loaded with Rod-shaped Thermoluminescent dosimeters (LiF:Mg,Ti TLDs) after common and individual calibration. Head and neck phantom was imaged, planned and irradiated conformally (3D-CRT) by linear accelerator (LINAC Siemens Artiste). The planned predicted doses by TPS at PTV and OAR regions were obtained and compared with the TLD measured doses using the phantom. Repeated TLD measurements were reproducible with a percent standard deviation of < 3.5%. Moreover, the average of dose discrepancies between TLDs reading and TPS predicted doses were found to be < 5.3%. The phantom’s preliminary results have proved to be a valuable tool for 3D-CRT treatment dose verification.

Matched MeSH terms: Radiotherapy, Conformal
A deadly hidden nodule

Lim JA

Am J Obstet Gynecol, 2018 11;219(5):502.
PMID: 29678504 DOI: 10.1016/j.ajog.2018.04.021
Matched MeSH terms: Melanoma/radiotherapy; Vaginal Neoplasms/radiotherapy
A feasibility study of adaptive radiation therapy for postprostatectomy prostate cancer

Meyers SM, Winter JD, Obeidi Y, Chung P, Menard C, Warde P, et al.

Med Dosim, 2023 11 18;49(2):150-158.
PMID: 37985297 DOI: 10.1016/j.meddos.2023.10.008

Postoperative prostate radiotherapy requires large planning target volume (PTV) margins to account for motion and deformation of the prostate bed. Adaptive radiation therapy (ART) can incorporate image-guidance data to personalize PTVs that maintain coverage while reducing toxicity. We present feasibility and dosimetry results of a prospective study of postprostatectomy ART. Twenty-one patients were treated with single-adaptation ART. Conventional treatments were delivered for fractions 1 to 6 and adapted plans for the remaining 27 fractions. Clinical target volumes (CTVs) and small bowel delineated on fraction 1 to 4 CBCT were used to generate adapted PTVs and planning organ-at-risk (OAR) volumes for adapted plans. PTV volume and OAR dose were compared between ART and conventional using Wilcoxon signed-rank tests. Weekly CBCT were used to assess the fraction of CTV covered by PTV, CTV D99, and small bowel D1cc. Clinical metrics were compared using a Student's t-test (p < 0.05 significant). Offline adaptive planning required 1.9 ± 0.4 days (mean ± SD). ART decreased mean adapted PTV volume 61 ± 37 cc and bladder wall D50 compared with conventional treatment (p < 0.01). The CTV was fully covered for 96% (97%) of fractions with ART (conventional). Reconstructing dose on weekly CBCT, a nonsignificant reduction in CTV D99 was observed with ART (94%) compared to conventional (96%). Reduced CTV D99 with ART was significantly correlated with large anterior-posterior rectal diameter on simulation CT. ART reduced the number of fractions exceeding our institution's small bowel D1c limit from 14% to 7%. This study has demonstrated the feasibility of offline ART for post-prostatectomy cancer. ART facilitates PTV volume reduction while maintaining reasonable CTV coverage and can reduce the dose to adjacent normal tissues.

Matched MeSH terms: Radiotherapy Dosage
A multi-center survey on adaptive radiation therapy for head and neck cancer in Malaysia

Yap LM, Jamalludin Z, Ng AH, Ung NM

Phys Eng Sci Med, 2023 Sep;46(3):1331-1340.
PMID: 37470929 DOI: 10.1007/s13246-023-01303-x

The survey is to assess the current state of adaptive radiation therapy (ART) for head and neck (H&N) cases among radiotherapy centers in Malaysia and to identify any implementation limitations. An online questionnaire was sent to all radiotherapy centers in Malaysia. The 24-question questionnaire consists of general information about the center, ART practices, and limitations faced in implementing ART. 28 out of 36 radiotherapy centers responded, resulting in an overall response rate of 78%. About 52% of the responding centers rescanned and replanned less than 5% of their H&N patients. The majority (88.9%) of the respondents reported the use Cone Beam Computed Tomography alone or in combination with other modalities to trigger the ART process. The main reasons cited for adopting ART were weight loss, changes in the immobilization fitting, and anatomical variation. The adaptation process typically occurred during week 3 or week 4 of treatment. More than half of the respondents require three days or more from re-simulation to starting a new treatment plan. Both target and organ at risk delineation on new planning CT relied heavily on manual delineation by physicians and physicists, respectively. All centers perform patient-specific quality assurance for their new adaptive plans. Two main limitations in implementing ART are "limited financial resources or equipment" and "limitation on technical knowledge". There is a need for a common consensus to standardize the practice of ART and address these limitations to improve the implementation of ART in Malaysia.

Matched MeSH terms: Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted/methods
Fulltext A new concept of the formation of hypoxic cells in tumors and its possible implications for radiotherapy and chemotherapy

Ng CE

Med J Malaysia, 1981 Mar;36(1):24-8.
PMID: 7321933

Hypoxic cells in tumors are proposed to consist of at least 2 types, depending on whether they remain hypoxic for long (chronic hypoxia) or short (acute hypoxia) periods. Experimental evidence of the possible presence ofacutely-hypoxic cells in one type of murine tumour is presented. Finally, the possible implications for radiotherapy and chemotherapy of the presence of acutely-hypoxic cells in human tumors is discussed briefly.

Matched MeSH terms: Neoplasms, Experimental/radiotherapy
A novel approach of dose mapping using a humanoid breast phantom in radiotherapy

Banjade DP, Ng BS, Zakir M, Tajuddin AA, Shukri A

Br J Radiol, 2002 Oct;75(898):812-8.
PMID: 12381690

A study of dose mapping techniques to investigate the dose distribution throughout a planned target volume (PTV) in a humanoid breast phantom exposed to a 6 MV photon beam similar to that of treatment conditions is described. For tangential breast irradiation using a 6 MV accelerator beam, the dose is mapped at various locations within the PTV using thermoluminescent dosemeters (TLDs) and radiographic films. An average size perspex breast phantom with the ability to hold the dosemeters was made. TLDs were exposed after packing them in various locations in a particular slice, as planned by the treatment planning system (TPS). To map the dose relative to the isocenter, films were exposed after tightly packing them in between phantom slices, parallel to the central axis of the beam. The dose received at every location was compared with the given dose as generated by the TPS. The mapped dose in each location in the isocentric slice from superficial to deep region was found to be in close agreement with the TPS generated dose to within +/-2%. Doses at greater depths and distant medial and lateral ends, however, were found to be lower by as much as 9.4% at some points. The mapped dose towards the superior region and closest inferior region from the isocenter was found to agree with those for TPS. Conversely, results for the farthest inferior region were found to be significantly different with a variance as much as 17.4% at some points, which is believed to be owing to the variation in size and shape of the contour. Results obtained from films confirmed this, showing similar trends in dose mapping. Considering the importance of accurate doses in radiotherapy, evaluating dose distribution using this technique and tool was found to be useful. This provides the opportunity to choose a technique and plan to provide optimum dose delivery for radiotherapy to the breast.

Matched MeSH terms: Radiotherapy/methods; Radiotherapy Dosage*
A pioneer experience in Malaysia on In-house Radio-labelling of (131)I-rituximab in the treatment of Non-Hodgkin's Lymphoma and a case report of high dose (131)I-rituximab-BEAM conditioning autologous transplant

Kuan JW, Law CS, Wong XQ, Ko CT, Awang ZH, Chew LP, et al.

Appl Radiat Isot, 2016 Oct;116:13-21.
PMID: 27472826 DOI: 10.1016/j.apradiso.2016.07.016

Radioimmunotherapy is an established treatment modality in Non-Hodgkin's lymphoma. The only two commercially available radioimmunotherapies - (90)Y-ibritumomab tiuxetan is expensive and (131)I-tositumomab has been discontinued from commercial production. In resource limited environment, self-labelling (131)I-rituximab might be the only viable practical option. We reported our pioneer experience in Malaysia on self-labelling (131)I-rituximab, substituting autologous haematopoietic stem cell transplantation (HSCT) and a patient, the first reported case, received high dose (131)I-rituximab (6000MBq/163mCi) combined with BEAM conditioning for autologous HSCT.

Matched MeSH terms: Radiotherapy Dosage
Fulltext A retrospective study of narrowband-UVB phototherapy for treatment of vitiligo in Malaysian patients

Adauwiyah J, Suraiya HH

Med J Malaysia, 2010 Dec;65(4):297-9.
PMID: 21901949 MyJurnal

Psoralen and ultraviolet light A (PUVA) was the mainstay of vitiligo treatment before the introduction of narrowband UVB(NB-UVB). Eighteen patients treated with NB-UVB in Hospital Kuala Lumpur were retrospectively analyzed. Eight patients had Fitzpatrick skin phototype III and 10 with phototype IV. The mean duration of disease was 7.3 +/- 5.4 years, and the mean body surface area affected was 19.3 +/- 16.2%. Mean duration of treatment was 14.3 +/- 9.6 months, number of session 113.5 +/- 88.6 times and cumulative dose 111.7 +/- 108.5 J/ cm2. Concomitant topical steroid was used in 88.9% patients. Repigmentation was moderate in 6 (40%) patients, good in 3 (20%), while 3 (20%) achieved excellent results. One patient (6.6%) showed no response and 2 (13.3%) showed poor repigmentation. Three patients developed side effects. NB-UVB phototherapy results in satisfactory repigmentation in our vitiligo patients and should be offered as a treatment option.

Matched MeSH terms: Vitiligo/radiotherapy*
A simplified approach for exit dose in vivo measurements in radiotherapy and its clinical application

Banjade DP, Shrestha SL, Shukri A, Tajuddin AA, Bhat M

Australas Phys Eng Sci Med, 2002 Sep;25(3):110-8.
PMID: 12416587

This is a study using LiF:Mg;Ti thermoluminescent dosimeter (TLD) rods in phantoms to investigate the effect of lack of backscatter on exit dose. Comparing the measured dose with anticipated dose calculated using tissue maximum ratio (TMR) or percentage depth dose (PDD) gives rise to a correction factor. This correction factor may be applied to in-vivo dosimetry results to derive true dose to a point within the patient. Measurements in a specially designed humanoid breast phantom as well as patients undergoing radiotherapy treatment were also been done. TLDs with reproducibility of within +/- 3% (1 SD) are irradiated in a series of measurements for 6 and 10 MV photon beams from a medical linear accelerator. The measured exit doses for the different phantom thickness for 6 MV beams are found to be lowered by 10.9 to 14.0% compared to the dose derived from theoretical estimation (normalized dose at dmax). The same measurements for 10 MV beams are lowered by 9.0 to 13.5%. The variations of measured exit dose for different field sizes are found to be within 2.5%. The exit doses with added backscatter material from 2 mm up to 15 cm, shows gradual increase and the saturated values agreed within 1.5% with the expected results for both beams. The measured exit doses in humanoid breast phantom as well as in the clinical trial on patients undergoing radiotherapy also agreed with the predicted results based on phantom measurements. The authors' viewpoint is that this technique provides sufficient information to design exit surface bolus to restore build down effect in cases where part of the exit surface is being considered as a target volume. It indicates that the technique could be translated for in vivo dose measurements, which may be a conspicuous step of quality assurance in clinical practice.

Matched MeSH terms: Neoplasms/radiotherapy*; Radiotherapy Dosage*
Fulltext A successful pregnancy outcome in treated vulval rhabdomyosarcoma

Ariza M, Rafaee T, Adeeb N, Muhaizan WM, Isa MR

Med J Malaysia, 1999 Sep;54(3):371-3.
PMID: 11045067

A 14 year old girl presented in 1986 with a huge perineal swelling which was progressively increasing in size and associated with loss of weight and loss of appetite. Biopsy from the mass revealed rhabdomyosarcoma of the vulva. She was treated with chemotherapy and radium implant. She responded well to the regime. Fibrosis of the vulva and vagina caused difficulty in consummation. Once it was corrected, she conceived easily and proceeded to a normal pregnancy and delivery.

Matched MeSH terms: Rhabdomyosarcoma/radiotherapy*; Vulvar Neoplasms/radiotherapy*
A systematic review on Chinese herbal treatment for radiotherapy-induced xerostomia in head and neck cancer patients

Nik Nabil WN, Lim RJ, Chan SY, Lai NM, Liew AC

Complement Ther Clin Pract, 2018 Feb;30:6-13.
PMID: 29389481 DOI: 10.1016/j.ctcp.2017.10.004

BACKGROUND: Over 80% of head and neck cancer patients suffer from radiotherapy-induced xerostomia (dry mouth). Xerostomia affects cancer patients' quality of life, and xerostomia sometimes persists throughout the patients' lifetime. This review aimed to evaluate the effectiveness and safety of Chinese herbs in relieving radiotherapy induced xerostomia.
METHODS: Systematic searches were conducted on 6 databases (English and Chinese). Studies published up till May 2017 were considered for inclusion.
RESULTS: A final 14 RCTs (total 994 head and neck cancer patients undergoing radiotherapy) compared Chinese herbs with no herbs, were included in analysis. Very low to moderate quality of evidence found Chinese herbal treatment may relief radiotherapy-induced xerostomia and other related complications (such as oral mucositis and loss of appetite) in head and neck cancer patients.
CONCLUSION: There is limited evidence that Chinese herbal treatment may relief radiotherapy-induced xerostomia and other related complications in head and neck cancer patients.

Matched MeSH terms: Head and Neck Neoplasms/radiotherapy*
A thermoluminescent dosimetry postal dose inter-comparison of radiation therapy centres in Malaysia

Rassiah P, Ng KH, DeWerd LA, Kunugi K

Australas Phys Eng Sci Med, 2004 Mar;27(1):25-9.
PMID: 15156705

A thermoluminescent dosimetry (TLD) postal dose inter-comparison was carried out amongst radiotherapy centres in Malaysia. The aim of this TLD inter-comparison was to compare the uniformity involved in the measurement of absorbed dose among the participating centres. A set of 5 TLD chips placed within acrylic trays were mailed to all participating centres for irradiation to an absorbed dose to water of 2 Gy. Measurements were made for 6 MV and 60Co photon beams. Results show an agreement of +/- 5% for all but three radiotherapy centres. The ratios of the TLD readings to that of the reference centre are comparable with other national/regional dose inter-comparisons. The importance of a proper ongoing quality assurance program is essential in maintaining the consistency and uniformity of doses delivered.

Matched MeSH terms: Radiotherapy/standards*; Radiotherapy Dosage/standards*; Radiotherapy Planning, Computer-Assisted/standards*
Fulltext ARCHERY: a prospective observational study of artificial intelligence-based radiotherapy treatment planning for cervical, head and neck and prostate cancer - study protocol

Aggarwal A, Court LE, Hoskin P, Jacques I, Kroiss M, Laskar S, et al.

BMJ Open, 2023 Dec 07;13(12):e077253.
PMID: 38149419 DOI: 10.1136/bmjopen-2023-077253

INTRODUCTION: Fifty per cent of patients with cancer require radiotherapy during their disease course, however, only 10%-40% of patients in low-income and middle-income countries (LMICs) have access to it. A shortfall in specialised workforce has been identified as the most significant barrier to expanding radiotherapy capacity. Artificial intelligence (AI)-based software has been developed to automate both the delineation of anatomical target structures and the definition of the position, size and shape of the radiation beams. Proposed advantages include improved treatment accuracy, as well as a reduction in the time (from weeks to minutes) and human resources needed to deliver radiotherapy.
METHODS: ARCHERY is a non-randomised prospective study to evaluate the quality and economic impact of AI-based automated radiotherapy treatment planning for cervical, head and neck, and prostate cancers, which are endemic in LMICs, and for which radiotherapy is the primary curative treatment modality. The sample size of 990 patients (330 for each cancer type) has been calculated based on an estimated 95% treatment plan acceptability rate. Time and cost savings will be analysed as secondary outcome measures using the time-driven activity-based costing model. The 48-month study will take place in six public sector cancer hospitals in India (n=2), Jordan (n=1), Malaysia (n=1) and South Africa (n=2) to support implementation of the software in LMICs.
ETHICS AND DISSEMINATION: The study has received ethical approval from University College London (UCL) and each of the six study sites. If the study objectives are met, the AI-based software will be offered as a not-for-profit web service to public sector state hospitals in LMICs to support expansion of high quality radiotherapy capacity, improving access to and affordability of this key modality of cancer cure and control. Public and policy engagement plans will involve patients as key partners.

Matched MeSH terms: Radiotherapy Planning, Computer-Assisted
ATM inhibition prevents interleukin-6 from contributing to the proliferation of glioblastoma cells after ionizing radiation

Lim YC, Quek H, Offenhäuser C, Fazry S, Boyd A, Lavin M, et al.

J Neurooncol, 2018 Jul;138(3):509-518.
PMID: 29564746 DOI: 10.1007/s11060-018-2838-0

Glioblastoma (GBM) is a highly fatal disease with a 5 year survival rate of less than 22%. One of the most effective treatment regimens to date is the use of radiotherapy which induces lethal DNA double-strand breaks to prevent tumour growth. However, recurrence occurs in the majority of patients and is in-part a result of robust radioresistance mechanisms. In this study, we demonstrate that the multifunctional cytokine, interleukin-6 (IL-6), confers a growth advantage in GBM cells but does not have the same effect on normal neural progenitor cells. Further analysis showed IL-6 can promote radioresistance in GBM cells when exposed to ionising radiation. Ablation of the Ataxia-telangiectasia mutated serine/threonine kinase that is recruited and activated by DNA double-strand breaks reverses the effect of radioresistance and re-sensitised GBM to DNA damage thus leading to increase cell death. Our finding suggests targeting the signaling cascade of DNA damage response is a potential therapeutic approach to circumvent IL-6 from promoting radioresistance in GBM.

Matched MeSH terms: Glioblastoma/radiotherapy*; Central Nervous System Neoplasms/radiotherapy*
Fulltext Absorbed dose calculation for a realistic CT-derived mouse phantom irradiated with a standard Cs-137 cell irradiator using a Monte Carlo method

Entezam A, Fielding A, Bradley D, Fontanarosa D

PLoS One, 2023;18(2):e0280765.
PMID: 36730280 DOI: 10.1371/journal.pone.0280765

Computed tomography (CT) derived Monte Carlo (MC) phantoms allow dose determination within small animal models that is not feasible with in-vivo dosimetry. The aim of this study was to develop a CT-derived MC phantom generated from a mouse with a xenograft tumour that could then be used to calculate both the dose heterogeneity in the tumour volume and out of field scattered dose for pre-clinical small animal irradiation experiments. A BEAMnrc Monte-Carlo model has been built of our irradiation system that comprises a lead collimator with a 1 cm diameter aperture fitted to a Cs-137 gamma irradiator. The MC model of the irradiation system was validated by comparing the calculated dose results with dosimetric film measurement in a polymethyl methacrylate (PMMA) phantom using a 1D gamma-index analysis. Dose distributions in the MC mouse phantom were calculated and visualized on the CT-image data. Dose volume histograms (DVHs) were generated for the tumour and organs at risk (OARs). The effect of the xenographic tumour volume on the scattered out of field dose was also investigated. The defined gamma index analysis criteria were met, indicating that our MC simulation is a valid model for MC mouse phantom dose calculations. MC dose calculations showed a maximum out of field dose to the mouse of 7% of Dmax. Absorbed dose to the tumour varies in the range 60%-100% of Dmax. DVH analysis demonstrated that tumour received an inhomogeneous dose of 12 Gy-20 Gy (for 20 Gy prescribed dose) while out of field doses to all OARs were minimized (1.29 Gy-1.38 Gy). Variation of the xenographic tumour volume exhibited no significant effect on the out of field scattered dose to OARs. The CT derived MC mouse model presented here is a useful tool for tumour dose verifications as well as investigating the doses to normal tissue (in out of field) for preclinical radiobiological research.

Matched MeSH terms: Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted/methods
Accurate measurement of exposure rate from a 60Co teletherapy source: deviations from the inverse-square law

Samat SB, Evans CJ, Kadni T, Dolah MT

Br J Radiol, 2000 Aug;73(872):867-77.
PMID: 11026863

A cylindrical gamma-ray 60Co source of activity alpha is predicted to produce an exposure rate X at a distance d in vacuum, given by X = gamma(T)(alpha/d2), where gamma(T) is the specific gamma-ray constant. It has been documented that this formula may be used to approximate X with an accuracy of 1% from a source of length l, provided that d/l > or = 5. It is shown that the formula is accurate to 0.1% under these conditions, provided that the distance is measured from the centre of the source. When absorption in the source and scattering in the collimator are considered, the position of the origin d = 0 can shift by a distance of the order of centimetres. Absorption in air between the source and the ionization chamber adds an exponential factor to the formula. It is shown that even when these modifications are included the discrepancy in the results, although generally less than 1%, is still large compared with the measurement errors. Some suggestions are made for the origin of this discrepancy.

Matched MeSH terms: Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted/methods*
Acne vulgarism treatment using ultra-short laser pulse generated by micro- and nano-ring resonator system

Jalil MA, Phelawan J, Aziz MS, Saktioto T, Ong CT, Yupapin PP

Artif Cells Nanomed Biotechnol, 2013 Apr;41(2):92-7.
PMID: 22991968 DOI: 10.3109/10731199.2012.700519

Acne vulgaris is adebilitating dermatologic disease, and is conventionally treated by laser therapy using a microring resonator system. An evolving understanding of laser-tissue interactions involving Propioni bacterium acneproducing porphyrins, and the development of lasers to target the sebaceous glands, has led to the development of an escalating number of laser light for acne treatment. The results show that the full width at half maximum of the proposed laser pulse of 0.15 nm can be generated using a microring resonator system. The power of the laser is 200 W and the wavelength laser is 1,032 nm, which is proposed as a treatment of acne vulgaris diseases.

Matched MeSH terms: Acne Vulgaris/radiotherapy*

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