Megavoltage Teletherapy Research Articles

Radiotherapy Resources in Latin America and the Caribbean: An International Atomic Energy Agency Analysis of Current and Projected Needs

The inequitable access to radiotherapy (RT) is recognized to be a complex undertaking that will require sustained work identifying gaps and mobilizing efforts to fill in those gaps. Data can support policy-makers as they embark on programs to reduce premature mortality from cancer in their countries and regions. The purpose of this analysis is to identify the current gaps and needs in Latin America and the Caribbean (LAC). We created a database of 41 countries in LAC using open-source data, including data on population size (UN Department of Economic and Social Affairs data), gross national income per capita (GNIPC) (World Bank Data), current and projected cancer incidence and mortality (Globocan 2020). The International Atomic Energy Agency (IAEA) Directory of Radiotherapy Centers (DIRAC) was used to identify the number and operational status of megavoltage (MV) teletherapy machines (Cobalt-60 and Linear Accelerators LINACs) and brachytherapy facilities (HDR and LDR). To calculate current and projected gaps in external beam RT (EBRT) facilities, we matched DIRAC data with Globocan cancer incidence data for 2020 and projections for 2025 and 2030 while applying a 64% optimal EBRT utilization rate (taking into account re-treatment). For brachytherapy, analysis took into account both HDR and LDR capacity and was primarily focused on needs based on current and projected incidence of cervical cancer cases in LAC. EBRT was available in 32 (76%) of 41 countries. There were 742 RT centers in 32 countries with a total of 1131 MV units. Average coverage in 2022 based on an optimal utilization rate of 64% was 64%. LINACs accounted for 87% of the total MV units and Cobalt-60 capacity decreased to 13% of total teletherapy capacity compared to capacity in 2018. Most countries clustered in the same range of GNIPC to teletherapy units per 1000 cases, however outliers were most notable in the Caribbean. The median GNIPC was $6340 and the median MV units per 1000 cancer cases were 1.4. The current deficit in MV units is estimated at 672 megavoltage units and projected to be 2455 units by 2030 representing more than double the current capacity. 28 out of 41 countries (68%) had brachytherapy including 279 installed services, both HDR and LDR. At a 75% optimal utilization rate of brachytherapy in locally advanced cervical cancer, the current brachytherapy capacity in LAC could treat 108,420 patients with cervical cancer/year, which meets the current needs in the region albeit with significant inequity in distribution of resources. There is 15% improvement in the current EBRT capacity in LAC compared to 2018. However, there is still shortage of at least 672 extra units needed. By 2030, the need for MV units will be double the current capacity. The current brachytherapy capacity meets needs albeit with inequitable distribution across the region primarily in the Caribbean.

Clinical utilization of radiation therapy in Korea between 2017 and 2019.

This study aimed to evaluate the clinical infrastructure and utilization of radiotherapy (RT) services in Korea between 2017 and 2019. We extracted the data of patients who underwent RT between 2017 and 2019 from the Health Insurance Review and Assessment Service. We further analyzed this data according to the diagnosis and treatment modalities of patients diagnosed with International Classification of Disease 10 (ICD-10) diagnostic codes C00-C97 and D00-D48. In addition, we collected statistics on RT facilities in Korea using a nationwide survey. The total number of patients who received RT in 2017, 2018, and 2019 were 77,901, 81,849, and 87,460, respectively. The number of patients diagnosed with ICD 10 C- and D-codes in 2019 was 86,339, of whom 39,467 were men and 46,872 women. The rate of utilization of RT among cancer patients was 30.4% in 2017 and 2018 and 30.9% in 2019. In 2019, the most common types of cancers treated with RT were breast, lung, prostate, colorectal, and liver cancers. Regarding the RT infrastructure in Korea, there were 95 radiation oncology centers, 237 megavoltage (MV) teletherapy units, 35 brachytherapy units, and two proton accelerators in 2019. There were 4.5 MV teletherapy machines per million. The number of patients treated with RT has increased consistently from 2017 to 2019. As the number of patients with cancer increases, it is expected that the RT infrastructure will be further expanded in Korea.

Clinical utilization of radiation therapy in Korea, 2016.

Radiotherapy (RT) is one of the primary cancer treatment modalities. To estimate the actual utilization of RT and infrastructure in Korea, the current study was performed. Data from 2012 to 2016 were extracted from the Health Insurance Review and Assessment Service. In addition, a nationwide survey was conducted to collect the statistics of RT facilities, equipment and human resources in Korea. The total number of patients treated with RT was 72 563 in 2016. The five cancers that were most commonly treated with RT in 2016 were breast, lung, colorectal, liver and prostate cancer. According to analyses of specific treatment modalities, the number of patients treated with intensity-modulated radiotherapy (IMRT), stereotactic radiation therapy (SRT) and proton therapy increased from 6670, 6306 and 50 in 2012 to 21584, 9048 and 703 in 2016, respectively. Ninety radiation oncology centers were working in 2015 and there were a total of 213 megavoltage teletherapy machines. In 2015, 310 patients were treated per megavoltage RT machine, 246 patients per radiation oncologist, 501 patients per medical physicist and 111 patients per radiotherapy technologist. In conclusion, the number of patients who underwent RT in Korea has increased steadily from 2012 to 2016. The IMRT utilization rate remarkably increased in 2016, and the number of patients treated with advanced treatment modalities such as IMRT, SRT and proton therapy is expected to increase.

Model for Estimating Power and Downtime Effects on Teletherapy Units in Low-Resource Settings.

PurposeMore than 6,500 megavoltage teletherapy units are needed worldwide, many in low-resource settings. Cobalt-60 units or linear accelerators (linacs) can fill this need. We have evaluated machine performance on the basis of patient throughput to provide insight into machine viability under various conditions in such a way that conclusions can be generalized to a vast array of clinical scenarios.Materials and MethodsData from patient treatment plans, peer-reviewed studies, and international organizations were combined to assess the relative patient throughput of linacs and cobalt-60 units that deliver radiotherapy with standard techniques under various power and maintenance support conditions. Data concerning the frequency and duration of power outages and downtime characteristics of the machines were used to model teletherapy operation in low-resource settings.ResultsModeled average daily throughput was decreased for linacs because of lack of power infrastructure and for cobalt-60 units because of limited and decaying source strength. For conformal radiotherapy delivered with multileaf collimators, average daily patient throughput over 8 years of operation was equal for cobalt-60 units and linacs when an average of 1.83 hours of power outage occurred per 10-hour working day. Relative to conformal treatments delivered with multileaf collimators on the respective machines, the use of advanced techniques on linacs decreased throughput between 20% and 32% and, for cobalt machines, the need to manually place blocks reduced throughput up to 37%.ConclusionOur patient throughput data indicate that cobalt-60 units are generally best suited for implementation when machine operation might be 70% or less of total operable time because of power outages or mechanical repair. However, each implementation scenario is unique and requires consideration of all variables affecting implementation.

A systematic review of radiotherapy capacity in low- and middle-income countries.

Objectives: The cancer burden in low- and middle-income countries (LMIC) is substantial. The purpose of this study was to identify and describe country and region-specific patterns of radiotherapy (RT) facilities in LMIC.Methods: A systematic review of the literature was undertaken. A search strategy was developed to include articles on radiation capacity in LMIC from the following databases: PubMed, Embase, CINAHL Plus, Global Health, and the Latin American and Caribbean System on Health Sciences Information. Searches included all literature up to April 2013.Results: A total of 49 articles were included in the review. Studies reviewed were divided into one of four regions: Africa, Asia, Eastern Europe, and South America. The African continent has the least amount of resources for RT. Furthermore, a wide disparity exists, as 60% of all machines on the continent are concentrated in Egypt and South Africa while 29 countries in Africa are still lacking any RT resource. A significant heterogeneity also exists across Southeast Asia despite a threefold increase in megavoltage teletherapy machines from 1976 to 1999, which corresponds with a rise in economic status. In LMIC of the Americas, only Uruguay met the International Atomic Energy Agency recommendations of 4 MV/million population, whereas Bolivia and Venezuela had the most radiation oncologists (>1 per 1000 new cancer cases). The main concern with the review of RT resources in Eastern Europe was the lack of data.Conclusion: There is a dearth of publications on RT therapy infrastructure in LMIC. However, based on limited published data, availability of RT resources reflects the countries’ economic status. The challenges to delivering radiation in the discussed regions are multidimensional and include lack of physical resources, lack of human personnel, and lack of data. Furthermore, access to existing RT and affordability of care remains a large problem.

Quantification of trends in radiation oncology infrastructure in Pakistan, 2004–2009

To provide objective estimates of radiation oncology infrastructure in Pakistan for the years 2004 and 2009 in order to quantify trends in radiotherapy facilities, patient load and to identify the future needs. Nationwide surveys using structured questionnaires were conducted in 2005 and 2010 by the Institute of Radiotherapy and Nuclear Medicine, Peshawar, to assess the status of radiation oncology infrastructure in 2004 and 2009. The data were analyzed to observe the trends. Megavoltage teletherapy machines increased from 37 in 2004 to 41 in 2009. New patients registered in all radiotherapy centers were 33 369 in 2004 and 46 114 in 2009. Conventional simulators used for tumour localization increased from 15 to 21 and computerized tomography simulators from 0 to 07. Radiation treatment planning systems for dose calculations of tumors and vital organs increased from 15 to 26 and brachytherapy units from 12 to 13. There were 725 patients per medical physicist in 2004 versus 632 in 2009. Patients per radiation oncologist were 439 in 2004 versus 549 in 2009. Number of radiotherapy technologists/shift/machine was 1.69 in 2004 versus 1.90 in 2009. Repair maintenance personnel improved from 2.11/2 megavoltage units in 2004 to 2.49 in 2009. While there was an increase in number of radiotherapy centers, equipment and human resources available, this was insufficient to comply with international guidelines. An adequate enhancement in radiation oncology infrastructure is needed to cope with the predicted rise in cancer incidence.

Radio frequency noise from an MLC: a feasibility study of the use of an MLC for linac-MR systems

Currently several groups are actively researching the integration of a megavoltage teletherapy unit with magnetic resonance (MR) imaging for real-time image-guided radiotherapy. The use of a multileaf collimator (MLC) for intensity-modulated radiotherapy for linac-MR units must be investigated. The MLC itself will likely reside in the fringe field of the MR and the motors will produce radio frequency (RF) noise. The RF noise power spectral density from a Varian 52-leaf MLC motor, a Varian Millennium MLC motor and a brushless fan motor has been measured as a function of the applied magnetic field using a near field probe set. For the Varian 52-leaf MLC system, the RF noise produced by 13 of 52 motors is studied as a function of distance from the MLC. Data are reported in the frequency range suitable for 0.2–1.5 T linac-MR systems. Below 40 MHz the Millennium MLC motor tested showed more noise than the Varian 52-leaf motor or the brushless fan motor. The brushless motor showed a small dependence on the applied magnetic field. Images of a phantom were taken by the prototype linac-MR system with the MLC placed in close proximity to the magnet. Several orientations of the MLC in both shielded and non-shielded configurations were studied. For the case of a non-shielded MLC and associated cables, the signal-to-noise ratio (SNR) was reduced when 13 of 52 MLC leaves were moved during imaging. When the MLC and associated cables were shielded, the measured SNR of the images with 13 MLC leaves moving was experimentally the same as the SNR of the stationary MLC image. When the MLC and cables are shielded, subtraction images acquired with and without MLC motion contains no systematic signal. This study illustrates that the small RF noise produced by functioning MLC motors can be effectively shielded to avoid SNR degradation. A functioning MLC can be incorporated into a linac-MR unit.

SU‐FF‐J‐76: Radio Frequency Noise From Clinical Linear Accelerators

Purpose: Several groups are actively pursuing the integration of an MRI with a megavoltage teletherapy treatment unit. Our system will use a 0.2 Tesla magnet for imaging and a 6MV linear accelerator (linac) for treatment. An important scientific aspect of this project is the possible radio frequency (RF) noise interference between the MRI and linac. The purpose of this work is to report on the measurement of the RF emissions in the treatment room of a clinical linac. Method and Materials: The electric (E) and magnetic (H) field components of the RF noise from a clinical linac were measured using commercially available field probes. Measurements were taken on a Varian 600C linac. The time response of the signal induced in the probes was captured by an appropriate oscilloscope. The discrete Fourier transforms of these time domain measurements were calculated to obtain the measured power as a function of frequency. A second set of measurements were taken to study the dependence of field strength on the location within the vault. Results: Our measurements indicate that the E field strength is on the order of V/m, around 8.5 MHz, and that most of the signal in the H field in concentrated at frequencies below 5 MHz. Besides a few peaks, in general toward higher frequencies both the E and H field strengths drop. We measured a power density of 14.6 μW/m2 at 8.5 MHz for a Varian 600C linac. Our measurements show that the measured field strength has little dependency on the measurement position within a treatment vault. Conclusion: Since an MRI coil receives power on the order of μWs during imaging, it will be important to properly shield or otherwise reduce this extraneous RF power in the linac‐MR unit.

SU-GG-T-371: Monte Carlo Neutron Shielding Evaluation of Treatment Vaults Built to NCRP 49 Or NCRP 151 Recommendations

Purpose: To use MCNP5 to compare and contrast the recommendations found in NCRP 49 and NCRP 151 pertaining to neutron shielding. Method and Materials: An Elekta SL25 accelerator head with nominal peak energy of 18MV was modeled in MCNP5 and verified against known measured beam characteristics.Neutron angular and energy distributions produced by the Elekta SL25 were calculated using the photoneutron production feature of MCNP5. These neutron distributions were then used as source terms for shielding calculations in simulated treatment vaults designed to either NCRP 49 or NCRP 151 standards. Results: The neutron penetration calculations indicate that shielding for megavoltage teletherapy units, i.e. those with energies greater than 10MV, should include materials designed to prevent neutron leakage. A quantitative assessment of neutron dose contributions to personnel outside of the treatment vaults will be presented. Conclusion: Although the phenomenon of photoneutron production has been well known for some time recommendations for shielding these neutrons in megavoltage teletherapy settings are relatively recent. This study may be used by those institutions considering upgrading existing units to ones with higher energies or by new sites to justify the added expense of incorporating shielding aimed at preventing neutron leakage.

Radiotherapy services in countries in transition: gross national income per capita as a significant factor

Background and purpose: The acquisition of radiotherapy by countries in transition (CITs) is an evolutionary process from having no resources whatsoever, to meeting the standards adopted by well-developed countries. The influence of the economic ability of a country to acquire and sustain this technology has intuitively been accepted as a major factor but has not before been subjected to analysis for a large group of countries. This information has been analysed to provide guidance to countries commencing and expanding radiotherapy services. Material and methods: The number of linear accelerators and 60Co megavoltage teletherapy machines in 72 CITs, those with gross national income per capita (GNI/cap)<$12 000 per annum (pa) and a sample of 12 countries with GNI/cap>$12 000 pa were expressed as machines per million population (MEV/mil) and used as an index of the ability of the country to provide a service. This figure was related to GNI/cap. The average populations of 24 further countries without radiotherapy were compared with 21 countries with radiotherapy facilities having the same range of GNI/cap. Results: The relationship log 10 MEV/mil=−2.90+0.85 log 10 GNI/cap was identified between the machines and income. Also verified was that small low income countries were less likely to have the technology than those with large populations. Conclusions: The increase in the number of teletherapy machines is closely linked to the GNI/cap of a country. Our sample of well developed countries failed to demonstrate a levelling off of equipment acquisition with income. In the lower income group, smaller countries were less likely to have radiotherapy services than those with large populations.

A comparison of the efficacy and complication rates of low dose-rate versus high dose-rate brachytherapy in the treatment of uterine cervical carcinoma

Purpose : To compare the outcome and complication rates for treatment of uterine cervical carcinoma with low dose-rate (LDR) vs. high dose-rate (HDR) brachytherapy at the University of Wisconsin Comprehensive Cancer Center (UWCCC). Methods and Materials : One-hundred ninety-eight evaluable patients with cervical carcinoma, Stages 1B to IIIB, treated with curative intent with a combination of megavoltage teletherapy and LDR brachytherapy from 1977 to 1988 were the subject of an initial review. In 1989, a HDR treatment program was initiated where all patients with cervical carcinoma. were subsequently treated with a combination of HDR brachytherapy and teletherapy. Using the linear-quadratic model (LQ), the dose and schedule of HDR brachytherapy and teletherapy were designed to give similar tumor control and late effects as LDR therapy. Technically, the HDR schedule required meticulous attention to treatment geometry to limit severe late effects. Forty patients treated with the HDR program with 2–4 year follow-up were reviewed and compared to the previous LDR patient group. The LDR and HDR treatment groups were comparable with regards to age, weight, stage distribution, bulk of disease, and histology. Results : No significant difference in survival was found between the LDR and HDR groups with 3-year actuarial overall survival being 66% and 77%, respectively. Three-year actuarial pelvic control rates were similar at 80% and 77% for the LDR and HDR groups, respectively. No significant difference in late treatment complications requiring hospitalization or surgery was found between the two treatment groups with a complication rate of 10% (20/198) for the LDR patients and 2.5% (1/40) for the HDR patients. Conclusion : As predicted by our LQ calculations, treatment results for LDR and HDR brachytherapy were similar with respect to survival, pelvic control and late complications in the treatment of cervical carcinoma. The HDR brachytherapy program at the UWCCC appears to be a safe and effective alternative to LDR therapy in the treatment of cervical carcinoma.

An alternative to conventional shielding for megavoltage therapy rooms.

Dry silica sand as an "in-wall" shielding medium for megavoltage teletherapy rooms is discussed. Shielding considerations, construction techniques, and survey results are presented for a 6-MV facility using sand shielding for both primary and secondary barriers.

Carcinoma of the nasopharynx: survival and patterns of recurrence.

We have analyzed survival, disease-free (NED) survival, and patterns of recurrence for 76 patients with carcinoma of the nasopharynx treated from June 1964 through July 1979. Patients with Stages I through IV, who were treated for cure, comprise the study group. Megavoltage teletherapy treatment was delivered to the primary bilateral neck and supraclavicular areas. Dose to the nasopharynx ranged from less than 55 Gy to 70 Gy with several patients receiving higher doses. The observed 5 year NED survival rates were: Stage I, 75%; Stage II, 20%; Stage III, 42%; and Stage IV, 31%. During a 5-year minimum follow-up for all patients, 46 or 60.5% failed. Ninety-five percent of these failures occurred within 3 years; only two patients relapsed after more than 5 years.

Transperineal interstitial implantation of prostate cancer: A new method

A method of transperineal interstitial implant of prostate without the need for surgical exploration was used to provide a boost dose of 3200 rad to the implanted volume in patients with relatively advanced Stage C carcinoma of the prostate. All patients were initially givern megavoltage teletherapy to a dose of 4320 rad in 24 treatments via anteroposterior and posteroanterior en bloc pelvic and para-aortic portals; then, lateral pelvic ports were used to give additional 1400 rad in 7 treatments. The implant was performed three to four weeks later. Twenty-three patients were treated since 1971; the follow-up period was a minimum of two years in all except three patients. Fifteen patients were alive disease-free; one died of ulcerative colitis, disease-free at 28 months and one was alive with disease at this writing. Disease was locally controlled among all patients except one (96%). The morbitity was insignificant and the quality of life was good. The time of recurrence was from three to nine months in the seven patients who failed., Six of these died before 30 months; three had poorly differentiated histology. No patient among those initially diagnosed by needle biopsy had failed whereas 50% of those whose diagnosis was by transurethral resection showed distant metastases; only one of these patients had concurrent local failure.

Spherical Lead Shields for Megavoltage Teletherapy

A new method of manufacturing individualized, focused lead shields for megavoltage teletherapy is described. Computerized film dosimetry demonstrated that in contrast to nonfocused shields, the new focused shields exhibit good maintenance of penumbra width as the distance between the edge of the beam and the central axis is increased.

Letter: Mathematical representation of megavoltage teletherapy beams.

The publication in the September issue of this journal of three consecutive papers (Wilkinson and Redmond, 1975; Kornelson and Young, 1975; Thomas and Haybittle, 1975) using empirical formulae to represent megavoltage teletherapy beams prompts us to raise some criticisms of this method and to suggest an alternative which differs both from empirical formulae and from methods requiring the storage of large quantities of data on the dose distribution in many beams (for example Milan and Bentley, 1974).

Primary squamous cell carcinoma of the larynx.

While many clinicians would intuitively believe that surgical treatment of laryngeal carcinoma is superior to irradiation, we have found that in many instances this is not the case. When the results of initial radiation therapy combined with the surgical salvage rates for irradiation failures are analyzed and compared with the results of initial surgery and subsequent salvage of surgical failures, the overall cure rates are quite comparable. This point has not been sufficiently emphasized in the treatment of laryngeal cancer. Its importance lies in the ability to offer a significant percentage of patients a form of treatment which carries with it much less functional morbidity without asking the patient to assume a greater risk with regard to the overall cure rate. This non-randomized retrospective study will analyze our experience in the treatment of laryngeal cancer with specific emphasis on the overall cure rate when megavoltage teletherapy is combined with surgical salvage of radiation failures.

Achievement of uniform dose without overlap in multi-port treatment fields, including inter-port shaped blocks.

The authors describe a technique for treating large areas with multiple ports without gaps or overlaps by rotating the therapy unit about the source. The overall effect is the same as if one large field were used with a single comprehensive set of precise shielding blocks. Minimal set-up time permits routine use of this method. Modifications for use with conventional megavoltage teletherapy units are discussed.

Effect of shadow trays on dose to superficial layers of skin in 6 MV X-ray therapy

It is common practice to attach plastic shadow trays to the collimating heads of megavoltage teletherapy units for holding lead shielding blocks. The presence of the trays leads to some electron contamination in the beam and to consequent increase in the skin dose. Using lithium fluoride and thin sheets of Lucite, the authors have measured actual doses at the surface and at depths of up to 25 mm in a Lucite phantom for 6 MV X-rays, both with and without a shadow tray. As expected, the increase in dose due to the tray depends on the field size. For example, for a field of 25*25 cm at an SSD of 100 cm, the tray (at a distance of 30 cm from the surface) increases the surface dose from 37 to 53% of the maximum dose, and the dose at a depth of 1 mm from 50 to 75%. The depth for an 80% dose changes from 2.6 to 1.4 mm. For a field of 5*5 cm, the changes are negligible. That the changes are due to electrons is very simply demonstrated by introducing a thin lead sheet under the shadow tray, when the doses return to their pre-tray levels. These results and their implications for skin-sparing effects were fully discussed.