Trends in the Use of Hypofractionation in Treatment of Breast Cancer in Botswana

PURPOSE/OBJECTIVE(S)

Clinical trials have shown that moderate hypofractionation (HF) is clinically effective as adjuvant treatment to breast conserving surgery or following mastectomy with advanced disease. ASTRO issued updated guidelines in 2018, expanding the population eligible to receive HF to all patients, regardless of age and tumor stage. Use of HF can promote efficient resource utilization for over-burdened health care systems; however, global adoption of HF has been previously only reported via ESTRO survey of individual physicians. These data note that HF following lumpectomy is 40% in Africa vs. >90% in North America, with limited data on the uptake of HF within individual African countries. In this study, we characterize temporal trends and clinical, socio-demographic factors associated with the use of HF in breast cancer in Botswana.

MATERIALS/METHODS

We retrospectively analyzed a cohort of breast cancer patients receiving curative intent radiation between 2015 and 2022 at the only radiation clinic in Botswana. We compared patients' characteristics between those who received HF vs. standard fractionation (SF) and report chi-square statistics when appropriate. We fit a multilevel mixed-effects logistic regression model with a random intercept for district while adjusting for fixed effects such as HIV infection status, laterality, hormone receptor status, and marital status.

RESULTS

A total of 234 patients were prescribed curative intent radiation between 2015 and 2022 in Gaborone, Botswana. Median age at diagnosis was 51 years old, and the majority of patients presented with stage III disease (61.9%, 109/234). 26.9% of this population were women living with HIV (WLWH), and 71% lived >100km from the hospital. HF was utilized overall in 59.4% (139/234) of patients. Most common fractionation patterns included: 4005cGy/15fx and 4267cG/16fx. One patient received ultra-HF (2600cGy/5fx). In unadjusted chi-square analysis, a higher proportion of HF was seen in right vs left-sided breast cancer (65.8% vs. 50.9%, p = 0.02), increasing year of diagnosis from 2015 - 2022 (p<0.001), and among patients >/ = 40 years of age vs. those <40 years of age (62.8% vs 42.1%, p = 0.017). Temporal trends show a significant increase in the utilization of HF starting from 23.8% (5/21) in 2015, to 61.5% (32/52) in 2018, and finally 100% (11/11) of cases in 2022. Our regression analysis shows that there is no statistically significant between-district variance or patient-level factors that associate with the uptake of HF. The overall utilization rate for HF between 2015-2022 was 59.4% (95% CI: 53.0%-65.5%).

CONCLUSION

Based on recent survey results the uptake of HF among African countries is lower than that of North America. To our knowledge, this is the first quantitative analysis of the utilization of HF over 5 years in an African country. Further analysis on factors related to physician prescription of hypofractionation is warranted, including influence of breast laterality, age, and primary surgery type.

An Analysis of Delays in Treatment Time for Prostate Cancer Patients in Sub-Saharan Africa

PURPOSE/OBJECTIVE(S)

Time interval from diagnosis of prostate cancer to treatment is an important predictor of survival outcomes for patients. These time intervals can be prolonged in resource-limited settings, such as those in Sub-Saharan Africa (SSA). The purpose of this project was to analyze the time interval between diagnosis and either hormonal or radiotherapy treatment for prostate cancer patients in Nigeria and Tanzania. The outcomes can inform the implementation of the recent Lancet Oncology Commission recommendations on increasing access to radiotherapy services in SSA to curb the growing cancer burden in the region.

MATERIALS/METHODS

Data were extracted from electronic patient records at the NSIA-LUTH Cancer Center (NLCC) in Lagos, Nigeria and at the Ocean Road Cancer Institute (ORCI) in Dar Es Salaam, Tanzania. Included patients were prostate cancer patients who received hypofractionated radiotherapy (HFRT) at ORCI between January 6 - June 16, 2022, and either HFRT or conventionally fractionated radiotherapy (CFRT) at NLCC between February 1 - July 27, 2022. Simple descriptive statistics were used to calculate the mean time interval between the patient's date of diagnosis of prostate cancer and the start of hormonal or radiotherapy treatment.

RESULTS

Time to hormonal therapy was collected for 23 ORCI patients and 28 NLCC patients. The mean time interval from date of diagnosis to start of hormonal therapy was 19.3 weeks for patients in Tanzania and 8.0 weeks for patients in Nigeria. Time to radiotherapy was collected for 23 ORCI patients and 50 NLCC patients. The mean time interval from date of diagnosis to start of radiotherapy was 59.13 weeks for patients in Tanzania and 48.5 weeks for patients in Nigeria.

CONCLUSION

Prostate cancer patients in Nigeria and Tanzania experience significant delay in receiving hormonal and radiotherapy treatment, especially when compared to wait times in well-resourced countries. For example, a recent assessment of U.S. patients in the National Cancer Database who were diagnosed with prostate cancer between 2004-2015 revealed that the mean interval from diagnosis to definitive therapy (either surgery or some form of radiotherapy) was 11.3 weeks - significantly less than the mean times documented in our study of SSA patients (Cone et al., 2020). Additionally, patients in Tanzania experienced longer treatment delays compared to patients in Nigeria, highlighting potential disparities in access to care between SSA countries. These prolonged delay times are likely to negatively impact survival and represent an intervention opportunity to alleviate the cancer crisis in SSA.

Characterization of DNA Damage Response-Associated Somatic Mutations in Borderline Resectable and Locally Advanced Pancreatic Cancer

PURPOSE/OBJECTIVE(S)

The role of radiation for pancreatic cancer remains controversial, with recent studies showing conflicting results, highlighting the need to develop biomarkers of radiation response. Despite its potential utility in predicting radiosensitivity, the landscape of somatic mutations in borderline resectable pancreatic cancer (BRPC) and locally advanced pancreatic cancer (LAPC), as related to DNA damage response (DDR), has not been well characterized. This study aimed to characterize the frequency of such mutations in a cohort of patients with BRPC/LAPC treated with neoadjuvant chemotherapy and stereotactic body radiotherapy (SBRT).

MATERIALS/METHODS

Mutational data was collected from patients with BRPC/LAPC treated at a single institution with neoadjuvant chemotherapy and SBRT, followed by surgical resection from 2016-2021. Chemotherapy consisted of modified FOLFIRINOX or gemcitabine/nab-paclitaxel, and patients were treated with SBRT in 33 Gy in 5 fractions. Genomic data was obtained from either endoscopic biopsy or surgical specimens, and next-generation sequencing was performed either in-house with a Solid Tumor Panel or with FoundationOne CDx. Specific emphasis was placed on the characterization of double-strand DNA break (DSB) repair genes, as this is the type of tumor cell damage traditionally induced by radiation therapy. Genes associated with the two main pathways of DSB repair, non-homologous end joining (NHEJ) and homologous repair (HR), were analyzed. Specific HR pathway mutations assessed were BLM, BRCA1/2, MRE11, NBN, PALB2, RAD50, RAD51B-D, and RAD54L, while PRKDC mutations were assessed for the NHEJ pathway. Mutations in ATM, an important initiator of DDR pathways, were also analyzed. Additionally, the frequency of mutations in TP53, CDKN2A and SMAD4 in patients with concomitant KRAS mutations was assessed.

RESULTS

Eighty-five patients were included in the study. Five (5.9%) patients had mutations in the NHEJ pathway of the PRKDC gene. Twenty (23.5%) patients had mutations in the HR pathway, including BRCA2 (10/85; 11.8%), PALB2 (5/85; 5.9%), BRCA1 (3/85; 3.5%), and RAD50 (1/85; 1.2%). Six (7.1%) patients had mutations in ATM. No patients were found to have mutations in BLM, RAD51B-D, RAD54L, or NBN. Amongst patients with KRAS mutations (72/85), concomitant mutations were observed in TP53 (47/85; 55.3%), CDKN2A (16/85; 18.8%), and SMAD4 (9/85; 10.6%).

CONCLUSION

Herein, we characterized the frequency of somatic mutations associated with DSB repair genes in patients with BRPC/LAPC. Data analysis on outcomes related to radiation response in patients with mutations in DDR pathways is ongoing, but will likely also benefit from multi-institutional efforts to increase the power to answer this question.

Can Advanced Radiotherapy Clinical Trials be Conducted in Resources Limited Countries?

PURPOSE/OBJECTIVE(S)

The Lancet Oncology Commission on Cancer in Sub-Saharan Africa (SSA) highlighted the region's increasing cancer incidence and mortality, and recommended a series of actions to address this growing crisis. One such approach recommended by the Commission to increase access to curative treatment is the use of hypofractionated radiotherapy (HFRT). Here we highlight the barriers and facilitators to launching HFRT in SSA, as identified through the HypoAfrica clinical trial.

MATERIALS/METHODS

HypoAfrica is a longitudinal multi-center clinical trial that was launched in late 2021 at three centers in Nigeria, Tanzania, and South Africa. The goal of HypoAfrica was to assess the feasibility of implementing HFRT for localized prostate cancer in SSA. To date, 155 of 182 subjects have been enrolled in this study. During the last year, a team of radiation oncology professionals from Africa, Europe, Australia, and USA met once every Saturday and reviewed the sites' data to identify the barriers to the implementation of HFRT and find solutions to overcome these challenges. With the intent to expand HFRT trials and practice to new SSA countries and radiotherapy centers, we also conducted an online survey to elucidate the readiness of radiotherapy centers across SSA to perform HFRT.

RESULTS

The major challenge identified by this team was securing high-quality data that will yield statistically significant results. Factors that contribute to quality data are: harmonization of machine and patient-specific quality assurance (QA) procedures across the centers, data quality harmonization, and challenges associated with machine maintenance. Immediate solutions implemented included introduction of low-cost QA tools for patient-specific QA measurements, ongoing training of the site's healthcare professionals, implementation of preventative maintenance for Linacs, and data centralization infrastructure. These actions have resulted in the production of a high-quality, standardized dataset. Planned longer-term solutions to HFRT challenges include implementation of ongoing training, telehealth for remote support and QA, and the creation of an Imaging and Radiation Oncology Core for Africa. The online survey indicated that 61% of respondents' institutions perform HFRT for palliative purposes, emphasizing the readiness of sites in SSA to utilize HFRT for curative purposes.

CONCLUSION

The study serves as a useful guide for increasing access to HFRT treatment in resource-limited settings and for conducting multicenter radiotherapy clinical trials.

Patient Reported Outcomes Following Palliative Whole Brain Radiation Therapy in Patients with Brain Metastasis

PURPOSE/OBJECTIVE(S)

Brain metastases (BM) are a common occurrence in patients with advanced cancers, and extremely challenging to treat, resulting in short survival periods. Consequently, whole brain radiation therapy (WBRT) remains the standard palliative intervention for patients with BM. The present study set to evaluate the efficacy of WBRT by assessing the quality of life (QoL) and survival outcomes in WBRT-treated patients with BM. It was hypothesized that the WBRT would enhance the QoL through alleviation of symptoms and functionality, and prolong patient survival.

MATERIALS/METHODS

This was a prospective, longitudinal, hospital-based single-center study. Consecutive sampling methodology was used to recruit 52 patients with BM undergoing WBRT. Patients were followed up on days 7, 30, 90 and 180 after WBRT. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 15-Palliative care (EORTC QLQ-C15-PAL) was employed to report patient responses in a Likert scale. A descriptive analysis and multi-trait scaling correlation was computed using IBM SPSS Statistics 29.0, 95% confidence interval. The overall survival analysis (Kaplan-Meier) was also performed.

RESULTS

The study cohort was predominantly females (82.7%), and accordingly, 65.4% of the respondents had a breast primary tumor. A Shapiro-Wilk test of normality revealed that the data was not normally distributed (sig. < 0.05), however, statistic values (W) closer to 1 suggested a good fit. A goodness-of-fit test ascertained the assumption, yielding non-significant Chi square Pearson (p = 0.325) and Deviance (p = 1.000) residuals. There was a significant correlation (p < 0.001) between physical functioning and emotional functioning. Median overall survival was 180 days (∼6 months). A total of 20 patients (38%) that survived up to 180 days reported alleviated symptoms and better functioning. A significant improvement in physical functioning (p < 0.001) and emotional functioning (p = 0.031) was reported at 180 days post WBRT, compared to baseline. Similarly, a significant improvement in visual disorders (p = 0.002), motor dysfunction (p = 0.031), and communication deficit (p = 0.001) was also reported. A significant alleviation of pain was reported at day 90 (p = 0.042) by 53% of the patients that survived.

CONCLUSION

WBRT is an effective palliative intervention in patients with BM, resulting in improved QoL and prolonged survival. More than 50% of patients that survived 3 months reported a significant alleviation of pain, and 38% of patients that survived for 6 months reported a significantly improved functioning. This demonstrated the effectiveness of WBRT in palliative care and will add to the body of data on the efficacy of radiotherapy.

Expanding Radiotherapy Access in Sub-Saharan Africa: An Analysis of Travel Burdens and Patient-Related Benefits of Hypofractionation

PURPOSE/OBJECTIVE(S)

The purpose of this project was to examine the travel burdens for radiotherapy patients in Nigeria, Tanzania, and South Africa, and to assess the patient-related benefits of hypofractionated radiotherapy (HFRT) for breast and prostate cancer patients in these countries. The outcomes can inform the implementation of the recent Lancet Oncology Commission recommendations on increasing the adoption of HFRT in Sub-Saharan Africa (SSA) to enhance radiotherapy access in the region.

MATERIALS/METHODS

Data were extracted from electronic patient records at the NSIA-LUTH Cancer Center (NLCC) in Lagos, Nigeria and the Inkosi Albert Luthuli Central Hospital (IALCH) in Durban, South Africa, from written records at the University of Nigeria Teaching Hospital (UNTH) Oncology Center in Enugu, Nigeria, and from phone interviews at Ocean Road Cancer Institute (ORCI) in Dar Es Salaam, Tanzania. Google Maps was used to calculate the shortest driving distance between a patient's home address and their respective radiotherapy center. QGIS was used to map the straight-line distances to each center. Descriptive statistics were used to compare transportation costs, time expenditures, and lost wages when using HFRT versus conventionally fractionated radiotherapy (CFRT) for breast and prostate cancer. All transportation- and wage-related cost data were contextualized within each country's monthly adjusted net national income (MANNI) per capita, as reported by 2020 data from the World Bank.

RESULTS

Patients in Nigeria (n = 390) traveled a median distance of 24.0 km (interquartile range (IQR) = 238.5 km) to NLCC and 86.7 km (IQR = 87.3 km) to UNTH, patients in Tanzania (n = 23) traveled a median distance of 537.0 km (IQR = 587.5 km) to ORCI, and patients in South Africa (n = 412) traveled a median distance of 18.0 km (IQR = 15.0 km) to IALCH. Estimated transportation cost savings for breast cancer patients in Lagos and Enugu were 12,895 Naira and 7,369 Naira (20% and 11% of MANNI per capita), respectively, and for prostate cancer patients were 25,329 and 14,276 Naira (38% and 22% of MANNI per capita), respectively. Prostate cancer patients in Tanzania saved a median of 137,765 Shillings (78% of MANNI per capita) in transportation costs. Significant time expenditures - a relevant consideration for patient convenience - were also saved for ORCI patients, including a median of 80.0 hours (includes travel, treatment, and wait times). Mean transportation cost savings for patients in South Africa were 4,777 Rand (72% of MANNI per capita) for breast cancer and 9,486 Rand (143% of MANNI per capita) for prostate cancer.

CONCLUSION

Cancer patients in SSA travel considerable distances to access radiotherapy services. HFRT decreases patient-related costs and time expenditures, which may increase radiotherapy access and alleviate the growing burden of cancer in the region.

Challenges and Opportunities for Increasing Adoption of Hypofractionated Radiotherapy in Low- and Middle-Income Countries

Purpose/Objective(s)

In the advent of the COVID-19 pandemic, professional societies including the American Society for Radiation Oncology and the National Comprehensive Cancer Network recommended increased adoption of evidence-based hypofractionated radiotherapy (HFRT), with benefits including significantly reducing the number of clinical visits for each patient to minimize potential exposure to infection, and reducing treatment costs and stress on limited workforce, particularly beneficial in Low-and-Middle-Income Countries (LMICs). Despite these benefits, HFRT adoption remains low, especially in LMICs. The purpose of this study is to investigate the challenges and opportunities for increased adoption of evidence-based HFRT in LMICs.

Materials/Methods

An IRB-approved survey was implemented in 18 sample radiotherapy centers in African LMIC to assess the challenges and utilization of HFRT. The experiences of three cancer centers were documented as part of an ongoing multi-center HFRT clinical trial designed to compare results with those reported for clinical trials involving North American and European Populations. Based on the findings assessed, challenges from the survey, and recorded experiences from the three centers, an online education and training program was developed in collaboration with the Global Health Catalyst, Radiation Knowledge and computer-based training tools for treatment planning, contouring, and online learning, with remote support provided by members from the international councils of ASTRO and AAPM.

Results

Only 8 of 18 surveyed clinics reported adopting HFRT as a common practice. Analysis of survey data demonstrated a significant need for training on contouring for radiation oncologists, and treatment planning and quality assurance. An education and training program was developed for implementation in the LMICs via a collaborative education model involving ASTRO and AAPM members who are faculty in USA institutions in collaboration with LMIC radiation oncology professionals.

Conclusion

The findings demonstrate a need for additional investment in infrastructure and training, as well as better ongoing education of oncology leaders on the benefits of increased adoption of evidence-based HFRT. The project also highlights opportunities and approaches for leveraging information and communication technology for collaborative high-impact global radiation oncology education, with the participation of members across both LMIC and USA institutions and professional societies. The HFRT training program provides a template for continuous education and training to increase the adoption of evidence-based approaches to HFRT that can significantly increase improved access to radiotherapy and reduce disparities in advancing globally the practice of radiation oncology. The impact of such a program and approach will be presented and discussed.

COVID-19 in Sub-Saharan Africa: A Multi-Institutional Survey of the Impact of the Global Pandemic on Cancer Care Resources

Purpose/Objective(s)

The COVID-19 pandemic has direct and indirect impact on patients with cancer. Low- and middle-income regions, especially sub-Saharan Africa, are especially vulnerable to a negative impact on cancer resources and outcomes. We report the initial indirect impact of COVID-19 on cancer care in the sub-Saharan Africa region approximately 14 months into the pandemic.

Materials/Methods

At the start of the pandemic, we created a consortium of African and North American cancer centers and NGOs for the distribution of factual and timely information and data on COVID-19 and cancer care. A survey was distributed to consortium members and other colleagues from the sub-Saharan Africa region to understand the impact of COVID-19 in cancer care resources. Survey respondents represent cancer experts from 8 centers in Ghana, Nigeria, Kenya, Ethiopia, South Africa, Rwanda, and Zimbabwe.

Results

All sites report SARS-COv-2 transmission amongst cancer patients and staff. A total of 48 staff developed COVID-19 infection with one site reporting a single death. Additionally, 62.5% of sites report loss of oncology physician or nursing staff due to redeployment for COVID-19 care resulting in minimal (20%), moderate (60%), or other (20%) impact on cancer care. All 8 sites report a government mandated lockdown with a median duration of 2.3 months (IQR .9-4.2 months). Impact of the lockdown on cancer care was reported as none (12.5%), minimal (12.5%), moderate (50%) and severe (25%). Additionally, we surveyed the impact of COVID-19 on resources in radiation, medical and surgical oncology services. A total of 25% of responders reported decreases in radiation resources while 37.5% reported changes in medical and surgical oncology resources. For radiation oncology, the most common impact was access to CT imaging for 3D-conformal planning (25%), access to brachytherapy (12.5%), and medical physics support (12.5%). For medical oncology, the most frequent impact was access to chemotherapy (37.5%) and blood products (12.5%), and loss of oncology ward space (12.5%). The most frequent impact for surgical oncology was access to operating rooms (37.5%), ventilators (12.5%), anesthesia (25%), blood products (25%), and other supply chain issues (25%). Of centers who reported impact on cancer care, severity of impact was none (50%) and moderate (50%) for radiation oncology; mild (25%) and moderate (75%) for medical oncology; and moderate (75%) and severe (25%) for surgical oncology.

Conclusion

Our survey identified diffuse impact of COVID-19 on all facets of cancer care across sub-Saharan Africa. Based on physician assessment of impact, the discipline of surgical oncology may be impacted the greatest. Additional studies measuring the impact of COVID-19 on cancer outcomes are ongoing.

A Monte Carlo study of I-125 prostate brachytherapy with gold nanoparticles: dose enhancement with simultaneous rectal dose sparing via radiation shielding

We investigate via Monte Carlo simulations a new ¹²⁵I brachytherapy treatment technique for high-risk prostate cancer patients via injection of Au nanoparticle (AuNP) directly into the prostate. The purpose of using the nanoparticles is to increase the therapeutic index via two synergistic effects: enhanced energy deposition within the prostate and simultaneous shielding of organs at risk from radiation escaping from the prostate. Both uniform and non-uniform concentrations of AuNP are studied. The latter are modeled considering the possibility of AuNP diffusion after the injection using brachy needles. We study two extreme cases of coaxial AuNP concentrations: centered on brachy needles and centered half-way between them. Assuming uniform distribution of 30 mg g^-1 of AuNP within the prostate, we obtain a dose enhancement larger than a factor of 2 to the prostate. Non-uniform concentration of AuNP ranging from 10 mg g^-1 and 66 mg g^-1 were studied. The higher the concentration in a given region of the prostate the greater is the enhancement therein. We obtain the highest dose enhancement when the brachytherapy needles are coincident with AuNP injection needles but, at the same time, the regions in the tail are colder (average dose ratio of 0.7). The best enhancement uniformity is obtained with the seeds in the tail of the AuNP distribution. In both uniform and non-uniform cases the urethra and rectum receive less than 1/3 dose compared to an analog treatment without AuNP. Remarkably, employing AuNP not only significantly increases dose to the target but also decreases dose to the neighboring rectum and even urethra, which is embedded within the prostate. These are mutually interdependent effects as more enhancement leads to more shielding and vice-versa. Caution must be paid since cold spot or hot spots may be created if the AuNP concentration versus seed position is not properly distributed respect to the seed locations.

Pathology and oncology in Africa: education and training for the future in cancer research– East African Regional Meeting

According to the World Health Organisation (WHO), deaths from non-communicable diseases (NCDs) will increase globally, with the largest increase being on the African continent. On our continent, projections have indicated that deaths from NCDs will exceed all combined communicable, maternal, perinatal and nutritional diseases as the most common causes of death by 2030. Hence, the importance of a functional and improved pathology system in the diagnosis of cancer cannot be debated.

Recently, the African Organization for Research and Training in Cancer (AORTIC) organised its East African regional meeting in Mwanza, Tanzania on 25–26 June 2015, with the focus being ‘Pathology and oncology: Education and training for the future in cancer research’. The main themes of the workshop were around improving cancer care and the role of twinning in Eastern Africa, in particular the Mwanza cancer project, telepathology, e-health and biobanking. The outcomes of a 2 day strategic meeting were developing an efficient and effective plan to guide the improvement in pathology training and cancer research in Africa.

Kilovoltage radiosurgery with gold nanoparticles for neovascular age-related macular degeneration (AMD): a Monte Carlo evaluation

This work uses Monte Carlo radiation transport simulation to assess the potential benefits of gold nanoparticles (AuNP) in the treatment of neovascular age-related macular degeneration with stereotactic radiosurgery. Clinically, a 100 kVp x-ray beam of 4 mm diameter is aimed at the macula to deliver an ablative dose in a single fraction. In the transport model, AuNP accumulated at the bottom of the macula are targeted with a source representative of the clinical beam in order to provide enhanced dose to the diseased macular endothelial cells. It is observed that, because of the AuNP, the dose to the endothelial cells can be significantly enhanced, allowing for greater sparing of optic nerve, retina and other neighboring healthy tissue. For 20 nm diameter AuNP concentration of 32 mg g(-1), which has been shown to be achievable in vivo, a dose enhancement ratio (DER) of 1.97 was found to be possible, which could potentially be increased through appropriate optimization of beam quality and/or AuNP targeting. A significant enhancement in dose is seen in the vicinity of the AuNP layer within 30 μm, peaked at the AuNP-tissue interface. Different angular tilting of the 4 mm beam results in a similar enhancement. The DER inside and in the penumbra of the 4 mm irradiation-field are almost the same while the actual delivered dose is more than one order of magnitude lower outside the field leading to normal tissue sparing. The prescribed dose to macular endothelial cells can be delivered using almost half of the radiation allowing reduction of dose to the neighboring organs such as retina/optic nerve by 49% when compared to a treatment without AuNP.

Targeted radiotherapy enhancement during electronic brachytherapy of accelerated partial breast irradiation (APBI) using controlled release of gold nanoparticles

Several studies have demonstrated low rates of local recurrence with brachytherapy-based accelerated partial breast irradiation (APBI). However, long-term outcomes on toxicity (e.g. telangiectasia) and cosmesis remain a major concern. The purpose of this study is to investigate the dosimetric feasibility of using targeted non-toxic radiosensitizing gold nanoparticles (GNPs) for localized dose enhancement to the planning target volume (PTV) during electronic brachytherapy APBI while reducing normal tissue toxicity. We propose to incorporate GNPs into a micrometer-thick polymer film on the surface of routinely used lumpectomy balloon applicators and provide subsequent treatment using a 50 kVp Xoft device. An experimentally determined diffusion coefficient was used to determine space-time customizable distribution of GNPs for feasible in-vivo concentrations of 7 mg/g and 43 mg/g. An analytical approach from previously published work was employed to estimate the dose enhancement due to GNPs as a function of distance up to 1 cm from the lumpectomy cavity surface. Clinically significant dose enhancement values of at least 1.2, due to 2 nm GNPs, were found at 1 cm away from the lumpectomy cavity wall when using electronic brachytherapy APBI. Higher customizable dose enhancement was also achieved at other distances as a function of nanoparticle size. Our preliminary results suggest that significant dose enhancement can be achieved to residual tumor cells targeted with GNPs during APBI with electronic brachytherapy.

Comprehensive quality assurance phantom for the small animal radiation research platform (SARRP)

PURPOSE

To develop and test the suitability and performance of a comprehensive quality assurance (QA) phantom for the Small Animal Radiation Research Platform (SARRP).

METHODS AND MATERIALS

A QA phantom was developed for carrying out daily, monthly and annual QA tasks including: imaging, dosimetry and treatment planning system (TPS) performance evaluation of the SARRP. The QA phantom consists of 15 (60 × 60 × 5 mm(3)) kV-energy tissue equivalent solid water slabs. The phantom can incorporate optically stimulated luminescence dosimeters (OSLD), Mosfet or film. One slab, with inserts and another slab with hole patterns are particularly designed for image QA.

RESULTS

Output constancy measurement results showed daily variations within 3%. Using the Mosfet in phantom as target, results showed that the difference between TPS calculations and measurements was within 5%. Annual QA results for the Percentage depth dose (PDD) curves, lateral beam profiles, beam flatness and beam profile symmetry were found consistent with results obtained at commissioning. PDD curves obtained using film and OSLDs showed good agreement. Image QA was performed monthly, with image-quality parameters assessed in terms of CBCT image geometric accuracy, CT number accuracy, image spatial resolution, noise and image uniformity.

CONCLUSIONS

The results show that the developed QA phantom can be employed as a tool for comprehensive performance evaluation of the SARRP. The study provides a useful reference for development of a comprehensive quality assurance program for the SARRP and other similar small animal irradiators, with proposed tolerances and frequency of required tests.