Single Fraction Treatment Research Articles

ALARA and IGRT in paediatric radiotherapy patients – A review

Purpose As low as reasonably achievable (ALARA) based protocols have been widely implemented to significant effect in diagnostic computed tomography (CT) scans for paediatric patients, but investigation of dose reduction techniques in paediatric cone beam CT (CBCT) IGRT are lacking. The purpose of this review is to report the level of dose from paediatric CBCT, the implications of this, and to investigate the potential for dose reduction. Methods A search and review of published studies investigating kV CBCT dose (in-field and out-of-field); long term effect of kV CBCT dose and dose reduction interventions was carried out. Dose studies included paediatric radiotherapy patients aged zero to nineteen years old, adult radiotherapy patients, and both paediatric and adult anthropomorphic phantoms. Results Nineteen articles were selected for review. Over a course of treatment using daily CBCT, the cumulative imaging dose can be comparable to the dose of a single treatment fraction and has the potential to be greater than peripheral doses from IMRT techniques. A number of dose reduction interventions have been proposed, which include: reducing tube energy and current; shielding radiosensitive structures; reducing the scan length/volume; reducing scan frequency; reducing rotational angle and using bow tie filters. Conclusion Paediatric patients are at an increased risk of developing second malignancies with daily CBCT. Particular consideration must be given to the use of CBCT in very young; female patients and close to radiosensitive structures. The imaging dose to these patients should be minimised, provided the image quality is sufficient for verification purposes.

33 Is hypofractionation safer than single-fraction radio surgery? The effect of fractionation on radionecrosis

Introduction: Radiation-induced brain necrosis (RN) is a relatively uncommon (5-20%) but potentially severe adverse effect of stereotactic radiosurgery (SRS) for brain metastasis(BM). We attempted to establish the effect of hypo-fractionation on RN rates by reviewing patients having simultaneous multi-fraction and single fraction treatment of BM at our centre. Methods: Patients receiving simultaneous 1 (20-24Gy) or 3 fraction (21-24Gy) SRS treatments were identified in our institution’s database. Serial post-SRS MRIs were reviewed to determine the lesion quotient (LQ), or maximum cross sectional area on T1 plus gadolinium divided by T2 FLAIR sequences. LQ less than 0.3 was considered RN. Result: Twenty-two patients were followed for a median 320 days. Sixteen patients developed radionecrosis in 21 of 62 lesions (33%), four of which were symptomatic (20%). Eleven of these lesions received 3 fractions and ten received one fraction. RN risk increased with increasing tumor volume (log odds ratio=1.12, p=0.04). There was no difference in incidence of RN in patients who received whole brain radiotherapy (WBRT) (p=0.11), hypo-fractionation (p=0.98) or had a higher maximum dose (p=0.71). Radiographic RN, however, did not clear in any patients who developed it. Eight patients developed a local recurrence (12%), six of which occurred in the single fraction group. Conclusion: Radionecrosis was significantly related to tumor volume but not fractionation, WBRT, or maximum dose. Overall, our results indicate patients receiving SRS for multiple brain metastasis have a higher rate of radionecrosis than the literature and poorer survival despite having equivalent local control.

Update of the systematic review of palliative radiation therapy fractionation for bone metastases

PurposeRadiation therapy is an effective modality for pain management of symptomatic bone metastases. We update the previous meta-analyses of randomized trials comparing single fraction to multiple fractions of radiation therapy in patients with uncomplicated bone metastases. MethodsA literature search was conducted in Ovid Medline, Embase, and Cochrane Central Register. Ten new randomized trials were identified since 2010, five with adequate and appropriate data for inclusion, resulting in a total of 29 trials that were analyzed. Forest plots based on each study’s odds ratios were computed using a random effects model and the Mantel–Haenszel statistic. ResultsIn intention-to-treat analysis, the overall response rate was similar in patients for single fraction treatments (61%; 1867/3059) and those for multiple fraction treatments (62%; 1890/3040). Similarly, complete response rates were nearly identical in both groups (23% vs 24%, respectively). Re-treatment was significantly more frequent in the single fraction treatment arm, with 20% receiving additional treatment to the same site versus 8% in the multiple fraction treatment arm (p < 0.01). No significant difference was seen in the risk of pathological fracture at the treatment site, rate of spinal cord compression at the index site, or in the rate of acute toxicity. ConclusionSingle fraction and multiple fraction radiation treatment regimens continue to demonstrate similar outcomes in pain control and toxicities, but re-treatment is more common for single fraction treatment patients.

A systematic review of palliative bone radiotherapy based on pain relief and retreatment rates.

Palliative radiotherapy has been shown to have effects on Quality of Life during painful bone metastasis. This review aimed to determine equivalence in pain relief (PR) and retreatment rate (RR) using both single and multi-fraction irradiations, based on evaluation of the trial's quality. We performed a systematic review since ICRU 50 Report (1993) to June 2017, then evaluated trials for reproducibility and good methodology criteria. We found five studies that were reproducible in both dose and volume prescription. One study used three-dimensional (3D) treatment planning. Equivalence between single and multi-fraction schedules was demonstrated for PR after 3 months, but a 2-3 time RR appeared after single-fraction schedules, notably in the first year after treatment (primarily during the first four months). Reserving long course therapy for well-preserved patients would allow for better long-term efficacy with lower RR, while altered patients would suffer less from single-fraction treatments. It appears that life expectancy might not be used as a criterion for this choice.

Myositis following spine radiosurgery for metastatic disease: a case series.

OBJECTIVE Spinal stereotactic body radiation therapy (SBRT) has emerged as an attractive method to deliver high doses of radiation to oligometastatic spinal tumors with radioresistant histology. Because SBRT is a palliative therapy, attention to potential radiation toxicities is paramount when counseling patients. The objective of this study was to report radiation-induced myositis after SBRT, a previously undescribed complication. METHODS A total of 667 patients received 891 spine SBRT treatments (either 24 Gy in 1 fraction or 27 Gy in 3 fractions) from 2011 to 2016 and underwent retrospective review. Eleven patients were identified as having radiographic evidence of myositis following SBRT. Clinical and pathologic results were collected, including receipt of anti-vascular endothelial growth factor (VEGF) therapy, radiation dose, equivalent dose in 2-Gy fractions (EQD2), biologically effective dose (BED), and volume of muscle treated. Treatment toxicities were classified according to the Common Terminology Criteria for Adverse Events (CTCAE; version 4.03). Univariate statistical analyses were performed to evaluate the relationships between radiation fractionation schedule and myositis and between anti-VEGF therapy and myositis. RESULTS The cumulative incidence of myositis was 1.9% at 1 year. The median of the mean dose administered to muscle with myositis was 17.5 Gy. The median EQD2 was 55.1 Gy, and the median BED was 82.7 Gy. The median time to the development of clinical symptoms was 1.4 months, while the median time to imaging evidence was 4.7 months. Two patients (18.2%) had CTCAE grade 3 complications. Single-fraction spine SBRT (HR 4.5, 95% CI 1.2-16.9; p = 0.027) was associated with increased risk of developing myositis whereas receipt of anti-VEGF therapy was not (HR 2.2, 95% CI 0.6-7.1; p = 0.2). CONCLUSIONS Radiation myositis following spinal radiosurgery is a rare but important complication. Single-fraction treatment schedules may be associated with increased risk of myositis but should be validated in a larger series.

Radiation Therapy Prophylaxis for Heterotopic Ossification in Non-Hip Sites

Background: Radiation therapy prophylaxis for heterotopic ossification is well-established for the hip, either pre or post-operatively. There is limited data for this treatment in non-hip sites. We report our institution’s experience. Methods: From October 2004 to August 2015, a total of 39 non-hip sites in 38 patients were treated with prophylactic radiation therapy for heterotopic ossification at our institution. An IRB approved retrospective review was performed. There were 15 patients who received treatments to the elbow, 13 to the knee (1 bilateral for a total of 14 knees), and 10 to other sites (leg stump (2), pubic symphysis (2), femur (1), foot (1), humerus stump (1), abdominal wall (1), shoulder (1), thigh (1)). All but 1 patient were treated with a single fraction treatment with 700 or 800 cGy. One patient received 2000 cGy in 10 fractions to the abdominal wall for heterotopic ossification extending from the xiphoid process. Results: Fifteen patients underwent treatment to the elbow with a median follow-up of 5 months (0 - 99). Median age for this group was 50 years (37 - 69). Nine (60.0%) patients had evidence of heterotopic ossification prior to surgery. All (100%) of the elbow patients were free from recurrence at last follow-up. There were no acute or late toxicities noted. For treatment to the knee, there were 4 (28.6%) recurrences, all in cases where there were pre-operative heterotopic ossification. There were two other recurrences in the non-hip, elbow or knee sites: one patient who received radiation therapy to the abdominal wall and one patient who underwent treatment to the thigh. Conclusions: Prophylactic radiation therapy with 700 cGy or 800 cGy in 1 fraction either before or after surgery remains a safe and effective treatment for both hip and most non-hip sites. Fractionated treatment may be used for larger treatment fields, however experience is limited.

Analysis of retreatment after radiotherapy for bone metastasis at a safety net hospital.

223 Background: The effectiveness of single fraction radiotherapy in the treatment of bone metastasis is firmly established by multiple prospective randomized controlled trials. These trials have also indicated a retreatment rate that is significantly higher for patients treated with single fraction radiotherapy. The reason for this is unclear. The prior studies have confirmed that there are no differences in any objective or subjective measure of response or durability of response. One proposed explanation may be a conscious or subconscious impact of practice based workload accounting for adopting a single fraction treatment strategy that may lead to excess retreatment prescription. In other words, does a decrease in workload accounting due to single fraction treatment lead to an increase in retreatment rates? Our large safety net teaching hospital follows a practice model where department funding is independent of workload accounting. We retrospectively reviewed our data on the radiotherapy of bone metastasis to see if this practice model had any impact on our retreatment rates. Methods: Between October 2012 and June 2017, 225 patients received treatment for 385 target lesions. All referred patients’ entire radiotherapy history was included whether or not it occurred during the target period. 196 target lesions received single fraction treatment and 189 received multiple fractions. 27 target lesions were retreated once and a single target lesion was retreated twice. Results: Target lesions treated with a single fraction resulted in a retreatment rate of 7.7% while multiple fraction treatment resulted in a retreatment rate of 6.4%. This difference was not statistically significant by Chi-Square analysis. Conclusions: Our retrospective analysis confirms no difference in retreatment rates between single and multi-fraction treatment. The retreatment rate is in agreement with the published response rate and introduces a possible explanation for the discordant rates observed in the published literature. Further analysis involving multiple practice models would help further explore these findings.

Gamma Knife Perfexion® radiosurgery and endo diode laser thermotherapy for choroidal melanoma with technical analysis: A case report.

Radiosurgery serves an important function in the treatment of patients with intraocular tumors and preserves visual function via organ conservation. Therefore, it is important to ensure the safety and precision of GK-SRS as a primary treatment for intraocular tumors. The present case study described a 57-year-old female with uveal melanoma treated with GK-SRS. Retrobulbar anesthesia following fixation of the treated eye, via the suture of two of the extraocular muscles to the stereotactic frame, was performed to immobilize the eye during treatment. Computed tomography (CT) scans were performed following eye fixation, immediately prior to and following GK-SRS, to validate the accuracy of the tumor localization. The eye movement analysis revealed that the gravity center point deviations of the tumor and lens during treatment were <0.110 mm. At least 95% of the tumor volume was covered by the prescription dose according to three sets of CT images. The patient underwent a trans pars plana vitrectomy owing to a right eye vitreous hemorrhage. A 37-month follow-up assessment revealed tumor shrinkage, and the disappearance of the serous retinal detachments was noted on the basis of ophthalmoscopy and orbital magnetic resonance imaging. No major complications developed during the follow-up period. Using our treatment protocol, GK-SRS is a non-invasive procedure which is used as a brief single fraction treatment for intraocular tumor. The eye fixation method used in the present study has high accuracy.

A prospective phase I comparison of toxicity and cosmesis outcomes of single-fraction IORT and hypofractionated radiotherapy with IORT boost in early-stage breast cancer

PurposeRadiation therapy is proven to reduce local recurrence in patients with early-stage breast cancer. To reduce toxicity, treatment time, and improve accuracy, intraoperative radiation therapy was used as definitive treatment or as a boost. The study's objective was to compare the short-term toxicity and cosmesis of single-fraction (SF) IORT and hypofractionated radiotherapy with IORT boost (HfB) given as definitive treatment. Methods and MaterialsBetween March 2011 and December 2013, 57 patients aged 45–91 years and 24 patients aged 43–83 years (total n = 81) with Stage 0–II were treated with SF or HfB (Mobetron, IntraOp Medical, Sunnyvale, CA). For SF treatment, 21 Gy was delivered using 4.5–6 cm applicators with electron energies from 6 to 12 MeV. For HfB, an intraoperative boost of 10 Gy was delivered using 4–7 cm applicators with energies from 4 to 12 MeV followed by whole-breast radiation with 40.5 Gy over 15 fractions. Toxicity was assessed at 2 weeks, 6 months, and 12 months per Radiation Therapy Oncology Group acute skin toxicity criteria and cosmesis. ResultsAt 12 months, SF and HfB were well tolerated by all patients with no Grade 3+ toxicity. At 1 year, Grade-2 toxicity was resolved. Ninety-eight percent of SF patients and ninety percent of HfB patients had 0–1 grade toxicity. In the SF and HfB groups, 100% of patients had excellent or good cosmesis at 12-month followup interval. The SF exhibited a more favorable cosmesis with a higher percentage of excellent scores compared with HfB (80.4% vs. 45%; p = 0.0033). ConclusionsAfter breast conservation surgery, SF or HfB may be an option for patients with early-stage breast cancer compared to conventional external beam radiotherapy.

The Effect of Vertebral Endplate Involvement on Spine Radiosurgery Outcomes

This study sought to evaluate local and adjacent vertebral body outcomes in patients treated with spine radiosurgery. The relationship between vertebral endplate involvement and clinical outcomes was also analyzed. 156 patients (361 spine segments and 452 endplates) with spine tumors treated with stereotactic body radiotherapy from January 2010 to December 2015 were retrospectively reviewed. Initial treatment fields were based on ASTRO consensus guidelines. Cox regression analysis was performed to search for possible predicting factors for time to local and adjacent vertebral body failure. Factors included endplate involvement, extraspinal extension of metastatic disease, fraction number, tumor histology (radioresistant vs. radiosensitive), performance status and gender. Median patient age was 66 years (range, 17-91 years), median follow-up was 7 months (range, 1-61 months). 16.8% of endplates reviewed had tumor involvement and fracture rate after radiosurgery was 7.5%. The overall local control rate was 85% at 6 months and 76% at 1 year. 57% of vertebral bodies received single fraction treatment (13-20 Gy), while 34% received three fraction treatment (range, 16-27 Gy), and 9% received five fraction treatment (25-40 Gy). Single fraction treatment was superior in terms of local control (p<0.05). Endplate involvement was significantly associated with adjacent vertebral body involvement (p<.05) and had a positive predictive value of 26%, and a mean time to adjacent failure of 23.5 months. Radiosurgery can achieve durable radiologic control of metastatic spinal disease with minimal toxicity. Endplate involvement may serve as a positive predictor for adjacent tumor spread.

The impact of different stereotactic radiation therapy regimens for brain metastases on local control and toxicity

PurposeStereotactic radiation therapy (SRT) enables focused, short course, high dose per fraction radiation delivery to brain tumors that are less ideal for single fraction treatment because of size, shape, or close proximity to sensitive structures. We sought to identify optimal SRT treatment regimens for maximizing local control while minimizing morbidity. Methods and materialsWe performed a retrospective review of patients treated with SRT for solid brain metastases using variable dose schedules between 2001 and 2011 at 3 academic hospitals. Endpoints included (1) local control, (2) acute toxicity (Common Toxicity Criteria for Adverse Events v3.0), and (3) symptomatic radionecrosis. Kaplan-Meier and a competing risks methodology were used to estimate the actuarial rate of local failure and assess the association of clinical and treatment covariates with time to local failure. ResultsA total of 156 patients was identified. Common tumor histologies included breast (21%), non-small cell lung (32%), melanoma (22%), small cell lung (9%), and renal cell carcinoma (6%). The majority of lesions were supratentorial (57%). Median target volume was 3.99 mL (range, 0.04-58.42). Median total SRT dose was 25 Gy (range, 12-36), median fractional dose was 5 Gy (range, 2.5-11), and median number of fractions was 5 (range, 2-10). Cumulative incidence of local progression at 3, 6, 12, 18, and 24 months was 11%, 22%, 29%, 34%, and 36%. Total prescription dose was the only factor significantly associated with time to local progression on univariate (P = .02) and multivariable analysis (P = .01, adjusted hazards ratio, 0.87). Five patients experienced seizures within 10 days of SRT and 5 patients developed radionecrosis. All patients with documented radionecrosis received prior radiation to the index lesion. ConclusionsOur series of SRT for brain metastases found total prescription dose to be the only factor associated with local control. Both acute and long-term toxicity events from SRT were modest.

Assessing the utilization of radiotherapy near end of life at a Finnish University Hospital: a retrospective cohort study

Background: Palliative radiotherapy can improve quality of life for cancer patients during the last months of life. However, very short life expectancy may devastate the benefit of the treatment. This single center study assesses the utilization of radiotherapy during the last weeks of life.Material and methods: All cancer patients (N = 38,982) treated with radiotherapy (N = 11,395) in Turku University Central Hospital during 2005–2013 were identified in the database consisting of electronic patient records. One fourth (N = 2904, 25.5%) of the radiotherapy treatments were given during the last year of life. The last radiotherapy treatments and the time from the last radiotherapy treatment to death were assessed in regards to patients’ age, cancer diagnosis, domicile, place of death and the treatment year. Treatments given during the last two weeks of life were also assessed regarding the goal of treatment and the reason for possible discontinuation.Results: The median time from the last fraction of radiotherapy to death was 84 d. During the last two weeks before death (N = 340), pain (29.4%) was the most common indication for radiotherapy. Treatment was discontinued in 40.6% of the patients during the last two weeks of life, and worsening of general condition was the most common reason for discontinuity (70.3%). The patients receiving radiotherapy during the last weeks of life were more likely to die in tertiary care unit. During the last year of life single-fraction treatment was used only in 7% of all therapy courses. There was a statistically significant (p < .05) decrease in the median number of fractions in the last radiotherapy treatment between 2005–2007 (8 fractions) and 2011–2013 (6 fractions).Conclusions: Up to 70% of the treatments during the last two weeks of life were not delivered to alleviate pain and utilization of single fraction radiotherapy during the last year of life was infrequent. These observations suggest that practice of radiotherapy during the last weeks of life should be revisited.

(P089) Comparison of Survival by Different Palliative Radiation Therapy Fractionation Schedules

Choice of palliative radiotherapy regimen has taken on greater importance in recent years with the 2013 ASTRO Choosing Wisely campaign recommending against protracted fractionation schemes for palliation of bone metastases and encouraging single-fraction treatment for appropriately selected patients. The aims of this project were to 1) determine survival based upon palliative fractionation scheme utilized and 2) determine additional factors which predict survival. We identified a cohort of 1292 patients (569 female, 723 male) treated with palliative intent from 2000-2014 who were treated according to one of four palliative treatment schedules: 37.5 Gy in 15 fractions (n= 318), 30 Gy in 10 fractions (n = 982), 20 Gy in 5 fractions (n = 262), 8 Gy in a single fraction (n = 139). Death dates were obtained from medical records, Social Security Death Index, and publicly-available obituaries. Performance status, marital status, burden of metastatic disease and insurance type were also noted. SAS was used to generate a multivariate model with time from treatment to death as a continuous dependent variable. We found that the length of treatment correlated directly with survival, with the exception of no significant difference between single-fraction and 5-fraction palliative regimens. Median survival was 13.4, 9.8, 7.0 and 6.9 months for 15, 10, 5 and single fraction treatments, respectively. Performance status and insurance status were also correlated with survival, with worse performance status and lack of insurance correlating with decreased survival. Given that patients receiving shorter courses of palliative radiotherapy have a shorter survival, this indicates we may be appropriately selecting shorter treatment for patients with limited survival. However, the lack of survival difference between patients treated with single-fraction and 5-fraction palliative regimens supports consideration of single-fraction treatment over 5-fraction treatment.

Considerations for Quality Improvement in Radiation Oncology Therapy for Patients with Uncomplicated Painful Bone Metastases.

Background: There is an increasing need for evidence-based efficiency in providing a growing amount of cancer care. One example of a quality gap is the use of multiple-fraction palliative radiation for patients with advanced cancer who have uncomplicated bone metastases; evidence suggests similar pain outcomes for treatment regimens with a lower burden of treatments. Methods: During the first phase of quality improvement work, we used RAND/UCLA appropriateness methodology to understand how radiation oncologists at one academic medical center rate the appropriateness of different treatment regimens for painful uncomplicated bone metastases. We compared radiation oncologist appropriateness ratings for radiation treatments with radiation therapy provided by these oncologists to patients with painful bone metastases between July 2012 and June 2013. Results: Appropriateness ratings showed that single-fraction (8 Gy) treatment (a low burden treatment) was consistently considered an appropriate option to treat a variety of uncomplicated bone metastases. The use of >10 fractions was consistently rated as inappropriate regardless of other factors. Eighty-one patients receiving radiation therapy for painful bone metastases during the study period had an available medical record for chart abstraction. Almost one-third of metastases were considered complicated because of a concern of spinal cord compression, a history of prior irradiation, or an associated pathological fracture. Among uncomplicated bone metastases, 25% were treated with stereotactic body radiation treatment (SBRT). Among the 54 uncomplicated bone metastases treated with conformal radiation, only one was treated with single-fraction treatment and 32% were treated with greater than 10 fractions. Conclusions: Treatment at the study site demonstrates room for improvement in providing low-burden radiation oncology treatments for patients with painful bone metastases. Choosing a radiation treatment schedule for patients with advanced cancer and painful bone metastases requires consideration of many medical and patient-centered factors. Our experience suggests that it will take more than the existence of guidelines to change practice in this area.

Clinical efficacy and safety of surface imaging guided radiosurgery (SIG-RS) in the treatment of benign skull base tumors.

Frameless, surface imaging guided radiosurgery (SIG-RS) is a novel platform for stereotactic radiosurgery (SRS) wherein patient positioning is monitored in real-time through infra-red camera tracking of facial topography. Here we describe our initial clinical experience with SIG-RS for the treatment of benign neoplasms of the skull base. We identified 48 patients with benign skull base tumors consecutively treated with SIG-RS at a single institution between 2009 and 2011. Patients were diagnosed with meningioma (n = 22), vestibular schwannoma (n = 20), or nonfunctional pituitary adenoma (n = 6). Local control and treatment-related toxicity were retrospectively assessed. Median follow-up was 65 months (range 61-72 months). Prescription doses were 12-13Gy in a single fraction (n = 18), 8Gy × 3 fractions (n = 6), and 5Gy × 5 fractions (n = 24). Actuarial tumor control rate at 5 years was 98%. No grade ≥3 treatment-related toxicity was observed. Grade ≤2 toxicity was associated with symptomatic lesions (p = 0.049) and single fraction treatment (p = 0.005). SIG-RS for benign skull base tumors produces clinical outcomes comparable to conventional frame-based SRS techniques while enhancing patient comfort.

Investigating the surface dose contribution of intrafractional kV imaging in CyberKnife-based stereotactic radiosurgery

CyberKnife treatment consists of hundreds of noncoplanar beams and numerous intrafractional images that can be taken during a single treatment fraction; thus, doses because of imaging should be considered in this technique. The aim of this study is to investigate the in-field and out-of-field surface doses induced from kV imaging system during stereotactic radiosurgery (SRS) treatment. The imaging-induced surface doses were measured at the center of the imaging field and within ±15-cm distance from the center in both craniocaudal and lateral directions. TLD100H thermoluminescence dosimeters and EBT2 gafchromic films were used to take the measurements at the locations of 0, ±5, ±10, and ±15 cm in the 2 orthogonal directions on abdominal region of a Rando phantom. The surface dose contributions of imaging system for the 4 most commonly used energy options of 90, 100, 110, and 120 kVp with 3 mAs options of 10, 30, and 90 mAs were measured and compared. Imaging dose values have a positive correlation with both parameters of energy and mAs. The energy options of 100, 110, and 120 kVp, in average, induced 60%, 101%, and 141% more doses per mAs than 90 kVp energy in the imaging field center. A threefold increase in mAs values, i.e., from 10 mAs to 30 mAs and from 30 mAs to 90 mAs, caused higher dose in field center with a factor of 2.53 ± 0.08 when the energy value was kept constant. The in-field dose distributions within ±10 cm in both directions showed a flat pattern with a standard deviation lower than 5%, whereas the out-of-field doses at ±15-cm distance from the field center suddenly dropped to almost half of the central doses. Although a single imaging attempt causes a very low dose compared with the therapeutic dose level, one should be aware of the cumulative surface dose increase with higher imaging number. Proper patient setup, fiducial usage, and reduction of both the mAs values and the imaging numbers should be, therefore, considered to keep the cumulative surface dose in a lower level.

On the use of volumetric-modulated arc therapy for single-fraction thoracic vertebral metastases stereotactic body radiosurgery

To retrospectively evaluate quality, efficiency, and delivery accuracy of volumetric-modulated arc therapy (VMAT) plans for single-fraction treatment of thoracic vertebral metastases using image-guided stereotactic body radiosurgery (SBRS) after RTOG 0631 dosimetric compliance criteria. After obtaining credentialing for MD Anderson spine phantom irradiation validation, 10 previously treated patients with thoracic vertebral metastases with noncoplanar hybrid arcs using 1 to 2 3D-conformal partial arcs plus 7 to 9 intensity-modulated radiation therapy beams were retrospectively re-optimized with VMAT using 3 full coplanar arcs. Tumors were located between T2 and T12. Contrast-enhanced T1/T2-weighted magnetic resonance images were coregistered with planning computed tomography and planning target volumes (PTV) were between 14.4 and 230.1cc (median = 38.0cc). Prescription dose was 16Gy in 1 fraction with 6MV beams at Novalis-TX linear accelerator consisting of micro multileaf collimators. Each plan was assessed for target coverage using conformality index, the conformation number, the ratio of the volume receiving 50% of the prescription dose over PTV, R50%, homogeneity index (HI), and PTV_1600 coverage per RTOG 0631 requirements. Organs-at-risk doses were evaluated for maximum doses to spinal cord (D0.03cc, D0.35cc), partial spinal cord (D10%), esophagus (D0.03cc and D5cc), heart (D0.03cc and D15cc), and lung (V5, V10, and maximum dose to 1000cc of lung). Dose delivery efficiency and accuracy of each VMAT-SBRS plan were assessed using quality assurance (QA) plan on MapCHECK device. Total beam-on time was recorded during QA procedure, and a clinical gamma index (2%/2mm and 3%/3mm) was used to compare agreement between planned and measured doses. All 10 VMAT-SBRS plans met RTOG 0631 dosimetric requirements for PTV coverage. The plans demonstrated highly conformal and homogenous coverage of the vertebral PTV with mean HI, conformality index, conformation number, and R50% values of 0.13 ± 0.03 (range: 0.09 to 0.18), 1.03 ± 0.04 (range: 0.98 to 1.09), 0.81 ± 0.06 (range: 0.72 to 0.89), and 4.2 ± 0.94 (range: 2.7 to 5.4), respectively. All 10 patients met protocol guidelines with maximum dose to spinal cord (average: 8.83 ± 1.9Gy, range: 5.9 to 10.9Gy); dose to 0.35cc of spinal cord (average: 7.62 ± 1.7Gy, range: 5.4 to 9.6Gy); and dose to 10% of partial spinal cord (average 6.31 ± 1.5Gy, range: 3.5 to 8.5Gy) less than 14, 10, and 10Gy, respectively. For all 10 patients, the maximum dose to esophagus (average: 9.41 ± 4.3Gy, range: 1.5 to 14.9Gy) and dose to 5cc of esophagus (average: 7.43 ± 3.8Gy, range: 1.1 to 11.8Gy) were kept less than protocol requirements 16Gy and 11.9Gy, respectively. In a similar manner, all 10 patients met protocol compliance criteria with maximum dose to heart (average: 4.62 ± 3.5Gy, range: 1.3 to 10.2Gy) and dose to 15cc of heart (average: 2.23 ± 1.8Gy, range: 0.3 to 5.6Gy) less than 22 and 16Gy, respectively. The dose to the lung was retained much lower than protocol guidelines for all 10 patients. The total number of monitor units was, on average, 6919 ± 1187. The average beam-on time was 11.5 ± 2.0 minutes. The VMAT plans demonstrated dose delivery accuracy of 95.8 ± 0.7%, on average, for clinical gamma passing rate with 2%/2mm criteria and 98.3 ± 0.8%, on average, with 3%/3mm criteria. All VMAT-SBRS plans were considered clinically acceptable per RTOG 0631 dosimetric compliance criteria. VMAT planning provided highly conformal and homogenous dose distributions for the lower-dose vertebral PTV and the spinal cord as well as organs-at-risk such as esophagus, heart, and lung. Higher QA pass rates and shorter beam-on time suggest that VMAT-SBRS is a clinically feasible, fast, and effective treatment option for patients with thoracic vertebral metastases.

Clinical Efficacy and Safety of Surface Imaging Guided Radiosurgery in the Treatment of Benign Skull Base Tumors

Frameless, surface imaging guided radiosurgery (SIG-RS) is a novel platform for stereotactic radiosurgery (SRS) wherein patient positioning is monitored in real-time through infra-red camera tracking of facial topography. Here we describe our initial clinical experience with SIG-RS for the treatment of benign neoplasms of the skull base. We identified 48 patients with benign skull base tumors consecutively treated with SIG-RS at a single institution between 2009 and 2011. Patients were diagnosed with meningioma (n = 22), vestibular schwannoma (n = 20), or nonfunctional pituitary adenoma (n = 6). Local control and treatment-related toxicity were retrospectively assessed. Median follow-up was 65 months (range 61–72 months). Prescription doses were 12–13 Gy in a single fraction (n = 18), 8 Gy × 3 fractions (n = 6), and 5 Gy × 5 fractions (n = 24). Actuarial tumor control rate at 5 years was 98%. No grade ≥3 treatment-related toxicity was observed. Grade ≤2 toxicity was associated with symptomatic lesions (p = 0.049) and single fraction treatment (p = 0.005). SIG-RS for benign skull base tumors produces clinical outcomes comparable to conventional frame-based SRS techniques while enhancing patient comfort.

SU‐F‐T‐212: A Comparison of Treatment Strategies for Intracranial Stereotactic Radiosurgery

Purpose:Stereotactic radiosurgery is an effective and noninvasive treatment for intracranial lesions that uses highly focused radiation beams in a single treatment fraction. The purpose of this study is to investigate the dosimetric differences between the treatment brain metastasis with a proton beam vs. intensity modulated radiation therapy (IMRT).Methods:Ten separate brain metastasis targets where chosen and treatment plans were created for each, using three different strategies: custom proton beam shaping devices, standardized proton beam shaping devices, and IMRT. Each plan was required to satisfy set parameters for providing adequate coverage and minimizing risk to adjacent tissues. The effectiveness of each plan was calculated by comparing the homogeneity index, conformity index, and V12 for each target using a paired one tailed T‐test (α=0.05). Specific comparison of the conformity indices was also made using a subcategory containing targets with volume&gt;1cc.Results:There was no significant difference between the homogeneity indices of the three plans (p&gt;0.05), showing that each plan has the capability of adequately covering the targets. There was a statistically significant difference (p&lt;0.01) between the conformity indices of the custom and the standard proton plan, as with the custom proton and IMRT (p&lt;0.01), with custom proton showing stronger conformity to the target in both cases. There was also a statistical difference between the V12 of all three plans (Custom v. Standardized: p=0.02, Custom v. IMRT: p&lt;0.01, Standardized v. IMRT: p&lt;0.01) with custom proton supplying the lowest dose to surrounding tissues. For large targets (volume&gt;1cc) there was no statistical difference between the proton plans and the IMRT treatment for the conformity index.Conclusion:A custom proton plan is the recommended treatment explored in this study as it is the most reliable way of effectively treating the target while sparing the maximum amount of normal tissue.

The Application of Human Factor and System Engineering in Understanding Hardware and Software Errors at the Odette Cancer Centre

Purpose/Aim: An urban cancer centre treats approximately 10000 courses of radiation therapy each year. 600 of these courses can be considered single fraction treatments, often administered for palliation. Although a small subset of a centre’s workload, these treatments can present a number of technical, clinical and social factors which may complicate the care of this patient population. Studies have indicated an association between this complexity and increased palliative radiation therapy error rates. The systems approach to improving quality and safety involves identifying this complex interplay of factors and mitigating the effects of the factors using strategic improvements. Method/Process: A clinically significant incident in which a patient receiving large dose single fraction treatments of palliative radiation was identified, incident analysis performed and a number of action items identified. This quality initiative focused on the implementation of a pretreatment checklist for high risk treatments. This checklist highlighted a number of risk factors often associated with single fraction patients including; laterality; previous tattoos; shifts; premedication; imaging considerations and other potential difficulties. A staff survey was performed to assess, usability, compliance, and confidence with the tool. Results/Benefits/Challenges: Of the staff surveyed (n1⁄427). 90.0% had used the checklist in their practice, identifying a usage rate of 78.4% of single fraction patients. The largest barriers to use identified included inadequate time and patients not viewed as enough of a risk. Staff identified that previous tattoos and shifts were the largest factors influencing their confidence that their patients were properly prepared for treatment; whereas identifying an imaging plan was noted as having the least influencing on their confidence. Conclusion/Impact/Outcomes: Incident analysis has identified the need for consideration of complexity and workload factors in designing process improvements for the delivery of safe care in palliative radiation therapy. The applied intervention of the high risk pre-treatment checklist resulted in a global confidence score of 71.1% for all items surveyed. Process improvements have the potential to improve the quality and safety of palliative radiation treatments and these improvements can arguably be applied to all aspects of radiation delivery.