Stereotactic ablative radiotherapy before resection to avoid delay for early-stage lung cancer or oligometastases during the COVID-19 pandemic: Pathologic outcomes from the SABR-BRIDGE protocol.

BACKGROUND: During coronavirus disease 2019 (COVID-19)-related operating room closures, some multidisciplinary thoracic oncology teams adopted a paradigm of stereotactic ablative radiotherapy (SABR) as a bridge to surgery, an approach called SABR-BRIDGE. This study presents the preliminary surgical and pathological results. METHODS: Eligible participants from four institutions (three in Canada and one in the United States) had early-stage presumed or biopsy-proven lung malignancy that would normally be surgically resected. SABR was delivered using standard institutional guidelines, with surgery >3 months following SABR with standardized pathologic assessment. Pathological complete response (pCR) was defined as absence of viable cancer. Major pathologic response (MPR) was defined as ≤10% viable tissue. RESULTS: Seventy-two patients underwent SABR. Most common SABR regimens were 34 Gy/1 (29%, n = 21), 48 Gy/3-4 (26%, n = 19), and 50/55 Gy/5 (22%, n = 16). SABR was well-tolerated, with one grade 5 toxicity (death 10 days after SABR with COVID-19) and five grade 2-3 toxicities. Following SABR, 26 patients underwent resection thus far (13 pending surgery). Median time-to-surgery was 4.5 months post-SABR (range, 2-17.5 months). Surgery was reported as being more difficult because of SABR in 38% (n = 10) of cases. Thirteen patients (50%) had pCR and 19 (73%) had MPR. Rates of pCR trended higher in patients operated on at earlier time points (75% if within 3 months, 50% if 3-6 months, and 33% if ≥6 months; p = .069). In the exploratory best-case scenario analysis, pCR rate does not exceed 82%. CONCLUSIONS: The SABR-BRIDGE approach allowed for delivery of treatment during a period of operating room closure and was well-tolerated. Even in the best-case scenario, pCR rate does not exceed 82%.

Stereotactic Radiation for the Comprehensive Treatment of Oligometastases (SABR-COMET): Extended Long-Term Outcomes.

PURPOSE: Long-term randomized data assessing the effect of ablative therapies in patients with oligometastases are lacking. The Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastases (SABR-COMET) randomized phase 2 trial was originally designed with 5 years of follow-up, but the trial was amended in 2016 to extend follow-up to 10 years. Herein we report oncologic outcomes beyond 5 years. METHODS AND MATERIALS: Patients were eligible if they had a controlled primary tumor and 1 to 5 metastases, with all metastases amenable to SABR. Patients were randomized in a 1:2 ratio between palliative standard-of-care treatment (control arm) versus SABR to all metastases plus standard of care (SABR arm). The primary endpoint was overall survival (OS) and secondary endpoints included progression-free survival (PFS), toxicity, quality of life (using the Functional Assessment of Cancer Therapy: General [FACT-G]), and time to new metastases. RESULTS: Ninety-nine patients were randomized between 2012 and 2016 (n = 33 in arm 1 vs n = 66 in arm 2). Primary tumor sites included lung (n = 18), breast (n = 18), colon (n = 18), prostate (n = 16), and other (n = 29). Eight-year OS was 27.2% in the SABR arm versus 13.6% in the control arm (hazard ratio, 0.50; 95% confidence interval, 0.30-0.84; P = .008). Eight-year PFS estimates were 21.3% versus 0.0%, respectively (hazard ratio, 0.45; 95% confidence interval, 0.28-0.72; P < .001). Rates of grade ≥ 2 acute or late toxic effects were 30.3% versus 9.1% (P = .019), with no new grade 3 to 5 toxic effects. FACT-G quality of life scores declined over time in both arms, but there were no differences in quality of life scores between arms. The use of systemic therapy overall was similar between arms, but patients in the SABR arm were less likely to require cytotoxic chemotherapy (33.3% vs 54.6%, respectively, P = .043). CONCLUSIONS: SABR achieved durable improvements in OS and PFS, with no new major toxicity signals with extended follow-up. A minority of patients randomized to the SABR arm (21.3%) achieved > 5 years of survival without recurrence.

Radiation-Induced Fibrosis in Patients with Head and Neck Cancer: A Review of Pathogenesis and Clinical Outcomes.

Radiotherapy-related fibrosis remains one of the most challenging treatment related side effects encountered by patients with head and neck cancer. Several established and ongoing novel therapies have been studied with paucity of data in how to best treat these patients. This review aims to provide researchers and health care providers with a comprehensive review on the presentation, etiology, and therapeutic options for this serious condition.

Is SABR Cost-Effective in Oligometastatic Cancer? An Economic Analysis of the SABR-COMET Randomized Trial.

PURPOSE: The phase 2 randomized study SABR-COMET demonstrated that in patients with controlled primary tumors and 1 to 5 oligometastatic lesions, SABR was associated with improved progression-free survival (PFS) compared with standard of care (SoC), but with higher costs and treatment-related toxicities. The aim of this study was to assess the cost-effectiveness of SABR versus SoC in this setting. METHODS AND MATERIALS: A Markov model was constructed to perform a cost-utility analysis from the Canadian health care system perspective. Utility values and transition probabilities were derived from individual-level data from the SABR-COMET trial. One-way, 2-way, and probabilistic sensitivity analyses were performed. Costs were expressed in 2018 CAD. A separate analysis based on US payer's perspective was performed. An incremental cost-effectiveness ratio (ICER) at a willingness-to-pay threshold of $100,000 per quality-adjusted life year (QALY) was used. RESULTS: In the base case scenario, SABR was cost-effective at an ICER of $37,157 per QALY gained. This finding was most sensitive to the number of metastatic lesions treated with SABR (ICER: $28,066 per QALY for 2, increasing to $64,429 per QALY for 5), difference in chemotherapy use (ICER: $27,173-$53,738 per QALY), and PFS hazard ratio (HR) between strategies (ICER: $31,548-$53,273 per QALY). Probabilistic sensitivity analysis revealed that SABR was cost-effective in 97% of all iterations. Two-way sensitivity analysis demonstrated a nonlinear relationship between the number of lesions and the PFS HR. To maintain cost-effectiveness for each additional metastasis, the HR must decrease by approximately 0.047. The US cost analysis yielded similar results, with an ICER of $54,564 (2018 USD per QALY) for SABR. CONCLUSIONS: SABR is cost-effective for patients with 1 to 5 oligometastatic lesions compared with SoC.

Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers: Long-Term Results of the SABR-COMET Phase II Randomized Trial.

PURPOSE: The oligometastatic paradigm hypothesizes that patients with a limited number of metastases may achieve long-term disease control, or even cure, if all sites of disease can be ablated. However, long-term randomized data that test this paradigm are lacking. METHODS: We enrolled patients with a controlled primary malignancy and 1-5 metastatic lesions, with all metastases amenable to stereotactic ablative radiotherapy (SABR). We stratified by the number of metastases (1-3 v 4-5) and randomized in a 1:2 ratio between palliative standard-of-care (SOC) treatments (arm 1) and SOC plus SABR (arm 2). We used a randomized phase II screening design with a primary end point of overall survival (OS), using an α of .20 (wherein P < .20 indicates a positive trial). Secondary end points included progression-free survival (PFS), toxicity, and quality of life (QOL). Herein, we present long-term outcomes from the trial. RESULTS: Between 2012 and 2016, 99 patients were randomly assigned at 10 centers internationally. The most common primary tumor types were breast (n = 18), lung (n = 18), colorectal (n = 18), and prostate (n = 16). Median follow-up was 51 months. The 5-year OS rate was 17.7% in arm 1 (95% CI, 6% to 34%) versus 42.3% in arm 2 (95% CI, 28% to 56%; stratified log-rank P = .006). The 5-year PFS rate was not reached in arm 1 (3.2%; 95% CI, 0% to 14% at 4 years with last patient censored) and 17.3% in arm 2 (95% CI, 8% to 30%; P = .001). There were no new grade 2-5 adverse events and no differences in QOL between arms. CONCLUSION: With extended follow-up, the impact of SABR on OS was larger in magnitude than in the initial analysis and durable over time. There were no new safety signals, and SABR had no detrimental impact on QOL.

A guide to 90Y radioembolization and its dosimetry.

Radioembolization gains continuous traction as a primarily palliative radiation treatment for hepatic tumours. A form of nuclear medicine therapy, Yttrium-90 containing microspheres are catheter guided and injected into the right, left, or a specifically selected hepatic artery. A multitude of comprehensive planning steps exist to ensure a thorough and successful treatment. Clear clinical and physiological guidelines have been established and nuclear imaging is used to plan and verify dose distributions. Radioembolization's treatment rationale is based on tumour and blood vessel dynamics that allow a targeted treatment approach. However, radioembolization's dosimetry is grossly oversimplified. In fact, the currently utilized clinical dosimetric standards (e.g. partition method) have persisted since the 1990s. Moreover, the multitude of radioembolization's intertwining components lies disjointed within the literature. Particularly relevant to new readers, this review provides a methodical guide that presents the treatment rationale behind every clinical step. The emerging dosimetry methods and its factors are further discussed to provide a comprehensive review on an essential research direction.

Quality of Life Outcomes After Stereotactic Ablative Radiation Therapy (SABR) Versus Standard of Care Treatments in the Oligometastatic Setting: A Secondary Analysis of the SABR-COMET Randomized Trial.

PURPOSE: Randomized data assessing the longitudinal quality of life (QoL) impact of stereotactic ablative radiation therapy (SABR) in the oligometastatic setting are lacking. METHODS AND MATERIALS: We enrolled patients who had a controlled primary malignancy with 1 to 5 metastatic lesions, with good performance status and life expectancy >6 months. We randomized in a 1:2 ratio between standard of care (SOC) treatment (SOC arm) and SOC plus SABR to all metastatic lesions (SABR arm). QoL was measured using the Functional Assessment of Cancer Therapy-General. QoL changes over time and between groups were assessed with linear mixed modeling. RESULTS: Ninety-nine patients were randomized. Median age was 68 years (range, 43-89), and 60% were male. The most common primary tumor types were breast (n = 18), lung (n = 18), colorectal (n = 18), and prostate (n = 16). Most patients (n = 92) had 1 to 3 metastases. Median follow-up was 26 months. Because of the previously reported inferior survival of the SOC arm, the time for attrition in QoL respondents to <10% of subjects was shorter in the SOC versus SABR arm (30 vs 42 months). In the whole cohort, QoL declined over time after randomization: There were significant declines in total Functional Assessment of Cancer Therapy-General score over time compared with baseline (P < .001) owing to declines in physical and functional subscales (both P < .001), with no declines in social and emotional subscales. However, the magnitudes of decline were small, and clinically meaningful changes were not seen at most time points. Comparison between arms showed no differences in QoL between the SABR and SOC arms in total score (P = .42) or in the physical (P = .98), functional (P = .59), emotional (P = .82), or social (P = .17) subscales. CONCLUSIONS: For patients with oligometastases, average QoL declines slowly over time regardless of treatment approach, although the changes are small in magnitude. The use of SABR, compared with SOC, was not associated with a QoL detriment.

Safety and Feasibility of Using Magnetic Resonance Imaging Criteria to Identify Patients With "Good Prognosis" Rectal Cancer Eligible for Primary Surgery: The Phase 2 Nonrandomized QuickSilver Clinical Trial.

IMPORTANCE: Chemoradiotherapy (CRT), followed by surgery, is the recommended approach for stage II and III rectal cancer. While CRT decreases the risk of local recurrence, it does not improve survival and leads to poorer functional outcomes than surgery alone. Therefore, new approaches to better select patients for CRT are important. OBJECTIVE: To conduct a phase 2 study to evaluate the safety and feasibility of using magnetic resonance imaging (MRI) criteria to select patients with "good prognosis" rectal tumors for primary surgery. DESIGN, SETTING, AND PARTICIPANTS: Prospective nonrandomized phase 2 study at 12 high-volume colorectal surgery centers across Canada. From September 30, 2014, to October 21, 2016, a total of 82 patients were recruited for the study. Participants were patients newly diagnosed as having rectal cancer with MRI-predicted good prognosis rectal cancer. The MRI criteria for good prognosis tumors included distance to the mesorectal fascia greater than 1 mm; definite T2, T2/early T3, or definite T3 with less than 5 mm of extramural depth of invasion; and absent or equivocal extramural venous invasion. INTERVENTIONS: Patients with rectal cancer with MRI-predicted good prognosis tumors underwent primary surgery. MAIN OUTCOMES AND MEASURES: The primary outcome was the proportion of patients with a positive circumferential resection margin (CRM) rate. Assuming a 10% baseline probability of a positive CRM, a sample size of 75 was estimated to yield a 95% CI of ±6.7%. RESULTS: Eighty-two patients (74% male) participated in the study. The median age at the time of surgery was 66 years (range, 37-89 years). Based on MRI, most tumors were midrectal (65% [n = 53]), T2/early T3 (60% [n = 49]), with no suspicious lymph nodes (63% [n = 52]). On final pathology, 91% (n = 75) of tumors were T2 or greater, 29% (n = 24) were node positive, and 59% (n = 48) were stage II or III. The positive CRM rate was 4 of 82 (4.9%; 95% CI, 0.2%-9.6%). CONCLUSIONS AND RELEVANCE: The use of MRI criteria to select patients with good prognosis rectal cancer for primary surgery results in a low rate of positive CRM and suggests that CRT may not be necessary for all patients with stage II and III rectal cancer. TRIAL REGISTRATION: ISRCTN.com identifier: ISRCTN05107772.

Stereotactic ablative radiotherapy versus standard of care palliative treatment in patients with oligometastatic cancers (SABR-COMET): a randomised, phase 2, open-label trial.

BACKGROUND: The oligometastatic paradigm suggests that some patients with a limited number of metastases might be cured if all lesions are eradicated. Evidence from randomised controlled trials to support this paradigm is scarce. We aimed to assess the effect of stereotactic ablative radiotherapy (SABR) on survival, oncological outcomes, toxicity, and quality of life in patients with a controlled primary tumour and one to five oligometastatic lesions. METHODS: This randomised, open-label phase 2 study was done at 10 hospitals in Canada, the Netherlands, Scotland, and Australia. Patients aged 18 or older with a controlled primary tumour and one to five metastatic lesions, Eastern Cooperative Oncology Group score of 0-1, and a life expectancy of at least 6 months were eligible. After stratifying by the number of metastases (1-3 vs 4-5), we randomly assigned patients (1:2) to receive either palliative standard of care treatments alone (control group), or standard of care plus SABR to all metastatic lesions (SABR group), using a computer-generated randomisation list with permuted blocks of nine. Neither patients nor physicians were masked to treatment allocation. The primary endpoint was overall survival. We used a randomised phase 2 screening design with a two-sided α of 0·20 (wherein p<0·20 designates a positive trial). All analyses were intention to treat. This study is registered with ClinicalTrials.gov, number NCT01446744. FINDINGS: 99 patients were randomised between Feb 10, 2012, and Aug 30, 2016. Of 99 patients, 33 (33%) were assigned to the control group and 66 (67%) to the SABR group. Two (3%) patients in the SABR group did not receive allocated treatment and withdrew from the trial; two (6%) patients in the control group also withdrew from the trial. Median follow-up was 25 months (IQR 19-54) in the control group versus 26 months (23-37) in the SABR group. Median overall survival was 28 months (95% CI 19-33) in the control group versus 41 months (26-not reached) in the SABR group (hazard ratio 0·57, 95% CI 0·30-1·10; p=0·090). Adverse events of grade 2 or worse occurred in three (9%) of 33 controls and 19 (29%) of 66 patients in the SABR group (p=0·026), an absolute increase of 20% (95% CI 5-34). Treatment-related deaths occurred in three (4·5%) of 66 patients after SABR, compared with none in the control group. INTERPRETATION: SABR was associated with an improvement in overall survival, meeting the primary endpoint of this trial, but three (4·5%) of 66 patients in the SABR group had treatment-related death. Phase 3 trials are needed to conclusively show an overall survival benefit, and to determine the maximum number of metastatic lesions wherein SABR provides a benefit. FUNDING: Ontario Institute for Cancer Research and London Regional Cancer Program Catalyst Grant.

NRG Oncology/RTOG 0438: A Phase 1 Trial of Highly Conformal Radiation Therapy for Liver Metastases.

PURPOSE: This study aimed to determine the feasibility and maximally tolerated dose of hypofractionated, conformal radiation therapy (RT) in patients with liver metastases. METHODS AND MATERIALS: Nonsurgical patients with ≤5 liver metastases (sum of maximal diameter of all lesions ≤8 cm) were included in the study. There were 4 dose levels: 35 Gy, 40 Gy (starting level), 45 Gy, and 50 Gy, in 10 fractions. The clinical target volume included metastases identified on contrast computed tomography or magnetic resonance imaging with a 5-mm margin within the liver. The planning target volume margin ranged from 4 to 30 mm, depending on breathing motion. Dose-limiting toxicities were defined as RT-related grade ≥4 hepatic or gastrointestinal toxicities or thrombocytopenia occurring within 90 days of the start of RT. RESULTS: A total of 26 patients with metastases from colorectal (8 patients), breast (7 patients) and other malignancies (11 patients) were enrolled between November 2005 and December 2010. Twenty-three patients were evaluable (8, 7, and 8 on the 40, 45, and 50 Gy dose levels, respectively). Two patients assigned to 50 Gy received 35 Gy owing to normal tissue limits, so 2 additional patients were treated to 50 Gy. There were no dose-limiting toxicities on any of the dose levels. On the 45 Gy dose level, 1 patient developed reversible grade 3 enteritis (37 days from RT start) and diarrhea (22 days); another patient developed grade 3 lymphopenia (23 days). At the 50 Gy dose level, 1 patient had grade 3 hyperglycemia (74 days), and another patient developed grade 3 lymphopenia (13 days), colonic hemorrhage (325 days), and colonic gastrointestinal obstruction (325 days). With a potential median follow-up of 66.1 months (range, 34.6-89.0 months), no other late toxicities were observed. CONCLUSIONS: Treatment of liver metastases with 50 Gy in 10 fractions was feasible and safe in a multi-institutional setting.

Comparison of survival and prognostic factors in patients treated with stereotactic body radiotherapy for oligometastases or oligoprogression.

BACKGROUND AND PURPOSE: Clinical challenges arise in the oligoprogressive (OP) state with little evidence to support the use of ablative strategies. Our aim is to report on outcomes and prognostic variables following stereotactic body radiotherapy (SBRT) for OP and oligometastases (OM). MATERIAL AND METHODS: Overall (OS) and progression-free survivals (PFS) were calculated for 163 patients for 209 lesions (106 OM and 57 OP) treated with SBRT over 9 years. OS and PFS comparisons were calculated using the Kaplan-Meier actuarial survival and log rank methods. Uni, multi-variate analyses and cumulative incidences of local failure were performed using the Cox modelling and Gray's test respectively. RESULTS: The median OS and PFS was 37 and 15 months versus 21.7 and 6.4 months in the OM and OP groups respectively (P = 0.02 and P = 0.01). Performance status (⩾2 HR 2.95) and number of metastases (1/2 vs ⩾3 HR 1.88) were independent prognosticators for survival. The 1/2-year PFS were 55%/25% versus 22%/6% in the OM and OP cohorts. Patterns of first relapse were four times higher outside the irradiated field and OP status (p = 0.03), ⩾3 metastasis (p = 0.002) and concurrent systemic therapy (p = 0.001) conferred a greater risk. Time to second-line treatment was 20 vs 11 months in the OM and OP groups (P = 0.001). CONCLUSION: Survival and distant relapse following SBRT to OM/OP is determined by the extent of metastatic disease and performance status. Future research should address the benefit of integrating SBRT with systemic therapies to allow deferral or continuation of therapeutic agents.

Long-term Outcomes of Induction Carboplatin and Gemcitabine Followed by Concurrent Radiotherapy With Low-dose Paclitaxel and Gemcitabine for Stage III Non-small-cell Lung Cancer.

BACKGROUND: Standard treatment for unresectable stage III non-small-cell lung cancer (NSCLC) is concurrent chemo-radiation (CRT). A regimen of induction carboplatin and gemcitabine followed by CRT was developed at the McGill University Health Centre to prevent delays in treatment initiation. We report the long-term outcomes with this regimen based on a pooled analysis of both protocol patients from a phase II study and nonprotocol patients. METHODS AND MATERIALS: Outcomes and toxicity data were retrieved for 142 patients with stage III NSCLC: 43 patients treated on protocol between January 2003 and November 2004, and 101 patients treated off-protocol between December 2004 and August 2013. Patients received 2 cycles of carboplatin with an area under the curve of 5 intravenously (IV) on day 1 and gemcitabine 1000 mg/m2 IV on days 1 and 8 every 3 weeks, followed on day 50 by CRT, 60 Gy/30 over 6 weeks, concomitantly with 2 cycles of paclitaxel 50 mg/m2 IV and gemcitabine 100 mg/m2 IV on days 1 and 8 every 3 weeks. RESULTS: The median overall survival was 23.2 months. With a median follow-up of 23.8 months, the 3-, 4-, and 5-year overall survival was 38%, 30%, and 26%, respectively. The median and 5-year progression-free survival rates were 12.5 months and 25%, respectively. Rates of grade ≥ 3 hematologic, esophageal, and respiratory toxicity were 20%, 10%, and 10%, respectively. Forty-eight patients received further lines of chemotherapy. CONCLUSION: The present analysis affirms the favorable toxicity profile of this novel induction chemotherapy, without apparent compromise in clinical outcomes, when compared with regimens using immediate concurrent CRT.

Stereotactic Ablative Radiation Therapy for the Treatment of Early-stage Non-Small-Cell Lung Cancer: CEPO Review and Recommendations.

BACKGROUND: Lung cancer is the second most diagnosed cancer and the leading cause of cancer-related mortality in Canada. Surgical resection is the treatment of choice for patients with stage I non-small-cell lung cancer (NSCLC). However, 20% to 30% of them are deemed medically inoperable and may be offered radiation therapy. Standard external-beam radiation therapy (EBRT) is associated with high rates of local recurrence and poor long-term survival. Stereotactic ablative radiation therapy (SABR) is increasingly being proposed for inoperable patients, and the use of this treatment modality for operable patients is also being contemplated. The objective of this guideline is to review the efficacy and safety of SABR in these two clinical situations and to develop evidence-based recommendations. METHOD: A review of the scientific literature published up to December 2013 was performed. A total of 44 publications were included. RECOMMENDATIONS: Considering the evidence available to date, the Comité de l'évolution des pratiques en oncologie recommends the following: (1) for medically operable patients with stage T1-2N0M0 NSCLC, surgery remains the standard treatment because comparative data regarding the efficacy of SABR and surgery are currently insufficient for SABR to be considered an equivalent alternative to surgery for these patients; (2) for medically inoperable patients with stage T1-2N0M0 NSCLC or medically operable patients who refuse surgery, SABR should be preferred to standard EBRT (grade B recommendation); (3) the biological equivalent dose (BED(10)) used for SABR treatment should be at least 100 Gy (grade B recommendation); (4) for patients with a central tumor, a large-volume tumor (large planning target volume) or severe pulmonary comorbidity, a risk-adaptive schedule should be used (dose reduction or increase in the number of fractions; grade B recommendation); (5) the choice of using SABR to treat NSCLC should be discussed within tumor boards; treatment with SABR (or with standard EBRT) should not be considered for patients whose life expectancy is very limited because of comorbidities (grade D recommendation).

Bayesian network ensemble as a multivariate strategy to predict radiation pneumonitis risk.

PURPOSE: Prediction of radiation pneumonitis (RP) has been shown to be challenging due to the involvement of a variety of factors including dose-volume metrics and radiosensitivity biomarkers. Some of these factors are highly correlated and might affect prediction results when combined. Bayesian network (BN) provides a probabilistic framework to represent variable dependencies in a directed acyclic graph. The aim of this study is to integrate the BN framework and a systems' biology approach to detect possible interactions among RP risk factors and exploit these relationships to enhance both the understanding and prediction of RP. METHODS: The authors studied 54 nonsmall-cell lung cancer patients who received curative 3D-conformal radiotherapy. Nineteen RP events were observed (common toxicity criteria for adverse events grade 2 or higher). Serum concentration of the following four candidate biomarkers were measured at baseline and midtreatment: alpha-2-macroglobulin, angiotensin converting enzyme (ACE), transforming growth factor, interleukin-6. Dose-volumetric and clinical parameters were also included as covariates. Feature selection was performed using a Markov blanket approach based on the Koller-Sahami filter. The Markov chain Monte Carlo technique estimated the posterior distribution of BN graphs built from the observed data of the selected variables and causality constraints. RP probability was estimated using a limited number of high posterior graphs (ensemble) and was averaged for the final RP estimate using Bayes' rule. A resampling method based on bootstrapping was applied to model training and validation in order to control under- and overfit pitfalls. RESULTS: RP prediction power of the BN ensemble approach reached its optimum at a size of 200. The optimized performance of the BN model recorded an area under the receiver operating characteristic curve (AUC) of 0.83, which was significantly higher than multivariate logistic regression (0.77), mean heart dose (0.69), and a pre-to-midtreatment change in ACE (0.66). When RP prediction was made only with pretreatment information, the AUC ranged from 0.76 to 0.81 depending on the ensemble size. Bootstrap validation of graph features in the ensemble quantified confidence of association between variables in the graphs where ten interactions were statistically significant. CONCLUSIONS: The presented BN methodology provides the flexibility to model hierarchical interactions between RP covariates, which is applied to probabilistic inference on RP. The authors' preliminary results demonstrate that such framework combined with an ensemble method can possibly improve prediction of RP under real-life clinical circumstances such as missing data or treatment plan adaptation.

ESTRO consensus guideline on target volume delineation for elective radiation therapy of early stage breast cancer.

BACKGROUND AND PURPOSE: Delineation of clinical target volumes (CTVs) is a weak link in radiation therapy (RT), and large inter-observer variation is seen in breast cancer patients. Several guidelines have been proposed, but most result in larger CTVs than based on conventional simulator-based RT. The aim was to develop a delineation guideline obtained by consensus between a broad European group of radiation oncologists. MATERIAL AND METHODS: During ESTRO teaching courses on breast cancer, teachers sought consensus on delineation of CTV through dialogue based on cases. One teacher delineated CTV on CT scans of 2 patients, followed by discussion and adaptation of the delineation. The consensus established between teachers was sent to other teams working in the same field, both locally and on a national level, for their input. This was followed by developing a broad consensus based on discussions. RESULTS: Borders of the CTV encompassing a 5mm margin around the large veins, running through the regional lymph node levels were agreed, and for the breast/thoracic wall other vessels were pointed out to guide delineation, with comments on margins for patients with advanced breast cancer. CONCLUSION: The ESTRO consensus on CTV for elective RT of breast cancer, endorsed by a broad base of the radiation oncology community, is presented to improve consistency.

Analytical modelling of regional radiotherapy dose response of lung.

Knowledge of the dose-response of radiation-induced lung disease (RILD) is necessary for optimization of radiotherapy (RT) treatment plans involving thoracic cavity irradiation. This study models the time-dependent relationship between local radiation dose and post-treatment lung tissue damage measured by computed tomography (CT) imaging. Fifty-eight follow-up diagnostic CT scans from 21 non-small-cell lung cancer patients were examined. The extent of RILD was segmented on the follow-up CT images based on the increase of physical density relative to the pre-treatment CT image. The segmented RILD was locally correlated with dose distribution calculated by analytical anisotropic algorithm and the Monte Carlo method to generate the corresponding dose-response curves. The Lyman-Kutcher-Burman (LKB) model was fit to the dose-response curves at six post-RT time periods, and temporal change in the LKB parameters was recorded. In this study, we observed significant correlation between the probability of lung tissue damage and the local dose for 96% of the follow-up studies. Dose-injury correlation at the first three months after RT was significantly different from later follow-up periods in terms of steepness and threshold dose as estimated from the LKB model. Dependence of dose response on superior-inferior tumour position was also observed. The time-dependent analytical modelling of RILD might provide better understanding of the long-term behaviour of the disease and could potentially be applied to improve inverse treatment planning optimization.

Stereotactic body radiotherapy for unresectable cholangiocarcinoma.

PURPOSE: To report outcomes of a single institution study of stereotactic body radiotherapy (SBRT) for unresectable cholangiocarcinoma. The dose-volume dependency of the observed gastrointestinal toxicity is explored. METHODS AND MATERIALS: Twenty-seven patients with unresectable cholangiocarcinoma (n=26 Klatskin tumours and one intrahepatic cholangiocarcinoma (IHCC)) were treated by linac-based SBRT. The dose schedule was 45Gy in three fractions prescribed to the isocenter. RESULTS: The median progression-free survival and overall survival were 6.7 and 10.6 months, respectively. With a median follow-up of 5.4 years, 6 patients had severe duodenal/pyloric ulceration and 3 patients developed duodenal stenosis. Duodenal radiation exposure was higher in patients developing moderate to high-grade gastrointestinal toxicity with the difference in mean maximum dose to 1cm(3) of duodenum reaching statistical significance. A statistically significant association between grade 2 ulceration and volume of duodenum exposed to selected dose levels was not established. CONCLUSION: The outcomes of SBRT for unresectable cholangiocarcinoma appear comparable to conventionally fractionated chemoradiotherapy with or without brachytherapy boost. The practical advantages of SBRT are of particular interest for such poor prognosis patients. Patient selection, however, is key in order to avoid compromising such practical gains with excessive gastrointestinal toxicity.