Single vs. multiple fraction non-inferiority trial of stereotactic ablative radiotherapy for the comprehensive treatment of oligo-metastases/progression: SIMPLIFY-SABR-COMET.

BACKGROUND: Radiotherapy delivery regimens can vary between a single fraction (SF) and multiple fractions (MF) given daily for up to several weeks depending on the location of the cancer or metastases. With limited evidence comparing fractionation regimens for oligometastases, there is support to explore toxicity levels to nearby organs at risk as a primary outcome while using SF and MF stereotactic ablative radiotherapy (SABR) as well as explore differences in patient-reported quality of life and experience. METHODS: This study will randomize 598 patients in a 1:1 ratio between the standard arm (MF SABR) and the experimental arm (SF SABR). This trial is designed as two randomized controlled trials within one patient population for resource efficiency. The primary objective of the first randomization is to determine if SF SABR is non-inferior to MF SABR, with respect to healthcare provider (HCP)-reported grade 3-5 adverse events (AEs) that are related to SABR. Primary endpoint is toxicity while secondary endpoints include lesional control rate (LCR), and progression-free survival (PFS). The second randomization (BC Cancer sites only) will allocate participants to either complete quality of life (QoL) questionnaires only; or QoL questionnaires and a symptom-specific survey with symptom-guided HCP intervention. The primary objective of the second randomization is to determine if radiation-related symptom questionnaire-guided HCP intervention results in improved reported QoL as measured by the EuroQoL-5-dimensions-5levels (EQ-5D-5L) instrument. The primary endpoint is patient-reported QoL and secondary endpoints include: persistence/resolution of symptom reporting, QoL, intervention cost effectiveness, resource utilization, and overall survival. DISCUSSION: This study will compare SF and MF SABR in the treatment of oligometastases and oligoprogression to determine if there is non-inferior toxicity for SF SABR in selected participants with 1-5 oligometastatic lesions. This study will also compare patient-reported QoL between participants who receive radiation-related symptom-guided HCP intervention and those who complete questionnaires alone. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT05784428. Date of Registration: 23 March 2023.

Comparing Kadish, TNM, and the modified Dulguerov staging systems for esthesioneuroblastoma.

BACKGROUND: Esthesioneuroblastoma (ENB) is a rare neuroendocrine tumor. The purpose of this study was to compare the Kadish, tumor-node-metastasis (TNM), and Dulguerov's modified TNM staging in order to determine the impact of the stage on primary surgical treatment selection, margin status, and survival. METHODS: The National Cancer Database (NCDB) was used to identify patients diagnosed with ENB between 2004 to 2015. Patients were excluded based on the ability to properly stage their disease as well as the availability of treatment data. RESULTS: Eight-hundred eighty-three patients had sufficient data for analysis. On multivariate analysis, age and government insurance were associated with primary surgical treatment, whereas tumor stage, gender, race, hospital type and volume, and comorbidity score were not. Age, charlson-deyo comorbidity (CDCC) score, hospital volume, and nodal status were found to be predictors of survival. Multivariate-analysis controlling for stage failed to demonstrate clear survival differences between staging in both TNM and Kadish systems. T-stage and the presence of regional nodal metastasis were associated with an increased risk of positive margins on multivariate analysis. CONCLUSION: Although primary surgical management and positive margins can be predicted by certain patient and tumor factors, clinical staging systems for ENB poorly predict prognosis over a 10-year horizon.

Radiation Therapy for Colorectal Liver Metastasis: The Effect of Radiation Therapy Dose and Chemotherapy on Local Control and Survival.

Purpose: Colorectal liver metastases (CLMs) represent a radioresistant histology. We aimed to investigate CLM radiation therapy (RT) outcomes and explore the association with treatment parameters. Methods and Materials: This retrospective analysis of CLM treated with RT at Memorial Sloan Kettering Cancer Center used Kaplan-Meier analysis to estimate freedom from local progression (FFLP), hepatic progression-free, progression-free, and overall survival (OS). Cox proportional hazards regression was used to evaluate association with clinical factors. Dose-response relationship was further evaluated using a mechanistic tumor control probability (TCP) model. Results: Ninety patients with 122 evaluable CLMs treated 2006 to 2019 with a variety of RT fractionation schemes with a median biologically effective dose (α/ß = 10; BED10) of 97.9 Gy (range, 43.2-187.5 Gy) were included. Median lesion size was 3.5 cm (0.7-11.8 cm). Eighty-seven patients (97%) received prior systemic therapy, and 73 patients (81%) received prior liver-directed therapy. At a median follow-up of 26.4 months, rates of FFLP and OS were 62% (95% CI, 53%-72%) and 75% (66%-84%) at 1 year and 42% (95% CI, 32%-55%) and 44% (95% CI, 34%-57%) at 2 years, respectively. BED10 below 96 Gy and receipt of ≥3 lines of chemotherapy were associated with worse FFLP (hazard ratio [HR], 2.69; 95% CI, 1.54-4.68; P < .001 and HR, 2.67; 95% CI, 1.50-4.74; P < .001, respectively) and OS (HR, 2.35; 95% CI, 1.35-4.09; P = .002 and HR, 4.70; 95% CI, 2.37-9.31; P < .001) on univariate analyses, which remained significant or marginally significant on multivariate analyses. A mechanistic Tumor Control Probability (TCP) model showed a higher 2-Gy equivalent dose needed for local control in patients who had been exposed to ≥ 3 lines of chemotherapy versus 0 to 2 (250 ± 29 vs 185 ± 77 Gy for 70% TCP). Conclusions: In a large single-institution series of heavily pretreated patients with CLM undergoing liver RT, low BED10 and multiple prior lines of systemic therapy were associated with lower local control and OS. These results support continued dose escalation efforts for patients with CLM.

Causes and impact of delays during the COVID-19 pandemic on head and neck cancer diagnosis.

BACKGROUND: The causes for delays during the COVID19 pandemic and their impact on head and neck cancer (HNC) diagnosis and staging are not well described. METHODS: Two cohorts were defined a priori for review and analysis-a Pre-Pandemic cohort (June 1 to December 31, 2019) and a Pandemic cohort (June 1 to December 31, 2020). Delays were categorized as COVID-19 related or not, and as clinician, patient, or policy related. RESULTS: A total of 638 HNC patients were identified including 327 in the Pre-Pandemic Cohort and 311 in the Pandemic Cohort. Patients in the Pandemic cohort had more N2-N3 category (41% vs. 33%, p = 0.03), T3-T4 category (63% vs. 50%, p = 0.002), and stage III-IV (71% vs. 58%, p < 0.001) disease. Several intervals in the diagnosis to treatment pathway were significantly longer in the pandemic cohort as compared to the Pre-Pandemic cohort. Among the pandemic cohort, 146 (47%) experienced a delay, with 112 related to the COVID-19 pandemic; 80 (71%) were clinician related, 15 (13%) were patient related, and 17 (15%) were policy related. CONCLUSIONS: Patients in the Pandemic cohort had higher stage disease at diagnosis and longer intervals along the diagnostic pathway, with COVID-19 related clinician factors being the most common cause of delay.

Prophylactic Radiation Therapy Versus Standard of Care for Patients With High-Risk Asymptomatic Bone Metastases: A Multicenter, Randomized Phase II Clinical Trial.

PURPOSE: External-beam radiation therapy (RT) is standard of care (SOC) for pain relief of symptomatic bone metastases. We aimed to evaluate the efficacy of radiation to asymptomatic bone metastases in preventing skeletal-related events (SRE). METHODS: In a multicenter randomized controlled trial, adult patients with widely metastatic solid tumor malignancies were stratified by histology and planned SOC (systemic therapy or observation) and randomly assigned in a 1:1 ratio to receive RT to asymptomatic high-risk bone metastases or SOC alone. The primary outcome of the trial was SRE. Secondary outcomes included hospitalizations for SRE and overall survival (OS). RESULTS: A total of 78 patients with 122 high-risk bone metastases were enrolled between May 8, 2018, and August 9, 2021, at three institutions across an affiliated cancer network in the United States. Seventy-three patients were evaluable for the primary end point. The most common primary cancer types were lung (27%), breast (24%), and prostate (22%). At 1 year, SRE occurred in one of 62 bone metastases (1.6%) in the RT arm and 14 of 49 bone metastases (29%) in the SOC arm (P < .001). There were significantly fewer patients hospitalized for SRE in the RT arm compared with the SOC arm (0 v 4, P = .045). At a median follow-up of 2.5 years, OS was significantly longer in the RT arm (hazard ratio [HR], 0.49; 95% CI, 0.27 to 0.89; P = .018), which persisted on multivariable Cox regression analysis (HR, 0.46; 95% CI, 0.23 to 0.85; P = .01). CONCLUSION: Radiation delivered prophylactically to asymptomatic, high-risk bone metastases reduced SRE and hospitalizations. We also observed an improvement in OS with prophylactic radiation, although a confirmatory phase III trial is warranted.

Implementation Strategies to Increase Clinical Trial Enrollment in a Community-Academic Partnership and Impact on Hispanic Representation: An Interrupted Time Series Analysis.

PURPOSE: Community-academic partnerships have the potential to improve access to clinical trials for under-represented minority patients who more often receive cancer treatment in community settings. In 2017, the Memorial Sloan Kettering (MSK) Cancer Center began opening investigator-initiated clinical trials in radiation oncology in targeted community-based partner sites with a high potential to improve diverse population accrual. This study evaluates the effectiveness of a set of implementation strategies for increasing overall community-based enrollment and the resulting proportional enrollment of Hispanic patients on trials on the basis of availability in community-based partner sites. METHODS: An interrupted time series analysis evaluating implementation strategies was conducted from April 2018 to September 2021. Descriptive analysis ofHispanic enrollment on investigator-initiated randomized therapeutic radiation trials open at community-based sites was compared with those open only at themain academic center. RESULTS: Overall, 84 patients were enrolled in clinical trials in the MSK Alliance, of which 48 (56%) identified as Hispanic. The quarterly patient enrollment pre- vs postimplementation increased from 1.39 (95% CI, -3.67 to 6.46) to 9.42 (95% CI, 2.05 to 16.78; P5 .017). In the investigator-initiated randomized therapeutic radiation trials open in the MSK Alliance, Hispanic representation was 11.5% and 35.9% in twometastatic trials and 14.2% in a proton versus photon trial. Inmatched trials open only at the main academic center, Hispanic representation was 5.6%, 6.0%, and 4.0%, respectively. CONCLUSION: A combination of practice-level and physician-level strategies implemented at community-based partner sites was associated with increased clinical trial enrollment, which translated to improved Hispanic representation. This supports the role Q:2 of strategic community-academic partnerships in addressing disparities in clinical trial enrollment.

Outcomes of Post-Operative Treatment with Concurrent Chemoradiotherapy (CRT) in High-Risk Resected Oral Cavity Squamous Cell Carcinoma (OCSCC): A Multi-Institutional Collaboration.

Adjuvant chemoradiation (CRT), with high-dose cisplatin remains standard treatment for oral cavity squamous cell carcinoma (OCSCC) with high-risk pathologic features. We evaluated outcomes associated with different cisplatin dosing and schedules, concurrent with radiation (RT), and the effect of cumulative dosing of cisplatin. An IRB-approved collaborative database of patients (pts) with primary OCSCC (Stage I-IVB AJCC 7th edition) treated with primary surgical resection between January 2005 and January 2015, with or without adjuvant therapy, was established from six academic institutions. Patients were categorized by cisplatin dose and schedule, and resultant groups compared for demographic data, pathologic features, and outcomes by statistical analysis to determine disease free survival (DFS) and freedom from metastatic disease (DM). From a total sample size of 1282 pts, 196 pts were identified with high-risk features who were treated with adjuvant CRT. Administration schedule of cisplatin was not significantly associated with DFS. On multivariate (MVA), DFS was significantly better in patients without perineural invasion (PNI) and in those receiving ≥200 mg/m2 cisplatin dose (p < 0.001 and 0.007). Median DFS, by cisplatin dose, was 10.5 (<200 mg/m2) vs. 20.8 months (≥200 mg/m2). Our analysis demonstrated cumulative cisplatin dose ≥200 mg/m2 was associated with improved DFS in high-risk resected OCSCC pts.

Evaluating compliance with process-related quality metrics and survival in oral cavity squamous cell carcinoma: Multi-institutional oral cavity collaboration study.

BACKGROUND: Process-related measures have been proposed as quality metrics in head and neck cancer care. A recent single-institution study identified four key metrics associated with increased survival. This study sought to validate the association of these quality metrics with survival in a multi-institutional cohort. METHODS: Multicenter retrospective study of patients with oral cavity squamous cell (1/2005-1/2015). Baseline patient and disease characteristics and compliance with quality metrics was evaluated. Association between compliance with quality metrics with overall survival (OS), disease-free survival (DFS), and disease-specific survival (DSS) was evaluated using Cox proportional hazards models. RESULTS: Failure to comply with two or more of the quality metrics was associated with worse OS, DFS, and DSS. Adherence to all or all but one of the quality metrics was found to be associated with improved survival. CONCLUSIONS: Process-related quality metrics are associated with increased survival in patients with oral cavity squamous cell carcinoma in a multi-institutional cohort.

Use of Preoperative Radiation Therapy in Early-stage and Locally Advanced Breast Cancer.

Purpose There is growing interest in delivering radiation preoperatively (preopRT) rather than postoperatively (postopRT) for breast cancer. Using the National Cancer Database, we evaluated the use and outcomes of preopRT in breast cancer. Methods We identified adult females diagnosed with non-metastatic breast cancer treated with definitive surgery and radiation between 2004 and 2014. Logistic regression models evaluated factors associated with use of preopRT in early-stage (clinical T1-3/N0-1) and locally advanced (clinical T4/N2-3) disease. Rates of breast-conserving surgery, breast reconstruction, positive surgical margins, and 30-day surgical readmissions were compared between patients receiving preopRT and postopRT. Results Of 373,595 patients who met our inclusion criteria, 1,245 (0.3%) patients received preopRT. Patients receiving preopRT were more likely to be of lower socioeconomic status and have tumors with higher T stage. Younger age and N1 (vs N0) disease predicted for use of preopRT in early-stage disease, while older age and N0 disease predicted for use of preopRT in the locally advanced setting. PreopRT patients were less likely to undergo breast-conserving surgery and more likely to have positive surgical margins. Rates of unplanned readmissions within 30 days of surgery were similar among patients treated with preopRT and postopRT. Conclusions PreopRT is a new treatment strategy for patients with breast cancer with different clinical and sociodemographic drivers of its use in the early-stage and locally advanced settings. We await the results of clinical trials studying the efficacy of this approach.

Timing of surgery and adjuvant radiation therapy for sinonasal malignancies: Effect of surgical approach.

BACKGROUND: Timely postoperative radiation therapy (RT) within 50 days of surgery for head and neck cancers provides a survival advantage. METHODS: Using the National Cancer Database, we performed a propensity score-matched analysis comparing patients undergoing open or endoscopic surgery for squamous cell carcinoma (SCC) of the nasal cavity and paranasal sinuses from 2010 to 2015. RESULTS: Among 168 pairs, patients undergoing endoscopic surgery had shorter time to surgery (24.2 vs 36.7 days, P < .001) and shorter postoperative time to RT (PTTR, 51.2 vs 58.4 days, P = .02). On multivariable linear regression, endoscopic surgery predicted shorter PTTR (ß = -7.6, P = .01). Using the Kaplan-Meier method, patients in the longest PTTR quartile had decreased overall survival (OS; Q1 vs Q4, 3-year OS 76.5% vs 53.3%, P = .007), a durable finding when adjusted for covariates (Q1 vs Q4, HR 0.50, P = .008). CONCLUSIONS: Patients undergoing endoscopic surgery for sinonasal SCC experience shorter PTTR. Shorter PTTR is associated with extended OS.

Long-term outcomes in oral cavity squamous cell carcinoma with adjuvant and salvage radiotherapy after surgery.

OBJECTIVE: Early-stage oral cavity squamous cell carcinoma (OCSCC) represents a heterogeneous group of patients, and locoregional recurrence rates are as high as 25% with surgery alone. Radiotherapy (RT) is typically reserved as part of salvage multimodality therapy after salvage surgery because it is generally thought that there is no significant detriment to salvage therapy. Our aim was to examine outcomes for recurrent OCSCC treated with salvage surgery and radiation and compare them to outcomes for patients treated with adjuvant postoperative RT upfront. METHODS: We identified 425 patients with OCSCC treated with postoperative RT at our institution. The 5-year rates of local failure, locoregional failure (LRF), survival, and distant metastasis (DM) were the main outcome measures. We performed a landmark analysis and examined the same outcomes in the adjuvant versus salvage cohorts using Cox proportional hazards and Fine-Gray competing risk method. RESULTS: The adjuvant cohort had higher tumor (T) (P < 0.0001) and nodal (N) (P < 0.0001) stage than the salvage cohort's stage at initial presentation. On multivariate analysis, a strategy of salvage RT experienced poorer overall survival (OS) compared to upfront adjuvant RT (hazard ratio [HR] 1.84; 95% confidence interval [CI], 1.26-2.70; P = 0.002). Moreover, salvage surgery followed by RT patients experienced increasing risk of LRF (HR 1.56; 95% CI, 1.18-2.06; P = 0.002) and (DM) (HR 1.53; 95% CI, 1.08-2.17; P = 0.02) on multivariate analysis. Additional analysis was performed excluding salvage cohort with advanced disease at initial presentation (T3-T4 and N2). Salvage RT treatment selection for early-stage OCSCC continued to experience significantly poorer OS as compared to adjuvant RT (HR 1.48; 95% CI, 1.002-2.19; P = 0.049). CONCLUSION: Early-stage OCSCC patients who are observed and experienced recurrence requiring salvage therapy (surgery and RT) have worse oncologic outcomes than locally advanced patients receiving upfront adjuvant RT. Prospective randomized studies are needed to identify high-risk subset of early-stage OCSCC comparing adjuvant RT versus observation, followed by salvage surgery and RT at recurrence. LEVEL OF EVIDENCE: 4. Laryngoscope, 2539-2545, 2018.

Patterns of nodal failure after intensity modulated radiotherapy for nasopharyngeal carcinoma.

OBJECTIVES: To evaluate the sites of nodal failure (NF) of nasopharyngeal carcinoma (NPC) treated with intensity-modulated radiation therapy (IMRT). STUDY DESIGN: Retrospective chart review. METHODS: We reviewed the records of 165 patients with nonmetastatic NPC treated with IMRT between July 1998 and April 2011 at our institution. Recurrent nodes were delineated on imaging and coregistered with the original treatment planning computed tomography. Failures were assessed as in-field, out-field, or marginal based on the relative volumes of the recurrent nodes covered by the original dose distribution. RESULTS: Ten patients had NF at a median follow-up of 70.4 months for surviving patients. The 3- and 5-year overall survival and NF rates were 88.7%, 76.0% and 5.8%, 7.7%, respectively. Six of the nodal failures were in-field, of which five occurred in level II; whereas four had out-field failures, all of which were in the protected parotid gland area. There were no recurrences in level 1b despite this region being protected. The cumulative 3- and 5-year failure rates in the parotid gland area were 2.2% and 3.1%, respectively. Three patients with parotid failure initially had subcentimeter, nonspecific nodules in the same locations of the parotid gland as the recurrent nodes. CONCLUSION: Nodal failure is uncommon after IMRT in NPC. Recurrence in the parotid gland region accounts for all of the out-field failures and 40% of NF in our study. Comprehensive assessment of nodules in or around the parotid gland is therefore a key aspect of treatment planning and follow-up. LEVEL OF EVIDENCE: 4. Laryngoscope, 2016 127:377-382, 2017.

Internal and external generalizability of temporal dose-response relationships for xerostomia following IMRT for head and neck cancer.

BACKGROUND AND PURPOSE: To study internal and external generalizability of temporal dose-response relationships for xerostomia after intensity-modulated radiotherapy (IMRT) for head and neck cancer, and to investigate potential amendments of the QUANTEC guidelines. MATERIAL AND METHODS: Objective xerostomia was assessed in 121 patients (nCohort1=55; nCohort2=66) treated to 70Gy@2Gy in 2006-2015. Univariate and multivariate analyses (UVA, MVA with 1000 bootstrap populations) were conducted in Cohort1, and generalizability of the best-performing MVA model was investigated in Cohort2 (performance: AUC, p-values, and Hosmer-Lemeshow p-values (pHL)). Ultimately and for clinical guidance, minimum mean dose thresholds to the contralateral and the ipsilateral parotid glands (Dmeancontra, Dmeanipsi) were estimated from the generated dose-response curves. RESULTS: The observed xerostomia rate was 38%/47% (3months) and 19%/23% (11-12months) in Cohort1/Cohort2. Risk of xerostomia at 3months increased for higher Dmeancontra and Dmeanipsi (Cohort1: 0.17·Dmeancontra+0.11·Dmeanipsi-8.13; AUC=0.90±0.05; p=0.0002±0.002; pHL=0.22±0.23; Cohort2: AUC=0.81; p<0.0001; pHL=0.27). The identified minimum Dmeancontra thresholds were lower than in the QUANTEC guidelines (Cohort1/Cohort2: Dmeancontra=12/19Gy; Dmeancontra, Dmeanipsi=16, 25/20, 26Gy). CONCLUSIONS: Increased Dmeancontra and Dmeanipsi explain short-term xerostomia following IMRT. Our results also suggest decreasing Dmeancontra to below 20Gy, while keeping Dmeanipsi to around 25Gy. Long-term xerostomia was less frequent, and no dose-response relationship was established for this follow-up time.

Dose painting with Gamma Knife: Two techniques for delivering different doses to areas of recurrent or residual tumor after resection of brain metastases.

PURPOSE: We investigated the feasibility of using Gamma Knife (GK) radiosurgery for "dose painting" to deliver higher doses to residual or recurrent nodules and surgical cavity after resection of brain metastases. METHODS AND MATERIALS: Two integrated boost techniques were developed with GK. The single-target technique delineated both the surgical cavity (cavity) and gross disease (nodule) as a single target. Dose was prescribed to the target with the goal of covering the nodule with a higher dose. The 2-target technique delineated the cavity and nodule as separate target volumes, each prescribed to its own dose and planned separately. Two cases were used to illustrate each technique. The single-target technique was used to deliver 16 Gy to a smaller cavity (7 cm(3)) and a 20-Gy integrated boost to 2 nodules (case 1). The 2-target technique was used to deliver 12 Gy to a larger cavity (21.5 cm(3)) and 20 Gy to a single nodule (case 2). RESULTS: For both cases, the cavity coverage with the prescribed dose was 100% with the standard plan and integrated boost techniques. For case 1, compared with a standard plan, the single-target technique improved the 20-Gy nodule coverage from 89.7% (nodule 1) and 97.9% (nodule 2) to 100% (both) and increased the minimum dose from 16.6 Gy to 20.8 Gy (nodule 1) and from 19.4 Gy to 20.8 Gy (nodule 2). For case 2, compared with a standard plan, the 2-target technique improved the 20-Gy nodule coverage from 4% to 100% and the minimum dose from 13.8 Gy to 21 Gy. CONCLUSIONS: Both GK integrated boost approaches allowed for effective delivery of higher doses to residual or recurrent nodules in a surgical cavity. In our experience, the single-target technique works well for small cavities, whereas the 2-target technique is well suited for larger cavities.

Variable impact of intracavitary brachytherapy fractionation schedule on biologically effective dose to organs at risk in patients with cervical cancer.

PURPOSE: To determine the effect of intracavitary brachytherapy (ICBT) fractionation schedule on biologically effective dose to organs at risk. METHODS AND MATERIALS: We reviewed records from 26 patients who had CT imaging during ICBT for International Federation of Gynecology and Obstetrics stage IB2-IVA cervical cancer. Using α/ß=10, we calculated hypothetical nominal doses to achieve a biologically effective dose at 2 Gy per fraction (EQD2α/ß=10) of 40 Gy to Point A for high-dose-rate ICBT with 1-15 fractions. Corresponding minimum EQD2α/ß=3s to the maximally irradiated 2 cc of rectum, bladder, and sigmoid were calculated for each fractionation scheme and added to EQD2α/ß=3 from external beam radiotherapy. Total EQD2α/ß=3s were compared with American Brachytherapy Society suggested dose constraints (rectum/sigmoid, ≤75 Gy; bladder, ≤90 Gy). RESULTS: Except for rectal EQD2α/ß=3 in three patients, the rectal, bladder, and sigmoid EQD2α/ß=3s decreased with increasing fractionation in all patients. Although the total rectal EQD2α/ß=3s were less than the American Brachytherapy Society rectal dose constraint in all patients at all fractionation schedules, the total bladder EQD2α/ß=3s routinely exceeded the bladder dose constraint, even at maximum fractionation. By contrast, increasing fractionation decreased the number of patients with doses exceeding the sigmoid dose constraint by 48%. CONCLUSIONS: The relationship between ICBT fractionation schedule and relative EQD2α/ß=3s to rectum, bladder, and sigmoid depends on individual anatomy. Fractionation optimization can improve therapeutic ratios by minimizing the risk or severity of toxic effects. For patients in whom many fractions optimize the therapeutic ratio, low-dose-rate or pulsed-dose-rate brachytherapy may be preferred.