SPARC, a phase-I trial of pre-operative, margin intensified, stereotactic body radiation therapy for pancreatic cancer.

BACKGROUND AND PURPOSE: Following resection of pancreatic cancer, risk of positive margins and local recurrence remain high, especially for borderline-resectable pancreatic cancer (BRPC). We aimed to establish the maximum tolerated dose of a margin-intensified five-fraction stereotactic body radiotherapy (SBRT) regimen designed to treat the region at risk. MATERIALS AND METHODS: We conducted a prospective multicentre phase-1 rolling-six dose-escalation study. BRPC patients received pre-operative SBRT, with one dose to the primary tumour and an integrated boost to the region where tumour was in contact with vasculature. Four dose-levels were proposed, with starting dose 30 Gy to primary PTV and 45 Gy to boost volume (PTV_R), in five daily fractions. Primary endpoint was maximum tolerated dose (MTD), defined as highest dose where zero of three or one of six patients experienced dose-limiting toxicity (DLT). RESULTS: Twelve patients were registered, eleven received SBRT. Radiotherapy was well tolerated with all treatment completed as scheduled. Dose was escalated one level up from starting dose without encountering any DLT (prescribed 32.5 Gy PTV, 47.5 Gy PTV_R). Nine serious adverse reactions or events occurred (seven CTCAE Grade 3, two Grade 4). Two patients went on to have surgical resection. Median overall survival for SBRT patients was 8.1 months. The study closed early when it was unable to recruit to schedule. CONCLUSION: Toxicity of SBRT was low for the two dose-levels that were tested, but MTD was not established. Few patients subsequently underwent resection of pancreatic tumour after SBRT, and it is difficult to draw conclusions regarding the safety or toxicity of these therapies in combination.

Superior outcomes of nodal metastases compared to visceral sites in oligometastatic colorectal cancer treated with stereotactic ablative radiotherapy.

BACKGROUND: Stereotactic ablative radiotherapy (SBRT) is a radical option for oligometastatic colorectal cancer (CRC) patients, but most data relate to visceral metastases. METHODS: A prospective, multi-centre database of CRC patients treated with SBRT was interrogated. Inclusion criteria were ECOG PS 0-2, ≤3 sites of disease, a disease free interval of >6 months unless synchronous liver metastases. Primary endpoints were local control (LC), progression free survival (PFS) and overall survival (OS). RESULTS: 163 patients (172 metastases) were analysed. The median FU was 16 months (IQR 12.2-22.85). The LC at 1 year was 83.8% (CI 76.4%-91.9%) with a PFS of 55% (CI 47%-64.7%) respectively. LC at 1 year was 90% (CI 83%-99%) for nodal metastases (NM), 75% (63%-90%) for visceral metastases (VM). NM had improved median PFS (9 vs 19 months) [HR 0.6, CI 0.38-0.94, p = 0.032] and median OS (32 months vs not reached) [HR 0.28, CI 0.18-0.7, p = 0.0062] than VM, regardless of whether the NM were located inside or outside the pelvis. On multivariate analysis, NM and ECOG PS 0 were significant good prognostic factors. An exploratory analysis suggests KRAS WT is also a good prognostic factor. CONCLUSION: Nodal site is an important prognostic determinant of SBRT that should incorporated into patient selection. We hypothesise this may have an immunoediting basis.

Systematic review and meta-analysis of small bowel dose-volume and acute toxicity in conventionally-fractionated rectal cancer radiotherapy.

INTRODUCTION: The limited radiation tolerance of the small-bowel causes toxicity for patients receiving conventionally-fractionated radiotherapy for rectal cancer. Safe radiotherapy dose-escalation will require a better understanding of such toxicity. We conducted a systematic review and meta-analysis using published datasets of small bowel dose-volume and outcomes to analyse the relationship with acute toxicity. MATERIALS AND METHODS: SCOPUS, EMBASE & MEDLINE were searched to identify twelve publications reporting small-bowel dose-volumes and toxicity data or analysis. Where suitable data were available (mean absolute volume with parametric error measures), fixed-effects inverse-variance meta-analysis was used to compare cohorts of patients according to Grade ≥3 toxicity. For other data, non-parametric examinations of irradiated small-bowel dose-volume and incidence of toxicity were conducted, and a univariate logistic regression model was fitted. RESULTS: On fixed-effects meta-analysis of three studies (203 patients), each of the dose-volume measures V5Gy-V40Gy were significantly greater (p < 0.00001) for patients with Grade ≥3 toxicity than for those without. Absolute difference was largest for the lowest dose-volume parameter; however relative difference increases with increasing dose. On logistic regression multiple small-bowel DVH parameters were predictive of toxicity risk (V5Gy, V10Gy, V30Gy - V45Gy), with V10Gy the strongest (p = 0.004). CONCLUSIONS: Analysis of published clinical cohort dose-volume data provides evidence for a significant dose-volume-toxicity response effect for a wide range of clinically-relevant doses in the treatment of rectal cancer. Both low dose and high dose are shown to predict toxicity risk, which has important implications for radiotherapy planning and consideration of dose escalation for these patients.

Modelling duodenum radiotherapy toxicity using cohort dose-volume-histogram data.

BACKGROUND AND PURPOSE: Gastro-intestinal toxicity is dose-limiting in abdominal radiotherapy and correlated with duodenum dose-volume parameters. We aimed to derive updated NTCP model parameters using published data and prospective radiotherapy quality-assured cohort data. MATERIAL AND METHODS: A systematic search identified publications providing duodenum dose-volume histogram (DVH) statistics for clinical studies of conventionally-fractionated radiotherapy. Values for the Lyman-Kutcher-Burman (LKB) NTCP model were derived through sum-squared-error minimisation and using leave-one-out cross-validation. Data were corrected for fraction size and weighted according to patient numbers, and the model refined using individual patient DVH data for two further cohorts from prospective clinical trials. RESULTS: Six studies with published DVH data were utilised, and with individual patient data included outcomes for 531 patients in total (median follow-up 16months). Observed gastro-intestinal toxicity rates ranged from 0% to 14% (median 8%). LKB parameter values for unconstrained fit to published data were: n=0.070, m=0.46, TD50(1) [Gy]=183.8, while the values for the model incorporating the individual patient data were n=0.193, m=0.51, TD50(1) [Gy]=299.1. CONCLUSIONS: LKB parameters derived using published data are shown to be consistent to those previously obtained using individual patient data, supporting a small volume-effect and dependence on exposure to high threshold dose.

A phase-I trial of pre-operative, margin intensive, stereotactic body radiation therapy for pancreatic cancer: the 'SPARC' trial protocol.

BACKGROUND: Standard therapy for borderline-resectable pancreatic cancer in the UK is surgery with adjuvant chemotherapy, but rates of resection with clear margins are unsatisfactory and overall survival remains poor. Meta-analysis of single-arm studies shows the potential of neo-adjuvant chemo-radiotherapy but the relative radio-resistance of pancreatic cancer means the efficacy of conventional dose schedules is limited. Stereotactic radiotherapy achieves sufficient accuracy and precision to enable pre-operative margin-intensive dose escalation with the goal of increasing rates of clear resection margins and local disease control. METHODS/DESIGN: SPARC is a "rolling-six" design single-arm study to establish the maximum tolerated dose for margin-intensive stereotactic radiotherapy before resection of pancreatic cancer at high risk of positive resection margins. Eligible patients will have histologically or cytologically proven pancreatic cancer defined as borderline-resectable per National Comprehensive Cancer Network criteria or operable tumour in contact with vessels increasing the risk of positive margin. Up to 24 patients will be recruited from up to 5 treating centres and a 'rolling-six' design is utilised to minimise delays and facilitate ongoing recruitment during dose-escalation. Radiotherapy will be delivered in 5 daily fractions and surgery, if appropriate, will take place 5-6 weeks after radiotherapy. The margin-intense radiotherapy concept includes a systematic method to define the target volume for a simultaneous integrated boost in the region of tumour-vessel infiltration, and up to 4 radiotherapy dose levels will be investigated. Maximum tolerated dose is defined as the highest dose at which no more than 1 of 6 patients or 0 of 3 patients experience a dose limiting toxicity. Secondary endpoints include resection rate, resection margin status, response rate, overall survival and progression free survival at 12 and 24 months. Translational work will involve exploratory analyses of the cytological and humoral immunological responses to stereotactic radiotherapy in pancreatic cancer. Radiotherapy quality assurance of target definition and radiotherapy planning is enforced with pre-trial test cases and on-trial review. Recruitment began in April 2015. DISCUSSION: This prospective multi-centre study aims to establish the maximum tolerated dose of pre-operative margin-intensified stereotactic radiotherapy in pancreatic cancer at high risk of positive resection margins with a view to subsequent definitive comparison with other neoadjuvant treatment options. TRIAL REGISTRATION: ISRCTN14138956 . Funded by CRUK.

Conformity analysis to demonstrate reproducibility of target volumes for Margin-Intense Stereotactic Radiotherapy for borderline-resectable pancreatic cancer.

BACKGROUND AND PURPOSE: Margin-directed neoadjuvant radiotherapy for borderline-resectable pancreatic cancer (BRPC) aims to facilitate clear surgical margins. A systematic method was developed for definition of a boost target volume prior to a formal phase-I study. MATERIAL AND METHODS: Reference structures were defined by two oncologists and one radiologist, target structures were submitted by eight oncologist investigators and compared using conformity indices. Resultant risk of duodenal bleed (NTCP) was modelled. RESULTS: For GTV, reference volume was 2.1cm3 and investigator mean was 6.03cm3 (95% CI 3.92-8.13cm3), for boost volume 1.1cm3 and 1.25cm3 (1.02-1.48cm3). Mean Dice conformity coefficient for GTV was 0.47 (0.38-0.56), and for boost volume was significantly higher at 0.61 (0.52-0.70, p=0.01). Discordance index (DI) for GTV was 0.65 (0.56-0.75) and for boost volume was significantly lower at 0.39 (0.28-0.49, p=0.001). NTCP using reference contours was 2.95%, with mean for investigator contour plans 3.93% (3.63-4.22%). Correlations were seen between NTCP and GTV volume (p=0.02) and NTCP and DI (correlation coefficient 0.83 (0.29-0.97), p=0.01). CONCLUSIONS: Better conformity with reference was shown for boost volume compared with GTV. Investigator GTV volumes were larger than reference, had higher DI scores and modelled toxicity risk. A consistent method of target structure definition for margin-directed pancreatic radiotherapy is demonstrated.