Dosimetric parameters correlate with duodenal histopathologic damage after stereotactic body radiotherapy for pancreatic cancer: Secondary analysis of a prospective clinical trial

The delivered dose assessment in pancreas SBRT with the target position determined using an in-house position monitoring system

PURPOSE

This study assessed the delivered dose accuracy in pancreas SBRT by incorporating the real-time target position determined using an in-house position monitoring system.

METHODS AND MATERIALS

An online image-based position monitoring system, SeedTracker, was developed to monitor radiopaque marker positions using monoscopic x-ray images, available from the Elekta XVI imaging system. This system was applied to patients receiving SBRT for pancreatic cancer on the MASTERPLAN Pilot trial (ACTRN 12617001642370). All patients were implanted pre-treatment with at least three peri-tumoral radiopaque markers for target localisation. During treatment delivery, marker positions were compared to expected positions delineated from the planning CT. The position tolerance of ±3mm from the expected position of the markers was set to trigger a gating event (GE) during treatment. The dosimetric impact of position deviations and actual dose delivered with position corrections was assessed by convolving the plan control point dose matrices with temporal target positions determined during treatment.

RESULTS

Eight patients were treated within this study. At least one GE was observed in 38% of the treatment fractions and more than one GE was observed in 10% of the fractions. The position deviations resulted in the mean(range) difference of -0.1(-1.1 - 0.4)Gy in minimum dose to tumour and 1.9(-0.1- 4.6)Gy increase to Dmax to duodenum compared to planned dose. In actual treatment delivery with the patient realignment, the mean difference of tumour min dose and duodenal Dmax was reduced to 0.1(-1.0 - 1.1)Gy and 1.1 (-0.7 - 3.3)Gy respectively compared to the planned dose.

CONCLUSIONS

The in-house real-time position monitoring system improved the treatment accuracy of pancreatic SBRT in a general-purpose linac and enabled assessment of delivered dose by incorporating the temporal target position during delivery. The intrafraction motion impacts the dose to tumour even if target position is maintained within a 3mm position tolerance.

Bulking agents in gastrointestinal endoscopy: present applications and future advances

PURPOSE OF REVIEW

Bulking agents are inert materials injected into an organ to affect the physical properties of the organ for a therapeutic purpose. Various agents have been developed to aid in the treatment of diseases like gastroesophageal reflux disease (GERD), fecal incontinence, obesity, malignancy, hemostasis, and tissue dissection. Here, we review the state of the art in bulking agents in gastrointestinal endoscopy, past failures, current limitations, and where we see the field heading in the future.

RECENT FINDINGS

Though bulking agents have been trialed for various different gastrointestinal diseases, there are currently limited uses in gastrointestinal endoscopy. Though various agents have been trialed for GERD, numerous complications and adverse events have limited its current use. However, for the treatment of fecal incontinence endoscopic bulking agent therapy is a reasonable option. Though in early stages of exploration, bulking agent therapy for enteric protection from radiotherapy may be a promising tool to improve treatment of pancreatic cancer. Bulking agents for tissue dissection have substantially improved lifting agents and complex polyp removal. Bulking agent therapy has not really been explored for endoscopic bariatric therapy or hemostasis but may be a fruitful area for exploration in the future.

SUMMARY

Bulking agent therapy has been trialed for various gastrointestinal diseases with mixed success. There is currently a therapeutic roll in the endoscopic management of fecal incontinence and tissue dissection. A future role in the treatment of GERD, obesity, malignancy, and hemostasis seem feasible.

The first real-time intrafraction target position monitoring in pancreas SBRT on an Elekta linear accelerator

To perform implanted fiducial based real-time target position monitoring in pancreas stereotactic body radiotherapy (SBRT) using the x-ray imaging system available in a Elekta linear accelerator. An in-house system was developed and clinically utilised for real-time target position monitoring of pancreas SBRT delivery. The developed system was used for the target position monitoring of a pancreas cancer patient treated in free breathing treatment within the study entitled 'Mfolfirinox And STEreotactic Radiotherapy for Patients with Locally Advanced paNcreas cancer (MASTERPLAN): a feasibility study' (ACTRN 12617001642370) consisting of five treatment fractions. The clinical efficacy of the system was studied by performing a retrospective cumulative dose assessment of delivered dose using observed position deviations. The developed system identified two events of baseline shifts in target position that exceeded the accepted tolerance level of ± 3 mm from reference planned position. The retrospective dose assessment study showed that if the position deviations were not detected and corrected for, the maximum dose to duodenum would have increased from 34.6 to 38.8 Gy. The first real-time position monitoring in pancreas SBRT on an Elekta linear accelerator was successfully performed. The developed system was shown to improve the safety and accuracy of SBRT delivery.

Dosimetric feasibility on hypofractionated intensity-modulated radiotherapy and simultaneous integrated boost for locally advanced unresectable pancreatic cancer with helical tomotherapy

Background

This dosimetric study on locally advanced pancreatic cancer (LAPC) and the surrounding gastrointestinal organs at risk (OARs) aimed at exploring the potential of further improving the internal dose and reducing the fractionation number by concurrent hypofractionated simultaneous integrated boost (SIB) radiotherapy using helical tomotherapy (HT).

Methods

We collected computed tomography positioning images from a LAPC study of 17 consecutive patients. Gross tumor volume (GTV)1, GTV2, and GTV3 were defined as the GTV minus a margin of 3, 6, and 9 mm from the external part in all directions, respectively. Under the same physical parameters and limited dose on normal organs, each case had 4 sets of SIB radiotherapy plans. Upon dose escalation, we statistically analyzed the difference of dosimetric parameters received by the OARs between group A [planning target volume (PTV)/GTV=50 Gy/70 Gy] and the other groups. According to the equivalent bioradiotherapy formula, we calculated the hypofractionated standard dose by converting the average tolerated dose of each OAR with the corresponding number of fractions. Then, we compared the dose and volume parameters of the gastrointestinal tract from the less-than-20-fraction modes with the corresponding gastrointestinal hypofractionated standard dose.

Results

For dose escalation, although there were a few differences in the parameters of the OAR between group A and group D, all OAR doses of group D (PTV/GTV/GTV1/GTV2/GTV3=50 Gy/70 Gy/80 Gy/90 Gy/100 Gy) were within the limited dose range. In the hypofractionated mode, there was a statistically significant difference between the gastrointestinal dose-volume parameters and the dose-limiting reference standard when the fraction number was less than 14 or 15 for group A or D, respectively.

Conclusions

The dose of the internal target can be increased to 100 Gy with 15 fractions in the hypofractionated SIB radiotherapy for LAPC with HT. The corresponding tolerance dose of OARs may also be acceptable.

Maximizing Tumor Control and Limiting Complications With Stereotactic Body Radiation Therapy for Pancreatic Cancer

PURPOSE

Stereotactic body radiation therapy (SBRT) and stereotactic ablative body radiation therapy is being increasingly used for pancreatic cancer (PCa), particularly in patients with locally advanced and borderline resectable disease. A wide variety of dose fractionation schemes have been reported in the literature. This HyTEC review uses tumor control probability models to evaluate the comparative effectiveness of the various SBRT treatment regimens used in the treatment of patients with localized PCa.

METHODS AND MATERIALS

A PubMed search was performed to review the published literature on the use of hypofractionated SBRT (usually in 1-5 fractions) for PCa in various clinical scenarios (eg, preoperative [neoadjuvant], borderline resectable, and locally advanced PCa). The linear quadratic model with α/β= 10 Gy was used to address differences in fractionation. Logistic tumor control probability models were generated using maximum likelihood parameter fitting.

RESULTS

After converting to 3-fraction equivalent doses, the pooled reported data and associated models suggests that 1-year local control (LC) without surgery is ≈79% to 86% after the equivalent of 30 to 36 Gy in 3 fractions, showing a dose response in the range of 25 to 36 Gy, and decreasing to less than 70% 1-year LC at doses below 24 Gy in 3 fractions. The 33 Gy in 5 fraction regimen (Alliance A021501) corresponds to 28.2 Gy in 3 fractions, for which the HyTEC pooled model had 77% 1-year LC without surgery. Above an equivalent dose of 28 Gy in 3 fractions, with margin-negative resection the 1-year LC exceeded 90%.

CONCLUSIONS

Pooled analyses of reported tumor control probabilities for commonly used SBRT dose-fractionation schedules for PCa suggests a dose response. These findings should be viewed with caution given the challenges and limitations of this review. Additional data are needed to better understand the dose or fractionation-response of SBRT for PCa.

Chemotherapy-based split stereotactic body radiation therapy for borderline resectable and locally advanced pancreatic cancer: study protocol of a prospective, single-arm phase II trial

INTRODUCTION

The question of how to administer adequate chemotherapy to synchronise stereotactic body radiation therapy (SBRT) treatment strategy to maximise the benefits of neoadjuvant therapy for the improved prognosis of patients with borderline resectable (BRPC) and locally advanced (LAPC) pancreatic cancer is a challenging and debatable issue. No studies have yet evaluated the efficacy of split-course SBRT as the neoadjuvant chemoradiotherapy regimen. We aimed to study whether neoadjuvant chemotherapy plus split-course SBRT results in better outcomes in BRPC and LAPC patients.

METHODS AND ANALYSIS

Treatment-naïve patients with radiographically confirmed BRPC or LAPC, supporting biopsy results and no severe comorbidities will be enrolled. They will be treated with nab-paclitaxel plus gemcitabine (nab-P+Gem) chemotherapy plus split-course SBRT, followed by an investigator's choice of continuation of treatment with nab-P+Gem or surgery. nab-P+Gem chemotherapy will commence on day 1 for each of six cycles: nab-paclitaxel 125 mg/m² intravenous infusion over approximately 30-45 min, followed by gemcitabine 1000 mg/m² intravenous infusion over about 30 min on days 1 and 15 of each 28-day cycle. During the first and second cycles of chemotherapy, SBRT will be given as a single irradiation of 10 Gy four times (days 2 and 16 of each 28-day cycle). The primary endpoint is progression-free survival; while the secondary outcomes are the time to treatment failure, disease control rate, overall response rate, overall survival, R0 resection rate and incidence of adverse effects.

ETHICS AND DISSEMINATION

The study protocol was approved by the Ethics Committee of Xiehe Affiliated Hospital of Fujian Medical University (No. 2019YF015-01). Results from our study will be disseminated in international peer-reviewed journals. All study procedures were developed in order to assure data protection and confidentiality.

TRIAL REGISTRATION NUMBER

NCT04289792.

Phase I/II Trial of Neoadjuvant Oregovomab-based Chemoimmunotherapy Followed by Stereotactic Body Radiotherapy and Nelfinavir For Locally Advanced Pancreatic Adenocarcinoma

OBJECTIVE

Cancer antigen (CA)-125 influences progression, metastasis, and outcomes in pancreatic cancer. This phase I/II trial (NCT01959672) evaluated the safety, efficacy, and immunologic correlates of chemoimmunotherapy (CIT) with oregovomab (anti-CA-125), followed by stereotactic body radiotherapy (SBRT) with the radiosensitizer nelfinavir.

MATERIALS AND METHODS

Following imaging, pathologic confirmation, and staging laparoscopy, subjects received three 3-week cycles of CIT (gemcitabine/leucovorin/fluorouracil/oregovomab). Thereafter, nelfinavir was delivered (1250 mg bid) for 5 weeks, with SBRT (40 Gy/5 fractions) occurring during the third week of nelfinavir. Following another cycle of CIT, pancreaticoduodenectomy was performed if resectable. Three more cycles of CIT were then delivered (total 7 cycles). In subjects with high (≥10 U/mL) CA-125, oregovomab (2 mg) was administered for 7 total doses (3 pre-SBRT, 1 between SBRT and resection, and 3 postoperatively). The enzyme-linked immunospot assay evaluated the development of CA-125-specific CD8 T-lymphocytes.

RESULTS

The trial was prematurely closed because gemcitabine/leucovorin/fluorouracil was replaced by FOLFIRINOX and gemcitabine/nab-paclitaxel as the standard of care. Median follow-up was 13 months. Of 11 enrolled patients, 10 had high CA-125; 1 patient suffered an unexpected cardiac-related death, so 9 subjects received oregovomab. Ten received SBRT and 4 underwent resection. Overall, 6/11 patients experienced any grade ≥3 event. The median survival and time to progression were 13 and 8.6 months, respectively. Five patients had samples available for immunospot testing, of whom 2 (40%) developed CA-125-specific CD8 T-lymphocytes.

CONCLUSION

A combined pancreatic cancer multimodality approach using CIT and radiosensitized radiotherapy is feasible and safe; delivery of immunotherapy can lead to T-cell immunity. Re-evaluation with modern systemic paradigms is recommended.

Evaluation of a Novel Absorbable Radiopaque Hydrogel in Patients Undergoing Image Guided Radiation Therapy for Borderline Resectable and Locally Advanced Pancreatic Adenocarcinoma

PURPOSE

We assessed the feasibility and safety of placing a radiopaque hydrogel in the pancreaticoduodenal groove via endoscopic ultrasound guidance in patients with borderline resectable/locally advanced pancreatic cancer (BR/LAPC).

METHODS AND MATERIALS

Hydrogel injections were done at time of fiducial placement to form blebs in the pancreaticoduodenal groove. Patients subsequently underwent simulation computed tomography (sim-CT) followed by hypofractionated stereotactic body radiotherapy (SBRT; 33 Gy in 5 fractions). Four to 8 weeks after SBRT, patients underwent CT re-evaluation for surgical candidacy and assessment of hydrogel location and size. Hydrogel placement was considered successful if identified in the pancreaticoduodenal groove on sim-CT scan. Stability was evaluated using equivalence testing analyses, with a null hypothesis of the presence of a ≥20% mean percentage change in volume and ≥2 mm change in the median and mean interbleb surface distance with a P value <.05 required to reject the null hypothesis and conclude equivalence. For patients undergoing pancreaticoduodenectomy, hydrogel sites were histologically examined for location and local inflammatory reactions.

RESULTS

Hydrogel placement was successful in 6 of the 6 evaluable patients. The average changes in median and mean interbleb distances were -0.43 mm and -0.35 mm, respectively, with P < .05. The average change in volume from sim-CT to post-SBRT CT was -1.0%, with P < .05. One patient experienced grade 3 nausea after fiducial/hydrogel placement, with no other adverse events to date.

CONCLUSIONS

These data demonstrate feasibility and safety of injecting a hydrogel marker in the pancreaticoduodenal groove in patients with BR/LAPC and set the stage for a follow-up clinical trial to place hydrogel as a spacer between the pancreatic tumor and dose-limiting, radiosensitive duodenum.

Feasibility of Using Hydrogel Spacers for Borderline-Resectable and Locally Advanced Pancreatic Tumors

This article has an accompanying continuing medical education activity, also eligible for MOC credit, on page e14 (https://www.gastrojournal.org/cme/home). Learning Objective: Upon completion of this CME activity, successful learners will be able to describe the pharmacokinetics of hydrogel, identify appropriate candidates for hydrogel injection among patients with pancreatic cancer, and describe key techniques to successfully inject hydrogel as well as the histopathologic findings associated with hydrogel.

Pancreatic cancer treated with SBRT: Effect of anatomical interfraction variations on dose to organs at risk

BACKGROUND AND PURPOSE

Interfraction shape and position variations of organs at risk (OARs) may increase uncertainty in dose delivery during stereotactic body radiotherapy (SBRT), potentially leading to overirradiation or concessions in planned tumor dose and/or coverage to prevent clinical constraints violation. The aim of our study was to quantitatively analyze the impact of anatomical interfraction variations on dose to OARs in pancreatic cancer (PC) treated by SBRT using a CyberKnife with integrated CT-on-rails.

MATERIALS AND METHODS

Thirty-five PC patients treated with SBRT (40 Gy/5 fractions) underwent a CT-scan in treatment position before each of the first three fractions using the CT-on-rails system. OARs (stomach, duodenum, bowel) were manually delineated and concatenated to one structure (Gastro-Intestinal Organ, GIO). To overlay the planned dose distribution, fiducial-based alignment of the fraction CT with the planning CT was performed. Planned DVH parameters of the OAR were compared to the parameters calculated in the fractions CTs.

RESULTS

Compared to the treatment plan, the median V35, D2, D5, D10 and Dmax of the fraction CTs in the GIO was increased by 1.0 (IQR: 0.2-2.6), 4.4% (0.4-10.8), 2.3% (0.2-7.5), 3.3% (-0.4 to 7.1), and 12.0% (5.0-18.9) respectively. Median increase was statistically significant for all parameters in GIO and for V35 in all critical structures at Wilcoxon test.

CONCLUSIONS

Anatomical interfraction variations increase OAR dose during SBRT for pancreatic cancer daily imaging using integrated CT/CyberKnife may allow to implement strategies to reduce the risk of OAR overirradiation during pancreatic SBRT.

Phase I trial of concurrent stereotactic body radiotherapy and nelfinavir for locally advanced borderline or unresectable pancreatic adenocarcinoma

INTRODUCTION

The HIV protease inhibitor nelfinavir (NFV) displays notable radiosensitizing effects. There have been no studies evaluating combined stereotactic body radiotherapy (SBRT) and NFV for borderline/unresectable pancreatic cancer. The primary objective of this phase I trial (NCT01068327) was to determine the maximum tolerated SBRT/NFV dose, and secondarily evaluate outcomes.

METHODS

Following initial imaging, pathologic confirmation, and staging laparoscopy, subjects initially received three 3-week cycles of gemcitabine/leucovorin/fluorouracil; patients without radiologic progression received 5-fraction SBRT/NFV. Dose escalation was as follows: (1) 25 Gy/625 mg BID ×3wks; (2) 25 Gy/1250 mg BID ×3wks; (3) 30 Gy/1250 mg BID ×3wks; (4) 35 Gy/1250 mg BID ×3wks; (5) 35 Gy/1250 mg BID ×5wks; and (6) 40 Gy/1250 mg BID ×5wks. Pancreaticoduodenectomy was performed thereafter if resectable; if not, gemcitabine/leucovorin/fluorouracil was administered.

RESULTS

Forty-six patients enrolled (10/2008-5/2013); 39 received protocol-directed therapy. Sixteen (41%) experienced any grade ≥2 event during and 1 month after SBRT. Four grade 3 and both grade 4 events occurred in a single patient at the initial dose level. 40 Gy/1250 mg BID ×5wks was the maximum tolerated dose. Five patients had late gastrointestinal bleeding (n = 2 superior mesenteric artery pseudo-aneurysm, n = 1 disease progression, n = 1 lower GI tract, n = 1 unknown location). The median overall survival was 14.4 months. Six (15%) patients recurred locally; median local failure-free survival was not reached. The median distant failure-free survival was 11 months, and median all failure-free survival was 10 months.

CONCLUSIONS

Concurrent SBRT (40 Gy)/NFV (1250 mg BID) for locally advanced pancreatic cancer is feasible and safe, although careful attention to treatment planning parameters is recommended to reduce the incidence of late gastrointestinal bleeding.

Health-related quality of life for gemcitabine and nab-paclitaxel plus radiotherapy versus gemcitabine and S-1 plus radiotherapy in patients with metastatic pancreatic cancer

Purpose

To compare the effects of gemcitabine and nab-paclitaxel (GT) plus stereotactic body radiation therapy (SBRT) or gemcitabine and S-1 (GS) plus SBRT on health-related quality of life (HRQOL) of metastatic pancreatic cancer.

Methods

Patients with biopsy-proven and radiographically metastatic pancreatic cancer were included. HRQOL was assessed using the Chinese version of Brief Pain Inventory (BPI) and 5-level European quality of life 5-dimensions (EQ-5D-5L). Data were analyzed with Spearman’s rank correlation, ordinal regression, and propensity score-matched analysis.

Results

A total of 75 and 89 patients received GT and GS, respectively. The median biological effective dose of GT group and GS group was 59.5 Gy (range 48–85.5 Gy) and 64.4 Gy (range 52.48–85.5 Gy) in 5–8 fractions, respectively. More patients in the GS group had improvement in BPI and EQ-5D-5L compared with those in the GT group (n=38 vs n=15, P<0.001; n=42 vs n=20, P<0.001). No differences of BPI scores were found between pre- and post-treatment in each group, while only the post-treatment EQ-5D-5L score was higher than that at baseline in GS the group (P<0.001). Compared with GS group, it was unlikely for patients receiving GT to have better BPI and EQ-5D-5L. After propensity-matched analysis, more patients in GS group had improvement in BPI and EQ-5D-5L (n=24 vs n=12, P=0.002; n=28 vs n=16, P=0.002). Furthermore, patients with GS had a superior overall survival than those with GT (11.1 months [95% CI: 10.6–11.6 months] vs 9.9 months [95% CI: 8.8–11.0 months]; P=0.005). Both incidences of grade 3 hematological (P=0.024) and gastrointestinal (P=0.049) toxicities were higher in the GT group.

Conclusion

GS may achieve better HRQOL than GT. Therefore, GS may be an alternative of GT for metastatic pancreatic cancer, especially for Asians.

Utilization of radiotherapy and stereotactic body radiation therapy for renal cell cancer in the USA

AIM

This study evaluated national practice patterns of cT1N0M0 renal cell cancer, with a focus on stereotactic body radiation therapy (SBRT) utilization.

METHODS

The National Cancer Database was queried (2004-2013) for patients with newly-diagnosed cT1a/bN0M0 renal cell cancer that received definitive treatment. Temporal trends in utilization were tabulated.

RESULTS

Altogether, 138,495 patients met inclusion criteria; 13,725 (9.9%) patients received ablative therapy, 57,924 (41.8%) partial nephrectomy, 67,168 (48.5%) radical nephrectomy and 308 (0.2%) external beam radiation therapy (EBRT). The proportion of EBRT that was SBRT increased substantially from 25% in 2004 to 95.4% in 2013, with a sharp inflection point from 2005 to 2006.

CONCLUSION

SBRT utilization has sharply risen over time; in most recent years, the vast majority of EBRT is delivered in the form of SBRT.

Approaches to stereotactic body radiation therapy for large (≥5 centimeter) non-small cell lung cancer

Although larger (≥5 cm) node-negative non-small cell lung cancer (NSCLC) lesions are altogether uncommon, their incidence may increase following the implementation of lung cancer screening. A rigorous assessment of stereotactic body radiation therapy (SBRT) for these challenging cases is imperative not only owing to concerns of increased risks when delivering ablative doses to large volumes, but also due to lack of prospective data, as these patients were excluded from seminal phase II SBRT trials. In addition to appraising the available institutional or multi-institutional experiences, multiple strategies to reduce toxicities are discussed. These include exploration of several different dose/fractionation schemes and regimens, as well as specialized techniques for SBRT treatment planning and delivery. Because these lesions have a higher rate of occult lymphatic or distant spread, the role of systemic therapies (including chemotherapy and immunotherapy) are also discussed. Altogether, the publication of several key reports, entirely over the last few years, has created a more solid foundation with which to utilize evidence-based management for this unique patient population.

Dose-escalated radiotherapy for unresectable or locally recurrent pancreatic cancer: Dose volume analysis, toxicity and outcome of 28 consecutive patients

PURPOSE

The role of radiotherapy for unresectable pancreatic cancer is controversial. A benefit of additional radiotherapy is supported by some observations. A dose-effect relationship was recently found by dose escalation employing image guided and intensity modulated radiotherapy.

METHODS

We retrospectively evaluated 28 consecutive patients, all with history of extensive prior therapies for unresectable locally advanced/ recurrent pancreatic cancer (LAPC/LRPC). Treatment was delivered by helical tomotherapy after daily position verification with computed tomography. Dose to the planned target volume (PTV) was 51 Gy, while the dose to the macroscopic tumor was escalated by a simultaneous integrated boost to a median cumulative dose of 66 Gy (60-66 Gy). Concomitant chemotherapy consisted mainly of capecitabine (n = 23).

RESULTS

10 of 28 patients presented acute toxicities > grade 2, one patient succumbed to gastrointestinal bleeding after treatment. No correlations of toxicities and dose volume histograms (DVH) of retrospectively delineated small bowel loops were observed, although average small bowel volume receiving ≥ 20 Gy was 374 ml. DVH analyses revealed a correlation of splenic parameters and acute toxicity: Vomiting, anorexia, dehydration, hematologic toxicity, fatigue, combined gastro-intestinal toxicity wit R-values between 0.392 and 0.561 (all p-values > 0.05). Only one patient developed late toxicities > grade 2. With an average follow-up time in surviving patients of 14 months median overall survival time was 19 months and median time to local recurrence 13 months. In 8 patients with available imaging of local recurrence: 5 in field recurrences, 2 marginal recurrences and one lymph node recurrence outside the high dose radiation field were observed. In univariate analysis only ΔCA-19-9 during radiotherapy was associated with local control (p = 0.029) and overall survival (p = 0.049).

CONCLUSION

Dose escalated normo-fractionated radiotherapy for LAPC/LRPC seems feasible and suitable to prolong local control and in consequence long-term survival. However, in-field local progression is still frequently observed and possibilities to increase the local effectiveness should be evaluated. Exposure of the spleen was predictive for acute toxicity and should be further investigated.

Biological determinants of radioresistance and their remediation in pancreatic cancer

Despite recent advances in radiotherapy, a majority of patients diagnosed with pancreatic cancer (PC) do not achieve objective responses due to the existence of intrinsic and acquired radioresistance. Identification of molecular mechanisms that compromise the efficacy of radiation therapy and targeting these pathways is paramount for improving radiation response in PC patients. In this review, we have summarized molecular mechanisms associated with the radio-resistant phenotype of PC. Briefly, we discuss the reversible and irreversible biological consequences of radiotherapy, such as DNA damage and DNA repair, mechanisms of cancer cell survival and radiation-induced apoptosis following radiotherapy. We further describe various small molecule inhibitors and molecular targeting agents currently being tested in preclinical and clinical studies as potential radiosensitizers for PC. Notably, we draw attention towards the confounding effects of cancer stem cells, immune system, and the tumor microenvironment in the context of PC radioresistance and radiosensitization. Finally, we discuss the need for examining selective radioprotectors in light of the emerging evidence on radiation toxicity to non-target tissue associated with PC radiotherapy.

Feasibility and reproducibility of substituting oral contrast with water for duodenal volume delineation in patients undergoing pancreatic stereotactic body radiotherapy

BACKGROUND

This is the first known report evaluating the feasibility of substituting oral contrast with water in efforts to delineate the duodenum for pancreatic stereotactic body radiotherapy (SBRT).

METHODS

From January 2015 to August 2016, 13 patients were simulated after ingestion of 8 ounces of water approximately 15-20 min prior to their simulation scan. We examined the feasibility of contouring the duodenum thereafter, and measured the duodenal volume as well as its variation. Comparison was made to 40 patients treated from January 2009 to February 2012 on a prospective trial who used oral contrast. Group comparisons were performed by the Mann-Whitney U test.

RESULTS

The duodenum was identified in all 13 patients who used water instead of oral contrast without subjective difficulty. In this group, the median duodenal volume was 72.86 cm³ (range, 44.61-130.90 cm³). In the oral contrast group, median duodenal volume was 86.21 cm³ (range, 50.11-157.89 cm³) There were no significant differences between groups (P=0.115). The approach was reproducible, as all patients were able to drink the same amount of water 15-20 min prior to each SBRT fraction to keep duodenal volumes subjectively similar to volumes on the simulation CT scan.

CONCLUSIONS

This novel approach is effective and reproducible in delineating the duodenum for treatment planning and daily setup.

Quantification of renal function following stereotactic body radiotherapy for pancreatic cancer: secondary dosimetric analysis of a prospective clinical trial

BACKGROUND

This is the first known study examining renal function following stereotactic body radiotherapy (SBRT) for pancreatic head adenocarcinoma.

METHODS

Thirty-eight borderline-resectable/unresectable patients, part of an ongoing prospective trial, underwent 3 cycles of gemcitabine/5-fluorouracil followed by SBRT (5 daily fractions of 5/6/7/8 Gy) and concurrent nelfinavir. Thereafter, in resectable cases, surgery was performed within 4-8 weeks. The last available pre-SBRT creatinine was recorded, along with the highest post-SBRT value. Glomerular filtration rate (GFR) was calculated by the commonly-utilized Modification of Diet in Renal Disease formula. GFR decline was defined as the post-SBRT nadir GFR minus the pre-SBRT GFR. Correlations with the V5-V30, and mean/maximum kidney doses was performed. Statistics included Pearson correlation, Mann-Whitney, and Fisher's exact tests.

RESULTS

The median total kidney volume was 355 cm³. Median dosimetric values were as follows: V5 (209 cm³), V10 (103 cm³), V15 (9 cm³), V20 (0 cm³), V25 (0 cm³); and mean (6.7 Gy) & maximum kidney dose (18.3 Gy). Median GFR change was -23 (range, -105 to 25) mL/min/1.73 cm². Of all dosimetric parameters, only V5 was significantly associated with changes in GFR (Pearson r = -0.40, p = 0.012). In patients with V5 < 210 cm³, median GFR change was -11.8 mL/min/1.73 cm², as compared with -37.1 mL/min/1.73 cm² change in those with V5 ≥ 210 cm³ (p = 0.02). A GFR change < -23 mL/min/1.73 cm² was observed in 6/20 (30%) patients with V5 < 210 cm³, versus 15/18 (83%) of those with V5 ≥ 210 cm³. Patients with V5 ≥ 210 cm³ were over ten times as likely to have GFR change < -23 mL/min/1.73 cm² (p = 0.003). Using linear regression, GFR change ≈ -0.1748 × V5(cm³) + 8.63.

CONCLUSIONS

In the first known analysis of renal function after pancreatic SBRT, evaluating patients on a prospective study, V5 ≥ 210 cm³ was associated with a post-SBRT GFR decline of >23 mL/min/1.73 cm². If V5 is kept <210 cm³, median GFR decline was only 11.8 mL/min/1.73 cm². Further validation is needed to ascertain definite dose-volume parameters and examine late renal decline.