A dosimetric comparison of proton and photon therapy in unresectable cancers of the head of pancreas

Study of a plastic scintillating plate-based quality assurance system for pencil beam scanning proton beams

INTRODUCTION

The purpose of this study was to evaluate a plastic scintillating plate-based beam monitoring system to perform quality assurance (QA) measurements in pencil beam scanning proton beam.

METHODS

Single spots and scanned fields were measured with the high-resolution dosimetry system, consisting of a plastic scintillation plate coupled to a camera in a dark box at the isocenter. The measurements were taken at 110-190 MeV beam energies with 30° gantry angle intervals at each energy. Spot positions were determined using the plastic scintillating plate-based dosimetry system at the isocenter for 70-230 MeV beam energies with 30° gantry angle intervals. The effect of gantry angle on dose distribution was also assessed by determining the scanning pattern for daily QA and 25 fields treated with intensity-modulated proton therapy.

RESULTS

Spot size, field flatness, and field symmetry of plastic scintillating plate-based dosimetry system were consistent with EBT3 at all investigated energies and angles. In all investigated energies and angles, the spot size measured was ±10% of the average size of each energy, the spot position measured was within ±2 mm, field flatness was within ±2%, and field symmetry was within ±1%. The mean gamma passing rates with the 3%/3 mm gamma criterion of the scanning pattern and 25 fields were 99.2% and 99.8%, respectively.

CONCLUSIONS

This system can be effective for QA determinations of spot size, spot position, field flatness, and field symmetry over 360° of gantry rotation in a time- and cost-effective manner, with spatial resolution comparable to that of EBT3 film.

Analysis of the cost-effectiveness of proton beam therapy for unresectable pancreatic cancer in Japan

BACKGROUND

Proton beam therapy (PBT) has recently been included in Japan's social health insurance benefits package. This study aimed to determine the cost-effectiveness of PBT for unresectable, locally advanced pancreatic cancer (LAPC) as a replacement for conventional photon radiotherapy (RT).

METHODS

We estimated the incremental cost-effectiveness ratio (ICER) of PBT as a replacement for three-dimensional conformal RT (3DCRT), a conventional photon RT, using clinical evidence in the literature and expense complemented by expert opinions. We used a decision tree and an economic and Markov model to illustrate the disease courses followed by LAPC patients. Effectiveness was estimated as quality-adjusted life years (QALY) using utility weights for the health state. Social insurance fees were calculated as the costs. The stability of the ICER against the assumptions made was appraised using sensitivity analyses.

RESULTS

The effectiveness of PBT and 3DCRT was 1.67610615 and 0.97181271 QALY, respectively. The ICER was estimated to be ¥5,376,915 (US$46,756) per QALY. According to the suggested threshold for anti-cancer therapy from the Japanese authority of ¥7,500,000 (US$65,217) per QALY gain, such a replacement would be considered cost-effective. The one-way and probabilistic sensitivity analyses demonstrated stability of the base-case ICER.

CONCLUSION

PBT, as a replacement for conventional photon radiotherapy, is cost-effective and justifiable as an efficient use of finite healthcare resources. Making it a standard treatment option and available to every patient in Japan is socially acceptable from the perspective of health economics.

Proton Therapy for Unresectable and Medically Inoperable Locally Advanced Pancreatic Cancer: Results From a Multi-Institutional Prospective Registry

Purpose

Compared with photon-based techniques, proton beam radiation therapy (PBT) may improve the therapeutic ratio of radiation therapy (RT) for locally advanced pancreatic cancer (LAPC), but available data have been limited to single-institutional experiences. This study examined the toxicity, survival, and disease control rates among patients enrolled in a multi-institutional prospective registry study and treated with PBT for LAPC.

Methods and Materials

Between March 2013 and November 2019, 19 patients with inoperable disease across 7 institutions underwent PBT with definitive intent for LAPC. Patients received a median radiation dose/fractionation of 54 Gy/30 fractions (range, 50.4-60.0 Gy/19-33 fractions). Most received prior (68.4%) or concurrent (78.9%) chemotherapy. Patients were assessed prospectively for toxicities using National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0. Kaplan-Meier analysis was used to analyze overall survival, locoregional recurrence-free survival, time to locoregional recurrence, distant metastasis-free survival, and time to new progression or metastasis for the adenocarcinoma cohort (17 patients).

Results

No patients experienced grade ≥3 acute or chronic treatment-related adverse events. Grade 1 and 2 adverse events occurred in 78.7% and 21.3% of patients, respectively. Median overall survival, locoregional recurrence-free survival, distant metastasis-free survival, and time to new progression or metastasis were 14.6, 11.0, 11.0, and 13.9 months, respectively. Freedom from locoregional recurrence at 2 years was 81.7%. All patients completed treatment with one requiring a RT break for stent placement.

Conclusions

Proton beam RT for LAPC offered excellent tolerability while still maintaining disease control and survival rates comparable with dose-escalated photon-based RT. These findings are consistent with the known physical and dosimetric advantages offered by proton therapy, but the conclusions are limited owing to the patient sample size. Further clinical studies incorporating dose-escalated PBT are warranted to evaluate whether these dosimetric advantages translate into clinically meaningful benefits.

Comparison of dosimetries of carbon-ion pencil beam scanning, proton pencil beam scanning and volumetric modulated arc therapy for locally recurrent rectal cancer

We compared the dose distributions of carbon-ion pencil beam scanning (C-PBS), proton pencil beam scanning (P-PBS) and Volumetric Modulated Arc Therapy (VMAT) for locally recurrent rectal cancer. The C-PBS treatment planning computed tomography (CT) data sets of 10 locally recurrent rectal cancer cases were randomly selected. Three treatment plans were created using identical prescribed doses. The beam angles for C-PBS and P-PBS were identical. Dosimetry, including the dose received by 95% of the planning target volume (PTV) (D95%), dose to the 2 cc receiving the maximum dose (D2cc), organ at risk (OAR) volume receiving > 15Gy (V15) and > 30Gy (V30), was evaluated. Statistical significance was assessed using the Wilcoxon signed-rank test. Mean PTV-D95% values were > 95% of the volume for P-PBS and C-PBS, whereas that for VMAT was 94.3%. However, PTV-D95% values in P-PBS and VMAT were < 95% in five and two cases, respectively, due to the OAR dose reduction. V30 and V15 to the rectum/intestine for C-PBS (V30 = 4.2 ± 3.2 cc, V15 = 13.8 ± 10.6 cc) and P-PBS (V30 = 7.3 ± 5.6 cc, V15 = 21.3 ± 13.5 cc) were significantly lower than those for VMAT (V30 = 17.1 ± 10.6 cc, V15 = 55.2 ± 28.6 cc). Bladder-V30 values with P-PBS/C-PBS (3.9 ± 4.8 Gy(RBE)/3.0 ± 4.0 Gy(RBE)) were significantly lower than those with VMAT (7.9 ± 8.1 Gy). C-PBS provided superior dose conformation and lower OAR doses compared with P-PBS and VMAT. C-PBS may be the best choice for cases in which VMAT and P-PBS cannot satisfy dose constraints. C-PBS could be another choice for cases in which VMAT and P-PBS cannot satisfy dose constraints, thereby avoiding surgical resection.

The Feasibility of Stereotactic Body Proton Beam Therapy for Pancreatic Cancer

Background/Purpose: This study aimed to evaluate the clinical outcomes of stereotactic body proton beam therapy (SBPT) for pancreatic cancer. Methods: This retrospective study included 49 patients who underwent SBPT for pancreatic cancer between 2017 and 2020. Survival outcomes, bowel-related toxicities, and failure patterns were analysed. SBPT was performed after induction chemotherapy in 44 (89.8%) patients. The dose-fractionation scheme included 60 gray (Gy) relative biological effectiveness (RBE) in five fractions (n = 42, 85.7%) and 50 GyRBE in five fractions (n = 7, 14.3%). The median follow-up was 16.3 months (range, 1.8−45.0 months). Results: During follow-up, the best responses were complete response, partial response, and stable disease in four (8.2%), 13 (26.5%), and 31 (63.3%) patients, respectively. The 2-year overall survival, progression-free survival, and local control (LC) rates were 67.6%, 38.0%, and 73.0%, respectively. Grade ≥ 3 gastroduodenal (GD) toxicity occurred in three (6.1%) patients. Among them, one patient underwent endoscopic haemostasis. The other two patients received surgical management. They were followed up without disease progression for >30 months after SBPT. Overall, there was no significant dosimetric difference between the grade ≥ 2 and lower toxicity groups. Conclusions: SBPT provides relatively high LC rates with acceptable toxicities in pancreatic cancer.

Proton Therapy in the Management of Pancreatic Cancer

Simple Summary

Radiation treatment plays a pivotal a role in the management of pancreatic cancer, mainly in the neoadjuvant setting for borderline resectable tumors and in the definitive setting for unresectable localized disease. Most of the studies on pancreatic cancer use photon-based radiation therapy modalities. However, there is a growing interest in the application of protons therapy for gastrointestinal cancers. This review summarizes the literature on the use of proton therapy in the management of pancreatic cancer.

Abstract

Radiation therapy plays a central role in the treatment of pancreatic cancer. While generally shown to be feasible, proton irradiation, particularly when an ablative dose is planned, remains a challenge, especially due to tumor motion and the proximity to organs at risk, like the stomach, duodenum, and bowel. Clinically, standard doses of proton radiation treatment have not been shown to be statistically different from photon radiation treatment in terms of oncologic outcomes and toxicity rates as per non-randomized comparative studies. Fractionation schedules and concurrent chemotherapy combinations are yet to be optimized for proton therapy and are the subject of ongoing trials.

Vital organ sparing with proton therapy for pediatric Hodgkin lymphoma: Toxicity and outcomes in 50 patients

BACKGROUND AND PURPOSE

With high survival rates for pediatric Hodgkin lymphoma (HL), attention has turned to minimizing treatment-related morbidity and mortality. Chemotherapy and dose of radiation to organs at risk (OARs) contribute to elevated risks of secondary malignancy and cardiopulmonary disease. We sought to characterize the radiation dose to OARs, toxicities, and outcomes for pediatric HL patients treated with proton therapy (PT).

MATERIALS AND METHODS

Fifty patients aged 11-21 with HL consecutively treated with PT were evaluated 1-2 months following completion of PT and every 6 months thereafter. Acute and late toxicities were captured retrospectively using CTCAE v5. Patterns of relapse were characterized, and survival was assessed using Kaplan-Meier method.

RESULTS

Most (47, 94%) patients received PT to the mediastinum. Median mean heart dose was 4.3 Gy (RBE) and median bilateral lung V20Gy was 5.8%. Median integral dose was 1.7 Gy. For the 27 female patients, a median mean dose of 0.4 and 0.3 Gy (RBE) was delivered to ipsilateral and contralateral breast tissue, respectively. No on-treatment grade 3-5 toxicities were seen. At a median follow-up of 5.3 years, no PT-related grade 3-5 toxicities or secondary malignancies developed. Five patients relapsed at a median time of 9.2 months after PT (range 2.5-24.9 months; 5-year recurrence free survival 90%). Recurrences were both in- and out-of-field in all 5 cases with no marginal failures. All relapsed patients were successfully salvaged (5-year overall survival 100%).

CONCLUSION

For pediatric HL patients, proton treatment resulted in marked dose sparing of OARs with low rates of toxicity, no marginal failures, and excellent 5-year survival.

Factors associated with long-term survival in gemcitabine-concurrent proton radiotherapy for non-metastatic locally advanced pancreatic cancer: a single-center retrospective study

Background

Factors associated with long-term survival in gemcitabine-concurrent proton radiotherapy (GPT) for non-metastatic, locally advanced pancreatic cancer (LAPC) remain unclear. This study aimed to determine the factors associated with long-term survival in GPT for non-metastatic LAPC.

Methods

The medical records of 123 patients with LAPC treated with GPT between February 2009 and December 2019 at Hyogo Ion Beam Medical Center were retrospectively reviewed to assess the factors associated with long-term survival outcomes.

Results

The median overall survival of the total cohort treated with GPT was 18.7 months. The 1- and 2-year overall, local progression-free, and progression-free survival rates were 70.4% and 35.7%, 78.2% and 59.0%, and 38.6% and 20.8%, respectively. Multivariate analysis revealed that LAPCs at the pancreatic body-tail and those without anterior peripancreatic invasion were independently associated with longer overall survival (P = 0.040 and P = 0.015, respectively). The median overall survival of patients with LAPC at the pancreatic body-tail and those with LAPC without anterior peripancreatic invasion were 24.1 and 28.1 months, respectively. LAPCs at the pancreatic body-tail had a higher volume ratio irradiated over 60 Gy equivalents at gross tumor volume than those at the pancreatic head (P < 0.001). LAPCs with anterior peripancreatic invasion had more peritoneal recurrence within 6 months after GTP than those without anterior peripancreatic invasion (P = 0.039).

Conclusions

GPT is a promising treatment option for patients with LAPC at the pancreatic body-tail and those with LAPC without anterior peripancreatic invasion.

A Beam-Specific Optimization Target Volume for Stereotactic Proton Pencil Beam Scanning Therapy for Locally Advanced Pancreatic Cancer

PURPOSE

We investigate two margin-based schemes for optimization target volumes (OTV), both isotropic expansion (2 mm) and beam-specific OTV, to account for uncertainties due to the setup errors and range uncertainties in pancreatic stereotactic pencil beam scanning (PBS) proton therapy. Also, as 2-mm being one of the extreme sizes of margin, we also study whether the plan quality of 2-mm uniform expansion could be comparable to other plan schemes.

METHODS AND MATERIALS

We developed 2 schemes for OTV: (1) a uniform expansion of 2 mm (OTV2mm) for setup uncertainty and (2) a water equivalent thickness-based, beam-specific expansion (OTVWET) on beam direction and 2 mm expansion laterally. Six LAPC patients were planned with a prescribed dose of 33 Gy (RBE) in 5 fractions. Robustness optimization (RO) plans on gross tumor volumes, with setup uncertainties of 2 mm and range uncertainties of 3.5%, were implemented as a benchmark.

RESULTS

All 3 optimization schemes achieved decent target coverage with no significant difference. The OTV2mm plans show superior organ at risk (OAR) sparing, especially for proximal duodenum. However, OTV2mm plans demonstrate severe susceptibility to range and setup uncertainties with a passing rate of 19% of the plans meeting the goal of 95% volume covered by the prescribed dose. The proposed dose spread function analysis shows no significant difference.

CONCLUSIONS

The use of OTVWET mimics a union volume for all scenarios in robust optimization but saves optimization time noticeably. The beam-specific margin can be attractive to online adaptive stereotactic body proton therapy owing to the efficiency of the plan optimization.

Investigate the Dosimetric and Potential Clinical Benefits Utilizing Stereotactic Body Radiation Therapy With Simultaneous Integrated Boost Technique for Locally Advanced Pancreatic Cancer: A Comparison Between Photon and Proton Beam Therapy

Purpose

To investigate the potential clinical benefits of using stereotactic body radiation therapy (SBRT) with simultaneous integrated boost (SIB) technique for locally advanced pancreatic cancer (LAPC) among different treatment modalities and planning strategies, including photon and proton.

Method

A total of 19 patients were retrospectively selected in this study: 13 cases with the tumor located in the head of the pancreas and 6 cases with the tumor in the body of the pancreas. SBRT-SIB plans were generated using volumetric modulated arc therapy (VMAT), two-field Intensity Modulated Proton Therapy (IMPT), and three-field IMPT. The IMPT used the robust optimization parameters of ± 3.5% range and 5-mm setup uncertainties. Root-mean-square deviation dose (RMSD) volume histograms were used to evaluate the target coverage robustness quantitatively. Dosimetric metrics based on the dose-volume histogram (DVH), homogeneity index (HI), and normal tissue complication probability (NTCP) were analyzed to evaluate the potential clinical benefits among different planning groups.

Results

With a similar CTV and SIB coverage, two-field IMPT provided a lower maximum dose for the stomach (median: 18.6GyE, p<0.05) and duodenum (median: 32.62GyE, p<0.05) when the target was located in the head of the pancreas compared to VMAT and three-field IMPT. The risks of gastric bleed (3.42%) and grade ≥ 3 GI toxicity (4.55%) were also decreased. However, for the target in the body of the pancreas, VMAT showed a lower maximum dose for the stomach (median 30.93GyE, p<0.05) and toxicity of gastric bleed (median: 8.67%, p<0.05) compared to two-field IMPT and three-field IMPT, while other maximum doses and NTCPs were similar. The RMSD volume histogram (RVH) analysis shows that three-field IMPT provided better robustness for targets but not for OARs. Instead, three-field IMPT increased the Dmean of organs such as the stomach, duodenum, and intestine.

Conclusion

The results indicated that the tumor locations could play a critical role in determining clinical benefits among different treatment modalities. Two-field IMPT could be a better option for LAPC patients whose tumors are located in the head of the pancreas. It provides lower severe toxicity for the stomach and duodenum. Nevertheless, VMAT is preferred for the body with better protection for the possibility of gastric bleed.

Normal Tissue Injury Induced by Photon and Proton Therapies: Gaps and Opportunities

Despite technological advances in radiation therapy (RT) and cancer treatment, patients still experience adverse effects. Proton therapy (PT) has emerged as a valuable RT modality that can improve treatment outcomes. Normal tissue injury is an important determinant of the outcome; therefore, for this review, we analyzed 2 databases: (1) clinical trials registered with ClinicalTrials.gov and (2) the literature on PT in PubMed, which shows a steady increase in the number of publications. Most studies in PT registered with ClinicalTrials.gov with results available are nonrandomized early phase studies with a relatively small number of patients enrolled. From the larger database of nonrandomized trials, we listed adverse events in specific organs/sites among patients with cancer who are treated with photons and protons to identify critical issues. The present data demonstrate dosimetric advantages of PT with favorable toxicity profiles and form the basis for comparative randomized prospective trials. A comparative analysis of 3 recently completed randomized trials for normal tissue toxicities suggests that for early stage non-small cell lung cancer, no meaningful comparison could be made between stereotactic body RT and stereotactic body PT due to low accrual (NCT01511081). In addition, for locally advanced non-small cell lung cancer, a comparison of intensity modulated RTwith passive scattering PT (now largely replaced by spot-scanned intensity modulated PT), PT did not provide any benefit in normal tissue toxicity or locoregional failure over photon therapy. Finally, for locally advanced esophageal cancer, proton beam therapy provided a lower total toxicity burden but did not improve progression-free survival and quality of life (NCT01512589). The purpose of this review is to inform the limitations of current trials looking at protons and photons, considering that advances in technology, physics, and biology are a continuum, and to advocate for future trials geared toward accurate precision RT that need to be viewed as an iterative process in a defined path toward delivering optimal radiation treatment. A foundational understanding of the radiobiologic differences between protons and photons in tumor and normal tissue responses is fundamental to, and necessary for, determining the suitability of a given type of biologically optimized RT to a patient or cohort.

Dose-escalated simultaneously integrated boost photon or proton therapy in pancreatic cancer in an in-silico study: Gastrointestinal organs remain critical

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Robustly optimized proton plans (rMFO-IMPT) with simultaneously integrated boost (SIB) were clinically applicable.

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Gastrointestinal organs reached critical dose values in rMFO-IMPT, VMAT and Tomotherapy techniques.

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rMFO-IMPT significantly reduced the low and intermediate dose to organs at risk.

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No clinically significant differences on results depending on tumor location or surgical status were observed.

Purpose

To compare the dosimetric results of an in-silico study among intensity-modulated photon (IMRT) and robustly optimized intensity-modulated proton (IMPT) treatment techniques using a dose-escalated simultaneously integrated boost (SIB) approach in locally recurrent or advanced pancreatic cancer patients.

Material and methods

For each of 15 locally advanced pancreatic cancer patients, a volumetric-modulated arc therapy (VMAT), a Tomotherapy (TOMO), and an IMPT treatment plan was optimized on free-breathing treatment planning computed tomography (CT) images. For the photon treatment plans, doses of 66 Gy and 51 Gy, both as SIB in 30 fractions, were prescribed to the gross tumor volume (GTV) and to the planning target volume (PTV), respectively. For the proton plans, a dose prescription of 66 Gy(RBE) to the GTV and of 51 Gy(RBE) to the clinical target volume (CTV) was planned. For each SIB-treatment plan, doses to the targets and OARs were evaluated and statistically compared.

Results

All treatment techniques reached the prescribed doses to the GTV and CTV or PTV. The stomach and the bowel, in particular the duodenum and the small bowel, were found to be frequently exposed to doses exceeding 50 Gy, irrespective of the treatment technique. For doses below 50 Gy, the IMPT technique was statistically significant superior to both IMRT techniques regarding decreasing dose to the OARs, e.g. volume of the bowel receiving 15 Gy (V_15Gy) was reduced for IMPT compared to VMAT (p = 0.003) and TOMO (p < 0.001).

Conclusion

With all photon and proton techniques investigated, the radiation dose to gastrointestinal OARs remained critical when treating patients with unresectable locally recurrent or advanced pancreatic cancer using a dose-escalated SIB approach.

Novel strategies using modern radiotherapy to improve pancreatic cancer outcomes: toward a new standard?

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive solid tumours with an estimated 5-year overall survival rate of 7% for all stages combined. In this highly resistant disease that is located in the vicinity of many radiosensitive organs, the role of radiotherapy (RT) and indications for its use in this setting have been debated for a long time and are still under investigation. Although a survival benefit has yet to be clearly demonstrated for RT, it is the only technique, other than surgery, that has been demonstrated to lead to local control improvement. The adjuvant approach is now strongly challenged by neoadjuvant treatments that could spare patients with rapidly progressive systemic disease from unnecessary surgery and may increase free margin (R0) resection rates for those eligible for surgery. Recently developed dose-escalated RT treatments, designed either to maintain full-dose chemotherapy or to deliver a high biologically effective dose, particularly to areas of contact between the tumour and blood vessels, such as hypofractionated ablative RT (HFA-RT) or stereotactic body RT (SBRT), are progressively changing the treatment landscape. These modern strategies are currently being tested in prospective clinical trials with encouraging preliminary results, paving the way for more effective treatment combinations using novel targeted therapies. This review summarizes the current literature regarding the use of RT for the treatment of primary PDAC, describes the limitations of conventional RT, and discusses the emerging role of dose-escalated RT and heavy-particle RT.

Radiobiological model-based approach to determine the potential of dose-escalated robust intensity-modulated proton radiotherapy in reducing gastrointestinal toxicity in the treatment of locally advanced unresectable pancreatic cancer of the head

Background

The purpose of this study was to determine the potential of escalated dose radiation (EDR) robust intensity-modulated proton radiotherapy (ro-IMPT) in reducing GI toxicity risk in locally advanced unresectable pancreatic cancer (LAUPC) of the head in term of normal tissue complication probability (NTCP) predictive model.

Methods

For 9 patients, intensity-modulated radiotherapy (IMRT) was compared with ro-IMPT. For all plans, the prescription dose was 59.4GyE (Gray equivalent) in 33 fractions with an equivalent organ at risk (OAR) constraints. Physical dose distribution was evaluated. GI toxicity risk for different endpoints was estimated using published NTCP Lyman Kutcher Burman (LKB) models for stomach, duodenum, small bowel, and combine stomach and duodenum (Stoduo). A Wilcoxon signed-rank test was used for dosimetry parameters and NTCP values comparison.

Result

The dosimetric results have shown that, with similar target coverage, ro-IMPT achieves a significant dose-volume reduction in the stomach, small bowel, and stoduo in low to high dose range in comparison to IMRT. NTCP evaluation for the endpoint gastric bleeding of stomach (10.55% vs. 13.97%, P = 0.007), duodenum (1.87% vs. 5.02%, P = 0.004), and stoduo (5.67% vs. 7.81%, P = 0.008) suggest reduced toxicity by ro-IMPT compared to IMRT. ∆NTCP _{IMRT – ro-IMPT} (using parameter from Pan et al. for gastric bleed) of ≥5 to < 10% was seen in 3 patients (33%) for stomach and 2 patients (22%) for stoduo. An overall GI toxicity relative risk (NTCP_ro-IMPT/NTCP_IMRT) reduction was noted (0.16–0.81) for all GI-OARs except for duodenum (> 1) with endpoint grade ≥ 3 GI toxicity (using parameters from Holyoake et al.).

Conclusion

With similar target coverage and better conformity, ro-IMPT has the potential to substantially reduce the risk of GI toxicity compared to IMRT in EDR of LAUPC of the head. This result needs to be further evaluated in future clinical studies.

Proton and carbon ion radiation therapy for locally advanced pancreatic cancer: A phase I dose escalation study

OBJECTIVE

To determine the maximum tolerated dose (MTD) of proton and carbon ion radiation therapy (PCRT) for locally advanced pancreatic cancer (LAPC).

METHODS

A single-institution, phase I dose escalation study was performed. The proton dose of 50.4 GyE in 28 fractions was delivered to clinical target volume, and carbon ion as a boost dose to gross tumor volume escalated from 12 GyE to 18 GyE with 3 GyE per fraction in 3 dose levels. The dose limiting toxicity (DLT) was defined as any treatment-related grade (G)3 or higher of non-hematological toxicity. The MTD was exceeded if ≥2 patients in a dose level developed DLT.

RESULTS

From May 2015 to July 2016, ten patients were enrolled, 3 in dose level 1, 4 in dose level 2, and 3 in dose level 3. With a median follow-up of 17.4 months, no patient developed a DLT, and the acute G1-2 of gastrointestinal (GI) and hepatic toxicity occurred in 40% of patients, and G1 of GI late toxicity, in 30%. The median overall survival was 17.3 months.

CONCLUSION

Higher than 50.4 GyE could be given by PCRT with slight toxicity and good tolerance for LAPC, and the tumor control and survival had been improved, but not significantly. Better outcome may be achieved using carbon ion radiation therapy with higher biological equivalent dose.

Proton beam re-irradiation for gastrointestinal malignancies: a systematic review

Background

Radiotherapy (RT) is part of the standard of care management of most gastrointestinal (GI) cancers. Even with advanced RT, systemic therapy, and surgical techniques, locoregional recurrences or second primary cancers can still occur within previously irradiated fields, which can present challenges in delivering effective and safe treatment. Options for reirradiation are often limited, but given the favorable dosimetric aspects of proton-beam RT, it may provide an effective and safe re-irradiation option for patients with recurrent or second primary GI cancers.

Methods

We conducted a systematic review as per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement protocol, assessing for reports of proton-beam reirradiation for recurrent or second primary GI cancers, primarily via PubMed. From the initial 373 articles identified, 7 articles were ultimately included in the analysis.

Results

The 7 included studies reported on proton-beam re-irradiation for the following disease sites: esophageal (n=2), pancreas (n=1), liver (n=2), rectal (n=1), and anal (n=1). Study sizes varied from as few as 1 to as many as 83 patients. Across studies, in patients who presented with tumor-related symptoms, palliation (stability/improvement) was achieved in 80-100% of the cases. Local control rates, with variable follow-up, ranged from 36-100%. All median overall survival values, when reported, were greater than 1 year. Across both liver studies, there were no cases of radiation-induced liver disease (RILD) from proton-beam re-irradiation. Across all studies, there were 2 acute (esophagopleural fistula in esophageal cancer, small bowel perforation in pancreatic cancer) and 1 late (esophageal ulcer in esophageal cancer) grade 5 toxicities, all favored to be due to progressive disease, rather than proton-beam re-irradiation. Two studies (1 esophageal, 1 rectal) generated comparison photon plans. One found that proton therapy reduced mean heart and lung doses, spinal cord dose, and lung V5Gy as compared to photon treatment, while resulting in higher lung V20Gy and V30Gy. The other found that protons decreased bowel V10Gy, V20Gy, and the dose to 200 and 150 cc of bowel, as compared to photons.

Conclusions

Based upon the published experiences, proton-beam re-irradiation for recurrent or second primary GI cancers appears effective for palliation, with good disease-control, limited toxicity, favorable dosimetry, and overall compares well with published non-proton-beam experiences. Given short follow-up, additional studies are warranted to determine if dosimetric advantages from proton therapy will translate into comparative toxicity benefits.

Proton beam radiotherapy for pancreas cancer

Pancreatic carcinoma is a challenging malignancy to manage with a very poor prognosis. Despite continued difficulties in its management, there have been incremental improvements in outcomes over the past several decades. Achieving the best oncologic outcomes requires a multimodality approach including surgery, chemotherapy, and radiotherapy. Proton radiotherapy enables the delivery of high-dose radiotherapy to the tumor or resection bed while sparing nearby critical organs. Due to their unique physical properties, protons can deliver radiotherapy dose distributions that are not achievable with photons (X-rays) even with advanced photon delivery techniques (e.g., intensity-modulated radiotherapy). Improved dose distributions can lead to reduced treatment toxicity and enable treatment intensification. As better chemotherapy regimens lead to better systemic disease control, it will become increasingly important that local-regional control is achieved. This will in part be accomplished by combining better radiotherapy with more active chemotherapies. Proton radiotherapy provides an excellent means for achieving this.

Dose-Volume and Radiobiological Model-Based Comparative Evaluation of the Gastrointestinal Toxicity Risk of Photon and Proton Irradiation Plans in Localized Pancreatic Cancer Without Distant Metastasis

Background: Radiobiological model-based studies of photon-modulated radiotherapy for pancreatic cancer have reported reduced gastrointestinal (GI) toxicity, although the risk is still high. The purpose of this study was to investigate the potential of 3D-passive scattering proton beam therapy (3D-PSPBT) in limiting GI organ at risk (OAR) toxicity in localized pancreatic cancer based on dosimetric data and the normal tissue complication probability (NTCP) model. Methods: The data of 24 pancreatic cancer patients were retrospectively analyzed, and these patients were planned with intensity-modulated radiotherapy (IMRT), volume-modulated arc therapy (VMAT), and 3D-PSPBT. The tumor was targeted without elective nodal coverage. All generated plans consisted of a 50.4-GyE (Gray equivalent) dose in 28 fractions with equivalent OAR constraints, and they were normalized to cover 50% of the planning treatment volume (PTV) with 100% of the prescription dose. Physical dose distributions were evaluated. GI-OAR toxicity risk for different endpoints was estimated by using published NTCP Lyman-Kutcher-Burman (LKB) models. Analysis of variance (ANOVA) was performed to compare the dosimetric data, and ΔNTCP_IMRT-PSPBT and ΔNTCP_VMAT-PSPBT were also computed. Results: Similar homogeneity and conformity for the clinical target volume (CTV) and PTV were exhibited by all three planning techniques (P > 0.05). 3D-PSPBT resulted in a significant dose reduction for GI-OARs in both the low-intermediate dose range (below 30 GyE) and the highest dose region (D _max and V _{50 GyE}) in comparison with IMRT and VMAT (P < 0.05). Based on the NTCP evaluation, the NTCP reduction for GI-OARs by 3D-PSPBT was minimal in comparison with IMRT and VMAT. Conclusion: 3D-PSPBT results in minimal NTCP reduction and has less potential to substantially reduce the toxicity risk of upper GI bleeding, ulceration, obstruction, and perforation endpoints compared to IMRT and VMAT. 3D-PSPBT may have the potential to reduce acute dose-limiting toxicity in the form of nausea, vomiting, and diarrhea by reducing the GI-OAR treated volume in the low-to-intermediate dose range. However, this result needs to be further evaluated in future clinical studies.

Contemporary management of borderline resectable pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive tumors, with a low rate of survival, likely due to the tendency of the tumor for early local and distant spread. Pancreatic cancer accounts for about 3% of all cancers in the US and about 7% of all cancer deaths. Surgical resection still represents the best curative treatment for PDAC, although only 10–20% of patients are upfront resectable at diagnosis, 50% has metastatic disease and 35% locally advanced cancer. The 5-year overall survival (OS) after curative resection is limited to 20%. Moreover among patients who undergo surgery, 30% develop early recurrence while most of them will eventually relapse. The risk of early failure after surgery could be associated with inadequate preoperative radiological staging, lack of radical surgery and differences in tumor aggressiveness. In recent years, more accurate patient categorization due to sophisticated imaging tools and techniques increase the survival rate while neoadjuvant treatment can help surgeons select patients who will benefit most from surgery. Neoadjuvant therapy includes chemotherapy alone, chemoradiotherapy, chemotherapy with chemoradiation and targeted therapies. The aim of this review is to present the available data concerning the management of patients with borderline PDAC.

Online adaptive magnetic resonance guided radiotherapy for pancreatic cancer: state of the art, pearls and pitfalls

BACKGROUND

Different studies have proved in recent years that hypofractionated radiotherapy (RT) improves overall survival of patients affected by locally advanced, unresectable, pancreatic cancer. The clinical management of these patients generally leads to poor results and is considered very challenging, due to different factors, heavily influencing treatment delivery and its outcomes. Firstly, the dose prescribed to the target is limited by the toxicity that the highly radio-sensitive organs at risk (OARs) surrounding the disease can develop. Treatment delivery is also complicated by the significant inter-fractional and intra-fractional variability of therapy volumes, mainly related to the presence of hollow organs and to the breathing cycle. The recent introduction of magnetic resonance guided radiotherapy (MRgRT) systems leads to the opportunity to control most of the aforementioned sources of uncertainty influencing RT treatment workflow in pancreatic cancer. MRgRT offers the possibility to accurately identify radiotherapy volumes, thanks to the high soft-tissue contrast provided by the Magnetic Resonance imaging (MRI), and to monitor the tumour and OARs positions during the treatment fraction using a high-temporal cine MRI. However, the main advantage offered by the MRgRT is the possibility to online adapt the RT treatment plan, changing the dose distribution while the patient is still on couch and successfully addressing most of the sources of variability.

SHORT CONCLUSION

Aim of this study is to present and discuss the state of the art, the main pitfalls and the innovative opportunities offered by online adaptive MRgRT in pancreatic cancer treatment.

Concurrent chemoradiotherapy using proton beams for unresectable locally advanced pancreatic cancer

BACKGROUND AND PURPOSE

We investigated clinical outcomes of proton beam concurrent chemoradiotherapy (CCRT) for unresectable, locally advanced pancreatic cancer (LAPC) patients.

MATERIALS AND METHODS

Records from 42 unresectable LAPC patients (21 male and 21 female, 39-83 years old) with IIB/III clinical staging of 1/41 treated by proton beam CCRT were retrospectively reviewed. Twelve patients received a conventional 50 Gray equivalents (GyE) in 25 fractions protocol and 30 others received a higher dose protocol of 54.0-67.5 GyE in 25-33 fractions. Gemcitabine or S-1 (Tegafur, Gimeracil and Oteracil) was used concurrently. Toxicity, overall survival (OS) and local control (LC) were examined.

RESULTS

Acute adverse events of grades 1, 2, 3 and 4 were found in 4, 15, 17 and 2 patients, respectively. All grade 3 and 4 events were hematologic. Late adverse events of grades 1 and 2 were found in 3 and 2 patients, respectively. No late adverse effects of grade 3 or higher were observed. The 1-year/2-year OS rates from the start of CCRT were 77.8/50.8% with median survival time (MST) of 25.6 months. The 1-year/2-year LC rate from CCRT start was 83.3/78.9% with a median time to local recurrence of more than 36 months. Total irradiation dose was the only significant factor in univariate analyses of OS and LC (p = 0.015 and 0.023, respectively).

CONCLUSION

Proton beam CCRT lengthened survival periods compared to previous photon CCRT data and higher dose irradiation prolonged LC and OS for unresectable LAPC patients. Proton beam therapy is therefore safe and effective in these cases.

Comparison of different treatment planning approaches for intensity-modulated proton therapy with simultaneous integrated boost for pancreatic cancer

BACKGROUND

Neoadjuvant radio(chemo)therapy of non-metastasized, borderline resectable or unresectable locally advanced pancreatic cancer is complex and prone to cause side-effects, e.g., in gastrointestinal organs. Intensity-modulated proton therapy (IMPT) enables a high conformity to the targets while simultaneously sparing the normal tissue such that dose-escalation strategies come within reach. In this in silico feasibility study, we compared four IMPT planning strategies including robust multi-field optimization (rMFO) and a simultaneous integrated boost (SIB) for dose-escalation in pancreatic cancer patients.

METHODS

For six pancreatic cancer patients referred for adjuvant or primary radiochemotherapy, four rMFO-IMPT-SIB treatment plans each, consisting of two or three (non-)coplanar beam arrangements, were optimized. Dose values for both targets, i.e., the elective clinical target volume [CTV, prescribed dose D_pres = 51Gy(RBE)] and the boost target [D_pres = 66Gy(RBE)], for the organs at risk as well as target conformity and homogeneity indexes, derived from the dose volume histograms, were statistically compared.

RESULTS

All treatment plans of each strategy fulfilled the prescribed doses to the targets (D_{pres(GTV,CTV)} = 100%, D_{95%,(GTV,CTV)} ≥ 95%, D_2%,(GTV,CTV) ≤ 107%). No significant differences for the conformity index were found (p > 0.05), however, treatment plans with a three non-coplanar beam strategy were most homogenous to both targets (p < 0.045). The median value of all dosimetric results of the large and small bowel as well as for the liver and the spinal cord met the dose constraints with all beam arrangements. Irrespective of the planning strategies, the dose constraint for the duodenum and stomach were not met. Using the three-beam arrangements, the dose to the left kidney could be significant decreased when compared to a two-beam strategy (p < 0.045).

CONCLUSION

Based on our findings we recommend a three-beam configuration with at least one non-coplanar beam for dose-escalated SIB with rMFO-IMPT in advanced pancreatic cancer patients achieving a homogeneous dose distribution in the target while simultaneously minimizing the dose to the organs at risk. Further treatment planning studies on aspects of breathing and organ motion need to be performed.

Proton beam therapy for gastrointestinal cancers: past, present, and future

Despite the conformality of modern X-ray therapy limiting high dose received by normal tissues the physical properties of X-rays make it impossible to avoid dose being delivered distal to the target. This "exit dose" is likely clinically significant especially for patients with gastrointestinal (GI) cancers when considering that even low dose received by the heart, lungs, bowel, and other radiosensitive structures can lead to morbidity and even may affect long-term tumor control. In contrast, proton beam therapy (PBT) delivers no "exit dose" and a growing body of literature suggests that this may improve clinical outcomes by reducing toxicity and even allowing for safe dose intensification to enhance tumor control. While there are not yet robust prospective data demonstrating the role of PBT for GI cancers, emerging retrospective data provide a strong rationale for continued study of how PBT may improve the therapeutic ratio for these patients. Here we review these data as well as discuss ongoing clinical trials of PBT for GI cancers.

Current and emerging radiotherapy strategies for pancreatic adenocarcinoma: stereotactic, intensity modulated and particle radiotherapy

The role of radiotherapy for locally advanced pancreatic cancer (LAPC) is unclear based on studies that used conventional doses and fractionation schedules. Modern radiotherapy techniques have not been studied in depth, however. We reviewed the literature on emerging methods of delivering higher doses of conformal radiotherapy using stereotactic body radiation, intensity modulated radiation, and particle beam radiation, highlighting clinical outcomes and toxicities. The literature review suggests low rates of acute and late toxicities when higher doses of radiation are given with careful attention to normal tissue dose constraints, including for stereotactic body radiotherapy (SBRT), escalated doses with intensity modulated radiation therapy (IMRT), and particle-based therapy. Retrospective evidence suggests prolonged survival for patients who receive biological equivalent doses above 70 Gy. Prospective trials that evaluate modern radiotherapy techniques are warranted for LAPC.

Pencil beam scanning versus passively scattered proton therapy for unresectable pancreatic cancer

Background

With an increasing number of proton centers capable of delivering pencil beam scanning (PBS), understanding the dosimetric differences in PBS compared to passively scattered proton therapy (PSPT) for pancreatic cancer is of interest.

Methods

Optimized PBS plans were retrospectively generated for 11 patients with locally advanced pancreatic cancer previously treated with PSPT to 59.4 Gy on a prospective trial. The primary tumor was targeted without elective nodal coverage. The same treatment couch, target coverage and normal tissue dose objectives were used for all plans. A Wilcoxon t-test was performed to compare various dosimetric points between the two plans for each patient.

Results

All target volume coverage goals were met in all PBS and passive scattering (PS) plans, except for the planning target volume (PTV) coverage goal (V100% >95%) which was not met in one PS plan (range, 81.8-98.9%). PBS was associated with a lower median relative dose (102.4% vs. 103.8%) to 10% of the PTV (P=0.001). PBS plans had a lower median duodenal V59.4 Gy (37.4% vs. 40.4%; P=0.014), lower small bowel median V59.4 Gy (0.11% vs. 0.37%; P=0.012), lower stomach median V59.4 Gy (0.01% vs. 0.1%; P=0.023), and lower median dose to 0.1 cc of the spinal cord {35.0 vs. 38.7 Gy [relative biological effectiveness (RBE)]; P=0.001}. Liver dose was higher in PBS plans for median V5 Gy (24.1% vs. 20.2%; P=0.032), V20 Gy (3.2% vs. 2.8%; P=0.010), and V25 Gy (2.6% vs. 2.2%; P=0.019). There was no difference in kidney dose between PBS and PS plans.

Conclusions

Proton therapy for locally advanced pancreatic cancer using PBS was not clearly associated with clinically meaningful reductions in normal tissue dose compared to PS. Some statistically significant improvements in PTV coverage were achieved using PBS. PBS may offer improved conformality for the treatment of irregular targets, and further evaluation of PBS and PS incorporating elective nodal irradiation should be considered.

Initial experience with intensity modulated proton therapy for intact, clinically localized pancreas cancer: Clinical implementation, dosimetric analysis, acute treatment-related adverse events, and patient-reported outcomes

Purpose

Pencil-beam scanning intensity modulated proton therapy (IMPT) may allow for an improvement in the therapeutic ratio compared with conventional techniques of radiation therapy delivery for pancreatic cancer. The purpose of this study was to describe the clinical implementation of IMPT for intact and clinically localized pancreatic cancer, perform a matched dosimetric comparison with volumetric modulated arc therapy (VMAT), and report acute adverse event (AE) rates and patient-reported outcomes (PROs) of health-related quality of life.

Methods and materials

Between July 2016 and March 2017, 13 patients with localized pancreatic cancer underwent concurrent capecitabine or 5-fluorouracil-based chemoradiation therapy (CRT) utilizing IMPT to a dose of 50 Gy (radiobiological effectiveness: 1.1). A VMAT plan was generated for each patient to use for dosimetric comparison. Patients were assessed prospectively for AEs and completed PRO questionnaires utilizing the Functional Assessment of Cancer Therapy-Hepatobiliary at baseline and upon completion of CRT.

Results

There was no difference in mean target coverage between IMPT and VMAT (P > .05). IMPT offered significant reductions in dose to organs at risk, including the small bowel, duodenum, stomach, large bowel, liver, and kidneys (P < .05). All patients completed treatment without radiation therapy breaks. The median weight loss during treatment was 1.6 kg (range, 0.1-5.7 kg). No patients experienced grade ≥3 treatment-related AEs. The median Functional Assessment of Cancer Therapy-Hepatobiliary scores prior to versus at the end of CRT were 142 (range, 113-163) versus 136 (range, 107-173; P = .18).

Conclusions

Pencil-beam scanning IMPT was feasible and offered significant reductions in radiation exposure to multiple gastrointestinal organs at risk. IMPT was associated with no grade ≥3 gastrointestinal AEs and no change in baseline PROs, but the conclusions are limited due to the patient sample size. Further clinical studies are warranted to evaluate whether these dosimetric advantages translate into clinically meaningful benefits.

Stereotactic Radiotherapy and Particle Therapy for Pancreatic Cancer

Pancreatic cancer is a devastating disease with poor survival outcomes. Recent studies have shown that the addition of radiotherapy to chemotherapy in the setting of locally advanced pancreatic cancer did not improve overall survival outcome. These studies commonly utilize conventional radiotherapy treatment fractionation and technique (typically 3-D conformal radiotherapy or intensity modulated radiotherapy). Although no clear benefit in overall survival was demonstrated in those studies, those who received radiotherapy did have a clear benefit in terms of local control. Therefore, there is increasing interest in exploring different techniques and/or modality of radiotherapy and dose/fractionation. Stereotactic radiotherapy, which employs a hypofractionated regimen, has the potential advantage of delivering a high dose of radiation to the tumor in a short period of time (typically over 5 days) with minimal dose to the surrounding normal structures. Particle therapy such as proton and carbon ion therapy are being explored as potential radiation modality that could cause greater biological damage to the tumor compared to photon treatment, with rapid dose falloff resulting in minimal to no dose to adjacent structures. This review will discuss the current literature and emerging roles of stereotactic radiotherapy and particle therapy in pancreatic cancer.

Proton beam reirradiation for locally recurrent pancreatic adenocarcinoma

BACKGROUND

Local recurrence following definitive treatment for pancreatic adenocarcinoma is common and can be associated with significant morbidity and mortality. Retreatment options for these patients are limited. Proton beam reirradiation (PRT) may limit dose and toxicity to previously irradiated normal tissues in patients without evidence of metastatic disease.

METHODS

Between 8/2010-2/2015, 15 patients with isolated, locally-recurrent pancreatic cancer were treated with PRT. Acute toxicity was graded using CTC v 4.0 and defined as occurring within 90 days. Kaplan-Meier survival analysis was performed from the start of PRT. A log-rank test was used to compare survival with or without concurrent chemotherapy.

RESULTS

Median follow-up was 15.7 months [2-48] from the start of PRT. The median clinical target volume (CTV) was 71 cc [15-200]. Ten (67%) patients received concurrent chemotherapy. Median PRT dose was 59.4 Gy (37.5-59.4 Gy). The median time interval from the prior treatment course was 26.7 months (7-461.3). There was a rate of 13% acute ≥ grade 3 toxicities attributed to PRT. The median overall survival (OS) was 16.7 months (95% CI, 4.7-36) and OS at 1 year was 67%. The "in-field" failure free survival at one year was 87%. The locoregional progression free survival (LPFS) and distant metastasis free survival (DMFS) at 1 year was 72% and 64% respectively. Concurrent chemotherapy was associated with a higher median survival.

CONCLUSIONS

PRT was well tolerated, resulted in prolonged clinical outcomes compared to historical controls, and should be considered as a treatment option with concurrent chemotherapy in selected patients with locally-recurrent pancreatic cancer.

The Role of Radiation Therapy for Pancreatic Cancer in the Adjuvant and Neoadjuvant Settings

Pancreatic cancer is the third leading cause of cancer-related death in the United States. Although surgery remains the only curative treatment, chemotherapy and radiation therapy are frequently used. In the adjuvant setting, radiation is usually delivered with chemotherapy to eradicate residual microscopic or macroscopic disease in the resection bed. Neoadjuvant radiation therapy has become more frequently utilized. This article reviews the historical and modern literature regarding radiation therapy in the neoadjuvant and adjuvant settings, focusing on the evolution of radiation therapy techniques and clinical trials in an attempt to identify patients best suited to receiving radiation therapy.

Comparing the dosimetric impact of interfractional anatomical changes in photon, proton and carbon ion radiotherapy for pancreatic cancer patients

Radiotherapy using charged particles is characterized by a low dose to the surrounding healthy organs, while delivering a high dose to the tumor. However, interfractional anatomical changes can greatly affect the robustness of particle therapy. Therefore, we compared the dosimetric impact of interfractional anatomical changes (i.e. body contour differences and gastrointestinal gas volume changes) in photon, proton and carbon ion therapy for pancreatic cancer patients. In this retrospective planning study, photon, proton and carbon ion treatment plans were created for 9 patients. Fraction dose calculations were performed using daily cone-beam CT (CBCT) images. To this end, the planning CT was deformably registered to each CBCT; gastrointestinal gas volumes were delineated on the CBCTs and copied to the deformed CT. Fraction doses were accumulated rigidly. To compare planned and accumulated dose, dose-volume histogram (DVH) parameters of the planned and accumulated dose of the different radiotherapy modalities were determined for the internal gross tumor volume, internal clinical target volume (iCTV) and organs-at-risk (OARs; duodenum, stomach, kidneys, liver and spinal cord). Photon plans were highly robust against interfractional anatomical changes. The difference between the planned and accumulated DVH parameters for the photon plans was less than 0.5% for the target and OARs. In both proton and carbon ion therapy, however, coverage of the iCTV was considerably reduced for the accumulated dose compared with the planned dose. The near-minimum dose ([Formula: see text]) of the iCTV reduced with 8% for proton therapy and with 10% for carbon ion therapy. The DVH parameters of the OARs differed less than 3% for both particle modalities. Fractionated radiotherapy using photons is highly robust against interfractional anatomical changes. In proton and carbon ion therapy, such changes can severely reduce the dose coverage of the target.

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

PURPOSE

Prospectively assess relationships between dosimetric parameters and histopathologic/clinical duodenal toxicities in patients on a phase I trial for pancreatic cancer.

METHODS

Forty-six borderline resectable/unresectable patients were enrolled on a prospective trial testing neoadjuvant gemcitabine/5-fluorouracil followed by SBRT (5 daily fractions of 5-8Gy) and concurrent nelfinavir. Post-SBRT surgery was performed in 13 resectable patients, which constituted the patient population herein. Pathologic duodenal damage was assessed using predetermined criteria: 1, no/minimal; 2, moderate; and 3, marked damage. Clinical toxicities were assessed per the Clinical Terminology Criteria for Adverse Events (CTCAE). Duodenal dosimetric parameters included V5-V40 and mean/maximum doses. Spearman correlation and linear regression evaluated associations between dosimetric parameters and clinical/pathologic duodenal toxicity.

RESULTS

The median duodenal mean and maximum doses were 20 and 37Gy. Median duodenal V5-V40 were 64, 62, 52, 39, 27, 14, 5 and 0cc, respectively. The median duodenal damage score was 2 (four 1, eight 2, and one 3). Higher duodenal damage scores correlated with higher duodenal mean doses (r=0.75, p=0.003), V35 (r=0.61, p=0.03), V30 (r=0.67, p=0.01), V25 (r=0.68, p=0.01), V20 (r=0.56, p=0.05), and the planning target volume (PTV) mean (r=0.59, p=0.03) and maximum (r=0.61, p=0.03) doses. Clinical toxicities did not correlate with dosimetric parameters or duodenal pathologic damage.

CONCLUSIONS

Duodenal histologic damage correlates with mean duodenal dose, V20-V35, and PTV mean/maximum doses.

Prospective study of proton beam radiation therapy for adjuvant and definitive treatment of thymoma and thymic carcinoma: Early response and toxicity assessment

BACKGROUND AND PURPOSE

Radiation is an important modality in treatment of thymic tumors. However, toxicity may reduce its overall benefit. We hypothesized that double-scattering proton beam therapy (DS-PT) can achieve excellent local control with limited toxicity in patients with thymic malignancies.

METHODS AND MATERIALS

Patients with thymoma or thymic carcinoma treated with DS-PT between 2011 and 2015 were prospectively analyzed for toxicity and patterns of failure on an IRB-approved study.

RESULTS

Twenty-seven consecutive patients were evaluated. Patients were a median of 56 years and had thymoma (85%). They were treated with definitive (22%), salvage (15%) or adjuvant (63%) DS-PT to a median of 61.2/1.8 Gy [CGE]. No patient experienced grade ⩾3 toxicity. Acute grade 2 toxicities included dermatitis (37%), fatigue (11%), esophagitis (7%), and pneumonitis (4%). Late grade 2 toxicity was limited to a single patient with chronic dyspnea. At a median follow-up of 2 years, 100% local control was achieved. Three-year regional control, distant control, and overall survival rates were 96% (95% CI 76-99%), 74% (95% CI 41-90%), and 94% (95% CI 63-99%), respectively.

CONCLUSIONS

This is the first cohort and prospective series of proton therapy to treat thymic tumors, demonstrating low rates of early toxicity and excellent initial outcomes.

Proton beams in cancer treatments: Clinical outcomes and dosimetric comparisons with photon therapy

PURPOSE

To review current evidence of the role of proton therapy (PT) in other tumors than skull base, sinusal/parasinusal, spinal and pediatric tumors; to determine medico-economic aspects raised by PT.

MATERIAL AND METHODS

A systematic review on Medline was performed with the following keywords: proton therapy, proton beam, protontherapy, cancer; publications with comparison between PT and photon-therapy were also selected.

RESULTS

In silico studies have shown superiority (better dose delivery to the target and/or to organs at risk) of PT toward photon-therapy in most of thoracic and abdominal malignant tumors. Potential benefits of PT could be: reduction of toxicities (including radiation-induced cancer), increase of tumor control through a dose-escalation approach, hypofractionation. Cost of treatment is always cited as an issue which actually can be managed by a precise patient selection making PT a cost-effective procedure. Comparison plan with photon therapy may be useful to determine the dosimetric and clinical advantages of PT (Normal Tissue Complications Probability).

CONCLUSION

PT may be associated with a great advantage compared to the best photon-therapies in various types of cancers. Accumulation of clinical data is on-going and will challenge the in silico data analysis. Some indications are associated with strong superiority of PT and may be discussed as a new standard within prospective observational studies.

Management of borderline resectable pancreatic cancer

Pancreatic cancer is the fourth most common cause of cancer death in the United States. Surgery remains the only curative option; however only 20% of the patients have resectable disease at the time of initial presentation. The definition of borderline resectable pancreatic cancer is not uniform but generally denotes to regional vessel involvement that makes it unlikely to have negative surgical margins. The accurate staging of pancreatic cancer requires triple phase computed tomography or magnetic resonance imaging of the pancreas. Management of patients with borderline resectable pancreatic cancer remains unclear. The data for treatment of these patients is primarily derived from retrospective single institution experience. The prospective trials have been plagued by small numbers and poor accrual. Neoadjuvant therapy is recommended and typically consists of chemotherapy and radiation therapy. The chemotherapeutic regimens continue to evolve along with type and dose of radiation therapy. Gemcitabine or 5-fluorouracil based chemotherapeutic combinations are administered. The type and dose of radiation vary among different institutions. With neoadjuvant treatment, approximately 50% of the patients are able to undergo surgical resections with negative margins obtained in greater than 80% of the patients. Newer trials are attempting to standardize the definition of borderline resectable pancreatic cancer and treatment regimens. In this review, we outline the definition, imaging requirements and management of patients with borderline resectable pancreatic cancer.

Proton therapy for pancreatic cancer

Radiotherapy is commonly offered to patients with pancreatic malignancies although its ultimate utility is compromised since the pancreas is surrounded by exquisitely radiosensitive normal tissues, such as the duodenum, stomach, jejunum, liver, and kidneys. Proton radiotherapy can be used to create dose distributions that conform to tumor targets with significant normal tissue sparing. Because of this, protons appear to represent a superior modality for radiotherapy delivery to patients with unresectable tumors and those receiving postoperative radiotherapy. A particularly exciting opportunity for protons also exists for patients with resectable and marginally resectable disease. In this paper, we review the current literature on proton therapy for pancreatic cancer and discuss scenarios wherein the improvement in the therapeutic index with protons may have the potential to change the management paradigm for this malignancy.

Gastrointestinal cancer: nonliver proton therapy for gastrointestinal cancers

Multimodality therapy for gastrointestinal (GI) cancers carries considerable risk for toxicity; even single-modality radiation therapy in this population carries with it a daunting side effect profile. Supportive care can certainly mitigate some of the morbidity, but there remain numerous associated acute and late complications that can compromise the therapy and ultimately the outcome. Gastrointestinal cancers inherently occur amid visceral organs that are particularly sensitive to radiotherapy, creating a very narrow therapeutic window for aggressive cell kill with minimal normal tissue damage. Radiation therapy is a critical component of locoregional control, but its use has historically been limited by toxicity concerns, both real and perceived. Fundamental to this is the fact that long-term clinical experience with radiation in GI cancers derives almost entirely from 2-dimensional radiation (plain x-ray-based planning) and subsequently 3-dimensional conformal radiation. The recent use of intensity-modulated photon-based techniques is not well represented in most of the landmark chemoradiation trials. Furthermore, the elusive search for efficacious but tolerable local therapy in GI malignancies raises the possibility that proton radiotherapy's physical and dosimetric differences relative to conventional therapy may make it better suited to the challenge. In many sites, local recurrences after chemoradiation pose a particular challenge, and reirradiation in these sites may be done successfully with proton radiotherapy.

Clinical decision tool for optimal delivery of liver stereotactic body radiation therapy: Photons versus protons

PURPOSE

Stereotactic body radiation therapy (SBRT) for treatment of liver tumors is often limited by liver dose constraints. Protons offer potential for more liver sparing, but clinical situations in which protons may be superior to photons are not well described. We developed and validated a treatment decision model to determine whether liver tumors of certain sizes and locations are more suited for photon versus proton SBRT.

METHODS AND MATERIALS

Six spherical mock tumors from 1 to 6 cm in diameter were contoured on computed tomography images of 1 patient at 4 locations: dome, caudal, left medial, and central. Photon and proton plans were generated to deliver 50 Gy in 5 fractions to each tumor and optimized to deliver equivalent target coverage and maximal liver sparing. Using these plans, we developed a hypothesis-generating model to predict the optimal modality for maximal liver sparing based on tumor size and location. We then validated this model in 10 patients with liver tumors.

RESULTS

Protons spared significantly more liver than photons for dome or central tumors ≥3 cm (dome: 134 ± 21 cm(3), P = .03; central: 108 ± 4 cm(3), P = .01). Our model correctly predicted the optimal SBRT modality for all 10 patients. For patients with dome or central tumors ≥3 cm, protons significantly increased the volume of liver spared (176 ± 21 cm(3), P = .01) and decreased the mean liver dose (8.4 vs 12.2 Gy, P = .01) while offering no significant advantage for tumors <3 cm at any location or for caudal and left medial tumors of any size.

CONCLUSIONS

When feasible, protons should be considered as the radiation modality of choice for dome and central tumors >3 cm to allow maximal liver sparing and potentially reduce radiation toxicity. Protons should also be considered for any tumor >5 cm if photon plans fail to achieve adequate coverage or exceed the mean liver threshold.