Current clinical evidence for proton therapy

Inhalation anesthesia without any intravenous management for pediatric proton beam therapy

INTRODUCTION

Proton beam therapy is an oncological treatment, argued to be an appropriate tumor irradiation technique for childhood solid tumors. Due to its duration and the need for immobility, many children require anesthesia for proton therapy sessions. As not many centers in the world provide this therapy, there is little published research about pediatric anesthesia for these cases, and the available data suggest a preference for intravenous anesthesia or combined intravenous and inhalation anesthesia. We conducted this study with the aim of describing and analyzing the inhalation anesthetic management of children undergoing proton therapy at our medical center, comparing our results with studies that have followed different anesthetic protocols.

METHODS

We reviewed two major databases (Web of Science and Scopus) to find papers that had addressed, to date, anesthesia for pediatric proton therapy. To describe our anesthetic management, we included all pediatric patients treated with proton therapy under anesthesia in our center between June 2020 and August 2021. The characteristics of the patients, their diagnoses, treatments, airway management, drugs administered, duration of induction, and recovery from anesthesia, and adverse effects where all recorded. All anesthesiologists followed a strict anesthetic protocol based only on inhalational anesthesia with sevoflurane delivered via laryngeal mask airway.

RESULTS

Of the total of 1082 papers found in Web of Science and Scopus on pediatric proton therapy, 11 have addressed its anesthetic management, using intravenous or combined intravenous and inhalation anesthesia. Between June 2020 and August 2021, 31 children were anesthetized in our center to receive proton therapy under inhalational anesthesia (total number of sessions: 873). The mean anesthesia induction time was 4.1 min (SD = 0.7, 95% CI [3.9, 4.4]). The mean anesthesia recovery time was 13.8 min (SD = 4.1, 95% CI [12.3, 15.3]). The percentage of non-serious adverse effects was 0.7% (Clopper-Pearson 95% CI [0.3, 1.5]). The percentage of serious adverse effects was 0.1% (Clopper-Pearson 95% CI [0, 0.6]), without statistically significant difference with other published works with different anesthetic approaches.

CONCLUSION

Inhalation anesthesia without any intravenous management for pediatric proton therapy is, in our experience, an effective technique with a complication rate similar to other anesthetic approaches.

Pure proton therapy for skull base chordomas and chondrosarcomas: A systematic review of clinical experience

Background

Skull base chordoma and chondrosarcoma are exceptionally rare bone tumors with high propensity for local recurrence. Different postoperative radiation modalities are often used to improve the clinical efficacy. Proton therapy (PT) might be among the most promising ones because of the unique ballistic characteristics of high-energy particles. However, previous meta-analysis often included studies with combined radiation techniques. No systematic review to date has directly analyzed the survival and toxicity of pure PT for these two types of malignancies.

Methods

By following the PRISMA guidelines, a systematic search of three databases was conducted. Articles were screened and data were extracted according to a prespecified scheme. R 4.2.0 software was used to conduct the meta-analysis. Normal distribution test was used for the incidence rate of each subgroup.

Results

A total of seven studies involving 478 patients were included in this analysis. The quality of included articles ranged from moderate to high quality. All patients were histopathologically diagnosed with chordoma or chondrosarcoma, and the follow-up time of the cohort ranged from 21 to 61.7 months. For PT planning, the median target volume ranged from 15 cc to 40 cc, and the administered median dose varied from 63 to 78.4 Gy_RBE at 1.8-2.0 Gy_RBE per fraction. The 1-, 2-, 3-, 5-, and 7-year local control and overall survival rates were 100%, 93%, 87%, 78%, and 68%, and 100%, 99%, 89%, 85%, and 68%, respectively. The late grade 3 or higher toxicities were reported in only two involved articles.

Conclusions

Until now, medical centers worldwide have exerted PT to improve outcomes of skull base chordomas and chondrosarcomas. PT not combined with other radiation modalities showed favorable local control and survival with a low incidence of severe radiation-induced toxicities, which manifests promising clinical benefits. However, high-quality evidence is still limited, requiring future clinical trials and prospective studies in selected patients.

Association of Race With Receipt of Proton Beam Therapy for Patients With Newly Diagnosed Cancer in the US, 2004-2018

IMPORTANCE

Black patients are less likely than White patients to receive guideline-concordant cancer care in the US. Proton beam therapy (PBT) is a potentially superior technology to photon radiotherapy for tumors with complex anatomy, tumors surrounded by sensitive tissues, and childhood cancers.

OBJECTIVE

To evaluate whether there are racial disparities in the receipt of PBT among Black and White individuals diagnosed with all PBT-eligible cancers in the US.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study evaluated Black and White individuals diagnosed with PBT-eligible cancers between January 1, 2004, and December 31, 2018, in the National Cancer Database, a nationwide hospital-based cancer registry that collects data on radiation treatment, even when it is received outside the reporting facility. American Society of Radiation Oncology model policies were used to classify patients into those for whom PBT is the recommended radiation therapy modality (group 1) and those for whom evidence of PBT efficacy is still under investigation (group 2). Propensity score matching was used to ensure comparability of Black and White patients' clinical characteristics and regional availability of PBT according to the National Academy of Medicine's definition of disparities. Data analysis was performed from October 4, 2021, to February 22, 2022.

EXPOSURE

Patients' self-identified race was ascertained from medical records.

MAIN OUTCOMES AND MEASURES

The main outcome was receipt of PBT, with disparities in this therapy's use evaluated with logistic regression analysis.

RESULTS

Of the 5 225 929 patients who were eligible to receive PBT and included in the study, 13.6% were Black, 86.4% were White, and 54.3% were female. The mean (SD) age at diagnosis was 63.2 (12.4) years. Black patients were less likely to be treated with PBT than their White counterparts (0.3% vs 0.5%; odds ratio [OR], 0.67; 95% CI, 0.64-0.71). Racial disparities were greater for group 1 cancers (0.4% vs 0.8%; OR, 0.49; 95% CI, 0.44-0.55) than group 2 cancers (0.3% vs 0.4%; OR, 0.75; 95% CI, 0.70-0.80). Racial disparities in PBT receipt among group 1 cancers increased over time (annual percent change = 0.09, P < .001) and were greatest in 2018, the most recent year of available data.

CONCLUSIONS AND RELEVANCE

In this cross-sectional study, Black patients were less likely to receive PBT than their White counterparts, and disparities were greatest for cancers for which PBT was the recommended radiation therapy modality. These findings suggest that efforts other than increasing the number of facilities that provide PBT will be needed to eliminate disparities.

Assessment of Proton Beam Therapy Use Among Patients With Newly Diagnosed Cancer in the US, 2004-2018

IMPORTANCE

Proton beam therapy (PBT) is a potentially superior technology to photon radiotherapy for tumors with complex anatomy, those surrounded by sensitive tissues, and childhood cancers.

OBJECTIVE

To assess patterns of use of PBT according to the present American Society of Radiation Oncology (ASTRO) clinical indications in the US.

DESIGN, SETTING, AND PARTICIPANTS

Individuals newly diagnosed with cancer between 2004 and 2018 were selected from the National Cancer Database. Data analysis was performed from October 4, 2021, to February 22, 2022. ASTRO's Model Policies (2017) were used to classify patients into group 1, for which health insurance coverage for PBT treatment is recommended, and group 2, for which coverage is recommended only if additional requirements are met.

MAIN OUTCOMES AND MEASURES

Use of PBT.

RESULTS

Of the 5 919 368 patients eligible to receive PBT included in the study, 3 206 902 were female (54.2%), and mean (SD) age at diagnosis was 62.6 (12.3) years. Use of PBT in the US increased from 0.4% in 2004 to 1.2% in 2018 (annual percent change [APC], 8.12%; P < .001) due to increases in group 1 from 0.4% in 2010 to 2.2% in 2018 (APC, 21.97; P < .001) and increases in group 2 from 0.03% in 2014 to 0.1% in 2018 (APC, 30.57; P < .001). From 2010 to 2018, among patients in group 2, PBT targeted to the breast increased from 0.0% to 0.9% (APC, 51.95%), and PBT targeted to the lung increased from 0.1% to 0.7% (APC, 28.06%) (P < .001 for both). Use of PBT targeted to the prostate decreased from 1.4% in 2011 to 0.8% in 2014 (APC, -16.48%; P = .03) then increased to 1.3% in 2018 (APC, 12.45; P < .001). Most patients in group 1 treated with PBT had private insurance coverage in 2018 (1039 [55.4%]); Medicare was the most common insurance type among those in group 2 (1973 [52.5%]).

CONCLUSIONS AND RELEVANCE

The findings of this study show an increase in the use of PBT in the US between 2004 to 2018; prostate was the only cancer site for which PBT use decreased temporarily between 2011 and 2014, increasing again between 2014 and 2018. These findings may be especially relevant for Medicare radiation oncology coverage policies.

Treatment plan comparison of proton vs photon radiotherapy for lower-grade gliomas

Background and purpose

Patients with lower-grade gliomas are long-term survivors after radiotherapy and may benefit from the reduced dose to normal tissue achievable with proton therapy. Here, we aimed to quantify differences in dose to the uninvolved brain and contralateral hippocampus and compare the risk of radiation-induced secondary cancer for photon and proton plans for lower-grade glioma patients.

Materials and methods

Twenty-three patients were included in this in-silico planning comparative study and had photon and proton plans calculated (50.4 Gy(RBE = 1.1), 28 Fx) applying similar dose constraints to the target and organs at risk. Automatically calculated photon plans were generated with a 3 mm margin from clinical target volume (CTV) to planning target volume. Manual proton plans were generated using robust optimisation on the CTV. Dose metrics of organs at risk were compared using population mean dose-volume histograms and Wilcoxon signed-rank test. Secondary cancer risk per 10,000 persons per year (PPY) was estimated using dose-volume data and a risk model for secondary cancer induction.

Results

CTV coverage (V95%>98%) was similar for the two treatment modalities. Mean dose (D_mean) to the uninvolved brain was significantly reduced from 21.5 Gy (median, IQR 17.1–24.4 Gy) with photons compared to 10.3 Gy(RBE) (8.1–13.9 Gy(RBE)) with protons. D_mean to the contralateral hippocampus was significantly reduced from 6.5 Gy (5.4–11.7 Gy) with photons to 1.5 Gy(RBE) (0.4–6.8 Gy(RBE)) with protons. The estimated secondary cancer risk was reduced from 6.7 PPY (median, range 3.3–10.4 PPY) with photons to 3.0 PPY (1.3–7.5 PPY) with protons.

Conclusion

A significant reduction in mean dose to uninvolved brain and contralateral hippocampus was found with proton planning. The estimated secondary cancer risk was reduced with proton therapy.

Future Perspectives of Proton Therapy in Minimizing the Toxicity of Breast Cancer Radiotherapy

The toxicity of radiotherapy is a key issue when analyzing the eligibility criteria for patients with breast cancer. In order to obtain better results, proton therapy is proposed because of the more favorable distribution of the dose in the patient’s body compared with photon radiotherapy. Scientific groups have conducted extensive research into the improved efficacy and lower toxicity of proton therapy for breast cancer. Unfortunately, there is no complete insight into the potential reasons and prospects for avoiding undesirable results. Cardiotoxicity is considered challenging; however, researchers have not presented any realistic prospects for preventing them. We compared the clinical evidence collected over the last 20 years, providing the rationale for the consideration of proton therapy as an effective solution to reduce cardiotoxicity. We analyzed the parameters of the dose distribution (mean dose, Dmax, V5, and V20) in organs at risk, such as the heart, blood vessels, and lungs, using the following two irradiation techniques: whole breast irradiation and accelerated partial breast irradiation. Moreover, we presented the possible causes of side effects, taking into account biological and technical issues. Finally, we collected potential improvements in higher quality predictions of toxic cardiac effects, like biomarkers, and model-based approaches to give the full background of this complex issue.

Perspectives on the model-based approach to proton therapy trials: A retrospective study of a lung cancer randomized trial

PURPOSE

The goal of this study was to assess whether a model-based approach applied retrospectively to a completed randomized controlled trial (RCT) would have significantly altered the selection of patients of the original trial, using the same selection criteria and endpoint for testing the potential clinical benefit of protons compared to photons.

METHODS AND MATERIALS

A model-based approach, based on three widely used normal tissue complication probability (NTCP) models for radiation pneumonitis (RP), was applied retrospectively to a completed non-small cell lung cancer RCT (NCT00915005). It was assumed that patients were selected by the model-based approach if their expected ΔNTCP value was above a threshold of 5%. The endpoint chosen matched that of the original trial, the first occurrence of severe (grade ≥3) RP.

RESULTS

Our analysis demonstrates that NTCP differences between proton and photon therapy treatments may be too small to support a model-based trial approach for lung cancer using RP as the normal tissue endpoint. The analyzed lung trial showed that less than 19% (32/165) of patients enrolled in the completed trial would have been enrolled in a model-based trial, prescribing photon therapy to all other patients. The number of patients enrolled was also found to be dependent on the type of NTCP model used for evaluating RP, with the three models enrolling 3%, 13% or 19% of patients. This result does show limitations in NTCP models which would affect the success of a model-based trial approach. No conclusion regarding the development of RP in patients randomized by the model-based approach could statistically be made.

CONCLUSIONS

Uncertainties in the outcome models to predict NTCP are the inherent drawback of a model-based approach to clinical trials. The impact of these uncertainties on enrollment in model-based trials depends on the predicted difference between the two treatment arms and on the set threshold for patient stratification. Our analysis demonstrates that NTCP differences between proton and photon therapy treatments may be too small to support a model-based trial approach for specific treatment sites, such as lung cancer, depending on the chosen normal tissue endpoint.

Harmonization of proton treatment planning for head and neck cancer using pencil beam scanning: first report of the IPACS collaboration group

Background and purpose: A collaborative network between proton therapy (PT) centres in Trento in Italy, Poland, Austria, Czech Republic and Sweden (IPACS) was founded to implement trials and harmonize PT. This is the first report of IPACS with the aim to show the level of harmonization that can be achieved for proton therapy planning of head and neck (sino-nasal) cancer.Methods: CT-data sets of five patients were included. During several face-to-face and online meetings, a common treatment planning protocol was developed. Each centre used its own treatment planning system (TPS) and planning approach with some restrictions specified in the treatment planning protocol. In addition, volumetric modulated arc therapy (VMAT) photon plans were created.Results: For CTV1, the average D_median was 59.3 ± 2.4 Gy(RBE) for protons and 58.8 ± 2.0 Gy(RBE) for VMAT (aim was 56 Gy(RBE)). For CTV2, the average D_median was 71.2 ± 1.0 Gy(RBE) for protons and 70.6 ± 0.4 Gy(RBE) for VMAT (aim was 70 Gy(RBE)). The average D_2% for the spinal cord was 25.1 ± 8.5 Gy(RBE) for protons and 47.6 ± 1.4 Gy(RBE) for VMAT. The average D_2% for chiasm was 46.5 ± 4.4 Gy(RBE) for protons and 50.8 ± 1.4 Gy(RBE) for VMAT, respectively. Robust evaluation was performed and showed the least robust plans for plans with a low number of beams.Discussion: In conclusion, several influences on harmonization were identified: adherence/interpretation to/of the protocol, available technology, experience in treatment planning and use of different beam arrangements. In future, all OARs that should be included in the optimization need to be specified in order to further harmonize treatment planning.

Maximum surgical resection and adjuvant intensity-modulated radiotherapy with simultaneous integrated boost for skull base chordoma

BACKGROUND

Local recurrence is common after surgical resection of clivus chordoma. We report the results of maximum surgical resection followed by intensity-modulated radiotherapy with simultaneous integrated boost (IMRT-SIB).

METHODS

We reviewed 14 consecutive clivus chordoma cases undergoing postoperative IMRT-SIB using the institutional protocol between 2005 and 2013. Total and near-total resections were achieved in 11 patients (78.6 %), partial in 2 patients (14.3 %), and 1 patient (7.1 %) received RT for recurrent tumor after total resection. Gross residual or the high-risk area defined the planning target volume (PTV)1; PTV2 was the postoperative tumor bed plus a 3-5-mm margin, and PTV3 was PTV2 plus a 5-10 mm margin. A moderate hypofractionation schedule was used: doses to PTV1, PTV2 and PTV3 were 3.9 Gy, 3.15 Gy and 2.8 Gy through 15 fractions for the first two patients, and the rest received 2.5 Gy, 2.2 Gy and 1.8 Gy through 25 fractions. The biologically equivalent dose in 2-Gy fractions (EQD2) was 65-68 Gy for PTV1, 52-56 Gy for PTV2, and 44.3-44.8 Gy for PTV3.

RESULTS

Median follow-up was 41 months. Eight patients were free of disease for median 42.5 months (range 23-91 months), four patients had stable disease for median 60.5 months (range 39-113 months), and 1 patient showed partial response for 38 months after RT. Local progression was seen in one patient who received EQD2 67.8 Gy after partial resection. Estimated 5-year progression-free and overall survival rates were 92.9 %. Surgery improved the neurologic deficit in six patients, and IMRT-SIB was well tolerated without lasting toxicity.

CONCLUSION

Our experience suggests that maximum resection and high-dose IMRT-SIB can achieve local control without significant morbidities.

A 20-Year Analysis of Clinical Trials Involving Proton Beam Therapy

Purpose

Clinical trials (CTs) in proton beam therapy (PBT) are important for determining its benefits relative to other treatments. An analysis of PBT trials is, thus, warranted to understand the current state of PBT CTs and the factors affecting current and future trials.

Materials and Methods

We queried the clinicaltrials.gov Website using the search terms: proton beam therapy, proton radiation, and protons. A total of 152 PBT CTs were identified. We used χ² analysis and logistic regression to evaluate trial characteristics.

Results

Most CTs were recruiting (n = 79; 52.0%), phase II (n = 95; 62.5%), open label (n = 134; 88.2%), single-group assignment (n = 84; 55.3%), and with primary treatment endpoints of safety and efficacy (n = 94; 61.8%). The primary treatment sites included gastrointestinal (n = 32; 21.1%), central nervous system (n = 31; 20.4%), lung (n = 21; 13.8%), prostate (n = 19; 12.5%), sarcoma (n = 15; 9.9%), and others (n = 24; 15.8%). Comparison studies between radiation modalities involved PBT and intensity-modulated photon therapy (n = 11; 7.2%), PBT and general photon therapy (n = 8; 5.3%), and PBT and carbon-ion therapy (n = 7; 4.6%). The PBT CTs underwent substantial growth after 2008 but now appear to be in decline. Nongovernmental institutions, comprising university centers, hospital systems, and research groups, have funded the greatest number of CTs (n= 106; 69.7%). The National Institutes of Health (NIH) were more likely to fund CTs involving the central nervous system (P = 0.02). Trials involving NIH funding were more likely to result in successful trial completion (P = 0.02).

Conclusion

Among PBT CTs, most were phase II trials, with a very few being phase III CTs. Funding of PBT CTs originating from industry or the NIH is limited. Recently, there has been a declining trajectory of newly initiated PBT trials. It is not yet clear whether this represents a true trend or just a pause in CT implementation. Despite multiple impediments to PBT CTs, the particle therapy community continues to work toward evidence generation.

The Quest for Evidence for Proton Therapy: Model-Based Approach and Precision Medicine

PURPOSE

Reducing dose to normal tissues is the advantage of protons versus photons. We aimed to describe a method for translating this reduction into a clinically relevant benefit.

METHODS AND MATERIALS

Dutch scientific and health care governance bodies have recently issued landmark reports regarding generation of relevant evidence for new technologies in health care including proton therapy. An approach based on normal tissue complication probability (NTCP) models has been adopted to select patients who are most likely to experience fewer (serious) adverse events achievable by state-of-the-art proton treatment.

RESULTS

By analogy with biologically targeted therapies, the technology needs to be tested in enriched cohorts of patients exhibiting the decisive predictive marker: difference in normal tissue dosimetric signatures between proton and photon treatment plans. Expected clinical benefit is then estimated by virtue of multifactorial NTCP models. In this sense, high-tech radiation therapy falls under precision medicine. As a consequence, randomizing nonenriched populations between photons and protons is predictably inefficient and likely to produce confusing results.

CONCLUSIONS

Validating NTCP models in appropriately composed cohorts treated with protons should be the primary research agenda leading to urgently needed evidence for proton therapy.

Novel targeted therapies in chordoma: an update

Chordomas are rare, locally aggressive skull base neoplasms known for local recurrence and not-infrequent treatment failure. Current evidence supports the role of maximal safe surgical resection. In addition to open skull-base approaches, the endoscopic endonasal approach to clival chordomas has been reported with favorable albeit early results. Adjuvant radiation is prescribed following complete resection, alternatively for gross residual disease or at the time of recurrence. The modalities of adjuvant radiation therapy reported vary widely and include proton-beam, carbon-ion, fractionated photon radiotherapy, and photon and gamma-knife radiosurgery. As of now, no direct comparison is available, and high-level evidence demonstrating superiority of one modality over another is lacking. While systemic therapies have yet to form part of any first-line therapy for chordomas, a number of targeted agents have been evaluated to date that inhibit specific molecules and their respective pathways known to be implicated in chordomas. These include EGFR (erlotinib, gefitinib, lapatinib), PDGFR (imatinib), mTOR (rapamycin), and VEGF (bevacizumab). This article provides an update of the current multimodality treatment of cranial base chordomas, with an emphasis on how current understanding of molecular pathogenesis provides a framework for the development of novel targeted approaches.

Position statement on ethics, equipoise and research on charged particle radiation therapy

The use of charged-particle radiation therapy (CPRT) is an increasingly important development in the treatment of cancer. One of the most pressing controversies about the use of this technology is whether randomised controlled trials are required before this form of treatment can be considered to be the treatment of choice for a wide range of indications. Equipoise is the key ethical concept in determining which research studies are justified. However, there is a good deal of disagreement about how this concept is best understood and applied in the specific case of CPRT. This report is a position statement on these controversies that arises out of a workshop held at Wolfson College, Oxford in August 2011. The workshop brought together international leaders in the relevant fields (radiation oncology, medical physics, radiobiology, research ethics and methodology), including proponents on both sides of the debate, in order to make significant progress on the ethical issues associated with CPRT research. This position statement provides an ethical platform for future research and should enable further work to be done in developing international coordinated programmes of research.

Skull base chordoma and chondrosarcoma: influence of clinical and demographic factors on prognosis: a SEER analysis

OBJECTIVE

Chordomas and chondrosarcomas are rare skull base tumors, with similar radiographic and clinical presentations. We investigated factors influencing long-term survival in these 2 tumors using the Surveillance Epidemiology and End Results (SEER) database.

METHODS

Patients with chordoma (n = 416) and chondrosarcoma (n = 269) within the skull base from 1983 to 2009 were identified within the SEER database. Kaplan-Meier curves and Cox proportional hazards models were used to test associations with survival. t tests and χ(2) tests were used to compare groups.

RESULTS

Chordoma and chondrosarcoma patients were similar demographically. Survival at 5 years was 65% for chordomas and 81.8% (P < 0.0001) for chondrosarcomas and at 10 years was 32.3% and 49.5% (P = 0.004). Multivariate analysis demonstrated chordomas had a worse prognosis even when we controlled for age and tumor size (hazard ratio 3.0, 95% confidence interval 1.9-4.7, P < 0.0001). For chordomas, multivariate analysis demonstrated increasing age and tumor size were significantly associated with reduced survival. For chondrosarcomas, multivariate analysis demonstrated older age, earlier decade of diagnosis, and mesenchymal subtype were significantly associated with reduced survival. Postoperative radiation was given to 42% and 41% of patients with chordomas and chondrosarcomas, respectively. The addition of radiation did not improve survival.

CONCLUSION

Consistent with previous case series, skull base chordomas have significantly worse prognosis than chondrosarcomas. Patients in the SEER database had worse survival overall compared with existing case series for both chordomas and chondrosarcomas, suggesting selection bias in the existing literature.

Current concepts in clinical radiation oncology

Based on its potent capacity to induce tumor cell death and to abrogate clonogenic survival, radiotherapy is a key part of multimodal cancer treatment approaches. Numerous clinical trials have documented the clear correlation between improved local control and increased overall survival. However, despite all progress, the efficacy of radiation-based treatment approaches is still limited by different technological, biological, and clinical constraints. In principle, the following major issues can be distinguished: (1) The intrinsic radiation resistance of several tumors is higher than that of the surrounding normal tissue, (2) the true patho-anatomical borders of tumors or areas at risk are not perfectly identifiable, (3) the treatment volume cannot be adjusted properly during a given treatment series, and (4) the individual heterogeneity in terms of tumor and normal tissue responses toward irradiation is immense. At present, research efforts in radiation oncology follow three major tracks, in order to address these limitations: (1) implementation of molecularly targeted agents and 'omics'-based screening and stratification procedures, (2) improvement of treatment planning, imaging, and accuracy of dose application, and (3) clinical implementation of other types of radiation, including protons and heavy ions. Several of these strategies have already revealed promising improvements with regard to clinical outcome. Nevertheless, many open questions remain with individualization of treatment approaches being a key problem. In the present review, the current status of radiation-based cancer treatment with particular focus on novel aspects and developments that will influence the field of radiation oncology in the near future is summarized and discussed.

Health economic controversy and cost-effectiveness of proton therapy

Owing to increasing healthcare costs, there is a need to examine whether the benefits of new technologies are worth the extra cost. In proton therapy, where the evidence in favor is limited, it is heavily debated whether the expected benefit justifies the higher capital and operating costs. The aim of this article was to explore the existing methodologies of economic evaluations (EEs) of particle therapy and recommend an approach for future data collection and analysis. We reviewed the published literature on health economics of proton therapy using accepted guidelines on performing EE. Different cost strategies were assessed and comparisons with other treatment modalities were made in terms of cost-effectiveness. Potential bias in the existing studies was identified and new methodologies proposed. The principal cause of bias in EEs of proton therapy is the lack of valid data on effects as well as costs. The introduction of proton therapy may be seriously hampered by the lack of outcome and cost data and the situation is likely to continue not only in terms of justifying the capital investment but also covering the operational costs. We identified an urgent need to collect appropriate data to allow for reimbursement of such novel technology. In the absence of level 1 evidence, well-performed modeling studies taking into account the available cost and outcome parameters, including the current uncertainties, can help to address the problem of limited outcome and health economic data. The approach of coverage with evidence development, in which evidence is collected in an ongoing manner in population-based registries along with dedicated financing, may allow technological advances with limited initial evidence of benefit and value, such as protons, to become available to patients in an early phase of their technology life cycle.

Initial clinical experience with scanned proton beams at the Italian National Center for Hadrontherapy (CNAO)

We report the initial toxicity data with scanned proton beams at the Italian National Center for Hadrontherapy (CNAO). In September 2011, CNAO commenced patient treatment with scanned proton beams within two prospective Phase II protocols approved by the Italian Health Ministry. Patients with chondrosarcoma or chordoma of the skull base or spine were eligible. By October 2012, 21 patients had completed treatment. Immobilization was performed using rigid non-perforated thermoplastic-masks and customized headrests or body-pillows as indicated. Non-contrast CT scans with immobilization devices in place and MRI scans in supine position were performed for treatment-planning. For chordoma, the prescribed doses were 74 cobalt grey equivalent (CGE) and 54 CGE to planning target volume 1 (PTV1) and PTV2, respectively. For chondrosarcoma, the prescribed doses were 70 CGE and 54 CGE to PTV1 and PTV2, respectively. Treatment was delivered five days a week in 35-37 fractions. Prior to treatment, the patients' positions were verified using an optical tracking system and orthogonal X-ray images. Proton beams were delivered using fixed-horizontal portals on a robotic couch. Weekly MRI incorporating diffusion-weighted-imaging was performed during the course of proton therapy. Patients were reviewed once weekly and acute toxicities were graded with the Common Terminology Criteria for Adverse Events (CTCAE). Median age of patients = 50 years (range, 21-74). All 21 patients completed the proton therapy without major toxicities and without treatment interruption. Median dose delivered was 74 CGE (range, 70-74). The maximum toxicity recorded was CTCAE Grade 2 in four patients. Our preliminary data demonstrates the clinical feasibility of scanned proton beams in Italy.

Charged particle therapy--optimization, challenges and future directions

The use of charged particle therapy to control tumours non-invasively offers advantages over conventional radiotherapy. Protons and heavy ions deposit energy far more selectively than X-rays, allowing a higher local control of the tumour, a lower probability of damage to healthy tissue, low risk of complications and the chance for a rapid recovery after therapy. Charged particles are also useful for treating tumours located in areas that surround tissues that are radiosensitive and in anatomical sites where surgical access is limited. Current trial outcomes indicate that accelerated ions can potentially replace surgery for radical cancer treatments, which might be beneficial as the success of surgical cancer treatments are largely dependent on the expertise and experience of the surgeon and the location of the tumour. However, to date, only a small number of controlled randomized clinical trials have made comparisons between particle therapy and X-rays. Therefore, although the potential advantages are clear and supported by data, the cost:benefit ratio remains controversial. Research in medical physics and radiobiology is focusing on reducing the costs and increasing the benefits of this treatment.

Standardized treatment planning methodology for passively scattered proton craniospinal irradiation

Background

As the number of proton therapy centers increases, so does the need for studies which compare proton treatments between institutions and with photon therapy. However, results of such studies are highly dependent on target volume definition and treatment planning techniques. Thus, standardized methods of treatment planning are needed, particularly for proton treatment planning, in which special consideration is paid to the depth and sharp distal fall-off of the proton distribution. This study presents and evaluates a standardized method of proton treatment planning for craniospinal irradiation (CSI).

Methods

We applied our institution’s planning methodology for proton CSI, at the time of the study, to an anatomically diverse population of 18 pediatric patients. We evaluated our dosimetric results for the population as a whole and for the two subgroups having two different age-specific target volumes using the minimum, maximum, and mean dose values in 10 organs (i.e., the spinal cord, brain, eyes, lenses, esophagus, lungs, kidneys, thyroid, heart, and liver). We also report isodose distributions and dose-volume histograms (DVH) for 2 representative patients. Additionally we report population-averaged DVHs for various organs.

Results

The planning methodology here describes various techniques used to achieve normal tissue sparing. In particular, we found pronounced dose reductions in three radiosensitive organs (i.e., eyes, esophagus, and thyroid) which were identified for optimization. Mean doses to the thyroid, eyes, and esophagus were 0.2%, 69% and 0.2%, respectively, of the prescribed dose. In four organs not specifically identified for optimization (i.e., lungs, liver, kidneys, and heart) we found that organs lateral to the treatment field (lungs and kidneys) received relatively low mean doses (less than 8% of the prescribed dose), whereas the heart and liver, organs distal to the treatment field, received less than 1% of the prescribed dose.

Conclusions

This study described and evaluated a standardized method for proton treatment planning for CSI. Overall, the standardized planning methodology yielded consistently high quality treatment plans and perhaps most importantly, it did so for an anatomically diverse patient population.

Particle therapy for noncancer diseases

Radiation therapy using high-energy charged particles is generally acknowledged as a powerful new technique in cancer treatment. However, particle therapy in oncology is still controversial, specifically because it is unclear whether the putative clinical advantages justify the high additional costs. However, particle therapy can find important applications in the management of noncancer diseases, especially in radiosurgery. Extension to other diseases and targets (both cranial and extracranial) may widen the applications of the technique and decrease the cost/benefit ratio of the accelerator facilities. Future challenges in this field include the use of different particles and energies, motion management in particle body radiotherapy and extension to new targets currently treated by catheter ablation (atrial fibrillation and renal denervation) or stereotactic radiation therapy (trigeminal neuralgia, epilepsy, and macular degeneration). Particle body radiosurgery could be a future key application of accelerator-based particle therapy facilities in 10 years from today.

Results of a multicentric in silico clinical trial (ROCOCO): comparing radiotherapy with photons and protons for non-small cell lung cancer

INTRODUCTION

This multicentric in silico trial compares photon and proton radiotherapy for non-small cell lung cancer patients. The hypothesis is that proton radiotherapy decreases the dose and the volume of irradiated normal tissues even when escalating to the maximum tolerable dose of one or more of the organs at risk (OAR).

METHODS

Twenty-five patients, stage IA-IIIB, were prospectively included. On 4D F18-labeled fluorodeoxyglucose-positron emission tomography-computed tomography scans, the gross tumor, clinical and planning target volumes, and OAR were delineated. Three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) photon and passive scattered conformal proton therapy (PSPT) plans were created to give 70 Gy to the tumor in 35 fractions. Dose (de-)escalation was performed by rescaling to the maximum tolerable dose.

RESULTS

Protons resulted in the lowest dose to the OAR, while keeping the dose to the target at 70 Gy. The integral dose (ID) was higher for 3DCRT (59%) and IMRT (43%) than for PSPT. The mean lung dose reduced from 18.9 Gy for 3DCRT and 16.4 Gy for IMRT to 13.5 Gy for PSPT. For 10 patients, escalation to 87 Gy was possible for all 3 modalities. The mean lung dose and ID were 40 and 65% higher for photons than for protons, respectively.

CONCLUSIONS

The treatment planning results of the Radiation Oncology Collaborative Comparison trial show a reduction of ID and the dose to the OAR when treating with protons instead of photons, even with dose escalation. This shows that PSPT is able to give a high tumor dose, while keeping the OAR dose lower than with the photon modalities.

Real-time 4-D radiotherapy for lung cancer

Respiratory motion considerably influences dose distribution, and thus clinical outcomes in radiotherapy for lung cancer. Breath holding, breath coaching, respiratory gating with external surrogates, and mathematical predicting models all have inevitable uncertainty due to the unpredictable variations of internal tumor motion. The amplitude of the same tumor can vary with standard deviations > 5 mm occurring in 23% of T1-2N0M0 non-small cell lung cancers. Residual motion varied 1-6 mm (95th percentile) for the 40% duty cycle of respiratory gating with external surrogates. The 4-D computed tomography is vulnerable to problems relating to the external surrogates. Real-time 4-D radiotherapy (4DRT), where the temporal changes in anatomy during the delivery of radiotherapy are explicitly considered in real time, is emerging as a new method to reduce these known sources of uncertainty. Fluoroscopic, real-time tumor-tracking technology using internal fiducial markers near the tumor has ± 2 mm accuracy, and has achieved promising clinical results when used with X-ray therapy. Instantaneous irradiation based on real-time verification of internal fiducial markers is considered the minimal requisite for real-time 4DRT of lung cancers at present. Real-time tracking radiotherapy using gamma rays from positron emitters in tumors is in the preclinical research stage, but has been successful in experiments in small animals. Real-time tumor tracking via spot-scanning proton beam therapy has the capability to cure large lung cancers in motion, and is expected to be the next-generation real-time 4DRT.

When to wait for more evidence? Real options analysis in proton therapy

PURPOSE

Trends suggest that cancer spending growth will accelerate. One method for controlling costs is to examine whether the benefits of new technologies are worth the extra costs. However, especially new and emerging technologies are often more costly, while limited clinical evidence of superiority is available. In that situation it is often unclear whether to adopt the new technology now, with the risk of investing in a suboptimal therapy, or to wait for more evidence, with the risk of withholding patients their optimal treatment. This trade-off is especially difficult when it is costly to reverse the decision to adopt a technology, as is the case for proton therapy. Real options analysis, a technique originating from financial economics, assists in making this trade-off.

METHODS

We examined whether to adopt proton therapy, as compared to stereotactic body radiotherapy, in the treatment of inoperable stage I non-small cell lung cancer. Three options are available: adopt without further research; adopt and undertake a trial; or delay adoption and undertake a trial. The decision depends on the expected net gain of each option, calculated by subtracting its total costs from its expected benefits.

RESULTS

In The Netherlands, adopt and trial was found to be the preferred option, with an optimal sample size of 200 patients. Increase of treatment costs abroad and costs of reversal altered the preferred option.

CONCLUSION

We have shown that real options analysis provides a transparent method of weighing the costs and benefits of adopting and/or further researching new and expensive technologies.

Recent advancements in multimodality treatment of gliomas

Gliomas account for the vast majority of malignant adult brain tumors. Even though tremendous effort has been made to optimize treatment of patients with high-grade glioma, the prognosis remains poor, especially for patients with glioblastoma. The dismal prognosis conferred by these tumors is in part caused by the tendency to diffusely infiltrate into neighboring brain tissue, but also by the inherent resistance of these tumors to both chemotherapy and radiation. This article reviews the recent advancements in multimodality treatment of patients with gliomas, both in the primary and recurrent setting, with an emphasis on the emerging targeted therapies. Moreover, the external beam radiotherapy options, including intensity modulated radiotherapy and particle (proton and carbon ion) radiotherapy are reviewed.

Current comprehensive management of cranial base chordomas: 10-year meta-analysis of observational studies

OBJECT

The role of surgery and adjuvant radiation therapy for cranial base chordomas is not well established. This meta-analysis measures the relationship of complete resection and type of adjuvant radiation therapy to 5-year progression-free survival (PFS) and overall survival (OS) of cranial base chordomas.

METHODS

A systematic MEDLINE search (1999-present) yielded 23 observational studies and 807 patients who fit inclusion criteria. The following analyses were performed: 1) Kaplan-Meier 5-year PFS and OS compared based on the extent of resection and type of adjuvant radiation therapy using the log-rank method; 2) a random-effects model comparing 5-year PFS with complete or incomplete resection; and 3) paired z-test comparisons of weighted average 5-year OS and PFS grouped by type of adjuvant radiation therapy.

RESULTS

The weighted average follow-up was 53.6 months. The weighted average 5-year PFS and OS were 50.8% and 78.4%, respectively. Complete resection conferred a higher 5-year PFS than incomplete resection from the random effects model (mean difference in PFS 20.7%; 95% CI 6.57%-34.91%). Patients with incomplete resection were 3.83 times more likely to experience a recurrence (95% CI 1.63-9.00) and 5.85 times more likely to die (95% CI 1.40-24.5) at 5 years versus patients with complete resection. There was no difference in 5-year OS by type of adjuvant radiation, although 5-year PFS was lower in patients receiving Gamma Knife surgery relative to carbon ion radiotherapy (p = 0.042) on paired z-test. No survival difference occurred between radiation therapy techniques on Kaplan-Meier analysis of compiled patient data.

CONCLUSIONS

Patients with complete resection of cranial base chordomas have a prolonged 5-year PFS and OS. Adjuvant proton-beam, carbon ion, and modern fractionated photon radiation therapy techniques offered a similar rate of PFS and OS at 5 years.

The potential benefit of radiotherapy with protons in head and neck cancer with respect to normal tissue sparing: a systematic review of literature

PURPOSE

Clinical studies concerning head and neck cancer patients treated with protons reporting on radiation-induced side effects are scarce. Therefore, we reviewed the literature regarding the potential benefits of protons compared with the currently used photons in terms of lower doses to normal tissue and the potential for fewer subsequent radiation-induced side effects, with the main focus on in silico planning comparative (ISPC) studies.

MATERIALS AND METHODS

A literature search was performed by two independent researchers on ISPC studies that included proton-based and photon-based irradiation techniques.

RESULTS

Initially, 877 papers were retrieved and 14 relevant and eligible ISPC studies were identified and included in this review. Four studies included paranasal sinus cancer cases, three included nasopharyngeal cancer cases, and seven included oropharyngeal, hypopharyngeal, and/or laryngeal cancer cases. Seven studies compared the most sophisticated photon and proton techniques: intensity-modulated photon therapy versus intensity-modulated proton therapy (IMPT). Four studies compared different proton techniques. All studies showed that protons had a lower normal tissue dose, while keeping similar or better target coverage. Two studies found that these lower doses theoretically translated into a significantly lower incidence of salivary dysfunction.

CONCLUSION

The results of ISPC studies indicate that protons have the potential for a significantly lower normal tissue dose, while keeping similar or better target coverage. Scanned IMPT probably offers the most advantage and will allow for a substantially lower probability of radiation-induced side effects. The results of these ISPC studies should be confirmed in properly designed clinical trials.

Proton-beam therapy for prostate cancer

The treatment options for prostate cancer include prostatectomy, external-beam irradiation, brachytherapy, cryosurgery, focused ultrasound, hormonal therapy, watchful waiting, and various combinations of these modalities. Because the prostate abuts the bladder and rectum, the dose distributions of external-beam irradiations and the accuracy of their placement play crucial roles in the probability of tumor cure and the incidence of posttreatment complications. Principal among the newer radiation technologies is proton-beam therapy (PBT), whose dose distributions make it possible to deliver higher tumor doses and smaller doses to surrounding normal tissues than from x-ray systems. However, as the 10-year cause-specific survival for early-stage disease treated by radiation therapy now exceeds 90%, and with severe late toxicities in the range of 2% to 3%, randomized clinical trials provide the only means to demonstrate improved outcomes from PBT. Short of the data provided by such trials, the efficacy of PBT can be gleaned only from reports in the clinical literature, and, to date, these reports are equivocal. In view of the current health care crisis and the higher costs of PBT for prostate cancer, it is reasonable to assess the viability of this in-vogue but not-so-new technology.

Design of and technical challenges involved in a framework for multicentric radiotherapy treatment planning studies

This report introduces a framework for comparing radiotherapy treatment planning in multicentric in silico clinical trials. Quality assurance, data incompatibility, transfer and storage issues, and uniform analysis of results are discussed. The solutions that are given provide a useful guide for the set-up of future multicentric planning studies or public repositories of high quality data.

Do we have enough evidence to implement particle therapy as standard treatment in lung cancer? A systematic literature review

BACKGROUND

The societal burden of lung cancer is high because of its high incidence and high lethality. From a theoretical point of view, radiotherapy with beams of protons and heavier charged particles, for example, carbon ions (C-ions), should lead to superior results, compared with photon beams. In this review, we searched for clinical evidence to justify implementation of particle therapy as standard treatment in lung cancer.

METHODS

A systematic literature review based on an earlier published comprehensive review was performed and updated through November 2009.

RESULTS

Eleven fully published studies, all dealing with non-small cell lung cancer (NSCLC), mainly stage I, were identified. No phase III trials were found. For proton therapy, 2- to 5-year local tumor control rates varied in the range of 57%-87%. The 2- and 5-year overall survival (OS) and 2- and 5-year cause-specific survival (CSS) rates were 31%-74% and 23% and 58%-86% and 46%, respectively. Radiation-induced pneumonitis was observed in about 10% of patients. For C-ion therapy, the overall local tumor control rate was 77%, but it was 95% when using a hypofractionated radiation schedule. The 5-year OS and CSS rates were 42% and 60%, respectively. Slightly better results were reported when using hypofractionation, 50% and 76%, respectively.

CONCLUSION

The present results with protons and heavier charged particles are promising. However, the current lack of evidence on the clinical (cost-)effectiveness of particle therapy emphasizes the need to investigate the efficiency of particle therapy in an adequate manner. Until these results are available for lung cancer, charged particle therapy should be considered experimental.