Proton-beam radiotherapy for early-stage lung cancer

Efficacy and Safety in Proton Therapy and Photon Therapy for Patients With Esophageal Cancer: A Meta-Analysis

Importance

Radiotherapy plays an important role in the treatment of esophageal cancer. Proton therapy has unique physical properties and higher relative biological effectiveness. However, whether proton therapy has greater benefit than photon therapy is still unclear.

Objective

To evaluate whether proton was associated with better efficacy and safety outcomes, including dosimetric, prognosis, and toxic effects outcomes, compared with photon therapy and to evaluate the efficacy and safety of proton therapy singly.

Data Sources

A systematic search of PubMed, Embase, the Cochrane Library, Web of Science, SinoMed, and China National Knowledge Infrastructure databases was conducted for articles published through November 25, 2021, and updated to March 25, 2023.

Study Selection

For the comparison of proton and photon therapy, studies including dosimetric, prognosis, and associated toxic effects outcomes were included. The separate evaluation of proton therapy evaluated the same metrics.

Data Extraction and Synthesis

Data on study design, individual characteristics, and outcomes were extracted. If I2 was greater than 50%, the random-effects model was selected. This meta-analysis is reported following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline.

Main Outcomes and Measures

The main outcomes were organs at risk (OARs) dosimetric outcomes, prognosis (overall survival [OS], progression-free survival [PFS], and objective response rate [ORR]), and radiation-related toxic effects.

Results

A total of 45 studies were included in the meta-analysis. For dosimetric analysis, proton therapy was associated with significantly reduced OARs dose. Meta-analysis showed that photon therapy was associated with poor OS (hazard ratio [HR], 1.31; 95% CI, 1.07-1.61; I2 = 11%), but no difference in PFS was observed. Subgroup analysis showed worse OS (HR, 1.42; 95% CI, 1.14-1.78; I2 = 34%) and PFS (HR, 1.48; 95% CI, 1.06-2.08; I2 = 7%) in the radical therapy group with photon therapy. The pathological complete response rate was similar between groups. Proton therapy was associated with significantly decreased grade 2 or higher radiation pneumonitis and pericardial effusion, and grade 4 or higher lymphocytopenia. Single-rate analysis of proton therapy found 89% OS and 65% PFS at 1 year, 71% OS and 56% PFS at 2 years, 63% OS and 48% PFS at 3 years, and 56% OS and 42% PFS at 5 years. The incidence of grade 2 or higher radiation esophagitis was 50%, grade 2 or higher radiation pneumonitis was 2%, grade 2 or higher pleural effusion was 4%, grade 2 or higher pericardial effusion was 3%, grade 3 or higher radiation esophagitis was 8%, and grade 4 or higher lymphocytopenia was 17%.

Conclusions and Relevance

In this meta-analysis, proton therapy was associated with reduced OARs doses and toxic effects and improved prognosis compared with photon therapy for esophageal cancer, but caution is warranted. In the future, these findings should be further validated in randomized clinical trials.

Dosimetry, Efficacy, Safety, and Cost-Effectiveness of Proton Therapy for Non-Small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) is the most common malignancy which requires radiotherapy (RT) as an important part of its multimodality treatment. With the advent of the novel irradiation technique, the clinical outcome of NSCLC patients who receive RT has been dramatically improved. The emergence of proton therapy, which allows for a sharper dose of build-up and drop-off compared to photon therapy, has potentially improved clinical outcomes of NSCLC. Dosimetry studies have indicated that proton therapy can significantly reduce the doses for normal organs, especially the lung, heart, and esophagus while maintaining similar robust target volume coverage in both early and advanced NSCLC compared with photon therapy. However, to date, most studies have been single-arm and concluded no significant changes in the efficacy for early-stage NSCLC by proton therapy over stereotactic body radiation therapy (SBRT). The results of proton therapy for advanced NSCLC in these studies were promising, with improved clinical outcomes and reduced toxicities compared with historical photon therapy data. However, these studies were also mainly single-arm and lacked a direct comparison between the two therapies. Currently, there is much emerging evidence focusing on dosimetry, efficacy, safety, and cost-effectiveness of proton therapy for NSCLC that has been published, however, a comprehensive review comparing these therapies is, to date, lacking. Thus, this review focuses on these aspects of proton therapy for NSCLC.

Physics of Particle Beam and Hypofractionated Beam Delivery in NSCLC

The dosimetric advantages of particle therapy lead to significantly reduced integral dose to normal tissues, making it an attractive treatment option for body sites such as the thorax. With reduced normal tissue dose comes the potential for dose escalation, toxicity reduction, or hypofractionation. While proton and heavy ion therapy have been used extensively for NSCLC, there are challenges in planning and delivery compared with X-ray-based radiation therapy. Particularly, range uncertainties compounded by breathing motion have to be considered. This article summarizes the current state of particle therapy for NSCLC with a specific focus on the impact of dosimetric uncertainties in planning and delivery.

Role of Proton Beam Therapy in Current Day Radiation Oncology Practice

Proton beam therapy (PBT), because of its unique physics of no–exit dose deposition in the tissue, is an exciting prospect. The phenomenon of Bragg peak allows protons to deposit their almost entire energy towards the end of the path of the proton and stops any further dose delivery. Braggs peak equips PBT with superior dosimetric advantage over photons or electrons because PBT doesn’t traverse the target/body but is stopped sharply at an energy dependent depth in the target/body. It also has no exit dose. Because of no exit dose and normal tissue sparing, PBT is hailed for its potential to bring superior outcomes. Pediatric malignancies is the most common malignancy where PBT have found utmost application. Nowadays, PBT is also being used in the treatment of other malignancies such as carcinoma prostate, carcinoma breast, head and neck malignancies, and gastrointestinal (GI) malignancies. Despite advantages of PBT, there is not only a high cost of setting up of PBT centers but also a lack of definitive phase-III data. Therefore, we review the role of PBT in current day practice of oncology to bring out the nuances that must guide the practice to choose suitable patients for PBT.

Proton Beam Therapy for Histologically or Clinically Diagnosed Stage I Non-Small Cell Lung Cancer (NSCLC): The First Nationwide Retrospective Study in Japan

PURPOSE

To investigate the efficacy and safety of proton beam therapy (PBT) for the treatment of stage I non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

Six hundred sixty-nine patients with 682 tumors histologically or clinically diagnosed stage I NSCLC according to the seventh edition of Union for International Cancer Control who received passive-scattering PBT from April 2004 and December 2013 in Japan were retrospectively reviewed to analyze survival, local control, and toxicities.

RESULTS

Of 669 patients, 486 (72.6%) were men, with a median age of 76 years (range, 42-94 years). NSCLC was histologically confirmed in 440 patients (65.7%). Clinical T stages included T1a (n = 265; 38.9%), T1b (n = 216; 31.7%), and T2a (n = 201; 29.4%). The total irradiation doses of PBT ranged from 74.4 to 131.3 biological effective dose GyE (median, 109.6 biological effective dose GyE). The median follow-up period was 38.2 months (range, 0.6-154.5 months) for all patients. The 3-year overall survival and progression-free survival rates for all patients were 79.5% and 64.1%, respectively. For patients with stage IA tumors, the 3-year overall survival and progression-free survival rates were 82.8% and 70.6%, respectively, and the corresponding rates for patients with stage IB tumors were 70.8% and 47.3%, respectively. The 3-year local progression-free rates for all, stage IA, and stage IB patients were 89.8%, 93.5%, and 79.4%, respectively. The incidence of grade 2, 3, 4, and 5 pneumonitis was 9.8%, 1.0%, 0%, and 0.7%, respectively. The incidence of grade ≥3 dermatitis was 0.4%. No grade 4 or severe adverse events, other than pneumonitis, were observed.

CONCLUSIONS

PBT appears to yield acceptable survival rates, with a low rate of toxicities.

Proton therapy for non-small cell lung cancer: the road ahead

Proton therapy is an evolving radiotherapy modality with indication for numerous cancer types. With the benefits of reducing dose and sparing normal tissue, protons offer a clear physical and dosimetric advantage over photon radiotherapy for many patients. However, its impact on one type of disease, non-small cell lung cancer (NSCLC), is still not fully understood. Our review aims to highlight the data for using proton therapy in NSCLC, with a focus on the clinical data-or lack thereof-supporting proton treatment for early and advanced stage disease. In evaluating these data, we consider how future directions and advances in proton technology give rise for hope in defining a role for protons in improving NSCLC outcomes. We close with considerations for next steps and the challenges ahead in using proton therapy for this unique patient population.

Proton therapy for early-stage non-small cell lung cancer (NSCLC)

In the setting of early-stage non-small cell lung cancer (NSCLC), defining the optimal clinical context for proton beam therapy (PBT) is challenging due to the increasing evidence demonstrating high rates of local control and good tolerance of stereotactic ablative body radiation (SABR). Given the relatively small percentage of lung and other critical structures treated with SABR, dosimetric studies comparing the two techniques have typically concluded that there are modest advantages to PBT, typically by reducing the low dose volumes, such as volume of lung receiving 5 Gy. This advantage may be more significant in treating larger tumors, multiple tumors, or central tumors. Most of the published studies are based on passive scattering PBT. Dosimetric benefits are likely to increase when pencil beam scanning/intensity-modulated proton therapy (IMPT) is employed, as has been observed in dosimetric reports in the locally advanced setting. More clinical data is needed regarding the safety and efficacy of stereotactic PBT in comparison to SABR. However, the only randomized trial that has been attempted closed early due to poor accrual, thus demonstrating the difficulty in designing trials in this context that incorporate a relevant and focused scientific question that can be extrapolated to clinical practice, yet also accrue sufficiently. The advent and increased use of advanced image-guided radiation therapy (IGRT) techniques in the context of proton therapy, as well as the widespread implementation of IMPT, will increase the potential benefit of PBT. The next 5-10 years will likely yield more appropriate, feasible studies that will help answer the question of patient selection for this advanced technology.

Advances in proton therapy in lung cancer

Lung cancer remains the leading cause of cancer deaths in the United States (US) and worldwide. Radiation therapy is a mainstay in the treatment of locally advanced non-small cell lung cancer (NSCLC) and serves as an excellent alternative for early stage patients who are medically inoperable or who decline surgery. Proton therapy has been shown to offer a significant dosimetric advantage in NSCLC patients over photon therapy, with a decrease in dose to vital organs at risk (OARs) including the heart, lungs and esophagus. This in turn, can lead to a decrease in acute and late toxicities in a population already predisposed to lung and cardiac injury. Here, we present a review on proton treatment techniques, studies, clinical outcomes and toxicities associated with treating both early stage and locally advanced NSCLC.

Proton beam therapy in non-small cell lung cancer: state of the art

This review summarizes the past and present status of proton beam therapy (PBT) for lung cancer. PBT has a unique characteristic called the Bragg peak that enables a reduction in the dose of normal tissue around the tumor, but is sensitive to the uncertainties of density changes. The heterogeneity in electron density for thoracic lesions, such as those in the lung and mediastinum, and tumor movement according to respiration necessitates respiratory management for PBT to be applied in lung cancer patients. There are two types of PBT - a passively scattered approach and a scanning approach. Typically, a passively scattered approach is more robust for respiratory movement and a scanning approach could result in a more conformal dose distribution even when the tumor shape is complex. Large tumors of centrally located lung cancer may be more suitably irradiated than with intensity-modulated radiotherapy (IMRT) or stereotactic body radiotherapy (SBRT). For a locally advanced lung cancer, PBT can spare the lung and heart more than photon IMRT. However, no randomized controlled trial has reported differences between PBT and IMRT or SBRT for early-stage and locally advanced lung cancers. Therefore, a well-designed controlled trial is warranted.

Advances in radiotherapy techniques and delivery for non-small cell lung cancer: benefits of intensity-modulated radiation therapy, proton therapy, and stereotactic body radiation therapy

The 21st century has seen several paradigm shifts in the treatment of non-small cell lung cancer (NSCLC) in early-stage inoperable disease, definitive locally advanced disease, and the postoperative setting. A key driver in improvement of local disease control has been the significant evolution of radiation therapy techniques in the last three decades, allowing for delivery of definitive radiation doses while limiting exposure of normal tissues. For patients with locally-advanced NSCLC, the advent of volumetric imaging techniques has allowed a shift from 2-dimensional approaches to 3-dimensional conformal radiation therapy (3DCRT). The next generation of 3DCRT, intensity-modulated radiation therapy and volumetric-modulated arc therapy (VMAT), have enabled even more conformal radiation delivery. Clinical evidence has shown that this can improve the quality of life for patients undergoing definitive management of lung cancer. In the early-stage setting, conventional fractionation led to poor outcomes. Evaluation of altered dose fractionation with the previously noted technology advances led to advent of stereotactic body radiation therapy (SBRT). This technique has dramatically improved local control and expanded treatment options for inoperable, early-stage patients. The recent development of proton therapy has opened new avenues for improving conformity and the therapeutic ratio. Evolution of newer proton therapy techniques, such as pencil-beam scanning (PBS), could improve tolerability and possibly allow reexamination of dose escalation. These new progresses, along with significant advances in systemic therapies, have improved survival for lung cancer patients across the spectrum of non-metastatic disease. They have also brought to light new challenges and avenues for further research and improvement.

Long-term outcome of phase I/II prospective study of dose-escalated proton therapy for early-stage non-small cell lung cancer

PURPOSE

The aim of this phase I/II study was to assess the long-term clinical benefits and toxicities of proton beam therapy for medically inoperable early-stage non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

From June 2006 to September 2011, 35 patients with medically inoperable T1N0M0 (central or superior location, 12 patients) or T2-3N0M0 (any location, 23 patients) NSCLC were treated with 87.5Gy at 2.5Gy/fraction of proton therapy. Toxicities were scored according to the Common Terminology Criteria for Adverse Events, version 4.0.

RESULTS

The median follow-up time was 83.1months (95% CI: 69.2-97.1months). For all 35 patients, the 1, 3, and 5-year overall survival rates were 85.7%, 42.9%, and 28.1%, respectively. The 5-year local recurrence-free, regional recurrence-free, and distant metastasis-free survival rates were 85.0%, 89.2%, and 54.4%, respectively. Different T stages had no effect on local and regional recurrence (p=0.499, p=1.00). However, with the increase in T stages, the distant metastasis rate increased significantly (p=0.006). The most common adverse effects were dermatitis (grade 2, 51.4%; grade 3, 2.9%) and radiation pneumonitis (grade 2, 11.4%; grade 3, 2.9%). Other grade 2 toxicities included esophagitis (2.9%), rib fracture (2.9%), heart toxicities (5.7%), and chest wall pain (2.9%).

CONCLUSIONS

According to our long-term follow-up data, proton therapy with ablative doses is well tolerated and effective in medically inoperable early-stage NSCLC. Systemic therapy should be considered to reduce the rate of distant metastasis in cases of T2 and T3 lesions.

Clinical Applications of Proton Radiation Treatment at Loma Linda University: Review of a Fifteen-year Experience

Proton radiation therapy has been used at Loma Linda University Medical Center for 15 years, sometimes in combination with photon irradiation, surgery, and chemotherapy, but often as the sole modality. Our initial experience was based on established studies showing the utility of protons for certain management problems, but since then we have engaged in a planned program to exploit the capabilities of proton radiation and expand its applications in accordance with progressively accumulating clinical data. Our cumulative experience has confirmed that protons are a superb tool for delivering conformal radiation treatments, enabling delivery of effective doses of radiation and sparing normal tissues from radiation exposure.

Consensus Statement on Proton Therapy in Early-Stage and Locally Advanced Non-Small Cell Lung Cancer

Radiation dose escalation has been shown to improve local control and survival in patients with non-small cell lung cancer in some studies, but randomized data have not supported this premise, possibly owing to adverse effects. Because of the physical characteristics of the Bragg peak, proton therapy (PT) delivers minimal exit dose distal to the target volume, resulting in better sparing of normal tissues in comparison to photon-based radiation therapy. This is particularly important for lung cancer given the proximity of the lung, heart, esophagus, major airways, large blood vessels, and spinal cord. However, PT is associated with more uncertainty because of the finite range of the proton beam and motion for thoracic cancers. PT is more costly than traditional photon therapy but may reduce side effects and toxicity-related hospitalization, which has its own associated cost. The cost of PT is decreasing over time because of reduced prices for the building, machine, maintenance, and overhead, as well as newer, shorter treatment programs. PT is improving rapidly as more research is performed particularly with the implementation of 4-dimensional computed tomography-based motion management and intensity modulated PT. Given these controversies, there is much debate in the oncology community about which patients with lung cancer benefit significantly from PT. The Particle Therapy Co-operative Group (PTCOG) Thoracic Subcommittee task group intends to address the issues of PT indications, advantages and limitations, cost-effectiveness, technology improvement, clinical trials, and future research directions. This consensus report can be used to guide clinical practice and indications for PT, insurance approval, and clinical or translational research directions.

A Phase 2 Trial of Concurrent Chemotherapy and Proton Therapy for Stage III Non-Small Cell Lung Cancer: Results and Reflections Following Early Closure of a Single-Institution Study

PURPOSE

Proton therapy has been shown to reduce radiation dose to organs at risk (OAR) and could be used to safely escalate the radiation dose. We analyzed outcomes in a group of phase 2 study patients treated with dose-escalated proton therapy with concurrent chemotherapy for stage 3 non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

From 2009 through 2013, LU02, a phase 2 trial of proton therapy delivering 74 to 80 Gy at 2 Gy/fraction with concurrent chemotherapy for stage 3 NSCLC, was opened to accrual at our institution. Due to slow accrual and competing trials, the study was closed after just 14 patients (stage IIIA, 9 patients; stage IIIB, 5 patients) were accrued over 4 years. During that same time period, 55 additional stage III patients were treated with high-dose proton therapy, including 7 in multi-institutional proton clinical trials, 4 not enrolled due to physician preference, and 44 who were ineligible based on strict entry criteria. An unknown number of patients were ineligible for enrollment due to insurance coverage issues and thus were treated with photon radiation. Median follow-up of surviving patients was 52 months.

RESULTS

Two-year overall survival and progression-free survival rates were 57% and 25%, respectively. Median lengths of overall survival and progression-free survival were 33 months and 14 months, respectively. There were no acute grade 3 toxicities related to proton therapy. Late grade 3 gastrointestinal toxicity and pulmonary toxicity each occurred in 1 patient.

CONCLUSIONS

Dose-escalated proton therapy with concurrent chemotherapy was well tolerated with encouraging results among a small cohort of patients. Unfortunately, single-institution proton studies may be difficult to accrue and consideration for pragmatic and/or multicenter trial design should be considered when developing future proton clinical trials.

Particle therapy for non-small cell lung tumors: where do we stand? A systematic review of the literature

This review article provides a systematic overview of the currently available evidence on the clinical effectiveness of particle therapy for the treatment of non-small cell lung cancer and summarizes findings of in silico comparative planning studies. Furthermore, technical issues and dosimetric uncertainties with respect to thoracic particle therapy are discussed.

Accelerated dose escalation with proton beam therapy for non-small cell lung cancer

Local tumor control remains challenging in many cases of non-small cell lung cancer (NSCLC), particularly those that involve large or centrally located tumors. Concurrent chemotherapy and radiation can maximize tumor control and survival for patients with locally advanced disease, but a substantial proportion of such patients cannot tolerate this therapy, and sequential chemoradiation regimens or radiation given alone at conventionally fractionated doses produces suboptimal results. An alternative approach is the use of hypofractionated proton beam therapy (PBT). The energy distribution of protons can be exploited to reduce involuntary irradiation of normal tissues, particularly the low-dose irradiation problematic in intensity-modulated (photon) radiation therapy (IMRT). Here we summarize current evidence on the use of hypofractionated PBT for both early-stage and locally advanced NSCLC, and the possibility of using hypofractionated regimens for patients who are not candidates for concurrent chemotherapy.

Evaluation and comparison of New 4DCT based strategies for proton treatment planning for lung tumors

Purpose

To evaluate different strategies for proton lung treatment planning based on four-dimensional CT (4DCT) scans.

Methods and Materials

Twelve cases, involving only gross tumor volumes (GTV), were evaluated. Single image sets of (1) maximum intensity projection (MIP3) of end inhale (EI), middle exhale (ME) and end exhale (EE) images; (2) average intensity projection (AVG) of all phase images; and (3) EE images from 4DCT scans were selected as primary images for proton treatment planning. Internal target volumes (ITVs) outlined by a clinician were imported into MIP3, AVG, and EE images as planning targets. Initially, treatment uncertainties were not included in planning. Each plan was imported into phase images of 4DCT scans. Relative volumes of GTVs covered by 95% of prescribed dose and mean ipsilateral lung dose of a phase image obtained by averaging the dose in inspiration and expiration phases were used to evaluate the quality of a plan for a particular case. For comparing different planning strategies, the mean of the averaged relative volumes of GTVs covered by 95% of prescribed dose and its standard deviation for each planning strategy for all cases were used. Then, treatment uncertainties were included in planning. Each plan was recalculated in phase images of 4DCT scans. Same strategies were used for plan evaluation except dose-volume histograms of the planning target volumes (PTVs) instead of GTVs were used and the mean and standard deviation of the relative volumes of PTVs covered by 95% of prescribed dose and the ipsilateral lung dose were used to compare different planning strategies.

Results

MIP3 plans without treatment uncertainties yielded 96.7% of the mean relative GTV covered by 95% of prescribed dose (standard deviations of 5.7% for all cases). With treatment uncertainties, MIP3 plans yielded 99.5% of mean relative PTV covered by 95% of prescribed dose (standard deviations of 0.7%). Inclusion of treatment uncertainties improved PTV dose coverage but also increased the ipsilateral mean lung dose in general, and reduced the variations of the PTV dose coverage among different cases. Plans based on conventional axial CT scan (CVCT) gave the poorest PTV dose coverage (about 96% of mean relative PTV covered by 95% isodose) compared to MIP3 and EE plans, which resulted in 100% of PTV covered by 95% isodose for tumors with relatively large motion. AVG plans demonstrated PTV dose coverage of 89.8% and 94.4% for cases with small tumors. MIP3 plans demonstrated superior tumor coverage and were least sensitive to tumor size and tumor location.

Conclusion

MIP3 plans based on 4DCT scans were the best planning strategy for proton lung treatment planning.

Advantages of proton therapy in non-small cell lung cancers

The advantage of proton therapy over conventional radiotherapy is enormous, with many clinical advantages. In this review, we summarized the important literature in the advantages of Proton Therapy in Non-small Cell Lung Cancers.

Proton therapy radiation pneumonitis local dose-response in esophagus cancer patients

PURPOSE

This study quantifies pulmonary radiation toxicity in patients who received proton therapy for esophagus cancer.

MATERIALS/METHODS

We retrospectively studied 100 esophagus cancer patients treated with proton therapy. The linearity of the enhanced FDG uptake vs. proton dose was evaluated using the Akaike Information Criterion (AIC). Pneumonitis symptoms (RP) were assessed using the Common Toxicity Criteria for Adverse Events version 4.0 (CTCAEv4). The interaction of the imaging response with dosimetric parameters and symptoms was evaluated.

RESULTS

The RP scores were: 0 grade 4/5, 7 grade 3, 20 grade 2, 37 grade 1, and 36 grade 0. Each dosimetric parameter was significantly higher for the symptomatic group. The AIC winning models were 30 linear, 52 linear quadratic, and 18 linear logarithmic. There was no significant difference in the linear coefficient between models. The slope of the FDG vs. proton dose response was 0.022 for the symptomatic and 0.012 for the asymptomatic (p=0.014). Combining dosimetric parameters with the slope did not improve the sensitivity or accuracy in identifying symptomatic cases.

CONCLUSIONS

The proton radiation dose response on FDG PET/CT imaging exhibited a predominantly linear dose response on modeling. Symptomatic patients had a higher dose response slope.

Three-dimensional radiochromic film dosimetry of proton clinical beams using a gafchromic EBT2 film array

In this work, three-dimensional (3D) film-based proton beam measurements were used for the first time to verify the patient-specific radiation dose distribution, beam range and compensator shape. Three passively scattered proton beams and one uniform scanning proton beam were directed onto an acrylic phantom with inserted Gafchromic EBT films. The average gamma index for a comparison of the dose distributions was less than one for 97.2 % of all pixels from the passively scattered proton beams and 98.1 % of all pixels for the uniform scanning proton beams, with a 3 % dose and a 3 mm distance-to-dose agreement tolerance limit. The results also showed that the average percentage of points within the acceptance criteria for proton beam ranges was 94.6 % for the passively scattered proton beams. Both the dose distribution and the proton beam range determined by the 3D EBT film measurement agreed well with the planning system values.

Proton therapy for lung cancer

Proton therapy is an emerging radiotherapy technology with the potential to improve the therapeutic index in the treatment of lung cancer patients. Since charged particles, such as protons, have a penetration length that can be modified by using different energies, protons offer the clinician the ability to modulate radiation dose deposition along the beam path. This facilitates an increase of the dose to the tumor target while minimizing the volume of normal tissue irradiation. Such precise delivery is particularly relevant in the setting of lung cancer where the targeted tissues are in close proximity to moderately radiation-sensitive organs like the spinal cord, heart, and esophagus, but are also effectively surrounded by the normal lung, which is extremely sensitive to radiation damage. Proton therapy has been investigated for the treatment of surgically curable yet medically inoperable patients as well as patients with regionally advanced disease.

An evidence based review of proton beam therapy: the report of ASTRO's emerging technology committee

Proton beam therapy (PBT) is a novel method for treating malignant disease with radiotherapy. The purpose of this work was to evaluate the state of the science of PBT and arrive at a recommendation for the use of PBT. The emerging technology committee of the American Society of Radiation Oncology (ASTRO) routinely evaluates new modalities in radiotherapy and assesses the published evidence to determine recommendations for the society as a whole. In 2007, a Proton Task Force was assembled to evaluate the state of the art of PBT. This report reflects evidence collected up to November 2009. Data was reviewed for PBT in central nervous system tumors, gastrointestinal malignancies, lung, head and neck, prostate, and pediatric tumors. Current data do not provide sufficient evidence to recommend PBT in lung cancer, head and neck cancer, GI malignancies, and pediatric non-CNS malignancies. In hepatocellular carcinoma and prostate cancer and there is evidence for the efficacy of PBT but no suggestion that it is superior to photon based approaches. In pediatric CNS malignancies PBT appears superior to photon approaches but more data is needed. In large ocular melanomas and chordomas, we believe that there is evidence for a benefit of PBT over photon approaches. PBT is an important new technology in radiotherapy. Current evidence provides a limited indication for PBT. More robust prospective clinical trials are needed to determine the appropriate clinical setting for PBT.

The clinical outcomes of proton beam radiation therapy for retinoblastomas that were resistant to chemotherapy and focal treatment

Purpose

To evaluate the clinical results of proton beam radiation therapy (PBRT) for treatment of retinoblastoma.

Methods

Children with retinoblastoma who were treated with chemotherapy and focal treatment such as brachytherapy and thermotherapy but showed no response or developed recurrences later received PBRT. The PBRT strategy was designed to concentrate the radiation energy to the retinoblastoma and spare the surrounding healthy tissue or organs.

Results

There were three patients who received PBRT. The first patient received PBRT because of an initial lack of tumor regression with chemotherapy and brachytherapy. This patient showed regression after PBRT. The second patient who developed recurrence of retinoblastoma as diffuse infiltrating subretinal seeding was taken PBRT. After complete regression, there was recurrence of tumor and the eye was enucleated. The third patient had unilateral extensively advanced retinoblastoma. Initial chemotherapy failed and tumor recurred. The tumor responded to PBRT and regressed significantly. However, the eye developed sudden multiple recurrences, so we had to perform enucleation.

Conclusions

PBRT for retinoblastoma was effective in cases of showing no response to other treatment modalities. However, it should be carefully applied when there was recurrence of diffuse infiltrating subretinal seeding or extensively advanced retinoblastoma initially.

Status of particle therapy for lung cancer

The current standard treatment for lung cancer, the most common type of cancer worldwide, depends on disease stage. Surgery is the treatment of choice for early-stage tumors, but radiotherapy is a good option for those with early-stage tumors who cannot undergo surgery, and radiotherapy in conjunction with chemotherapy is the standard of care for locally advanced tumors. Although advances in photon (x-ray)-based radiotherapy involving three-dimensional conformal radiotherapy and intensity-modulated radiotherapy allow radiation doses to be escalated beyond the traditional limit of 60 Gy, this dose is not considered to be sufficient for tumor eradication. Moreover, the improvements in local control and survival conferred by concurrent chemotherapy come at the cost of considerable toxicity owing to inadvertent irradiation of surrounding normal tissues, and this toxicity often limits the radiation dose that can be delivered. Unfortunately for patients with locally advanced lung cancer, local control and survival remain poor. Attempts to improve clinical outcomes for patients with lung cancer have led to the use of charged particle therapy in an effort to exploit the physical properties of such particles to escalate the dose to the tumor while simultaneously limiting the dose to nearby structures, thereby enhancing the therapeutic ratio and potentially improving cancer cure rates. This review summarizes the rationale for and challenges associated with the use of charged particles for lung cancer therapy and reviews the clinical experience to date with using protons and carbon ions for early-stage and locally advanced stage non-small cell lung cancer.

Review of clinical experience with ion beam radiotherapy

The article describes both the early development of oncology as a core discipline at the University of Heidelberg Hospital and the first steps towards ion beam treatment, from the pilot project carried out in co-operation with the Gesellschaft für Schwerionenforschung Darmstadt to the initial start-up of clinical service at the Heidelberg Heavy Ion Centre (HIT). We present an overview, based on data published in the literature, of the available clinical evidence relating the use of ion beam therapy to treat major indications in active particle centres. A rationale for the use of particle therapy in each of these indications is given. In view of the limited availability of data, we discuss the necessity to conduct clinical trials. We also look forward towards the next activities to be undertaken at the HIT.

Current clinical evidence for proton therapy

Proton beam therapy provides the opportunity for more localized delivery of ionizing radiation with the potential for improved normal tissue avoidance to reduce treatment related morbidity and to allow for dose escalation to improve disease control and survival without increased toxicity. However, a systematic review of published peer-reviewed literature reported previously and updated here is devoid of any clinical data demonstrating benefit in terms of survival, tumor control, or toxicity in comparison with best conventional treatment for any of the tumors so far treated including skull base and ocular tumors, prostate cancer and childhood malignancies. The current lack of evidence for benefit of protons should provide a stimulus for continued research. Well designed in silico clinical trials using validated normal tissue complication probability-models are important to predict the magnitude of benefit for individual tumor sites but the future use of protons should be guided by clear evidence of benefit demonstrated in well-designed prospective studies, away from commercial influence, and this is likely to require international collaboration. Any complex and expensive technology, including proton therapy, should not be employed on the basis of belief alone and requires testing to avoid inappropriate use of potential detriment to future patients.

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.

The potential of proton beam radiation therapy in lung cancer (including mesothelioma)

A Swedish group of oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy. The estimations have been based on current statistics of tumour incidence, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours and normal tissues. It is estimated that about 350 patients with lung cancer and about 20 patients with mesothelioma annually may benefit from proton beam therapy.

Radiation techniques in neuro-oncology

Radiation therapy plays a critical role in the management of tumors of the brain. A variety of radiotherapy techniques have been used to treat these tumors. This review describes both classic and more recent and advanced techniques available to manage these tumors. Included is a discussion of standard two- and three-dimensional radiation, as well as intensity-modulated radiotherapy, image-guided radiation therapy, stereotactic radiosurgery, and heavy particles.

Identifying patients with peripheral-type early non-small cell lung cancer (T1N0M0) for whom irradiation of the primary focus alone could lead to successful treatment

We investigated the indication of radiotherapy in operable patients with peripheral-type early non-small cell lung cancer (T1N0M0 (TNM staging in 1997)). The subjects comprised 396 patients with non-small cell lung cancer in whom the clinical stage was evaluated as IA. We examined age, gender, Brinkmann's index, histopathological type, the grade of histopathological differentiation, tumour diameter and the level of carcinoembryonic antigen as factors involved in lymph node metastasis. Lymph node metastasis was detected in 79 patients (20%). Factors such as the grade of histopathological differentiation and tumour diameter were involved in lymph node metastasis. In well-differentiated lesions, the probability of metastasis was <10% even when the tumour diameter exceeded 2 cm. However, the probability rapidly increased with tumour size in moderately and poorly differentiated lesions. Among the patients with peripheral-type early non-small cell lung cancer (T1N0M0), the risk of lymph node metastasis was low in those with well-differentiated carcinoma and those with moderately differentiated lesions measuring </=1.5 cm in diameter. The proportion of our patients fitting these criteria was approximately 30%. For these patients, stereotactic body radiotherapy and particle therapy may be indicated.

Advanced-technology radiation therapy for bone sarcomas

BACKGROUND

Bone sarcomas are rare primary tumors. Radiation therapy (RT) can be useful in securing local control in cases where negative surgical margins cannot be obtained or where tumors are not resected. Recent technical advances in RT offer the opportunity to deliver radiation to these tumors with higher precision, thus allowing higher doses to the tumor target with lower doses to critical normal tissues, which can improve local tumor control and/or reduce treatment-related morbidity.

METHODS

The authors conducted a survey of recent technical developments that have been applied to the RT for bone sarcomas.

RESULTS

RT techniques that show promise include intensity-modulated photon radiation therapy, 3-D conformal proton RT, intensity-modulated proton RT, heavy charged-particle RT, intraoperative RT, and brachytherapy. All of these techniques permit the delivery of higher radiation doses to the target and less dose to normal tissue than had been possible with conventional 3-D conformal radiation techniques. Protons deliver substantially less dose to normal tissues than photons.

CONCLUSIONS

Data from clinical studies using these advanced radiation techniques suggest that they can improve the therapeutic ratio (the ratio of local control efficacy to the risk of complications). This is expected to improve the treatment outcome for these challenging tumors.

Proton therapy in lung cancer: clinical outcomes and technical issues. A systematic review

BACKGROUND AND PURPOSE

To determine whether, according to the currently available literature, proton therapy (PT) has a role in the treatment of non-small-cell lung cancer (NSCLC), to assess its safety and efficacy and to evaluate the main technical issues specifically related to this treatment technique.

MATERIALS AND METHODS

During March 2007, two independent researchers conducted a systematic review of the current data on the treatment of NSCLC with PT.

RESULTS

In total, 113 reports were retrieved, 17 of which were included in the analysis. There were no prospective trials (randomized or non-randomized). Nine uncontrolled single-arm studies were available from three PT centers, providing clinical outcomes for 214 patients in total. These reports were mainly related to stage I-II tumors, with results comparable to those obtained with surgery, without significant toxicity. In addition, two papers were found that compared photon and proton dose distributions, which showed a potential for dose escalation and/or a sparing of the organ at risk with PT. Finally, six studies analyzed dosimetric and technical issues related with PT, mainly underlining the difficulties in designing dose distributions that are representative of the dose actually delivered during treatment.

CONCLUSIONS

Although from a physical point of view PT is a good option for the treatment of NSCLC, limited data are available on its application in the clinical practice. Furthermore, the application of PT to lung cancer does present technical challenges. Because of the small number of institutions involved in the treatment of this disease, number of patients, and methodological weaknesses of the trials it is therefore not possible to draw definitive conclusions about the superiority of PT with respect to the photon techniques currently available for the treatment of NSCLC.

Inter- and intrafractional movement-induced dose reduction of prostate target volume in proton beam treatment

PURPOSE

To quantify proton radiotherapy dose reduction in the prostate target volume because of the three-dimensional movement of the prostate based on an analysis of dose-volume histograms (DVHs).

METHODS AND MATERIALS

Twelve prostate cancer patients underwent scanning in supine position, and a target contour was delineated for each using a proton treatment planning system. To simulate target movement, the contour was displaced from 3 to 15 mm in 3-mm intervals in the superior-to-inferior (SI), inferior-to-superior (IS), anterior-to-posterior (AP), posterior-to-anterior (PA), and left-to-right (LR) directions.

RESULTS

For both intra- and interfractional movements, the average coverage index and conformity index of the target were reduced in all directions. For interfractional movements, the magnitude of dose reduction was greater in the LR direction than in the AP, PA, SI. and IS directions. Although the reduction of target dose was proportional to the magnitude of intrafractional movement in all directions, a proportionality between dose reduction and the magnitude of interfractional target movement was clear only in the LR direction. Like the coverage index and conformity index, the equivalent uniform dose and homogeneity index showed similar reductions for both types of target movements.

CONCLUSIONS

Small target movements can significantly reduce target proton radiotherapy dose during treatment of prostate cancer patients. Attention should be given to interfractional target movement along the longitudinal direction, as image-guided radiotherapy may be ineffective if margins are not sufficient.

Particle therapy in lung cancer: where do we stand?

BACKGROUND

From a theoretical point of view, charged particles should lead to superior results compared to photons. In this review, we searched for clinical evidence that protons or C-ions are really beneficial to patients with lung cancer.

METHODS

A systematic literature review based on an earlier published comprehensive review was performed and updated until November 1st 2007.

RESULTS

Ten fully published series, all dealing with non-small cell lung cancer (NSCLC), mainly stage I, were identified. No phase III trials were found. On proton therapy, 2-5 year local tumor control rates varied between 87% and 57%. The 2 year/5 year overall survival and 2 year/5 year cause specific survival varied between 31-74%/23% and 58-86%/46%, respectively. Late side effects were observed in about 10% of the patients. For C-ion therapy, the local tumor control rate was 77%, while 95% when using a hypofractionated radiation schedule. The 5 year overall survival and cause specific survival rates were 42% and 60%, respectively. Slightly better results were reported when using hypofractionation, 50% and 76%, respectively. The reported late side effects for C-ions were 4%.

CONCLUSION

The results with charged particles, at least for stage I disease, seem to be promising. A gain can be expected in reduction of late side effects, especially after treatment with C-ions. Available data demonstrate that particle therapy in general is a safe and feasible treatment modality. Although current results are promising, more evidence is required before particle therapy can become internationally the standard treatment for (subsets of) lung cancer patients.

Carbon ion radiotherapy for stage I non-small cell lung cancer using a regimen of four fractions during 1 week

BACKGROUND

A phase I/II study was first conducted for the treatment of stage I non-small cell lung cancer (NSCLC) from 1994 to 1999 to determine the optimal dose. On the basis on the results, a phase II study using a regimen of four fractions during 1 week was performed. The purpose of the present study was to determine the local control and 5-year survival rates.

METHODS

From December 2000 to November 2003, 79 patients with 80 primary lesions were treated. Using a fixed dose of 52.8 GyE for stage IA NSCLC and 60.0 GyE for stage IB NSCLC in four fractions during 1 week, the primary tumors were irradiated with carbon beams alone. The average age of the patients was 74.8 years. Sixty-two (78.5%) of these patients were medically inoperable. Local control and survival were determined using the Kaplan-Meier method. The data were statistically processed using the log-rank test.

RESULTS

All patients were observed for a minimum of 3 years or until death, with a median follow-up time of 38.6 months, ranging from 2.5 to 72.2 months. The local control rate for all patients was 90% (T1: 98%, T2: 80%). The patients' 5-year lung cancer-specific survival rate was 68% (IA: 87%, IB: 42%). The overall survival was 45% (IA: 62%, IB: 25%). Half of the deaths were attributable to intercurrent diseases. No toxic reactions in the lung greater than grade 3 were detected.

CONCLUSION

Carbon ion beam radiotherapy with a regimen of four fractions during 1 week has been proven as a valid alternative to surgery for stage I NSCLC and to offer particular benefits, especially for elderly and inoperable patients.