Considerations in fractionated proton radiation therapy: clinical potential and results

Proton beam therapy for bone sarcomas of the skull base and spine: A retrospective nationwide multicenter study in Japan

We conducted a retrospective, nationwide multicenter study to evaluate the clinical outcomes of proton beam therapy for bone sarcomas of the skull base and spine in Japan. Eligibility criteria included: (i) histologically proven bone sarcomas of the skull base or spine; (ii) no metastases; (iii) ≥20 years of age; and (iv) no prior treatment with radiotherapy. Of the 103 patients treated between January 2004 and January 2012, we retrospectively analyzed data from 96 patients who were followed-up for >6 months or had died within 6 months. Seventy-two patients (75.0%) had chordoma, 20 patients (20.8%) had chondrosarcoma, and four patients (7.2%) had osteosarcoma. The most frequent tumor locations included the skull base in 68 patients (70.8%) and the sacral spine in 13 patients (13.5%). Patients received a median total dose of 70.0 Gy (relative biological effectiveness). The median follow-up was 52.6 (range, 6.3-131.9) months. The 5-year overall survival, progression-free survival, and local control rates were 75.3%, 49.6%, and 71.1%, respectively. Performance status was a significant factor for overall survival and progression-free survival, whilst sex was a significant factor for local control. Acute Grade 3 and late toxicities of ≥Grade 3 were observed in nine patients (9.4%) each (late Grade 4 toxicities [n = 3 patients; 3.1%]). No treatment-related deaths occurred. Proton beam therapy is safe and effective for the treatment of bone sarcomas of the skull base and spine in Japan. However, larger prospective studies with a longer follow-up are warranted.

Fractionated proton radiotherapy for benign cavernous sinus meningiomas

PURPOSE

To evaluate the efficacy of fractionated proton radiotherapy for a population of patients with benign cavernous sinus meningiomas.

METHODS AND MATERIALS

Between 1991 and 2002, 72 patients were treated at Loma Linda University Medical Center with proton therapy for cavernous sinus meningiomas. Fifty-one patients had biopsy or subtotal resection; 47 had World Health Organization grade 1 pathology. Twenty-one patients had no histologic verification. Twenty-two patients received primary proton therapy; 30 had 1 previous surgery; 20 had more than 1 surgery. The mean gross tumor volume was 27.6 cm(3); mean clinical target volume was 52.9 cm(3). Median total doses for patients with and without histologic verification were 59 and 57 Gy, respectively. Mean and median follow-up periods were 74 months.

RESULTS

The overall 5-year actuarial control rate was 96%; the control rate was 99% in patients with grade 1 or absent histologic findings and 50% for those with atypical histology. All 21 patients who did not have histologic verification and 46 of 47 patients with histologic confirmation of grade 1 tumor demonstrated disease control at 5 years. Control rates for patients without previous surgery, 1 surgery, and 2 or more surgeries were 95%, 96%, and 95%, respectively.

CONCLUSIONS

Fractionated proton radiotherapy for grade 1 cavernous sinus meningiomas achieves excellent control rates with minimal toxicities, regardless of surgical intervention or use of histologic diagnosis. Disease control for large lesions can be achieved by primary fractionated proton therapy.

Number of patients potentially eligible for proton therapy

A group of Swedish radiation oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy in a facility where one of the principal aims is to facilitate randomized and other studies in which the advantage of protons can be shown and the magnitude of the differences compared with optimally administered conventional radiation treatment, also including intensity-modulated radiation therapy (IMRT) and brachytherapy, can be shown. The estimations have been based on current statistics of tumour incidence in Sweden, 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 together with information on normal tissue complication rates. In Sweden, it is assessed that between 2200 and 2500 patients annually are eligible for proton beam therapy, and that for these patients the potential therapeutic benefit is so great as to justify the additional expense of proton therapy. This constitutes between 14-15% of all irradiated patients annually.

The potentials of proton beam radiation therapy in malignant lymphoma, thymoma and sarcoma

A group of Swedish 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. Besides sarcomas of the base of skull, which are classical sites for proton beam therapy, it is estimated that about 40 patients yearly in Sweden with sarcomas at other sites are candidates for proton beam therapy. About 20 patients each with malignant lymphomas, chiefly in the mediastinum, and thymomas are also candidates to decrease doses to surrounding heart and lungs.

Le traitement par neutrons : hadronthérapie partie II : bases physiques et expérience clinique

Neutrons have radiobiological characteristics, which differ from those of conventional radiotherapy beams (photons) and which offer a theoretical advantage over photons to fight radioresistance by the differential relative biological effect of them between normal and tumour tissues. Neutron therapy beneficed of great interest between 1975 and 1985. Many of phase III trials were conducted and indications have been definitively deducted of them. After briefly describing the properties of neutron beams, this review discusses the indication of neutron therapy on the basis of the clinical results. Salivary, prostate tumours and sarcomas are the main indications of neutron therapy. In concern to the prostate cancers, other alternative treatments reduce the neutron therapy field. For sarcomas, the lack of randomised trials limits the impact of the interest of neutrons. For other tumours, the ratio benefice/risk of neutron therapy is inferior to these obtained with photons and they could not be considered like classical indications.

Recent Advances in Radiotherapy for Head and Neck Cancers

Advancements in surgery have made it possible to resect cancers that had previously been regarded as incurable. Similarly, new developments in radiation oncology have helped improve the outlook for patients with locally advanced or recurrent head and neck cancers. Among these advancements are refinements in altered fractionation, three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic radiosurgery and fractionated stereotactic radiotherapy, neutron-beam radiotherapy, charged-particle radiotherapy, and intraoperative radiotherapy. These recent developments have allowed radiation oncologists to escalate the dose of radiation delivered to tumors while minimizing the dose delivered to surrounding normal tissue. Additionally, more continues to be learned about the optimum delivery of chemotherapy. This article provides an update on the status of these new developments in the treatment of head and neck cancers.

The role of proton therapy in the treatment of large irradiation volumes: a comparative planning study of pancreatic and biliary tumors

PURPOSE

The purpose of this study was to examine the potential benefit of proton therapy for abdominal tumors. Extensive comparative planning was conducted investigating the most up-to-date photon and proton irradiation technologies.

METHODS AND MATERIALS

A number of rival plans were generated for four patients: two inoperable pancreatic tumors, one inoperable and one postoperative biliary duct tumor. The dose prescription goal for these large targets was 50 Gy, followed by a boost dose up to 20 Gy to a smaller planning target volume (PTV). Photon plans were developed using "forward" planning of coplanar and noncoplanar conformal fields and "inverse" planning of intensity-modulated (IM) fields. Proton planning was simulated as administered using the so called spot-scanning technique. Plans were evaluated on the basis of normal tissues' dose-volume constraints (Emami B, Lyman J, Brown A, et al. Tolerance of normal tissue to therapeutic irradiation. Int J Radiat Oncol Biol Phys 1990;21:109-122) and coverage of treatment volumes with prescribed doses.

RESULTS

For all cases, none of the forward calculated photon plans was able to deliver 50 Gy to large PTVs at the same time respecting the dose-volume constraints on all critical organs. Nine evenly spaced IM fields achieved or nearly achieved all maximum dose constraints to critical structures for two out of three inoperable patients. IM plans also obtained good results for the postoperative patient, even though the dose to the liver was very close to the maximum allowed. In all cases, photon irradiation of large PTV1s to 50 Gy followed by a 20 Gy boost entailed a risk very close to or higher than 5% for serious complications to the kidneys, liver, or bowel. Simple arrangements of 2, 3, and 4 proton fields obtained better dose conformation to the target, allowing the delivery of planned doses including the boost to all patients, without excessive risk of morbidity. Dose homogeneity inside the targets was also superior with protons.

CONCLUSION

For the irradiation of large PTVs located in the abdominal cavity, where multiple, parallel structured organs surround the target volumes, proton therapy, delivered with a sophisticated isocentric technique, has the potential to achieve superior dose distributions compared with state-of-the-art photon irradiation techniques. IM photon plans obtain better results in the postoperative case, because the reduced volume lessens the effect of the unavoidable increase of integral dose to surrounding tissues.

Prognostic factors in chordoma of the sacrum and mobile spine: a study of 39 patients

BACKGROUND

The prognosis of patients with chordoma of the sacrum and mobile spine has been reported to be dismal and attributable in the majority of cases to intralesional surgery. The purpose of this study was to evaluate the clinical outcome of these patients using modern surgical principles aimed at complete resection and to identify prognostic factors.

METHODS

The clinical and morphologic features, type of surgery, and follow-up of 39 consecutive patients with chordoma were reviewed and analyzed statistically.

RESULTS

Thirty sacral and 9 mobile spine chordomas (size range, 3-20 cm; mean, 8 cm) occurring in 22 women and 17 men (median age, 55 years) were analyzed. The preoperative morphologic diagnosis was based on fine-needle aspiration (FNA) biopsy, core needle biopsy, or incisional biopsy. The final surgical margins were wide in 23 patients and marginal or intralesional in 16. The mean follow-up was 8.1 years (range, 0.1-23 years). Seventeen patients (44%) developed local recurrences and 11 patients (28%) developed metastases. The estimated 5-, 10-, 15-, and 20-year survival rates were 84%, 64%, 52%, and 52%, respectively. Local recurrence was associated significantly with an increased risk of metastasis and tumor-related death (P < 0.001).

CONCLUSIONS

New surgical techniques have improved local control and survival of patients with sacral or spinal chordoma significantly and have decreased progressive neurologic deterioration. Larger tumor size, performance of an invasive morphologic diagnostic procedure outside of the tumor center, inadequate surgical margins, microscopic tumor necrosis, Ki-67 > 5%, and local recurrence were found to be adverse prognostic factors. FNA is the preferred method for establishing the preoperative morphologic diagnosis of chordoma.

Analysis of the relationship between tumor dose inhomogeneity and local control in patients with skull base chordoma

PURPOSE

When irradiating a tumor that abuts or displaces any normal structures, the dose constraints to those structures (if lower than the prescribed dose) may cause dose inhomogeneity in the tumor volume at the tumor-critical structure interface. The low-dose region in the tumor volume may be one of the reasons for local failure. The aim of this study is to quantitate the effect of tumor dose inhomogeneity on local control and recurrence-free survival in patients with skull base chordoma.

METHODS AND MATERIALS

132 patients with skull base chordoma were treated with combined photon and proton irradiation between 1978 and 1993. This study reviews 115 patients whose dose-volume data and follow-up data are available. The prescribed doses ranged from 66.6 Cobalt-Gray-Equivalent (CGE) to 79.2 CGE (median of 68.9 CGE). The dose to the optic structures (optic nerves and chiasm), the brain stem surface, and the brain stem center was limited to 60, 64, and 53 CGE, respectively. We used the dose-volume histogram data derived with the three-dimensional treatment planning system to evaluate several dose-volume parameters including the Equivalent Uniform Dose (EUD). We also analyzed several other patient and treatment factors in relation to local control and recurrence-free survival.

RESULTS

Local failure developed in 42 of 115 patients, with the actuarial local control rates at 5 and 10 years being 59% and 44%. Gender was a significant predictor for local control with the prognosis in males being significantly better than that in females (P = 0.004, hazard ratio = 2.3). In a Cox univariate analysis, with stratification by gender, the significant predictors for local control (at the probability level of 0.05) were EUD, the target volume, the minimum dose, and the D5cc dose. The prescribed dose, histology, age, the maximum dose, the mean dose, the median dose, the D90% dose, and the overall treatment time were not significant factors. In a Cox multivariate analysis, the models including gender and EUD, or gender and the target volume, or gender and the minimum target dose were significant. The more biologically meaningful of these models is that of gender and EUD.

CONCLUSION

This study suggests that the probability of recurrence of skull base chordomas depends on gender, target volume, and the level of target dose inhomogeneity. EUD was shown to be a useful parameter to evaluate dose distribution for the target volume.

Intensity modulation methods for proton radiotherapy

The characteristic Bragg peak of protons or heavy ions provides a good localization of dose in three dimensions. Through their ability to deliver laterally and distally shaped homogenous fields, protons have been shown to be a precise and practical method for delivering highly conformal radiotherapy. However, in an analogous manner to intensity modulation for photons, protons can be used to construct dose distributions through the application of many individually inhomogeneous fields, but with the localization of dose in the Bragg peak providing the possibility of modulating intensity within each field in two or three dimensions. We describe four different methods of intensity modulation for protons and describe how these have been implemented in an existing proton planning system. As a preliminary evaluation of the efficacy of these methods, each has been applied to an example case using a variety of field combinations. Dose-volume histogram analysis of the resulting dose distributions shows that when large numbers of fields are used, all techniques exhibit both good target homogeneity and sparing of neighbouring critical structures, with little difference between the four techniques being discerned. As the number of fields is decreased, however, only a full 3D modulation of individual Bragg peaks can preserve both target coverage and sparing of normal tissues. We conclude that the 3D method provides the greatest flexibility for constructing conformal doses in challenging situations, but that when large numbers of beam ports are available, little advantage may be gained from the additional modulation of intensity in depth.

Particle beam therapy (hadrontherapy): basis for interest and clinical experience

The particle or hadron beams deployed in radiotherapy (protons, neutrons and helium, carbon, oxygen and neon ions) have physical and radiobiological characteristics which differ from those of conventional radiotherapy beams (photons) and which offer a number of theoretical advantages over conventional radiotherapy. After briefly describing the properties of hadron beams in comparison to photons, this review discusses the indications for hadrontherapy and analyses accumulated experience on the use of this modality to treat mainly neoplastic lesions, as published by the relatively few hadrontherapy centres operating around the world. The analysis indicates that for selected patients and tumours (particularly uveal melanomas and base of skull/spinal chordomas and chondrosarcomas), hadrontherapy produces greater disease-free survival. The advantages of hadrontherapy are most promisingly realised when used in conjunction with modern patient positioning, radiation delivery and focusing techniques (e.g. on-line imaging, three-dimensional conformal radiotherapy) developed to improve the efficacy of photon therapy. Although the construction and running costs of hadrontherapy units are considerably greater than those of conventional facilities, a comprehensive analysis that considers all the costs, particularly those resulting from the failure of less effective conventional radiotherapy, might indicate that hadrontherapy could be cost effective. In conclusion, the growing interest in this form of treatment seems to be fully justified by the results obtained to date, although more efficacy and dosing studies are required.

New particles in radiotherapy: an introduction

Since the discovery of x-rays and radioactivity, the radiotherapeutic management of malignancy has seen numerous spectacular improvements. Beside the widely used photons and electrons, one area of particular interest is the development and refinement of what has become known as "new particles". In this paper we give a brief outline of the properties of such particles and catalogue the impact these have made on the clinical outcome.

Optimization of radiotherapy for patients with cranial chordoma. A review of dose-response ratios for photon techniques

BACKGROUND

Cranial chordomas arise adjacent to critical neural tissues within the notochordal remnants in the clivus, frequently compromising adequate surgical removal of the primary tumor and making difficult the delivery of an adequate dose of radiotherapy. The optimal dose and fractionation have not been established.

METHODS

The results of radiation combined with surgery, radiation alone, and surgery alone were compared based on the cases of 159 patients reported in the literature. An analysis of the optimal biologically equivalent doses (BED) was performed using the linear-quadratic formula on 47 patients.

RESULTS

Past techniques using conventional photon irradiation have shown no dose-response relationship. Survival is improved for patients undergoing surgery followed by radiotherapy.

CONCLUSION

Combined surgery and postoperative radiation is preferable to radiotherapy or surgery alone for management of cranial chordoma. Newer radiotherapeutic approaches will allow increased dose delivery to the target volume without an anticipated increase in radiation morbidity. It is believed that this will increase tumor control. Recent results of studies using charged particle therapy in cranial chordoma suggest that this may be an alternative way to optimize radiotherapy.

A new, effective, and safe therapeutic option using proton irradiation for hepatocellular carcinoma

BACKGROUND/AIMS

Conventional radiation is almost useless for hepatocellular carcinoma (HCC) because of the severe adverse effects of the irradiation to the accompanying liver cirrhosis. In contrast, the proton beam has Bragg peak, which limits distribution of the beam. The aim of this study was to prove the usefulness of proton irradiation for HCC.

METHODS

The proton irradiation was performed in 32 nodular lesions in 24 patients with HCC who had unresectable tumors or serious complications; the proton irradiation was performed either as monotherapy (15 lesions) or as combination therapy to insufficient Lipiodol-targeted chemotherapy (Kodama Co. Ltd., Tokyo, Japan) (17 lesions). The energy was 250 MeV, and 50-87 Gy (76.5 +/- 9.5, mean +/- SD) in total was irradiated for a time period of 17-69 days.

RESULTS

After 1 year, size reduction was seen in 12 out of 13 lesions (92%) in the monotherapy group and 9 out of 9 lesions (100%) in the combination therapy group; after 2 years, size reduction was seen 4 out of 5 lesions (80%) in the monotherapy group and 5 out of 5 lesions (100%) in the combination therapy group. Local tumor control has being assured for 2 years of the observation, which is continuing for another 2 years. None of the patients have experienced any serious adverse effects.

CONCLUSIONS

These results show that proton irradiation is a new, safe, and effective therapeutic option in cases of HCC, even in patients with unresectable tumors or those with serious complications.

Conformal radiotherapy at the Royal Marsden Hospital (UK)

Conformal radiotherapy seeks to allow increased intensity of radiation by reducing the volume of normal tissues within the treatment volume. Techniques have developed secondary to improvements in three-dimensional imaging and accessible treatment technology is based on computer-controlled multileaf collimators to create an irregular radiation beam shape. Preliminary clinical work in the Royal Marsden Hospital seeks to quantify the toxicity reduction achievable by conformal techniques in the context of a prospective randomized pelvic radiotherapy trial which has now recruited 240 patients. The data accumulated during this trial will allow comparison of conformal and conventional radiotherapy and also analysis of the impact of dose and volume of a particular organ on both acute and late toxicity. Assessments have revealed that conformal techniques reduced significantly the treatment volume of normal tissues, e.g. by a mean of 54% for rectum and 42% for bladder. However, a relationship between volume and acute toxicity has not been established. Late toxicity is currently being analysed. Dose escalation trials in thoracic and in pelvic tumours are planned.

Prospects for proton-beam radiotherapy

Proton beams are already being employed for radiation therapy in 15 centres worldwide and over a dozen more are planned. Good clinical results have been reported in uveal melanomas and in sarcomas of the skull base. Calculated dose distributions for the treatment of brain, lung, head and neck and pelvic tumours predict an improvement relative to multiple-field or conformal photon radiotherapy. Protons may well provide high-precision radiotherapy that will lead to improved treatment of certain tumours in specific anatomical locations.

Current developments in proton therapy: a review

The use of high-energy protons in radiotherapy was first proposed in 1946. In the last decade there has been a significant growth in the number of centres using protons in the treatment of malignant and non-malignant disease. To date (January 1993) a total of more than 11,500 patients have been treated world-wide. Encouraging clinical results have been reported in the literature. The purpose of this article is to outline the advantages of proton beams and to review current developments in physics and engineering applied to the field of proton therapy with particular emphasis on proton accelerator technology and the development of proton therapy facilities. The production of clinically useful beams is discussed and the relative merits of different treatment systems compared. Reference is also made to the factors affecting the absorbed dose in a patient and to proton radiobiology together with the results of studies of comparisons of treatment planning with protons with that using conventional photon therapy. The dosimetry of proton beams is also reviewed.

Skull base chordomas: a review of 38 patients, 1958-88

The presentation and results of treatment are reviewed for 38 patients with skull base chordoma treated at the National Hospital for Neurology and Neurosurgery between 1958 and 1988. With few exceptions, previous studies have combined results for clival and sacral chordomas, or for chordomas and other similar tumours such as chondrosarcoma, and thus it is difficult to be specific about effects of therapy. This study included histological review using immunohistochemistry to confirm diagnosis. Analysis of the survival data for our patients suggests that there are two subgroups with distinct survival patterns: one group with high mortality within the first 5 years, and a second group with an indolent disease process and near normal life expectancy. The age of the patients at presentation ranged from 7 to 78 years, with a mean of 44.3 years. Male: female distribution was 6:5. The commonest presentation was with cranial nerve palsy (94%) or with headache (60%). The most frequently involved cranial nerve was the VIth (60%), followed by the IXth and Xth (40% each). Comparing our results with those of 50 years ago, there was little improvement in the outlook for these patients, despite improvements in surgical approaches and the use of radiotherapy. The promising results in skull base tumours using proton therapy must be treated with caution until definite criteria for diagnosis and outcome have been established. There is a case for a multicentre prospective study of this disease.

Clinical results of fractionated proton therapy

PURPOSE

Preliminary results of a multi-site Phase I-II clinical trial investigating the efficacy of high-energy proton beams in a wide variety of human malignancies are reported.

METHODS AND MATERIALS

Since 1983 proton radiotherapy using 250 MeV proton beams produced by a booster synchrotron of the National Laboratory for High Energy Physics has been carried out at Proton Medical Research Center, University of Tsukuba. As of September 1990, a total of 147 patients received a partial or full treatment with proton beams with curative intent; 92 patients (63%) were treated with proton beams alone and 55 patients (37%) with combined photon and proton beams. There were 91 males and the mean age was 61.8 years old. The follow-up observation period ranged from 10 to 97 months. With regard to a total tumor dose, nearly 80% of patients received 70 Gy or more and 53% received 80 Gy or more. While dose-fractionations used depended upon tumor sites, the large majority of patients received substantially high radiation doses in terms of larger total doses (> 70 Gy) and larger fraction sizes (> 2.5 Gy) than those traditionally used. This fractionation regimen has been used because of limited availability of the accelerator or a shortage of machine time (27-30 weeks/year, 3-3.5 hr/day), and also by the expectation that the superior dose distribution possible with protons will permit administration of high radiation doses without increasing morbidities. In connection with this, we have determined the target volume by setting margins around the tumor boundary as practically small as possible, ranging from 5 to 10 mm.

RESULTS AND CONCLUSIONS

The current trial has been based on a site and dose searching program, hence a wide variety of tumor sites including the aerodigestive organs has been treated. So far, our judgment is that proton therapy has proven of potential advantage in treatment of the lung, esophageal, liver, uterine cervix, prostate, and head and neck malignancies; and of possible value in treatment of high-grade gliomas, and gastric, urinary bladder, and pediatric tumors.

Chordoma-natural history, treatment and prognosis. The Florence Radiotherapy Department experience (1956-1990) and a critical review of the literature

Fifteen cases of chordoma, seen between 1956 and 1990 at the Florence Radiotherapy Department are reported. Twelve of them were treated with radiotherapy and surgery, while one was left untreated. We analyzed the course of the disease in the treated cases, with particular emphasis on the problem of symptom control. The natural history of the disease seemed to be only marginally affected by the treatment and new therapeutic options are strongly needed. While actuarial survival rates at 5 and 10 years were 58% and 35% respectively (owing to the slow growth rate of this neoplasm), 10 years' symptomatic progression-free, symptom-free, and disease-free survival rates were only 25%, 17% and 8% respectively.

A dose response analysis of injury to cranial nerves and/or nuclei following proton beam radiation therapy

The low tolerance of the central nervous system (CNS) limits the radiation dose which can be delivered in the treatment of many patients with brain and head and neck tumors. Although there are many reports concerning the tolerance of the CNS, few have examined individual substructures of the brain and fewer still have had detailed dose information. This study has both. A three dimensional planning system was used to develop the combined proton beam/photon beam treatments for 27 patients with skull-base tumors. The cranial nerves and their related nuclei were delineated on the planning CT scans and the radiation dose to each was determined from three dimensional dose distributions. In the 594 CNS structures (22 structures/patient in 27 patients), there have been 17 structures (in 5 patients) with clinically manifest radiation injury, after a mean follow-up time of 74 months (range 40-110 months). From statistical analyses, dose is found to be a significant predictor of injury. Using logistic regression analysis, we find that, for each cranial nerve, at 60 Cobalt Gray Equivalent (CGE) the complication rate is 1% (0.5-3% with 95% confidence) and that the 5% complication rate occurs at 70 CGE (64-81 CGE with 95% confidence). The slope of the dose response curve (at 50%) is 3.2 (2.2-5.4 with 95% confidence). No significant relationship between dose and latency period for nerve injury was found.