Dose escalation study of carbon ion radiotherapy for locally advanced head-and-neck cancer

Application of carbon-ion beams or gamma-rays on primary tumors does not change the expression profiles of metastatic tumors in an in vivo murine model

PURPOSE

To clarify how carbon-ion radiotherapy (C-ion) on primary tumors affects the characteristics of subsequently arising metastatic tumor cells.

METHODS AND MATERIALS

Mouse squamous cell carcinomas, NR-S1, in synergic C3H/HeMsNrs mice were irradiated with a single dose of 5-50 Gy of C-ion (290 MeV per nucleon, 6-cm spread-out Bragg peak) or gamma-rays ((137)Cs source) as a reference beam. The volume of the primary tumors and the number of metastatic nodules in lung were studied, and histologic analysis and microarray analysis of laser-microdissected tumor cells were also performed.

RESULTS

Including 5 Gy of C-ion and 8 Gy of gamma-rays, which did not inhibit the primary tumor growth, all doses used in this study inhibited lung metastasis significantly. Pathologic findings showed no difference among the metastatic tumor nodules in the nonirradiated, C-ion-irradiated, and gamma-ray-irradiated groups. Clustering analysis of expression profiles among metastatic tumors and primary tumors revealed a single cluster consisting of metastatic tumors different from their original primary tumors, indicating that the expression profiles of the metastatic tumor cells were not affected by the local application of C-ion or gamma-ray radiotherapy.

CONCLUSION

We found no difference in the incidence and histology, and only small differences in expression profile, of distant metastasis between local C-ion and gamma-ray radiotherapy. The application of local radiotherapy per se or the type of radiotherapy applied did not influence the transcriptional changes caused by metastasis in tumor cells.

The proangiogenic factor ephrin-A1 is up-regulated in radioresistant murine tumor by irradiation

While the pre-treatment status of cancer is generally correlated with outcome, little is known about microenvironmental change caused by anti-cancer treatment and how it may affect outcome. For example, treatment may lead to induction of gene expression that promotes resistance to therapy. In the present study, we attempted to find a gene that was both induced by irradiation and associated with radioresistance in tumors. Using single-color oligo-microarrays, we analyzed the gene expression profiles of two murine squamous cell carcinomas, NR-S1, which is highly radioresistant, and SCCVII, which is radiosensitive, after irradiation with 137-Cs gamma rays or carbon ions. Candidate genes were those differentially regulated between NR-S1 and SCCVII after any kind of irradiation. Four genes, Efna1 (Ephrin-A1), Sprr1a (small proline-rich protein 1A), Srgap3 (SLIT-ROBO Rho GTPase activating protein 3) and Xrra1 [RIKEN 2 days neonate thymus thymic cells (NOD) cDNA clone E430023D08 3'], were selected as candidate genes associated with radiotherapy-induced radioresistance. We focused on Efna1, which encodes a ligand for the Eph receptor tyrosine kinase known to be involved in the vascular endothelial growth factor (VEGF) pathway. We used immunohistochemical methods to detect expression of Ephrin-A1, VEGF, and the microvascular marker CD31 in radioresistant NR-S1 tumor cells. Ephrin-A1 was detected in the cytoplasm of NR-S1 tumor cells after irradiation, but not in SCCVII tumor cells. Irradiation of NR-S1 tumor cells also led to significant increases in microvascular density, and up-regulation of VEGF expression. Our results suggest that radiotherapy-induced changes in gene expression related with angiogenesis might also modulate microenvironment and influence responsiveness of tumors.

Comparative study of dose distribution between carbon ion radiotherapy and photon radiotherapy for head and neck tumor

PURPOSE

A comparative treatment planning study has been performed between carbon ion radiotherapy (CIRT) and photon radiotherapy [three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT)] to assess the potential improvements and limitations that could result for locally advanced, nonresectable head and neck tumors.

MATERIALS AND METHODS

Seven patients, originally treated with CIRT, were randomly selected for the comparative study. The evaluations analyzed using dose-volume histogram parameters, conformity index, inhomogeneity coefficient, and dose to the organs at risk (OARs).

RESULTS

The mean conformity index was 1.46, 1.43, and 1.22 for 3D-CRT, IMRT, and CIRT, respectively. The mean inhomogeneity coefficient was 0.05, 0.07, and 0.02 for 3D-CRT, IMRT, and CIRT respectively. Photon plans resulted in greater volumes of normal tissues at 10% to 95% isodose levels compared with the corresponding carbon ion plans where the volumes increased by a factor of 1.2 to 2.7 for 3D-CRT and 1.2 to 2.0 for IMRT.

CONCLUSION

CIRT has the potential to improve the target dose conformity, inhomogeneity coefficient, and OAR sparing when compared with 3D-CRT and IMRT. Compared with 3D-CRT, normal tissue exposure was reduced mainly in the mid-to low-isodose levels using IMRT. Additional improvement was obtained using CIRT.

Intensity-modulated radiotherapy for sinonasal tumors: Ghent University Hospital update

PURPOSE

To report the long-term outcome of intensity-modulated radiotherapy (IMRT) for sinonasal tumors.

METHODS AND MATERIALS

Between July 1998 and November 2006, 84 patients with sinonasal tumors were treated with IMRT to a median dose of 70 Gy in 35 fractions. Of the 84 patients, 73 had a primary tumor and 11 had local recurrence. The tumor histologic type was adenocarcinoma in 54, squamous cell carcinoma in 17, esthesioneuroblastoma in 9, and adenoid cystic carcinoma in 4. The tumors were located in the ethmoid sinus in 47, maxillary sinus in 19, nasal cavity in 16, and multiple sites in 2. Postoperative IMRT was performed in 75 patients and 9 patients received primary IMRT.

RESULTS

The median follow-up of living patients was 40 months (range, 8-106). The 5-year local control, overall survival, disease-specific survival, disease-free survival, and freedom from distant metastasis rate was 70.7%, 58.5%, 67%, 59.3%, and 82.2%, respectively. No difference was found in local control and survival between patients with primary or recurrent tumors. On multivariate analysis, invasion of the cribriform plate was significantly associated with lower local control (p = 0.0001) and overall survival (p = 0.0001). Local and distant recurrence was detected in 19 and 10 patients, respectively. Radiation-induced blindness was not observed. One patient developed Grade 3 radiation-induced retinopathy and neovascular glaucoma. Nonocular late radiation-induced toxicity comprised complete lacrimal duct stenosis in 1 patient and brain necrosis in 3 patients. Osteoradionecrosis of the maxilla and brain necrosis were detected in 1 of the 5 reirradiated patients.

CONCLUSION

IMRT for sinonasal tumors provides low rates of radiation-induced toxicity without blindness with high local control and survival. IMRT could be considered as the treatment of choice.

Long-term outcome following radical temporal bone resection for lateral skull base malignancies: a neurosurgical perspective

OBJECT

Primary temporal bone malignancy is a rare form of tumor for which the therapeutic strategy remains controversial. In this study, the authors reviewed their experience with radical temporal bone resection (TBR) of such lesions and analyzed the long-term results to provide treatment recommendations.

METHODS

Between 1994 and 2006, 17 patients (10 men and 7 women) underwent total or subtotal TBR for primary temporal bone malignancies. Tumors were graded according to the University of Pittsburgh system. The effects of surgical margins and tumor extensions on patient survival were analyzed using the Kaplan-Meier method.

RESULTS

All tumors, except 1, were graded T4 (most advanced). Subtotal TBR was performed in 14 patients, and total TBR was performed in 3. The surgical margin was tumor negative in 10 patients and tumor positive in 7. For large tumors extending into the infratemporal fossa or encroaching on the jugular foramen, orbitozygomatic (3 patients) and posterior transjugular (4 patients) approaches were combined with the standard approach, and en bloc resection with a negative margin was achieved in all cases but 1. The follow-up time ranged from 0.3-11.6 years (mean 3.3 years). The 5-year recurrence-free and disease-specific survival rates were 67.5 and 60.1%, respectively. When a negative surgical margin was achieved, the survival rates improved to 100 and 89%, respectively.

CONCLUSIONS

The neurosurgical skull base technique could improve the probability of en bloc resection with a tumor-free margin for extensive temporal bone malignancies, which would cure a subset of patients. The active participation of neurosurgeons would improve patient care in this field.

Radiobiologic parameters and local effect model predictions for head-and-neck squamous cell carcinomas exposed to high linear energy transfer ions

PURPOSE

To establish the radiobiologic parameters of head-and-neck squamous cell carcinomas (HNSCC) in response to ion irradiation with various linear energy transfer (LET) values and to evaluate the relevance of the local effect model (LEM) in HNSCC.

METHODS AND MATERIALS

Cell survival curves were established in radiosensitive SCC61 and radioresistant SQ20B cell lines irradiated with [33.6 and 184 keV/n] carbon, [302 keV/n] argon, and X-rays. The results of ion experiments were confronted to LEM predictions.

RESULTS

The relative biologic efficiency ranged from 1.5 to 4.2 for SCC61 and 2.1 to 2.8 for SQ20B cells. Fixing an arbitrary D(0) parameter, which characterized survival to X-ray at high doses (>10 Gy), gave unsatisfying LEM predictions for both cell lines. For D(0) = 10 Gy, the error on survival fraction at 2 Gy amounted to a factor of 10 for [184 keV/n] carbon in SCC61 cells. We showed that the slope (s(max)) of the survival curve at high doses was much more reliable than D(0). Fitting s(max) to 2.5 Gy(-1) gave better predictions for both cell lines. Nevertheless, LEM could not predict the responses to fast and slow ions with the same accuracy.

CONCLUSIONS

The LEM could predict the main trends of these experimental data with correct orders of magnitude while s(max) was optimized. Thus the efficiency of carbon ions cannot be simply extracted from the clinical response of a patient to X-rays. LEM should help to optimize planning for hadrontherapy if a set of experimental data is available for high-LET radiations in various types of tumors.

What is the role of radiotherapy in the treatment of mucosal melanoma of the head and neck?

Mucosal melanoma of the head and neck is a rare, poor prognosis tumour with a high tendency to recur locally and regionally after surgical resection. A number of centres have used radiotherapy to sterilize positive and close margins after non-radical surgery or to treat inoperable cases. The present article discusses the literature data to analyze the possible indications for radiotherapy in terms of patient selection and treatment strategy. In the majority of the available retrospective series, postoperative radiotherapy improves the local control of mucosal melanomas, but its effect on survival has not yet been sufficiently investigated. Radiobiological studies show a high heterogeneity in behaviour of irradiated melanoma cells and the clinical implications of this will be illustrated. In the future, a better understanding of the radiosensitivity of this rare tumour and the availability of new technical modalities might allow for a more profitable incorporation of radiotherapy into a multidisciplinary strategy.

Carbon ion radiotherapy for vaginal malignant melanoma: a case report

Malignant melanoma of the vagina is a very rare neoplasm and resistant to conventional radiotherapy. We report a case of vaginal malignant melanoma that was locally well controlled by carbon ion radiotherapy. A 55-year-old postmenopausal woman presented with abnormal vaginal bleeding. On pelvic and imaging examinations, an irregular mass of the posterior vaginal wall sized 7.5 x 5 x 5 cm, an enlarged right inguinal lymph node, and two lung metastases were observed. Histologic diagnosis based on positive immunostaining for HMB-45 was malignant melanoma. She received dacarbazine-based chemotherapy and carbon ion radiotherapy for vaginal and inguinal tumor sites with 57.6 Gy equivalent dose per 16 fractions using five ports. Six months later, she was also given carbon ion radiotherapy for regrowing lung metastasis with 52.8 Gy equivalent dose per four fractions using four ports. She died 19 months after initial treatment due to brain metastases. The primary irradiated tumor disappeared completely 12 months after initial treatment. The vaginal tumor, right inguinal lymph node, and lung tumor treated with carbon ion radiotherapy did not show any evidence of recurrence until her death. Carbon ion radiotherapy may be of value for vaginal malignant melanoma as a conservative approach.

A systematic literature review of the clinical and cost-effectiveness of hadron therapy in cancer

BACKGROUND

In view of the continued increase in the number of hadron (i.e. neutron, proton and light or heavy ion) therapy (HT) centres we performed a systematic literature review to identify reports of the efficacy of HT.

METHODS

Eleven databases were searched systematically. No limit was applied to language or study design. Established experts were contacted for unpublished data. Data on outcomes were extracted and summarised in tabular form.

RESULTS

Seven hundred and seventy three papers were identified. For proton and heavy ion therapy, the number of RCTs was too small to draw firm conclusions. Based on prospective and retrospective studies, proton irradiation emerges as the treatment of choice for some ocular and skull base tumours. For prostate cancer, the results were comparable with those from the best photon therapy series. Heavy ion therapy is still in an experimental phase.

CONCLUSION

Existing data do not suggest that the rapid expansion of HT as a major treatment modality would be appropriate. Further research into the clinical and cost-effectiveness of HT is needed. The formation of a European Hadron Therapy Register would offer a straightforward way of accelerating the rate at which we obtain high-quality evidence that could be used in assessing the role of HT in the management of cancer.

Particle radiation therapy using proton and heavier ion beams

Particle beams like protons and heavier ions offer improved dose distributions compared with photon (also called x-ray) beams and thus enable dose escalation within the tumor while sparing normal tissues. Although protons have a biologic effectiveness comparable to photons, ions, because they are heavier than protons, provide a higher biologic effectiveness. Recent technologic developments in the fields of accelerator engineering, treatment planning, beam delivery, and tumor visualization have stimulated the process of transferring particle radiation therapy (RT) from physics laboratories to the clinic. This review describes the physical, biologic, and technologic aspects of particle beam therapy. Clinical trials investigating proton and carbon ion RT will be summarized and discussed in the context of their relevance to recent concepts of treatment with RT.

Future Issues in Highly Conformal Radiotherapy for Head and Neck Cancer

Improving the conformity of the radiation dose to targets in the head and neck promises reduced toxicity and, in some cases, potentially improved local-regional tumor control. Intensity-modulated radiotherapy (IMRT) is a method that allows highly conformal delivery of radiotherapy. In recent years, its use has spread rapidly in both academic and community radiation oncology facilities. The use of IMRT has raised multiple issues related to target definition, optimal treatment delivery methods, and the need to account for anatomic changes occurring during therapy. Some of these issues are reviewed in this article.

Clinical Results of Carbon Ion Radiotherapy at NIRS

In 1994 a Phase I/II clinical study on carbon ion radiotherapy was begun at NIRS using HIMAC, which was then the world's only heavy ion accelerator complex dedicated to medical use in a hospital environment. Among several types of ion species, we have chosen carbon ions for cancer therapy because they had the most optimal properties in terms of possessing, both physically and biologically, the most effective dose-localization in the body. The purpose of the clinical study was to investigate the efficacy of carbon ion radiotherapy against a variety of tumors as well as to develop effective techniques for delivering an efficient dose to the tumor. The RBE of carbon ions was estimated to be 2.0 to 3.0 along the SOBP for acute skin reactions. As of August 2006, a total of 2,867 patients had been entered into Phase I/II or Phase II studies and analyzed for toxicity and local tumor response. The results have shown that carbon ion radiotherapy has the potential ability to provide a sufficient dose to the tumor with acceptable morbidity in the surrounding normal tissues. Tumors that appear to respond favorably to carbon ions include locally advanced tumors and those with histologically non-squamous cell type of tumors such as adenocarcinoma, adenoid cystic carcinoma, malignant melanoma, hepatoma, and bone/soft tissue sarcoma. By taking advantage of the biological and physical properties of high-LET radiation, the efficacy of treatment regimens with small fractions in short treatment times has been confirmed for almost all types of tumors in carbon ion radiotherapy.

Particle beam radiotherapy for head and neck tumors: radiobiological basis and clinical experience

BACKGROUND

Head and neck tumors are often located near critical organs, making it impossible to deliver a dose of conventional radiotherapy high enough to eradicate the disease. Our aim was to review the potential benefits and available clinical experience of particle beam therapy (hadrontherapy) in the treatment of these tumors.

METHODS

A review of the literature was carried out through a MEDLINE search (publications between 1980 and 2005).

RESULTS

A review of the available clinical data shows that particle beam therapy can offer several radiobiological and physical advantages over conventional photon radiotherapy: improved dose distribution permits dose escalation within the target and optimal sparing of normal tissue. Preclinical and clinical studies suggest that there may be benefits to using hadrontherapy for tumors characterized by poor radiosensitivity and critical location. At present, the most used hadrons are protons and, as yet on an experimental basis, carbon ions. It is now well accepted that there are certain indications for using proton therapy for skull base tumors (chordoma and chondrosarcoma), paranasal sinus carcinomas, selected nasopharyngeal tumors, and neutron/ion therapy for salivary gland carcinomas (in particular, adenoid cystic tumors). Its viability in other cases, such as locally advanced squamous cell carcinoma, melanoma, soft tissue sarcoma, and bone sarcoma, is still under investigation.

CONCLUSIONS

Hadrontherapy can be beneficial in the treatment of tumors characterized by poor radiosensitivity and critical location. Further clinical and radiobiological studies are warranted for improved selection of patient population.

Radiation Therapy With Charged Particles

Charged particle beams can offer an improved dose conformation to the target volume as compared with photon radiotherapy, with better sparing of normal tissue structures close to the target. In addition, beams of ions heavier than (4)He exhibit a strong increase of the linear energy transfer in the Bragg peak as compared with the entrance region. These physical and biological properties are much more favorable than in photon radiotherapy. As a consequence, particle therapy with protons and heavy ions has gained increasing interest worldwide, and many clinical centers are considering introducing radiation therapy with charged particles. This contribution summarizes the physical and technical principles of charged particle therapy with protons and heavy ions. It briefly reviews the clinical experience gathered so far with proton therapy and gives a more detailed summary of the recent results in carbon ion therapy of skull base tumors, head and neck tumors, non-small-cell lung cancer, hepatocellular carcinomas, bone and soft-tissue sarcomas, and prostate cancer.

Commissioning of a conformal irradiation system for heavy-ion radiotherapy using a layer-stacking method

The commissioning of conformal radiotherapy system using heavy-ion beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC) is described in detail. The system at HIMAC was upgraded for a clinical trial using a new technique: large spot uniform scanning with conformal layer stacking. The system was developed to localize the irradiation dose to the target volume more effectively than with the old system. With the present passive irradiation method using a ridge filter, a scatterer, a pair of wobbler magnets, and a multileaf collimator, the width of the spread-out Bragg peak (SOBP) in the radiation field could not be changed. With dynamic control of the beam-modifying devices during irradiation, a more conformal radiotherapy could be achieved. In order to safely perform treatments with this conformal therapy, the moving devices should be watched during irradiation and the synchronousness among the devices should be verified. This system, which has to be safe for patient irradiations, was constructed and tested for safety and for the quality of the dose localization realized. Through these commissioning tests, we were successfully able to prepare the conformal technique using layer stacking for patients. Subsequent to commissioning the technique has been applied to patients in clinical trials.

Enhancement of SPHK1 in vitro by carbon ion irradiation in oral squamous cell carcinoma

PURPOSE

The purpose of this study was to assess the gene expression changes in oral squamous cell carcinoma (OSCC) cells after carbon ion irradiation.

METHODS AND MATERIALS

Three OSCC cell lines (HSC2, Ca9-22, and HSC3) were irradiated with accelerated carbon ion beams or X-rays using three different doses. The cellular sensitivities were determined by clonogenic survival assay. To identify genes the expression of which is influenced by carbon ion irradiation in a dose-dependent manner, we performed Affymetrix GeneChip analysis with HG-U133 plus 2.0 arrays containing 54,675 probe sets. The identified genes were analyzed using the Ingenuity Pathway Analysis Tool to investigate the functional network and gene ontology. Changes in mRNA expression in the genes were assessed by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

We identified 98 genes with expression levels that were altered significantly at least twofold in each of the three carbon-irradiated OSCC cell lines at all dose points compared with nonirradiated control cells. Among these, SPHK1, the expression of which was significantly upregulated by carbon ion irradiation, was modulated little by X-rays. The function of SPHK1 related to cellular growth and proliferation had the highest p value (p = 9.25e-7 to 2.19e-2). Real-time reverse transcriptase-polymerase chain reaction analysis showed significantly elevated SPHK1 expression levels after carbon ion irradiation (p < 0.05), consistent with microarray data. Clonogenic survival assay indicated that carbon ion irradiation could induce cell death in Ca9-22 cells more effectively than X-rays.

CONCLUSIONS

Our findings suggest that SPHK1 helps to elucidate the molecular mechanisms and processes underlying the biologic response to carbon ion beams in OSCC.

Radiotherapy in the treatment of mucosal melanoma of the upper aerodigestive tract: Analysis of 74 cases. A Rare Cancer Network study

PURPOSE

To retrospectively analyze a series of mucosal melanoma of the upper aerodigestive tract to determine the prognostic factors and contribute to understanding the role of radiotherapy in the therapeutic strategy.

METHODS AND MATERIALS

Seventy-four patients were analyzed. The most frequent locations were nasal and oral, in 31 patients (41.9%) and 12 patients (16.2%), respectively. Sixty-three patients (85.1%) were in Stage I, 5 (6.8%) in Stage II, and 6 (8.1%) in Stage III. Treatment consisted of surgery in 17 patients (23.0%), surgery and radiotherapy in 42 (56.8%), radiotherapy in 11 (14.9%), and chemo-immunotherapy in 4 (5.4%). Median follow-up was 20 months.

RESULTS

Local control at 3 years was 57% after surgery alone and 71% after surgery and radiotherapy. Overall and disease-free survival rates, respectively, were 41% and 31% at 3 years and 14% and 22% at 10 years. After univariate analysis, female gender, melanosis, tumor size </=3 cm, Stage I, postoperative radiotherapy, and complete remission were favorable prognostic factors. Stage I and melanosis were confirmed by multivariate analysis.

CONCLUSIONS

Local control was improved by postoperative radiotherapy, despite survival being as poor as in other published series. Stage I and melanosis at diagnosis were the most favorable prognostic factors.

Long-term local control of recurrent adenoid cystic carcinoma in the parotid gland with radiotherapy and intraarterial infusion chemotherapy

We report a case of postoperative recurrence of adenoid cystic carcinoma in the left parotid gland treated with radiotherapy and arterial infusion chemotherapy. A 52-year-old woman had a history of surgical resection for an adenoid cystic carcinoma arising from the left parotid gland 25 years before. Despite two reoperations for local recurrence after the initial surgery, she had a third local recurrence in the remnant of the left parotid gland. The patient was treated with a concurrent combination of radiotherapy (60 Gy/30F) and intraarterial infusion chemotherapy with carboplatin (750 mg/30 days) from which she obtained a complete response. The patient has remained free of local progression 54 months after treatment. Radiotherapy and arterial infusion chemotherapy is effective treatment for local recurrence of adenoid cystic carcinoma in the head and neck.

Dose escalation study of carbon ion radiotherapy for locally advanced carcinoma of the uterine cervix

PURPOSE

To evaluate the toxicity and efficacy of carbon ion radiotherapy (CIRT) for locally advanced cervical cancer by two phase I/II clinical trials.

METHODS AND MATERIALS

Between June 1995 and January 2000, 44 patients were treated with CIRT. Thirty patients had Stage IIIB disease, and 14 patients had Stage IVA disease. Median tumor size was 6.5 cm (range, 4.2-11.0 cm). The treatment consisted of 16 fractions of whole pelvic irradiation and 8 fractions of local boost. In the first study, the total dose ranged from 52.8 to 72.0 gray equivalents (GyE) (2.2-3.0 GyE per fraction). In the second study, the whole pelvic dose was fixed at 44.8 GyE, and an additional 24.0 or 28.0 GyE was given to the cervical tumor (total dose, 68.8 or 72.8 GyE).

RESULTS

No patient developed severe acute toxicity. In contrast, 8 patients developed major late gastrointestinal complications. The doses resulting in major complications were > or =60 GyE. All patients with major complications were surgically salvaged. The 5-year local control rate for patients in the first and second studies was 45% and 79%, respectively. When treated with > or =62.4 GyE, the local control was favorable even for the patients with stage IVA disease (69%) or for those with tumors > or =6.0 cm (64%).

CONCLUSIONS

In CIRT for advanced cervical cancer, the dose to the intestines should be limited to <60 GyE to avoid major complications. Although the number of patients in this study was small, the results support continued investigation to confirm therapeutic efficacy.

Examination of GyE system for HIMAC carbon therapy

PURPOSE

A retrospective analysis was made to examine appropriateness in the estimation of the biologic effectiveness of carbon-ion radiotherapy using resultant data from clinical trials at the heavy-ion medical accelerator complex (HIMAC) at the National Institute of Radiological Sciences in Chiba, Japan.

METHODS AND MATERIALS

At HIMAC, relative biologic effectiveness (RBE) values of therapeutic carbon beams were determined based on experimental results of cell responses, on values expected with the linear-quadratic model, and based on experiences with neutron therapy. We use fixed RBE values independent of dose levels, although this apparently contradicts radiobiologic observations. Our RBE system depends only on LET of the heavy-ion radiation fields. With this RBE system, over 2,000 patients have been treated by carbon beams. With data from these patients, the local control rate of non-small-cell lung cancer was analyzed to verify the clinical RBE of the carbon beam. The local control rate was compared with rates published by groups from Gunma University and Massachusetts General Hospital. Using a simplified tumor control probability (TCP) model, clinical RBE values were obtained for different levels of TCP.

RESULTS

For the 50% level of the clinical TCP, the RBE values nearly coincide with those for in vitro human salivary gland cell survival at 10%. For the higher levels of clinical TCP, the RBE values approach closer to those adapted in clinical trials at HIMAC.

MR Imaging of Brain Injury Induced by Carbon Ion Radiotherapy for Head and Neck Tumors

To clarify the characteristics of magnetic resonance (MR) imaging of radiation-induced brain injury following carbon ion radiotherapy and to observe the changes in lesions over time, we evaluated 40 patients with radiation-induced brain injury from carbon ion radiotherapy for head and neck tumors. Their primary lesions received a radiation dose of 48 to 70.4 Gray equivalent (GyE) in 16 to 18 fractions. MR imaging of radiation-induced brain injury was graded as follows: Grade 1: change in focal white matter; focal contrast enhancement and surrounding edema; Grade 2: nonenhanced area or cystic lesion in enhanced lesion; Grade 3: focal necrosis with mass effect; and Grade 4: mass effect requiring surgical intervention. Radiation-induced brain injury appeared as early as 2 months and as late as 57 months after carbon ion therapy (mean interval, 22.2 months). MR findings of initial lesion were Grade 1 in 26 cases (65.0%), Grade 2 in 13 (32.5%), and Grade 3 in 1 (2.5%). Brain injury was always found in the radiation field initially, but cystic lesion and edema later extended outside the field in 10 cases (25.0%). In follow-up MR studies, size of edema or enhanced lesion was reduced in 17 patients (42.5%) without treatment. Two cases with large cystic lesions required surgery. Improvement of radiation-induced brain injury was observed more often than had been previously described. Because edema and cystic lesion can occasionally extend outside the radiation field, such findings do not exclude the possibility of radiation-induced brain injury. Careful observation is recommended because cystic lesions can enlarge enough to require surgical treatment in some cases.