Photon Radiation Treatment Research Articles

Radiotherapy with Helium Ions Has the Potential to Improve Both Endocrine and Neurocognitive Outcome in Pediatric Patients with Ependymoma

Ependymomas are the third most-frequent pediatric brain tumors. To prevent local recurrence, the resection site should be irradiated. Compared to photon radiation treatment, proton therapy often achieves even better results regarding target coverage and organ-sparing. Due to their physical properties, helium ions could further reduce side effects, providing better protection of healthy tissue despite similar target coverage. In our in silico study, 15 pediatric ependymoma patients were considered. All patients underwent adjuvant radiotherapeutic treatment with active-scanned protons at Heidelberg Ion Beam Therapy Center (HIT). Both helium ion and highly conformal IMRT plans were calculated to evaluate the potential dosimetric advantage of ion beam therapy compared to the current state-of-the-art photon-based treatments. To estimate the potential clinical benefit of helium ions, normal tissue complication probabilities (NTCP) were calculated. Target coverage was comparable in all three modalities. As expected, the integral dose absorbed by healthy brain tissue could be significantly reduced with protons by up to -48% vs. IMRT. Even compared to actively scanned protons, relative dose reductions for critical neuronal structures of up to another -39% were achieved when using helium ions. The dose distribution of helium ions is significantly superior when compared to proton therapy and IMRT due to the improved sparing of OAR. In fact, previous studies could clearly demonstrate that the dosimetric advantage of protons translates into a measurable clinical benefit for pediatric patients with brain tumors. Given the dose-response relationship of critical organs at risk combined with NTCP calculation, the results of our study provide a strong rationale that the use of helium ions has the potential to even further reduce the risk for treatment related sequelae.

Proton Therapy in the Management of Pancreatic Cancer.

Simple SummaryRadiation treatment plays a pivotal a role in the management of pancreatic cancer, mainly in the neoadjuvant setting for borderline resectable tumors and in the definitive setting for unresectable localized disease. Most of the studies on pancreatic cancer use photon-based radiation therapy modalities. However, there is a growing interest in the application of protons therapy for gastrointestinal cancers. This review summarizes the literature on the use of proton therapy in the management of pancreatic cancer. Radiation therapy plays a central role in the treatment of pancreatic cancer. While generally shown to be feasible, proton irradiation, particularly when an ablative dose is planned, remains a challenge, especially due to tumor motion and the proximity to organs at risk, like the stomach, duodenum, and bowel. Clinically, standard doses of proton radiation treatment have not been shown to be statistically different from photon radiation treatment in terms of oncologic outcomes and toxicity rates as per non-randomized comparative studies. Fractionation schedules and concurrent chemotherapy combinations are yet to be optimized for proton therapy and are the subject of ongoing trials.

EPEN-15. Radiotherapy with helium ions has the potential to improve both endocrine and neurocognitive outcome in pediatric patients with ependymoma

BACKGROUND: Ependymoma are the third most frequent pediatric brain tumors. To prevent local recurrence, the resection site should be irradiated. Especially the treatment of pediatric patients requires precise dose application and optimal protection of organs at risk. Compared to photon radiation treatment, proton therapy often achieves better results regarding target coverage and organ-sparing. Due to their physical properties, helium ions can further reduce side effects, providing better protection of healthy tissue despite similar target coverage. PATIENTS AND METHODS: In our in-silico study, 15 pediatric patients (median age six years) with ependymoma located in the posterior cranial fossa were considered. All patients underwent adjuvant radiotherapeutic treatment with active scanned protons at Heidelberg Ion-Beam Therapy Center (HIT). Both helium ion and highly conformal IMRT plans were calculated to evaluate the potential dosimetric (and clinical) benefit of ion beam therapy compared to the current state of the art photon-based treatments. RESULTS: Target coverage was comparable in all three modalities (He, H+, Ph): homogeneity indices (HI) and inhomogeneity coefficients (IC) of HIHe=5.8±3.8, HIH+=7.5±4.0, HIPh=6.4±4.3, ICHe=0.2±0.1, ICH+=0.2±0.1, ICPh=0.2±0.1. As expected, the integral dose absorbed by the healthy brain tissue could be reduced significantly using helium ions versus IMRT (-45.3%±15.1%). Based on our preliminary results, even compared to active scanned protons – currently the most precise radiation technique worldwide – the relative dose reduction for critical neuronal structures using helium ions on average amounts to -27.2%±14.4%. CONCLUSION: Previous studies could clearly demonstrate that the dosimetric advantage of protons translates into a measurable clinical benefit for pediatric patients with brain tumors. Given the dose response relationship of critical organs at risk, the results of our in-silico study provide a strong rationale that the use of helium ions has the potential to even further reduce the risk for treatment related sequelae.

Photon versus proton neurotoxicity: Impact on mitochondrial function and 8-OHdG base-excision repair mechanism in human astrocytes

This study assesses and compares the neurotoxic effects of proton and photon radiation on mitochondrial function and DNA repair capabilities of human astrocytes. Human astrocytes received either proton (0.5 Gy and 3 Gy), photon (0.5 Gy and 3 Gy), or sham-radiation treatment. The mRNA expression level of the DNA repair protein OGG1 was determined via RT-qPCR. The levels of 8-OHdG in the cell media were measured via ELISA. Real-time kinetic analysis of extracellular oxygen consumption rates was performed to assess mitochondrial function. Radiation-induced changes in mitochondrial mass and oxidative activity were assessed using fluorescent imaging with MitoTracker™ Green FM and MitoTracker™ Orange CM-H2TMRos dyes respectively. PCR was used to quantify the alteration in the mitochondrial DNA content, measured as the mitochondrial to nuclear DNA ratio. A significant increase in mitochondrial mass and levels of reactive oxygen species was observed after radiation treatment. Additionally, real-time PCR analysis indicated a significant depletion of mitochondrial DNA content in the irradiated cells when compared to the control. This was accompanied by a decreased gene expression of the DNA base-excision repair protein OGG1 and reduced clearance of 8-OHdG adducts from the genome. Photon radiation treatment was associated with a more detrimental cellular impact when compared to the same dose of proton radiation. These results are indicative of a radiation-induced dose-dependent decrease in mitochondrial function, an increase in senescence and astrogliosis, and impairment of the DNA repair capabilities in healthy glial cells. Photon irradiation was associated with a more significant disruption in mitochondrial function and base-excision repair mechanisms in vitro in comparison to proton treatment.

External photon radiation treatment for prostate cancer: Uncomplicated and cancer-free control probability assessment of 36 plans

PurposeTo perform a systematic and thorough assessment, using the Uncomplicated and Cancer-Free Control Probability (UCFCP) function, of a broad range of photon prostate cancer RT treatments, on the same scenario (a unique pelvic CT set). UCFCP considers, together with the probabilities of local tumour control (TCP) and deterministic (late) sequelae (NTCP), the second primary cancer risk (SPCR) due to photon and neutron peripheral doses. Methods and materialsThirty-six radiotherapy plans were produced for the same CT. 6, 10, 15 and 18 MV 3DCRT, IMRT and VMAT (77.4 Gy in 43 fractions) and 6 and 10 MV SBRT (36.25 Gy in 5 fractions with flattened and FFF beams) for Elekta, Siemens and Varian Linacs plans were included. DVH and peripheral organ dosimetry were used to compute TCP, NTCP, and SPCR (the competition and LNT models) for further plan ranking. ResultsBiological models (and parameters) used predicted an outcome which is in agreement with epidemiological findings. SBRT plans showed the lowest SPCR and a below average NTCPrectal. High energy plans did not rank worse than the low energy ones. Intensity modulated plans were ranked above the 3D conformal techniques. ConclusionsAccording to UCFCP, the best plans were the10 MV SBRTs. SPCR rates were low and did not show a substantial impact on plan ranking. High energy intensity-modulated plans did not increase in excess the average of SPCR. Even more, they ranked among the best, provided that MU were efficiently managed.

The efficacy of neutron radiation therapy in treating salivary gland malignancies

ObjectivesRadiation therapy is commonly used to treat head and neck malignancies. While there is abundant research regarding photon radiation therapy, literature on neutron radiotherapy (NRT) and oral complications is limited. This study aims to determine: (1) the 6-year and 10-year locoregional control and survival rates, (2) factors associated with locoregional control and survival and (3) the frequency of oral complications in patients undergoing NRT for salivary gland malignancies. Materials and methodsThis is a retrospective cohort study. The sample was composed of patients with salivary gland malignancies treated with NRT between 1997 and 2010. Data were extracted from patient charts, telephone surveys, and social security records. Multivariate competing risk and Cox regression models were used to assess predictors of locoregional control and survival. ResultsThe sample was composed of 545 subjects with a mean age of 54.2 years (±16). The predominant tumor and location were adenoid cystic carcinoma (47%) and the parotid (56%). Multivariate analysis indicated that positive surgical margins, biopsied/inoperable malignancies, neck involvement, and lymphovascular invasion were prognostic risk factors associated with decreased survival. The 6- and 10-year locoregional control rates were 84% and 79%. The 6- and 10-year survival rates were 72% and 62%. Osteoradionecrosis developed in 3.4% of subjects. ConclusionsThe 6- and 10-year locoregional control and survival rates compare favorably to rates reported for conventional photon radiation. Osteoradionecrosis rates were comparable to that of photon radiation treatment (2–7%). Given the potential benefits of NRT, healthcare professionals should be educated regarding its indications and oral complications.

Cherenkov-excited Multi-Fluorophore Sensing in Tissue-Simulating Phantoms and In Vivo from External Beam Radiotherapy.

In this work, Cherenkov-excited molecular sensing was used to assess the potential for simultaneous quantitative sensing of two NIR fluorophores within tissue-simulating phantoms through spectral separation of signals. Cherenkov emissions induced by external beam gamma photon radiation treatment to tissues/tissue-simulating phantoms were detectable over the 500-900-nm wavelength range. The presence of blood was demonstrated to reduce the integrated intensity of detected Cherenkov emissions by nearly 50%, predominantly at wavelengths below 620 nm. The molecular dyes, IRDye 680RD and IRDye 800CW, have excitation and emission spectra at longer wavelengths than the strongest blood absorption peaks, and also where the intensity of Cherenkov light is at its lowest, so that the emission signal relative to background signal is maximized. Tissue phantoms composed of 1% intralipid and 1% blood were used to simulate human breast tissue, and vials containing fluorophore were embedded in the media, and irradiated with gamma photons for Cherenkov excitation. We observed that fluorescence emissions excited by the Cherenkov signal produced within the phantom could be detected at 5-mm depth into the media within a 0.1-25 μ M fluorophore concentration range. The detected fluorescence signals from these dyes showed linear relationships with radiation doses down to the cGy level. In vivo tests were successful only within the range near a μ M, suggesting that these could be used for metabolic probes in vivo where the local concentrations are near this range.

Consolidative proton therapy after chemotherapy for patients with Hodgkin lymphoma

BackgroundWe investigated early outcomes for patients receiving chemotherapy followed by consolidative proton therapy (PT) for the treatment of Hodgkin lymphoma (HL).Patients and methodsFrom June 2008 through August 2015, 138 patients with HL enrolled on either IRB-approved outcomes tracking protocols or registry studies received consolidative PT. Patients were excluded due to relapsed or refractory disease. Involved-site radiotherapy field designs were used for all patients. Pediatric patients received a median dose of 21 Gy(RBE) [range 15–36 Gy(RBE)]; adult patients received a median dose of 30.6 Gy(RBE) [range, 20–45 Gy(RBE)]. Patients receiving PT were young (median age, 20 years; range 6–57). Overall, 42% were pediatric (≤18 years) and 93% were under the age of 40 years. Thirty-eight percent of patients were male and 62% female. Stage distribution included 73% with I/II and 27% with III/IV disease. Patients predominantly had mediastinal involvement (96%) and bulky disease (57%), whereas 37% had B symptoms. The median follow-up was 32 months (range, 5–92 months).ResultsThe 3-year relapse-free survival rate was 92% for all patients; it was 96% for adults and 87% for pediatric patients (P = 0.18). When evaluated by positron emission tomography/computed tomography scan response at the end of chemotherapy, patients with a partial response had worse 3-year progression-free survival compared with other patients (78% versus 94%; P = 0.0034). No grade 3 radiation-related toxicities have occurred to date.ConclusionConsolidative PT following standard chemotherapy in HL is primarily used in young patients with mediastinal and bulky disease. Early relapse-free survival rates are similar to those reported with photon radiation treatment, and no early grade 3 toxicities have been observed. Continued follow-up to assess late effects is critical.

SU‐F‐T‐261: Reconstruction of Initial Photon Fluence Based On EPID Images

Purpose:Verifying an algorithm to reconstruct relative initial photon fluence for clinical use. Clinical EPID and CT images were acquired to reconstruct an external photon radiation treatment field. The reconstructed initial photon fluence could be used to verify the treatment or calculate the applied dose to the patient.Methods:The acquired EPID images were corrected for scatter caused by the patient and the EPID with an iterative reconstruction algorithm. The transmitted photon fluence behind the patient was calculated subsequently. Based on the transmitted fluence the initial photon fluence was calculated using a back‐projection algorithm which takes the patient geometry and its energy dependent linear attenuation into account. This attenuation was gained from the acquired cone‐beam CT or the planning CT by calculating a water‐equivalent radiological thickness for each irradiation direction. To verify the algorithm an inhomogeneous phantom consisting of three inhomogeneities was irradiated by a static 6 MV photon field and compared to a reference flood field image.Results:The mean deviation between the reconstructed relative photon fluence for the inhomogeneous phantom and the flood field EPID image was 3% rising up to 7% for off‐axis fluence. This was probably caused by the used clinical EPID calibration, which flattens the inhomogeneous fluence profile of the beam.Conclusion:In this clinical experiment the algorithm achieved good results in the center of the field while it showed high deviation of the lateral fluence. This could be reduced by optimizing the EPID calibration, considering the off‐axis differential energy response. In further progress this and other aspects of the EPID, eg. field size dependency, CT and dose calibration have to be studied to realize a clinical acceptable accuracy of 2%.

Individual patient information to select patients for different radiation techniques

Background and purposeProton therapy is an emerging technique in radiotherapy which results in less dose to the normal tissues with similar target dose than photon therapy, the current standard. Patient-level simulation models support better decision making on which patients would benefit most. Materials and methodsA simulation model was developed tracking individual patients' status regarding the primary tumour and multiple complications. As a proof of principle, the model was populated based on information from a cohort of 1013 head and neck cancer patients. Dose–volume parameters for photon and proton radiation treatment plans were then fed into the model to compare outcomes in terms of length and quality of life and select patients that would benefit most. ResultsThe illustrative model could adequately replicate the outcomes of photon therapy in the cohort. Improvements from proton therapy varied considerably between patients. The model projects medium-term outcomes for specific individuals and determines the benefits of applying proton rather than photon therapy. ConclusionsWhile the model needs to be fed with more and especially recent data before being fully ready for use in clinical practice, it could already distinguish between patients with high and low potential benefits from proton therapy. Benefits are highest for patients with both good prognosis and high expected damage to adjacent organs. The model allows for selecting such patients a priori based on patient relevant outcomes.

EVOLUTION OF THIN-FILM STRUCTURES BY THERMAL AND PULSED PHOTON EFFECTS

Presents a review of works devoted to the study of thermal effects in thin-film patterns of the Ag-Cu, Au-Pt and Cu-Ni and comparative study of the effect of pulsed photon radiation treatment xenon lamps and heat treatment equivalent temperature conditions on the process of recrystallization of single-phase polycrystalline films of noble metals Au, Pt and Pd.

Neutron Beam Radiation Therapy: An Overview of Treatment and Oral Complications When Treating Salivary Gland Malignancies

There is limited information in the literature regarding the oral complications of neutron radiotherapy, with an associated lack of guidelines for their management. The purpose of this study was to review the indications, dosing, prognosis, and oral complications of neutron radiotherapy for salivary gland malignancies. This is a retrospective case series of patients with salivary gland malignancies treated with neutron radiotherapy by the Radiation Oncology Department at the University of Washington from 1997 to 2006. Variables included patient demographics, tumor staging and characteristics, operative treatment, final diagnosis, operative and pathologic findings (ie, perineural invasion, lymph node involvement, and skull base invasion), dosing, complications, and locoregional control and survival rates. Data were extracted from patients' charts and by telephone for follow-up and quality-of-life information. The sample was composed of 140 patients (49% men, 51% women) with a mean age of 53 years (standard deviation, 15 yr). Adenoid cystic carcinoma of the submandibular gland was the most common tumor type and location. Post-treatment trismus occurred in 56%. Acute mucositis and xerostomia occurred in approximately 88 and 89% of patients, respectively. Osteoradionecrosis was reported in 5.7% of patients. The 6-year survival rate was 58% and the 6-year locoregional control was 72%. The current standard neutron dose for head and neck tumors is 1.15 neutron Gray (nGy) 4 times per week for 4 weeks (total, 18.4 nGy), which is an equivalent amount of radiation as the standard 60 to 70 Gy given for 6 to 7 weeks with conventional photon radiation. The 6-year overall survival of 58% found in this study compares favorably to the survival rate reported in the literature for traditional photon radiation treatment of advanced salivary gland tumors. The dental profession should be educated regarding neutron radiotherapy and its indications, dosing methods, and oral complications.

Dynamic PET/CT measurements of induced positron activity in a prostate cancer patient after 50-MV photon radiation therapy

BackgroundThe purpose of this work was to reveal the research interest value of positron emission tomography (PET) imaging in visualizing the induced tissue activity post high-energy photon radiation treatment. More specifically, the focus was on the possibility of retrieving data such as tissue composition and physical half-lives from dynamic PET acquisitions, as positron-emitting radionuclides such as 15O, 11C, and 13N are produced in vivo during radiation treatment with high-energy photons (>15 MeV). The type, amount, and distribution of induced positron-emitting radionuclides depend on the irradiated tissue cross section, the photon spectrum, and the possible perfusion-driven washout.MethodsA 62-year-old man diagnosed with prostate cancer was referred for palliative radiation treatment of the pelvis minor. A total dose of 8 Gy was given using high-energy photon beams (50 MV) with a racetrack microtron, and 7 min after the end of irradiation, the patient was positioned in a PET/computed tomography (CT) camera, and a list-mode acquisition was performed for 30 min. Two volumes of interests (VOIs) were positioned on the dynamic PET/CT images, one in the urinary bladder and the other in the subcutaneous fat. Analysis of the measured relative count rate was performed in order to compute the tissue compositions and physical half-lives in the two regions.ResultsDynamic analysis from the two VOIs showed that the decay constants of activated oxygen and carbon could be deduced. Calculation of tissue composition from analyzing the VOI containing subcutaneous fat only moderately agreed with that of the tabulated International Commission on Radiation Units & Measurements (ICRU) data of the adipose tissue. However, the same analysis for the bladder showed a good agreement with that of the tabulated ICRU data.ConclusionsPET can be used in visualizing the induced activity post high-energy photon radiation treatment. Despite the very low count rate in this specific application, wherein 7 min after treatment was about 5% of that of a standard 18F-FDG PET scan, the distribution of activated tissue elements (15O and 11C) could be calculated from the dynamic PET data. One possible future application of this method could possibly be to measure and determine the tumor tissue composition in order to identify any hypoxic or necrotic region, which is information that can be used in the ongoing therapy planning process.Trial registrationThe official name of the trial committee of this study is ‘Regionala etikprövningsnämnden i Stockholm’ (FE 289, Stockholm, SE-17177, Sweden). The unique identifying number is 2011/1789-31/2.

Feasibility of deformation-independent tumor-tracking radiotherapy during respiration

To evaluate the feasibility of tumor-tracking radiotherapy that does not consider tumor deformation during respiration. Four-dimensional computed tomography (4D-CT) data, which considers 10 phases of the respiration cycle, were acquired in 4 patients with lung cancer and 4 patients with liver cancer. Initial treatment plans were established at the end of the inhalation phase (phase 1). As a simulation of deformation-free tumor-tracking radiotherapy, the beam center of the initial plan was moved to the tumor center for all other phases, and the tumor shape acquired from phase 1 was used for all 10 phases. The feasibility of this method was analyzed based on assessment of equivalent uniform dose (EUD), homogeneity index (HI) and coverage index (COV). In photon radiation treatment, movement-induced dose reduction was not particularly significant, with 0.5%, 17.3% and 2.8% average variation in EUD, HI and COV, respectively. In proton radiation treatment, movement-induced dose reduction was more significant, with 0.3%, 40.5% and 2.2% average variation in EUD, HI and COV, respectively. Proton treatment is more sensitive to tumor movement than is photon treatment, and that it is reasonable to disregard tumor deformation during photon therapy employing tumor-tracking radiotherapy.

Enhancement of Radiation Response in Osteosarcoma and Rhabomyosarcoma Cell Lines by Histone Deacetylase Inhibition

Histone deacetylase inhibitors (HDACIs) can enhance the sensitivity of cells to photon radiation treatment (XRT) by altering numerous molecular pathways. We investigated the effect of pan-HDACIs such as suberoylanilide hydroxamic acid (SAHA) on radiation response in two osteosarcoma (OS) and two rhabdomyosarcoma (RMS) cell lines. Clonogenic survival, cell cycle analysis, and apoptosis were examined in OS (KHOS-24OS, SAOS2) and RMS (A-204, RD) cell lines treated with HDACI and HDACI plus XRT, respectively. Protein expression was investigated via immunoblot analysis, and cell cycle analysis and measurement of apoptosis were performed using flow cytometry. SAHA induced an inhibition of cell proliferation and clonogenic survival in OS and RMS cell lines and led to a significant radiosensitization of all tumor cell lines. Other HDACI such as M344 and valproate showed similar effects as investigated in one OS cell line. Furthermore, SAHA significantly increased radiation-induced apoptosis in the OS cell lines, whereas in the RMS cell lines radiation-induced apoptosis was insignificant with and without SAHA. In all investigated sarcoma cell lines, SAHA attenuated radiation-induced DNA repair protein expression (Rad51, Ku80). Our results show that HDACIs enhance radiation action in OS and RMS cell lines. Inhibition of DNA repair, as well as increased apoptosis induction after exposure to HDACIs, can be mechanisms of radiosensitization by HDACIs.

SU‐GG‐J‐72: Study of Constant Beam Shaping Method in Tumor Tracking Radiotherapy during Respiration

Purpose: To evaluate the tumor tracking radiotherapy without consideration for the deformation of moving tumor. Method: Four dimensional computed tomography (4D CT) corresponding to every 10% phase intervals were acquired for 4 lung and 4 liver cancer patients treated in our institution and the initial treatment planning was established for the end of inhalation phase (phase 1). Results: As a simulation of deformation‐free tumor tracking radiotherapy, the beam center of initial plan was moved to the tumor center in other phases and the constant tumor shape acquired from phase 1 was assumed in all phases. The feasibility of the proposed method was analyzed based on various dosimetric tools such as equivalent uniform dose (EUD), homogeneity index (HI), coverage index (COV), etc. In photon radiation treatment, the movement‐induced dose reduction was not that critical showing 0.5%, 17.3% and 2.8% as the average variation of EUD, HI, COV, respectively. This difference become greater in proton treatment, which shows the change of 0.3%, 40.5%, 2.2% compared to initial EUD, HI, COV, respectively. Conclusion:These results suggest that proton is more sensitive than photon in tumor movement and the deformation of tumor may be disregarded in tumor tracking radiotherapy for photon treatment.

Dose escalation with proton or photon radiation treatment for pancreatic cancer

Purpose The purpose was to determine the optimal radiation therapy modality (three-dimensional conformal photon-radiation therapy [3DCRT], intensity-modulated photon-radiation therapy [IMRT], or passive-scattering proton therapy [PT]) for safe dose escalation (72 Gy) in pancreatic tumors in different positions relative to organs at risk (OAR) anatomy. Methods and materials A 3-cm pancreatic tumor was virtually translated every 5 mm over 5 cm laterally. We generated two plans for each of the three techniques (3DCRT, IMRT, and PT), one that adhered to target coverage objectives and another to meet OAR sparing constraints with best coverage. We evaluated distances between gross tumor volumes and isodoses and compared dose–volume histograms. Results IMRT was more conformal in higher gradient dose regions circumferentially, but tumor positions with anteriorly located small bowel benefited more from PT. 3DCRT plans resulted in inadequate target coverage. The V 15Gy (mean ± SD) were as follows for the IMRT and PT plans, respectively: stomach, 48% ± 4% vs 5% ± 3% ( p < 0.0001); and small bowel, 61% ± 8% vs 9% ± 4% ( p < 0.0001). Conclusions Our study showed that the optimal radiation therapy modality for safe dose escalation depends on pancreatic tumor position in relation to OAR anatomy.

Dose Escalation with Proton or Photon Radiation Treatment for Pancreatic Cancer

Dose Escalation with Proton or Photon Radiation Treatment for Pancreatic Cancer

PET imaging for treatment verification of ion therapy: Implementation and experience at GSI Darmstadt and MGH Boston

Ion beams offer the possibility of improved conformation of the dose delivered to the tumor with better sparing of surrounding tissue and critical structures in comparison to conventional photon and electron external radiation treatment modalities. Full clinical exploitation of this advantage can benefit from in vivo confirmation of the actual beam delivery and, in particular, of the ion range in the patient. During irradiation, positron emitters like 15O (half-life T 1/2≈2 min) and 11C ( T 1/2≈20 min) are formed in nuclear interactions between the ions and the tissue. Detection of this transient radioactivity via positron emission tomography (PET) and comparison with the expectation based on the prescribed beam application may serve as an in vivo, non-invasive range validation method of the whole treatment planning and delivery chain. For technical implementation, PET imaging during irradiation (in-beam) requires the development of customized, limited angle detectors with data acquisition synchronized with the beam delivery. Alternatively, commercial PET or PET/CT scanners in close proximity to the treatment site enable detection of the residual activation from long-lived emitters shortly after treatment (offline). This paper reviews two clinical examples using a dedicated in-beam PET scanner for verification of carbon ion therapy at GSI Darmstadt, Germany, as well as a commercial offline PET/CT tomograph for post-radiation imaging of proton treatments at Massachusetts General Hospital, Boston, USA. Challenges as well as pros and cons of the two imaging approaches in dependence of the different ion type and beam delivery system are discussed.

Anaplastic glioma after high-dose proton–photon radiation treatment for low-grade skull base chondrosarcoma

We report the case of a 63-year-old man who developed an anaplastic oligoastrocytoma of the brain stem and midbrain 13 years after postoperative high-dose proton-photon radiation therapy for a recurrent low-grade chondrosarcoma of the skull base. To our knowledge, this is the first reported case of an anaplastic glioma after proton-photon irradiation.