Precise Dose Distribution Research Articles

Comparison of dosimetric characteristics between stationary and rotational gamma ray stereotactic radiosurgery systems based on Monte Carlo simulation

Stationary and rotational source are two types of source configuration used in commercial Gamma Ray Stereotactic Radiosurgery Systems (GRSRSs). However, it is unclear which one is better in dosimetric performance for clinical use. In this study, precise dose distributions in high resolution of the single source channel of two GRSRSs (the Elekta Leksell Gamma Knife® Model 4C (LGK 4C) for stationary GRSRS and the OUR XGD for rotational GRSRS) were generated by Monte Carlo simulation. Because of the geometrical symmetry, the overall dose distribution is generated by combining the transformed dose distributions of the single source channel. Output factors and penumbra widths were calculated and compared. The differences of output factors between two GRSRSs are minor. The penumbra widths of dose profile from all sources of the LGK 4C are 2.2-1.3-1.4 mm, 3.5-1.6-1.7 mm, 5.8-2.2-2.4 mm, and 7.2-2.6-3.0 mm (in XY-(+Z)-(−Z) form) for the secondary collimator of 4 mm, 8 mm, 14 mm, and 18 mm, respectively and those of the OUR XGD are 3.1-2.3-2.4 mm, 4.0-2.4-2.5 mm, 5.8-2.6-3.0 mm, and 7.2-3.0-3.6 mm for the secondary collimator of 5 mm, 10 mm, 15 mm, and 20 mm, respectively. The dose profiles in Z direction are not symmetrical, because all sources are distributed in +Z direction. Secondly, since the sources are located in higher latitude in the OUR XGD (14°–43°) comparing with that in the LGK 4C (6°–36°), the penumbra widths in Z direction of the OUR XGD are larger than those of the LGK 4C. Thirdly, although the penumbra widths of dose profiles from the single source channel of the LGK 4C are smaller than those of the OUR XGD, with rotational source configuration the OUR XGD has smaller penumbra width of dose profile from all sources in X–Y plane when the secondary collimator is more than 10 mm.

Clinical utility of RapidArc™ radiotherapy technology.

RapidArc™ is a radiation technique that delivers highly conformal dose distributions through the complete rotation (360°) and speed variation of the linear accelerator gantry. This technique, called volumetric modulated arc therapy (VMAT), compared with conventional radiotherapy techniques, can achieve high-target volume coverage and sparing damage to normal tissues. RapidArc delivers precise dose distribution and conformity similar to or greater than intensity-modulated radiation therapy in a short time, generally a few minutes, to which image-guided radiation therapy is added. RapidArc has become a currently used technology in many centers, which use RapidArc technology to treat a large number of patients. Large and small hospitals use it to treat the most challenging cases, but more and more frequently for the most common cancers. The clinical use of RapidArc and VMAT technology is constantly growing. At present, a limited number of clinical data are published, mostly concerning planning and feasibility studies. Clinical outcome data are increasing for a few tumor sites, even if only a little. The purpose of this work is to discuss the current status of VMAT techniques in clinical use through a review of the published data of planning systems and clinical outcomes in several tumor sites. The study consisted of a systematic review based on analysis of manuscripts retrieved from the PubMed, BioMed Central, and Scopus databases by searching for the keywords “RapidArc”, “Volumetric modulated arc radiotherapy”, and “Intensity-modulated radiotherapy”.

Fast CPU-based Monte Carlo simulation for radiotherapy dose calculation

Monte-Carlo (MC) simulations are considered to be the most accurate method for calculating dose distributions in radiotherapy. Its clinical application, however, still is limited by the long runtimes conventional implementations of MC algorithms require to deliver sufficiently accurate results on high resolution imaging data. In order to overcome this obstacle we developed the software-package PhiMC, which is capable of computing precise dose distributions in a sub-minute time-frame by leveraging the potential of modern many- and multi-core CPU-based computers. PhiMC is based on the well verified dose planning method (DPM). We could demonstrate that PhiMC delivers dose distributions which are in excellent agreement to DPM. The multi-core implementation of PhiMC scales well between different computer architectures and achieves a speed-up of up to 37 compared to the original DPM code executed on a modern system. Furthermore, we could show that our CPU-based implementation on a modern workstation is between 1.25 and 1.95 faster than a well-known GPU implementation of the same simulation method on a NVIDIA Tesla C2050. Since CPUs work on several hundreds of GB RAM the typical GPU memory limitation does not apply for our implementation and high resolution clinical plans can be calculated.

Late-responding normal tissue cells benefit from high-precision radiotherapy with prolonged fraction delivery times via enhanced autophagy.

High-precision radiotherapy (HPR) has established its important role in the treatment of tumors due to its precise dose distribution. Given its more complicated delivery process, HPR commonly requires more fraction delivery time (FDT). However, it is unknown whether it has an identical response of prolonged FDT on different normal tissues. Our results showed that fractionated irradiation with prolonged FDTs (15, 36, and 50 minutes) enhanced cell surviving fractions for normal tissue cells compared with irradiation with an FDT of 2 minutes. However, the late-responding normal cell line HEI-OC1 was more responsive to prolonged FDTs and demonstrated higher surviving fractions and significantly decreased apoptosis and DNA damage compared to the acute-responding normal cell line HaCaT. Increased autophagy mediated via the ATM-AMPK pathway was observed in HEI-OC1 cells compared with HaCaT cells when irradiated with prolonged FDTs. Furthermore, treatment with the autophagy inhibitor 3-MA or ATM inhibitor KU55933 resulted in enhanced ROS accumulation and attenuation of the effect of prolonged FDT-mediated protection on irradiated HEI-OC1 cells. Our results indicated that late-responding normal tissue cells benefitted more from prolonged FDTs compared with acute-responding tissue cells, which was mainly attributed to enhanced cytoprotective autophagy mediated via the ATM/AMPK signaling pathway.

Reduction of Salmonella enterica serotype Poona and background microbiota on fresh-cut cantaloupe by electron beam irradiation

The efficacy of electron beam (e-beam) irradiation processing to reduce Salmonella enterica serotype Poona on surfaces of fresh-cut cantaloupe, and the impact of e-beam irradiation processing on the numbers of indigenous microorganisms were determined. Additionally, the D10-value for S. Poona reduction on the cut cantaloupe was also determined. Fresh-cut cantaloupe pieces, inoculated with S. Poona to 7.8log10CFU/g, were exposed to 0.0, 0.7, or 1.5kGy. Surviving S. Poona, lactic acid bacteria (LAB), and fungi (yeasts, molds) were periodically enumerated on appropriate media over 21days of storage at 5°C. Cantaloupe surface pH was measured for irradiated cantaloupe across the 21day storage period. To determine the D10-value of S. Poona, cantaloupe discs were inoculated and exposed to increasing radiation dosages between 0 and 1.06kGy; surviving pathogen cells were selectively enumerated. S. Poona was significantly reduced by irradiation; immediate reductions following exposure to 0.7 and 1.5kGy were 1.1 and 3.6log10CFU/g, respectively. After 21days, S. Poona numbers were between 4.0 and 5.0log10CFU/g less than untreated samples at zero-time. Yeasts were not reduced significantly (p≥0.05) by e-beam irradiation and grew slowly but steadily during storage. Counts of LAB and molds were initially reduced with 1.5kGy (p<0.05) but then LAB recovered grew to high numbers, whereas molds slowly declined for irradiated and control samples. Cantaloupe pH declined during storage, with the greatest decrease in untreated control cantaloupe (p<0.05). The D10-value for S. Poona was determined to be 0.211kGy, and this difference from the reductions observed in the cut cantaloupe studies may be due to the more precise dose distribution obtained in the thin and flat cantaloupe pieces used for the D10-value experiments. The effect of e-beam irradiation at the same doses used in this study was determined in previous studies to have no negative effect in the quality of the cut cantaloupe. Therefore, incorporation of low dosage ionizing irradiation and consistent application of irradiation processing can significantly improve the microbiological safety of fresh-cut cantaloupe.

Exquisite CCD camera design for an optical computed tomography scanner

The OCT (Optical Computed Tomography) in order to obtain the precise dose distribution relies on high accuracy (low noise) and high spatial resolution of the image capture system. Therefore, this study proposes a high-resolution CCD-based camera systems design. Part of the low noise, we propose a variety of CCD signal processing to eliminate noise, such as bias clamp, random noise and pixel response non-uniformity. According to the experiment results, our CCD signal processing algorithm can guarantee low noise output. At exposure time of 150ms, the coefficient of variation of the pixel is reduced from 12.37% to 0.51% by flat-field correction, in the same measurement standards, our system SNR (30.12dB) better than other brand CCD camera (25.31dB) and other brand CMOS camera (29.53dB). Part of the high spatial resolution, we propose high-performance camera design (optical lens, image sensor, image processing) to ensure high spatial resolution output. In MTF50 (Modulation Transfer Function 50%), our camera (1024×1024) get the 745LW/PH (Line Width/Picture Height), close to 73% of the limited resolution; another brand CCD camera (1024×768) of 358 LW/PH, about 46.6% of the limited resolution; another brand CMOS camera (3648×2736) of 1628 LW/PH, about 59.5% of the limited resolution. Therefore, our camera with a high precision and high spatial resolution design, it can to meet in OCT and increase accuracy of the dose distribution.

Dosimetry of dose distributions in radiotherapy of patients with surgical implants

Abstract The investigation was performed in order to evaluate the use of Gafchromic EBT films for measurements of dose distributions created during radiotherapy in tissues surrounding titanium or resorbable implants used for joining and consolidating facial bones. Inhomogeneous dose distributions at implant–tissue interfaces can be the reason of normal tissue complications observed in radiotherapy patients after surgery with implants. The dose measured at a depth of 2.5 cm on contact surfaces, proximal and distal to the beam source, between the titanium implant and the phantom material was 109% and 92% respectively of the reference dose measured in a homogeneous phantom. For the resorbable implants the doses measured on the proximal and the distal contact surfaces were 102% and 101% respectively of the reference dose. The resorbable implants affect the homogeneity of dose distribution at a significantly lesser degree than the titanium implants. Gafchromic EBT films allowed for precise dose distribution measurements at the contact surfaces between tissue equivalent materials and implants.

The potential of helical tomotherapy in the treatment of head and neck cancer.

A decade after its first introduction into the clinic, little is known about the clinical impact of helical tomotherapy (HT) on head and neck cancer (HNC) treatment. Therefore, we analyzed the basics of this technique and reviewed the literature regarding HT's potential benefit in HNC. The past two decades have been characterized by a huge technological evolution in photon beam radiotherapy (RT). In HNC, static beam intensity-modulated radiotherapy (IMRT) has shown superiority over three-dimensional conformal RT in terms of xerostomia and is considered the standard of care. However, the next-generation IMRT, the rotational IMRT, has been introduced into the clinic without any evidence of superiority over static beam IMRT other than being substantially faster. Of these rotational techniques, HT is the first system especially developed for IMRT in combination with image-guided RT. HT is particularly promising for the treatment of HNC because its sharp dose gradients maximally spare the many radiosensitive organs at risk nearby. In addition, HT's integrated computed tomography scan assures a very precise dose administration and allows for some adaptive RT. Because HT is specifically developed for IMRT in combination with (integrated) image-guidance, it allows for precise dose distribution ("dose painting"), patient setup, and dose delivery. As such, it is an excellent tool for difficult HNC irradiation. The literature on the clinical results of HT in HNC all show excellent short-term (≤2 years) results with acceptable toxicity profiles. However, properly designed trials are still warranted to further substantiate these results.

La radiothérapie assistée par l’imagerie nucléaire : les volumes cibles

Nuclear imaging plays a key role in the management of malignant tumours by radiation oncologists. Focusing on lung cancers, this review emphasizes how FDG PET/CT is determinant for initial staging and indication of curative-intent radiotherapy. The treatment machines are nowadays able to achieve precise dose distributions, taking into account the functional characteristics of malignant tumours and their evolution during radiotherapy. Major technical difficulties still have to be overcome, not the least being the inescapable necessity to register all images on a planning CT scan. The clinical validation of these innovative approaches and their diffusion in daily routine require a very close collaboration between both specialties, based on a common language and understanding of radiotherapy target volumes.

Monte Carlo-based dose reconstruction in a rat model for scattered ionizing radiation investigations

Purpose: In radiation biology, rats are often irradiated, but the precise dose distributions are often lacking, particularly in areas that receive scatter radiation. We used a non-dedicated set of resources to calculate detailed dose distributions, including doses to peripheral organs well outside of the primary field, in common rat exposure settings.Materials and methods: We conducted a detailed dose reconstruction in a rat through an analog to the conventional human treatment planning process. The process consisted of: (i) Characterizing source properties of an X-ray irradiator system, (ii) acquiring a computed tomography (CT) scan of a rat model, and (iii) using a Monte Carlo (MC) dose calculation engine to generate the dose distribution within the rat model. We considered cranial and liver irradiation scenarios where the rest of the body was protected by a lead shield. Organs of interest were the brain, liver and gonads. The study also included paired scenarios where the dose to adjacent, shielded rats was determined as a potential control for analysis of bystander effects.Results: We established the precise doses and dose distributions delivered to the peripheral organs in single and paired rats. Mean doses to non-targeted organs in irradiated rats ranged from 0.03–0.1% of the reference platform dose. Mean doses to the adjacent rat peripheral organs were consistent to within 10% those of the directly irradiated rat.Conclusions: This work provided details of dose distributions in rat models under common irradiation conditions and established an effective scenario for delivering only scattered radiation consistent with that in a directly irradiated rat.

Optimization Of Robust Beam Angles To Patient Setup Errors For Head and Neck Cancer In Hadron Particle Therapy

In hadron particle therapy, precise depth dose distribution around the target tumor can be produced by using a compensator in a depth dose shaping system, which is produced based on lateral and distal distributions in electron density of each patient's computed tomography image. However, the precise dose distribution fitted with a tumor shape could be fragile for slight misalignment between the compensator and the tumor, especially if the abrupt lateral distribution of the electron density projection (e.g.

Beam stability improvement of the HIMAC synchrotron using a feed-forward system for magnet power supplies

In order to realize a precise dose distribution in heavy-ion cancer therapy, high beam stability is required for the accelerator complex. Owing to load fluctuation caused by the upper ring, which is one of the two rings in HIMAC, current dips of ≈5–10 Hz were observed in the power supply for the bending/quadrupole magnet of the other lower ring. The parameters of the beam stability, such as the spill variation, the beam position, and the size, were adversely affected by the current dips. In order to suppress these current dips, we developed a new feed-forward system in the magnet power supply. We verified the performance of the feed-forward system by measuring the suppression of the current dips. We also performed beam experiments to measure the variation of the horizontal tune and the structure of the beam spill, which is slowly extracted by the resonance method. The experimental result showed that the current dips were successfully reduced by the system to Δ I/ I ∼ 10 −6. It was also confirmed that the horizontal tune and the spill structure could be stabilized by the current dip suppression.

DOSIMETRIC IMPACT OF DAILY SETUP VARIATIONS DURING TREATMENT OF CANINE NASAL TUMORS USING INTENSITY‐MODULATED RADIATION THERAPY

Intensity-modulated radiation therapy (IMRT) can be employed to yield precise dose distributions that tightly conform to targets and reduce high doses to normal structures by generating steep dose gradients. Because of these sharp gradients, daily setup variations may have an adverse effect on clinical outcome such that an adjacent normal structure may be overdosed and/or the target may be underdosed. This study provides a detailed analysis of the impact of daily setup variations on optimized IMRT canine nasal tumor treatment plans when variations are not accounted for due to the lack of image guidance. Setup histories of ten patients with nasal tumors previously treated using helical tomotherapy were replanned retrospectively to study the impact of daily setup variations on IMRT dose distributions. Daily setup shifts were applied to IMRT plans on a fraction-by-fraction basis. Using mattress immobilization and laser alignment, mean setup error magnitude in any single dimension was at least 2.5 mm (0-10.0 mm). With inclusions of all three translational coordinates, mean composite offset vector was 5.9 +/- 3.3 mm. Due to variations, a loss of equivalent uniform dose for target volumes of up to 5.6% was noted which corresponded to a potential loss in tumor control probability of 39.5%. Overdosing of eyes and brain was noted by increases in mean normalized total dose and highest normalized dose given to 2% of the volume. Findings suggest that successful implementation of canine nasal IMRT requires daily image guidance to ensure accurate delivery of precise IMRT distributions when non-rigid immobilization techniques are utilized. Unrecognized geographical misses may result in tumor recurrence and/or radiation toxicities to the eyes and brain.

SU‐FF‐T‐411: Boundary Study of Bragg Peak Shift and Bragg Peak Degradation in Proton Dose Calculation

Purpose: The purpose of this work is to study the Bragg peak shifts and degradation caused by density and boundary changes in proton beam dose calculation Method and Material: Proton beam delivery provides promising dose characteristics as radiation dose can conform tightly to tumor while sparing surrounding healthy tissues. Proton particles deposit energy in a narrow range around the Bragg peak and as such the dose calculation is more challenging for that the Bragg peak is sensitive to tissue density, tissue composition and organ boundaries along the proton track path. We simulated a few scenarios to study the proton Bragg peak shift due to density and Bragg peak degradation due to change and boundary changes. The calculation of the three dimension dose matrix was performed using a 2 × 2 × 1 mm3 voxels in the depth peak dose range in water phantom after some rough simulation for the dose peak estimation. Results: Bragg peak shift at the iso‐center slice were found to follow a linear relationship with the density of heterogeneity insert based on our simulations with density ranging [0.4 2.0] g/cm∧3 which we studied. Bragg peak degradation and proton dose changed significantly due to low density and small beams size. Proton dose degraded when high energy proton beam irradiated to low density material. Proton dose degraded also when small beam with beam radius at several mm range. Conclusion: Proton dose calculation depends on many factors as Bragg peak is sensitive to tissue density and composition. Besides that, there exist several scenarios causing Bragg peak shift due to density change, causing Bragg peak degradation due to low density and small proton beam. The Monte Carlo simulation is a very accurate solution to provide precise dose distribution in inhomogeneous structures by simulating transport and energy deposition.

SU‐GG‐I‐118: A Novel Method of MRI Correlate with Electron Density Information for Radiotherapy Treatment Planning

Purpose: MRI (Magnetic Resonance Image) provided excellent soft tissue resolution and functional images for treatment target delineation. For MRI based treatment planning, electron density of the organ or structures of interest were manual assigned. In this study, we developed a new method to correlate MRI images with electron density information for radiotherapy treatment planning dose calculation. Method and Materials: We implement a neural‐network structure with two MRI sequences inputs and the output end correlates with CT images that belong to the same patient to be a training target. The iterative training process was designed to keep the best fit parameters of neural‐network in order to enlarge the similarity between Neural‐Network outputs and CT images. After the training process, MR images can be converted into a Homemade CT like image (HCT) for radiotherapy treatment plan dose calculation. The real CT □CT with union density and HCT were compared and analyzed with their characteristics for radiotherapy dose calculation. Results: Our HCT provides more precise, convenient and heterogeneous dose distribution than manual assigned or union density for MRI‐only treatment plans. The Monitor Unit calculated from prescribe dose was within ± 3% when compared with CT based treatment planning. Conclusion: A novel method of MRI correlates with electron density information for Treatment Planning dose calculation purpose was purposed. The converting algorithm was created by a nonlinear method, and searching for solutions using numerical approaching.

WE-A-350-01: IMRT in the Treatment of Gynecological Malignancies

IMRT presented a major advancement in the radiotherapeutic management of gynecologic cancer. It has been shown that IMRT has reduced the incidence and severity of radiation‐related toxicity in this disease site. However, the precise dose distribution produced by IMRT is less forgiving and great care is required in order to achieve the intended results. An adequate understanding of the entire process ‐from proper patient selection to positioning/immobilization to treatment planning and delivery‐ is essential. The primary goal of this presentation is to provide a practical overview of IMRT for gynecological malignancies. A discussion of the steps in the GYN IMRT process will include patient selection, immobilization, simulation, structure delineation, planning strategies and parameters, PTV and critical organdose objectives, plan evaluation, QA, and potential delivery issues. Guidelines and practical examples of the GYN IMRT process will be presented. At our institution, gynecologic patients are treated in the supine position with customized immobilization devices (alpha cradles), which are indexed to the treatment table. Oral, intravenous and rectal contrasts are used to aid in the delineation of the CTV and surrounding normal tissues. The CTV consists of the contrast enhanced vessels to identify common, external, and internal nodal regions along with the upper half of the vagina, parametrial tissues, presacral region and uterus (if present). A PTV is added to the CTV based on measured set‐up uncertainties and organ motion data. Several recent studies have addressed these issues and will be reviewed here. For treatment planning, 9 equally spaced co‐planar beams are generally used. Input parameters derived for treatment planning were developed over time, and their evolution will be discussed. Treatment plans are evaluated primarily based on the PTV coverage and normal tissue DVHs. Evaluation of small bowel is based on a normal tissue complication probability (NTCP) curve for the incidence of acute gastrointestinal toxicity of IMRT patients treated in our clinic. From this analysis, acceptable plans are those in which <200 cc of the small bowel region receives 45 Gy (prescription dose). We have also recently defined bone marrow constraints for patients receiving concomitant chemotherapy, and these will be discussed. Finally, current research and future directions for GYN IMRT will be introduced. For instance, image‐guided radiotherapy (IGRT) has received increasing attention as a component of IMRT planning and delivery. We will discuss the potential role of novel image‐guidance techniques in GYN IMRT. In addition, we will present IGRT/IMRT techniques that are currently being considered to provide an alternative or supplement to brachytherapy. Clinical examples of each of these approaches will be presented. Educational Objectives: 1. To provide an educational review of the practical aspects of IMRT planning for gynecologic malignancies. 2. To understand and review the criteria for IMRT plan evaluation in gynecologic patients. 3. To review the planning methods used to achieve plan acceptance criteria. 4. To discuss the role of IGRT technologies in this disease site.

Compact carbon-therapy facility and next-generation irradiation scheme

Heavy-ion therapy is one of the important methods for the cancer treatment. More than 3400 patients were treated between 1994 and 2007 at Heavy Ion Medical Accelerator in Chiba (HIMAC). For the promotion of carbon-ion therapy, a compact carbon-therapy facility was developed. The size of the new facility is three times smaller, while the accelerator can supply the beams similar to those used at HIMAC. The new irradiation system was developed in order to obtain a precise dose distribution for moving and/or deforming organs.

More optimal dose distributions for moving lung tumours: A planning study

Background and purposeTarget volumes for moving lung tumours encompass the full range of respiratory motion, increasing the risk of lung complications. Intensity modulated radiotherapy (IMRT) allows for more precise dose distributions. Distributions corresponding to the probability density function (PDF) of tumour motion may better spare lung yet deliver adequate target dose. The planning study purpose is to compare and evaluate different dose distributions on a moving lung tumour: (A) conformal RT (CRT) encompassing the full range of tumour motion, (B) CRT encompassing the modal tumour position only, and (C) an IMRT technique where the dose delivered corresponds to the tumour PDF. Materials and methodsA 5cm diameter spherical target within a rectangular lung equivalent phantom was treated using a parallel-opposed pair technique with a 1.5cm margin around the tumour (in the beam's eye view). Asymmetrical sinusoidal (superior–inferior) target movement (peak-trough=3cm) was simulated for different dose distributions (prescription dose=60Gy). Equivalent uniform dose (EUD) for the tumour and normal tissue complication probabilities (NTCPs) for radiation pneumonitis were evaluated. ResultsThe EUDs were 60.0, 48.5, and 57.9Gy while the NTCPs were 5, 1, and 3% for cases A, B, and C, respectively (assuming survival fraction, SF2Gy=0.5). ConclusionsSince these results rely on unvalidated radiobiologic models, they must be interpreted cautiously. However, more optimized dose distributions for moving lung targets appear feasible and can reduce lung complications with only a negligible impact on the expected EUD and, thus, deserve further study.

Verification of the computational dosimetry system in JAERI (JCDS) for boron neutron capture therapy

Clinical trials for boron neutron capture therapy (BNCT) by using the medical irradiation facility installed in Japan Research Reactor No. 4 (JRR-4) at Japan Atomic Energy Research Institute (JAERI) have been performed since 1999. To carry out the BNCT procedure based on proper treatment planning and its precise implementation, the JAERI computational dosimetry system (JCDS) which is applicable to dose planning has been developed in JAERI. The aim of this study was to verify the performance of JCDS. The experimental data with a cylindrical water phantom were compared with the calculation results using JCDS. Data of measurements obtained from IOBNCT cases at JRR-4 were also compared with retrospective evaluation data with JCDS. In comparison with phantom experiments, the calculations and the measurements for thermal neutron flux and gamma-ray dose were in a good agreement, except at the surface of the phantom. Against the measurements of clinical cases, the discrepancy of JCDS's calculations was approximately 10%. These basic and clinical verifications demonstrated that JCDS has enough performance for the BNCT dosimetry. Further investigations are recommended for precise dose distribution and faster calculation environment.

Spot Scanning Using Radioactive 11C Beams for Heavy-Ion Radiotherapy

A scheme for spot scanning using 11C beams has been developed in order to form and verify a three-dimensionally conformal irradiation field for cancer radiotherapy. By selecting the momentum spread of a 11C beam, we could considerably decrease the distal falloff of the irradiation field, thus conserving the beam quality. To estimate and optimize the dose distribution in the irradiation field, it is essential to evaluate the precise dose distribution of spot beams. The coupling of the lateral dose and depth-dose distributions originating from a wide momentum spread should be taken into account to calculate the dose distribution of 11C beams. The reconstructed dose distribution of the irradiation field was in good agreement with the experimental results, i.e., within ±0.2%. An irradiation field of 35×35×43 mm3 was optimized and spot scanning using 11C beams was carried out. The flatness was within ±2.3% with an error of 1% in the detector resolution.