Jeonghoon Park

Proton beam therapy reduces the incidence of acute haematological and gastrointestinal toxicities associated with craniospinal irradiation in pediatric brain tumors.

Abstract Background. The benefits of proton beam craniospinal irradiation (PrBCSI) in children have been extensively reported in dosimetric studies. However, there is limited clinical evidence supporting the use of PrBCSI. We compared the acute toxicity of PrBCSI relative to that of conventional photon beam CSI (PhBCSI) in children with brain tumours. Material and methods. We prospectively evaluated the haematological and gastrointestinal toxicities in 30 patients who underwent PrBCSI between April 2008 and December 2012. As a reference group, we retrospectively evaluated the medical records of 13 patients who underwent PhBCSI between April 2003 and April 2012. The median follow-up time from starting CSI was 22 months (range 2–118 months). The mean irradiation dose was 32.1 Gy (range 23.4–39.6 Gy) and 29.4 CGE (cobalt grey equivalents; range 19.8–39.6), in the PrBCSI and PhBCSI groups, respectively (p = 0.236). Results. There was no craniospinal fluid space relapse after curative therapy in either group of patients. Thrombocytopenia was less severe in the PrBCSI group than in the PhBCSI group (p = 0.012). The recovery rates of leukocyte and platelet counts measured one month after treatment were significantly greater in the PrBCSI group than in the PhBCSI group (p = 0.003 and p = 0.010, respectively). Diarrhoea was reported by 23% of patients in the PhBCSI group versus none in the PrBCSI group (p = 0.023). Conclusions. The incidence rates of thrombocytopenia and diarrhoea were lower in the PrBCSI group than in the PhBCSI group. One month after completing treatment, the recovery from leukopenia and thrombocytopenia was better in patients treated with PrBCSI than in those treated with PhBCSI.

Understanding the Treatment Strategies of Intracranial Germ Cell Tumors: Focusing on Radiotherapy

Intracranial germ cell tumors (ICGCT) occur in 2-11% of children with brain tumors between 0-19 years of age. For treatment of germinoma, relatively low radiation doses with or without chemotherapy show excellent 10 year survival rate of 80-100%. Past studies showed that neoadjuvant chemotherapy combined with focal radiotherapy resulted in unacceptably high rates of periventricular tumor recurrence. The use of generous radiation volume which covers the whole ventricular space with later boost treatment to primary site is considered as standard treatment of intracranial germinomas. For non-germinomatous germ cell tumors (NGGCT), 10-year overall survival rate is still much inferior than that of intracranial germinoma despite intensive chemotherapy and high-dose radiotherapy. Craniospinal radiotherapy combined with cisplatin-based chemotherapy provides the best treatment outcome for NGGCT; 60-70% of overall survival rate. There is a debate on the surgical role whether surgery can contribute to improved treatment outcome of NGGCT when added to combined chemoradiotherapy. Because higher dose of radiotherapy is required for treatment of NGGCT than for germinoma, it is tested whether whole ventricular irradiation can replace craniospinal irradiation in intermediate risk group of NGGCT to minimize radiation-related late toxicity in the recent studies. To minimize the treatment-related neural deficit and late sequelae while maintaining long-term survival rate of ICGCT patients, optimized administration of chemotherapy and radiotherapy should be selected. Use of technically upgraded radiotherapy modalities such as intensity-modulated radiotherapy or proton beam therapy is expected to bring an improved neurocognitive outcome with longitudinal assessment of the patients.

Development of a novel proton dosimetry system using an array of fiber-optic Cerenkov radiation sensors.

This study describes the development and evaluation of a new dosimetric system for proton therapy using an array of fiber-optic Cerenkov radiation sensors (AFCRS). The AFCRS was superior to a conventional, multi-layer ion chamber (MLIC) system in real-time data acquisition and cost effectiveness.

A comparison of the quality assurance of four dosimetric tools for intensity modulated radiation therapy

Abstract Background. This study was designed to compare the quality assurance (QA) results of four dosimetric tools used for intensity modulated radiation therapy (IMRT) and to suggest universal criteria for the passing rate in QA, irrespective of the dosimetric tool used. Materials and methods. Thirty fields of IMRT plans from five patients were selected, followed by irradiation onto radiochromic film, a diode array (Mapcheck), an ion chamber array (MatriXX) and an electronic portal imaging device (EPID) for patient-specific QA. The measured doses from the four dosimetric tools were compared with the dose calculated by the treatment planning system. The passing rates of the four dosimetric tools were calculated using the gamma index method, using as criteria a dose difference of 3% and a distance-to-agreement of 3 mm. Results. The QA results based on Mapcheck, MatriXX and EPID showed good agreement, with average passing rates of 99.61%, 99.04% and 99.29%, respectively. However, the average passing rate based on film measurement was significantly lower, 95.88%. The average uncertainty (1 standard deviation) of passing rates for 6 intensity modulated fields was around 0.31 for film measurement, larger than those of the other three dosimetric tools. Conclusions. QA results and consistencies depend on the choice of dosimetric tool. Universal passing rates should depend on the normalization or inter-comparisons of dosimetric tools if more than one dosimetric tool is used for patient specific QA.

Verification of Dose Profiles Generated by the Convolution Algorithm of the Gamma Knife® Radiosurgery Planning System

Purpose A convolution algorithm that takes into account electron‐density inhomogeneity was recently introduced to calculate dose distributions for the Gamma Knife (GK) Perfexion™ treatment planning program. The accuracies of the dose distributions computed using the convolution method were assessed using an anthropomorphic phantom and film dosimetry. Methods Absorbed‐dose distributions inside a phantom (CIRS Radiosurgery Head Phantom, Model 605) were calculated using the convolution method of the GK treatment‐planning software (Leksell Gamma Plan® version 10.1; LGP) for various combinations of collimator size, location, direction of calculation plane, and number of shots. Computed tomography (CT) images of the phantom and a data set of CT number versus electron density were provided to the LGP. Calculated distributions were exported as digital‐image communications in medicine—radiation therapy (DICOM‐RT) files. Three types of radiochromic film (GafChromic® MD‐V2‐55, MD‐V3, and EBT2) were irradiated inside the phantom using GK Perfexion™ Scanned images of the measured films were processed following standard radiochromic film‐handling procedures. For a two‐dimensional quantitative evaluation, gamma index pass rates (GIPRs) and normalized agreement‐test indices (NATIs) were obtained. Image handling and index calculations were performed using a commercial software package (DoseLab Pro version 6.80). Results The film‐dose calibration data were well fitted with third‐order polynomials (R2 ≥ 0.9993). The mean GIPR and NATI of the 93 analyzed films were 99.3 ± 1.1% and 0.8 ± 1.3, respectively, using 3%/1.0 mm criteria. The calculated maximum doses were 4.3 ± 1.7% higher than the measured values for the 4 mm single shots and 1.8 ± 0.7% greater than those for the 8 mm single shots, whereas differences of only 0.3 ± 0.9% were observed for the 16 mm single shots. The accuracy of the calculated distribution was not statistically related to the collimator size, number of shots, or centrality of location (P > 0.05, independent‐sample t‐test). The plans in the axial planes exhibited poorer agreement with the measured distributions than the plans in the coronal or sagittal planes; however, their GIPR values (≥ 96.9%) were clinically acceptable. The plans for an arbitrary virtual target of volume 1.6 cm3 at an axial plane close to the top of the phantom showed the worst agreement and the greatest fluctuation (GIPR = 96.9 ± 1.2%, NATI = 3.9 ± 1.7). Conclusions The measured accuracies of the dose distributions calculated by the convolution algorithm of the LGP were within the clinically acceptable range (GIPR ≥ 96.9%) for various configurations of collimator size, location, direction of calculation plane, and number of shots. Due to the intrinsic asymmetry in the dose distribution along the z‐axis, the treatment plan should also be verified in coronal or sagittal plane.

Two-dimensional in vivo rectal dosimetry using an endorectal balloon with unfoldable radiochromic film during prostate cancer radiotherapy

BACKGROUND AND PURPOSE The present study aims to investigate the feasibility of two-dimensional (2D) in vivo rectal dosimetry using an endorectal balloon for the radiotherapy of prostate cancer. MATERIALS AND METHODS The endorectal balloon was equipped with an unfoldable radiochromic film. The film was unrolled as the balloon was inflated, and rolled as it was deflated. Its mechanical and imaging properties were tested, and the dosimetric effectiveness was evaluated in clinical photon and proton beams. RESULTS The size of the endorectal balloon including the film was linearly proportional to the volume of water filled in the balloon, and its position could be identified by X-ray radiography. The loss of dose information due to film cutting was within ±1mm from the cutting line. Applying linear interpolation on cut film, the gamma passing rate was more than 95% for 2%/2mm criteria. The measured dose profiles agreed with the plan within 3% and 4% for the photon and proton beams, respectively. A dose-volume histogram of the anterior rectal wall could be obtained from the measured dose distribution in the balloon, which also agreed well with the plan. CONCLUSIONS 2D in vivo rectal dosimetry is feasible using the endorectal balloon with a radiochromic film in the radiotherapy of prostate cancer.

The volumetric change and dose-response relationship following hypofractionated proton therapy for chordomas

Chordomas are rare, slow-growing tumors that arise from the remnant of the primitive notochord. They are characterized by a locally aggressive growth pattern and high recurrence rates. The most common site is the sacrococcygeal area (50%), followed by the skull base (35%). The remaining 15% of cases occur in the midline along the path of the notochord, and primarily involve the cervical vertebrae [1]. The management of chordomas is challenging, because they lie in the vicinity of critical structures, such as the optic pathway/brainstem/spinal cord for skull base and cervical vertebral tumors, and the small intestine/rectum/spinal nerves for sacrococcygeal tumors. These anatomic structures often limit surgical access and resectability, as well as the delivery of high radiation doses. a dose-response relationship has been reported for chordomas: 80% of tumors were controlled in patients treated with  80 cobalt gray equivalents (CGE  proton dose in Gy  1.1), whereas only 20% were controlled in patients treated with 40–60 CGE [2]. Proton therapy has been used to precisely deliver radiation to the target, sparing the normal critical structures [3–5]. The optimal dose/fractionation is, however, not well defined. In this study, we prospectively evaluated volumetric tumor response following hypofractionated proton therapy (PT) and tried to determine the optimal dose to achieve local control with a literature review of patients with chordomas.

Proton radiography and computed tomography with dynamic water range shifter

We introduce a novel dynamic water range shifter (DWRS) that enables range shifting of a mono-energetic proton beam for the purpose of obtaining a water equivalent path length (WEPL). A scintillation screen and a charge-coupled device (CCD) camera were assembled with a mirror for a detecting system. We acquired two sets of proton radiographs with and without the scanned object, and calculated 2D distribution of the WEPL. We first optimized measurement conditions, i.e., the sampling interval and the nearest sampling point from the surface. Then we evaluated the performance of the proton radiography system by use of the step phantoms and a patient-specific range compensator. The step phantom measurement was designed to evaluate WEPL accuracy and standard deviation, and the patient-specific compensator was utilized to evaluate image quality dependency on the shifting motions of the DWRS. Based on the optimization and evaluation in the radiographic setting, a cylindrical phantom having multiple insert holes was used to obtain proton CT and the image contrasts of the holes were evaluated. This study successfully demonstrates the feasibility of using the DWRS for proton radiography and CT.

Clinical Outcomes of Proton Beam Therapy for Choroidal Melanoma at a Single Institute in Korea

Purpose This study retrospectively evaluated the clinical outcomes and complications of proton beam therapy (PBT) in a single institution in Korea and quantitatively analyzed the change in tumor volume after PBT using magnetic resonance imaging (MRI). Materials and Methods Twenty-four treatment-naïve patients who underwent PBT for choroidal melanoma between 2009 and 2015 were reviewed. Dose fractionation was 60-70 cobalt gray equivalents over 5 fractions. Orbital MRIs were taken at baseline and 3, 6, and 12 months after PBT and annually thereafter. The tumor volume was reconstructed and evaluated by stacking the tumor boundary in each thin-sliced axial T1-weighted image using MIM software. Results The median follow-up duration was 36.5 months (range, 9 to 82 months). One patient had suspicious local progression and two patients had distant metastasis. The 3-year local progression-free survival, distant metastasis-free survival, and overall survival rates were 95.8%, 95.8%, and 100%,respectively. Five Common Terminology Criteria for Adverse Event ver. 4.03 grade 3-4 toxicities were observed in four patients (16.7%), including one with neovascular glaucoma. The mean tumor volume at the baseline MRI was 0.565±0.084 mL (range, 0.074 to 1.610 mL), and the ratios of the mean volume at 3, 6, and 12 months to that at baseline were 81.8%, 67.3%, and 60.4%, respectively. Conclusion The local controlrate and complication profile after PBT in patientswith choroidal melanoma in Korea were comparable with those reported in a previous PBT series. The change in tumor volume after PBT exhibited a gradual regression pattern on MRI.