Kazuhiko Tsuchiya

Physical aspects of a real-time tumor-tracking system for gated radiotherapy

PURPOSE To reduce uncertainty due to setup error and organ motion during radiotherapy of tumors in or near the lung, by means of real-time tumor tracking and gating of a linear accelerator. METHODS AND MATERIALS The real-time tumor-tracking system consists of four sets of diagnostic X-ray television systems (two of which offer an unobstructed view of the patient at any time), an image processor unit, a gating control unit, and an image display unit. The system recognizes the position of a 2.0-mm gold marker in the human body 30 times per second using two X-ray television systems. The marker is inserted in or near the tumor using image guided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within a given tolerance from its planned coordinates relative to the isocenter. The accuracy of the system and the additional dose due to the diagnostic X-ray were examined in a phantom, and the geometric performance of the system was evaluated in 4 patients. RESULTS The phantom experiment demonstrated that the geometric accuracy of the tumor-tracking system is better than 1.5 mm for moving targets up to a speed of 40 mm/s. The dose due to the diagnostic X-ray monitoring ranged from 0.01% to 1% of the target dose for a 2.0-Gy irradiation of a chest phantom. In 4 patients with lung cancer, the range of the coordinates of the tumor marker during irradiation was 2.5-5.3 mm, which would have been 9.6-38.4 mm without tracking. CONCLUSION We successfully implemented and applied a tumor-tracking and gating system. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic X-ray exposure.

Registration accuracy and possible migration of internal fiducial gold marker implanted in prostate and liver treated with real-time tumor-tracking radiation therapy (RTRT)

BACKGROUND AND PURPOSE We have developed a linear accelerator synchronized with a fluoroscopic real-time tumor-tracking system to reduce errors due to setup and organ motion. In the real-time tumor-tracking radiation therapy (RTRT) system, the accuracy of tumor tracking depends on the registration of the markers coordinates. The registration accuracy and possible migration of the internal fiducial gold marker implanted into prostate and liver was investigated. MATERIALS AND METHODS Internal fiducial gold markers were implanted in 14 patients with prostate cancer and four patients with liver tumors. Computed tomography (CT) was carried out as a part of treatment planning in the 18 patients. A total of 72 follow-up CT scans were taken. We calculated the relative relationship between the coordinates of the center of mass (CM) of the organs and those of the marker. The discrepancy in the CM coordinates during a follow-up CT compared to those recorded during the planning CT was used to study possible marker migration. RESULTS The standard deviation (SD) of interobserver variations in the CM coordinates was within 2.0 and 0.4 mm for the organ and the marker, respectively, in seven observers. Assuming that organs do not shrink, grow, or rotate, the maximum SD of migration error in each direction was estimated to be less than 2.5 and 2.0 mm for liver and prostate, respectively. There was no correlation between the marker position and the time after implantation. CONCLUSION The degree of possible migration of the internal fiducial marker was within the limits of accuracy of the CT measurement. Most of the marker movement can be attributed to the measurement uncertainty, which also influences registration in actual treatment planning. Thus, even with the gold marker and RTRT system, a planning target volume margin should be used to account for registration uncertainty.

Three-dimensional movement of a liver tumor detected by high-speed magnetic resonance imaging

OBJECTIVE Three-dimensional (3D) movement of a spherical liver tumor during respiration was investigated with magnetic resonance imaging (MRI) using a high-speed sequence. METHODS A marker was placed on the surface of the patient as a reference of distance. Repetition time (TR) was 7.7 ms, echo time (TE) was 4.2 ms, flip angle was 20 degrees, section thickness was 8 mm, and a 256 x 128 matrix was used. The acquisition time was 1.0 s followed by an interval of 0.5 s. The 20 tumor contours extracted during 30 s were superimposed on sagittal and coronal MR images. RESULTS The maximum value of tumor edge location was 3.9 cm in the cranio-caudal direction, 2.3 cm in the ventro-dorsal direction, and 3.1 cm in the lateral direction. The mean length of tumor displacement observed was 2.1 cm in the cranio-caudal direction, 0.8 cm in the ventro-dorsal and 0.9 cm in the left-right direction, respectively. The locus of the center of the tumor contour in the sagittal cross section was inclined at 23 degrees and in the coronal cross section was inclined at 18 degrees to the cranio-caudal axis of body. CONCLUSION In conclusion, 3D movement of a spherical liver tumor was detected using rapid MRI sequential examinations. Magnetic resonance imaging has a potential to improve the accuracy of the planning target volume of a liver tumor.

Magnetic resonance imaging system for three-dimensional conformal radiotherapy and its impact on gross tumor volume delineation of central nervous system tumors.

PURPOSE We developed an MRI system for three-dimensional planning in radiotherapy. Its contribution on gross tumor volume (GTV) delineation of central nervous system (CNS) diseases was evaluated. METHODS AND MATERIALS The MRI system, with corrected distortion, was registered on computed tomography (CT) by means of fiducial/anatomic landmarks. In 41 consecutive patients with various CNS diseases, GTVs determined by MRI/CT registration (MR/CT-GTV) and CT alone (CT-GTV) were compared. Hard copies of diagnostic MRI were shown to doctors when CT-GTV was determined to simulate a conventional planning situation. Multi-observer volumetric analysis was conducted, assessing interobserver deviations among four radiation oncologists and intermethodological deviations between MR/CT-GTV and CT-GTV. RESULTS Overall, the mean of geometric distortion was significantly reduced from 1.08 mm to 0.3 mm by distortion correction (p < 0.0001). The contribution of the correction was apparent at >12.0 cm radius from the center of the magnetic field. Interobserver deviation was significantly reduced by MR/CT registration (p = 0.005). The improvement was significant for acoustic neurinoma (p = 0.038), astrocytomas (p = 0.043), and lesions at the cerebellum/brainstem (p = 0.008). The regression coefficient between MR/CT-GTV and CT-GTV was <0.9 for cerebellum/brainstem lesions, suggesting that MRI/CT-GTV was smaller than CT-GTV. CONCLUSIONS This system is feasible for three-dimensional planning and was shown to reduce interobserver deviations in GTV delineation for CNS diseases.

Randomized phase II trial of concomitant chemoradiotherapy using weekly carboplatin or daily low-dose cisplatin for squamous cell carcinoma of the head and neck

PURPOSEThis randomized, phase II study aimed to compare concomitant Chemoradiotherapy using weekly carboplatin or daily low-dose cisplatin as a treatment for squamous cell carcinoma of the head and neck. PATIENTS AND METHODSOne hundred nineteen patients with moderate-to advanced-stage disease were eligible for the study. Fifty-three patients had stage II disease, 28 had stage III, and the remaining 38 had stage IV disease. Primary tumor sites included the larynx (N = 63), oropharynx (N = 30), hypopharynx (N = 23), and oral cavity (N = 3). Each patient received either a weekly carboplatin dose (100 mg/m2) in one arm or daily cisplatin (4 mg/m2) in the other arm for the initial 4 weeks of radiotherapy. The radiotherapy dose of 65 Gy was given in 26 fractions over 45 days, dependent on a good tumor response at 40 Gy. Forty-nine (81.7%) of 60 patients treated with carboplatin and 41 (69.5%) of 59 patients treated with cisplatin received the full dose of radiotherapy. Surgical resection was optionally used for the remaining patients. RESULTSThe median follow-up time was 63 months. The local control rate at 5 years was 56.2% for the carboplatin-treated arm and 35.5% for the cisplatin-treated arm, respectively. The 5-year overall survival rate did not significantly differ between treatments: 71.4% for carboplatin and 66.0% for cisplatin. Hematologic toxicity was more frequent in the carboplatin-treated arm. No difference was observed in surgical complications or in radiation-related adverse effects. DISCUSSIONThese findings suggest that weekly carboplatin treatment is preferable to daily low-dose cisplatin. This could be because the total dose of cisplatin was too low to be effective.

Stereotactic body radiotherapy using gated radiotherapy with real-time tumor-tracking for stage I non-small cell lung cancer

BackgroundTo clarify the clinical outcomes of two dose schedule of stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC) using a real-time tumor-tracking radiation therapy (RTRT) system in single institution.MethodsUsing a superposition algorithm, we administered 48 Gy in 4 fractions at the isocenter in 2005–2006 and 40 Gy in 4 fractions to the 95% volume of PTV in 2007–2010 with a treatment period of 4 to 7 days. Target volume margins were fixed irrespective of the tumor amplitude.ResultsIn total, 109 patients (79 T1N0M0 and 30 T2N0M0). With a median follow-up period of 25 months (range, 4 to 72 months), the 5-year local control rate (LC) was 78% and the 5-year overall survival rate (OS) was 64%. Grade 2, 3, 4, and 5 radiation pneumonitis (RP) was experienced by 15 (13.8%), 3 (2.8%), 0, and 0 patients, respectively. The mean lung dose (MLD) and the volume of lung receiving 20 Gy (V20) were significantly higher in patients with RP Grade 2/3 than in those with RP Grade 0/1 (MLD p = 0.002, V20 p = 0.003). There was no correlation between larger maximum amplitude of marker movement and larger PTV (r = 0.137), MLD (r = 0.046), or V20 (r = 0.158).ConclusionsSBRT using the RTRT system achieved LC and OS comparable to other SBRT studies with very low incidence of RP, which was consistent with the small MLD and V20 irrespective of tumor amplitude. For stage I NSCLC, SBRT using RTRT was suggested to be reliable and effective, especially for patients with large amplitude of tumor movement.

Sonazoid-enhanced sonography for guiding radiofrequency ablation for hepatocellular carcinoma: better tumor visualization by Kupffer-phase imaging and vascular-phase imaging after reinjection

PurposeThe purpose of this study was to assess the usefulness of contrast harmonic sonography with a newly developed sonographic contrast agent as a means of guidance for percutaneous radiofrequency (RF) ablation of hepatocellular carcinoma (HCC).Materials and methodsA total of 52 consecutive HCC lesions in 42 patients with HCC who underwent percutaneous RF ablation were included in this study. Altogether, 40 lesions in 35 patients were untreated HCC, and 12 lesions in 7 patients were local tumor progression of an HCC that had already been treated by other methods. We investigated tumors by Kupffer-phase imaging and vascular-phase imaging after reinjection. We performed RF ablation guided by Sonazoid-enhanced sonography using Kupffer-phase imaging and vascular-phase imaging after reinjection.ResultsConventional sonography identified 30 (57%) of 52 HCCs, whereas Sonazoid-enhanced sonography detected 50 (96%) of 52 HCCs (P < 0.01, McNemar’s χ2 test). Complete ablation was achieved at a single session in 48 of 50 tumors.ConclusionSonazoid-enhanced sonography is a useful technique for guiding RF ablation of HCCs, even when treating local progression of a previously treated HCC.

Superselective intra-arterial cisplatin infusion and concomitant radiotherapy for maxillary sinus cancer

Background:The purpose of this study was to evaluate the efficacy of superselective cisplatin infusion with concomitant radiotherapy (RADPLAT) for previously untreated patients with the squamous cell carcinoma of maxillary sinus (SCC-MS).Methods:Between 1999 and 2010, 54 patients were given superselective intra-arterial infusions of cisplatin (100–120 mg m−2 per week) with simultaneous intra-venous infusions of thiosulfate to neutralise cisplatin toxicity and conventional radiotherapy (65–70 Gy).Results:One patient (1.9%) was diagnosed with T2, 14 (25.9%) with T3, 27 (50%) with T4a, and 12 (22.2%) with T4b disease. Lymph-node involvement was present in 12 patients (22.2%). During the median follow-up period of 6.4 years, the 5-year local progression-free and overall survival rates were 65.8 and 67.9% for all patients, respectively. No patient died as a result of treatment toxicity or experienced a cerebrovascular accident. Osteonecrosis (n=5), brain necrosis (n=1), and ocular/visual problems (n=14) were observed as late adverse reactions.Conclusion:We have shown excellent overall survival and local progression-free rate in SCC-MS patients treated by RADPLAT with acceptable rates of acute and late toxicity. A multi-institutional trial is needed to prove that this strategy is a feasible and effective approach for the treatment of SCC-MS.

[18F]fluoromisonidazole and a New PET System With Semiconductor Detectors and a Depth of Interaction System for Intensity Modulated Radiation Therapy for Nasopharyngeal Cancer

PURPOSE The impact of a new type of positron emission tomography (New PET) with semiconductor detectors using 18F-labeled fluoromisonidazole (FMISO)-guided intensity modulated radiation therapy (IMRT) was compared with a state-of-the-art PET/computed tomography (PET/CT) system in nasopharyngeal cancer (NPC) patients. METHODS AND MATERIALS Twenty-four patients with non-NPC malignant tumors (control group) and 16 patients with NPC were subjected to FMISO-PET. The threshold of the tumor-to-muscle (T/M) ratio in each PET scan was calculated. The hypoxic volume within the gross tumor volume (GTVh) was determined using each PET (NewPETGTVh and PET/CTGTVh, respectively). Dose escalation IMRT plans prescribing 84 Gy to each GTVh were carried out. RESULTS The threshold of the T/M ratio was 1.35 for New PET and 1.23 for PET/CT. The mean volume of NewPETGTVh was significantly smaller than that of PET/CTGTVh (1.5±1.6 cc vs 4.7±4.6 cc, respectively; P=.0020). The dose escalation IMRT plans using New PET were superior in dose distribution to those using PET/CT. Dose escalation was possible in all 10 New PET-guided plans but not in 1 PET/CT-guided plan, because the threshold dose to the brainstem was exceeded. CONCLUSIONS New PET was found to be useful for accurate dose escalation in FMISO-guided IMRT for patients with NPC.

Contrast‐enhanced sonography‐guided radiofrequency ablation for the local recurrence of previously treated hepatocellular carcinoma undetected by b‐mode sonography

The purpose of this study was to assess the usefulness of contrast‐enhanced sonography (CEUS) with Sonazoid to demonstrate local recurrence of hepatocellular carcinoma previously treated with radiofrequency ablation (RFA) and not seen on conventional sonography, prior to repeat RFA.