Robustness of patient positioning for interfractional error in carbon ion radiotherapy for stage I lung cancer: Bone matching versus tumor matching

Carbon range verification with 718 keV Compton imaging

Carbon ion radiotherapy is a sophisticated radiation treatment modality because of its superiority in achieving precise dosage distribution and high biological effectiveness. However, there exist beam range uncertainties that affect treatment efficiency. This problem can be resolved if the clinical beam could be monitored precisely in real-time, such as by imaging the prompt gamma emission from the target. In this study, we performed real-time detection and imaging of 718 keV prompt gamma emissions using a Si/CdTe Compton camera. We conducted experiments on graphite phantoms using clinical carbon ion beams of 290 MeV/u energy. Compton images were reconstructed using simple back-projection methods from the energy events of 718 keV prompt gamma emissions. The peak intensity position in reconstructed 718 keV prompt gamma images was few millimeters below the Bragg peak position. Moreover, the dual- and triple-energy window images for all positions of phantoms were not affected by scattered gammas, and their peak intensity positions were approximately similar to those observed in the reconstructed 718 keV prompt gamma images. In conclusion, the findings of the current study demonstrate the feasibility of using our Compton camera for real-time beam monitoring of carbon ion beams under clinical beam intensity.

Dosimetric Impact of Inter-Fraction Anatomical Changes in Carbon Ion Boost Treatment for High-Risk Prostate Cancer (AIRC IG 14300)

Rectum and bladder volumes play an important role in the dose distribution reproducibility in prostate cancer adenocarcinoma (PCa) radiotherapy, especially for particle therapy, where density variation can strongly affect the dose distribution. We investigated the reliability and reproducibility of our image-guided radiotherapy (IGRT) and treatment planning protocol for carbon ion radiotherapy (CIRT) within the phase II mixed beam study (AIRC IG 14300) for the treatment of high-risk PCa. In order to calculate the daily dose distribution, a set of synthetic computed tomography (sCT) images was generated from the cone beam computed tomography (CBCT) images acquired in each treatment session. Planning target volume (PTV) together with rectum and bladder volume variation was evaluated with sCT dose-volume histogram (DVH) metric deviations from the planning values. The correlations between the bladder and rectum volumes, and the corresponding DVH metrics, were also assessed. No significant difference in the bladder, rectum, and PTV median volumes between the planning computed tomography (pCT) and the sCT was found. In addition, no significant difference was assessed when comparing the average DVHs and median DVH metrics between pCT and sCT. Dose deviations determined by bladder and rectum filling variations demonstrated that dose distributions were reproducible in terms of both target coverage and organs at risk (OARs) sparing.

Robust Angle Selection in Particle Therapy

The popularity of particle radiotherapy has grown exponentially over recent years owing to the marked advantage of the depth–dose curve and its unique biological property. However, particle therapy is sensitive to changes in anatomical structure, and the dose distribution may deteriorate. In particle therapy, robust beam angle selection plays a crucial role in mitigating inter- and intrafractional variation, including daily patient setup uncertainties and tumor motion. With the development of a rotating gantry, angle optimization has gained increasing attention. Currently, several studies use the variation in the water equivalent thickness to quantify anatomical changes during treatment. This method seems helpful in determining better beam angles and improving the robustness of planning. Therefore, this review will discuss and summarize the robust beam angles at different tumor sites in particle radiotherapy.

Adaptive planning based on single beam optimization in passive scattering carbon ion radiotherapy for patients with pancreatic cancer

Background

Daily anatomical deviations may distort the dose distribution in carbon ion radiotherapy (CIRT), which may cause treatment failure. Therefore, this study aimed to perform re-planning to maintain the dose coverage in patients with pancreatic cancer with passive scattering CIRT.

Methods

Eight patients with pancreatic cancer and 95 daily computed tomography (CT) sets were examined. Two types of adaptive plans based on new range compensators (RCs) (AP-1) and initial RCs (AP-2) were generated. In AP-2, each beam was optimized by manually adjusting the range shifter thickness and spread-out Bragg peak size to make dose reduction by < 3% of the original plan. Doses of the original plan with bone matching (BM) and tumor matching (TM) were examined for comparison. We calculated the accumulated dose using the contour and intensity-based deformable image registration algorithm. The dosimetric differences in respect to the original plan were compared between methods.

Results

Using TM and BM, mean ± standard deviations of daily CTV V95 (%) difference from the original plan was − 5.1 ± 6.2 and − 8.8 ± 8.8, respectively, but 1.2 ± 3.4 in AP-1 and − 0.5 ± 2.1 in AP-2 (P < 0.001). AP-1 and AP-2 enabled to maintain a satisfactory accumulated dose in all patients. The dose difference was 1.2 ± 2.8, − 2,1 ± 1.7, − 7.1 ± 5.2, and − 16.5 ± 15.0 for AP-1, AP-2, TM, and BM, respectively. However, AP-2 caused a dose increase in the duodenum, especially in the left–right beam.

Conclusions

The possible dose deterioration should be considered when performing the BM, even TM. Re-planning based on single beam optimization in passive scattering CIRT seems an effective and safe method of ensuring the treatment robustness in pancreatic cancer. Further study is necessary to spare healthy tissues, especially the duodenum.

Robustness of daily dose for each beam angle and accumulated dose for inter-fractional anatomical changes in passive carbon-ion radiotherapy for pancreatic cancer: Bone matching versus tumor matching

PURPOSE

We aimed to assess the robustness of accumulated dose distributions for inter-fractional changes in passive carbon-ion radiotherapy for pancreatic cancer.

METHODS

Ninety-five daily CT image sets acquired after the treatment of eight patients with pancreatic cancer were used in this prospective study. Dose distributions with treatment beam fields were recalculated for bone matching (BM) and tumor matching (TM) positions on all daily CT images, the accumulated doses being calculated using deformable image registration methods. The prescribed dose was 55.2 Gy (relative biological effectiveness [RBE]) in 12 fractions. Dose volume parameters of V95 (%) for CTV and GTV, and D2cc (Gy(RBE)) for the stomach and duodenum were evaluated.

RESULTS

The medians (range) of CTV V95 (%) were 91.9 (86.1-100.0), 80.5 (56.1-90.6), and 86.4 (72.5-96.5) for the Plan, accumulated with BM and TM, respectively; GTV values (%) were 98.0 (85.7-100.0), 93.3 (65.7-99.9), and 96.2 (84.8-100.0), respectively. There were significant differences between all combinations apart from the Plan and TM for both targets. The values of stomach D2cc (Gy(RBE)) were 36.0 (16.9-43.4), 36.7 (17.9-45.0), and 35.2 (16.8-43.5), respectively; duodenum values (Gy(RBE)) were 25.2 (21.3-40.3), 30.1 (23.3-48.6), and 28.3 (20.4-50.6), respectively. There was a significant difference between the Plan and BM for duodenum only.

CONCLUSIONS

TM is recommended over BM because it can achieve higher target dose coverage than BM. Nevertheless, it is not enough in some cases. Further technical improvements are necessary to improve the target dose coverage.

Impact of Inter-fractional Anatomical Changes on Dose Distributions in Passive Carbon-Ion Radiotherapy for Prostate Cancer: Comparison of Vertical and Horizontal Fields

Purpose: We quantified the inter-fractional changes associated with passive carbon-ion radiotherapy using vertical and horizontal beam fields for prostate cancer.

Methods: In total, 118 treatment-room computed tomography (TRCT) image sets were acquired from 10 patients. Vertical (anterior–posterior) and horizontal (left–right) fields were generated on the planning target volume identified by treatment planning CT. The dose distribution for each field was recalculated on each TRCT image set at the bone-matching position and evaluated using the dose–volume parameters for the prostate and rectum V95 values. To confirm adequate margins, we generated vertical and horizontal fields with 0-, 2-, 4-, and 6-mm isotropic margins from the prostate and recalculated the dose distributions on all TRCT image sets. Sigmoid functions were fitted to a plot of acceptable ratios (that is, when prostate V95 > 98%) vs. the isotropic margin size to identify the margin at which this ratio was achieved in 95% of patients with a vertical or horizontal field.

Results: The prostate V95 values (mean ± standard deviation) were 99.89 ± 0.62% and 99.99 ± 0.00% with vertical and horizontal fields, respectively; this difference was not statistically significant (p = 0.067). The rectum V95 values were 1.93 ± 1.25 and 1.88 ± 0.96 ml with vertical and horizontal fields, respectively; the difference was not statistically significant (p = 0.432). The estimated adequate margins were 2.2 and 3.0 mm for vertical and horizontal fields, respectively.

Conclusions: Although there is no significant difference, horizontal fields offer higher reproducibility for prostate dosing than vertical fields in our clinical setting, and 3.0 mm was found to be an adequate margin for inter-fractional changes.

Use of a Si/CdTe Compton Camera for In vivo Real-Time Monitoring of Annihilation Gamma Rays Generated by Carbon Ion Beam Irradiation

The application of annihilation gamma-ray monitoring to the adaptive therapy of carbon ion radiotherapy (C-ion RT) requires identification of the peak intensity position and confirmation of activated elements with annihilation gamma-rays generated at the C-ion-irradiated site from those transported to unirradiated sites. Real-time monitoring of C-ion-induced annihilation gamma-rays was implemented using a Compton camera in a mouse model. An adult C57BL/6 mouse was anesthetized, and C-ion beams were directed into the abdomen at 1 × 10⁹ particles/s for 20 s. The 511 keV annihilation gamma-rays, generated by the interaction between the irradiated C-ion beam and the target mouse, were detected using a silicon/cadmium telluride (Si/CdTe) Compton camera for 20 min immediately after irradiation. The irradiated site and the peak intensity position of 511 keV gamma emissions due to C-ion beam irradiation on a mouse were observed at the abdomen of the mouse by developing Compton images. Moreover, the positron emitter transport was observed by evaluating the range of gamma-ray emission after the C-ion beam irradiation on the mouse. Our data suggest that by confirming the peak intensity and beam range of C-ion RT with Si/CdTe-based Compton camera, it would be possible to reduce the intra-fractional and inter-fractional dose distribution degradation. Therefore, the results of this study would contribute to the future development of adaptive therapy with C-ion RT for humans.

Impact of interfractional anatomical variation and setup correction methods on interfractional dose variation in IMPT and VMAT plans for pancreatic cancer patients: A planning study

Purpose

To investigate the impact of interfractional anatomical changes and setup correction methods on dose distributions in pancreatic cancer patients under breath‐hold conditions.

Methods

Three intensity‐modulated proton therapy (IMPT) plans with different beam arrangements and one volumetric‐modulated arc therapy (VMAT) plan prescribing 54 Gy in 30 fractions were created for 10 patients who underwent three additional CT scans performed at an interval of 1–2 weeks. The additional CT sets were rigidly registered to the simulation CT set using both bone‐matching (BM) and organ‐matching (OM) methods in each patient. Recalculated dose distributions and dose–volume indices on the additional CT sets using either the BM or the OM method were compared with the simulation values.

Results

Differences in the gross tumor volume D_98% value from the simulation sets ranged from −0.8 to −5.9% on average. In addition, the variations were larger with OM compared with BM for two IMPT plans. Meanwhile, differences in the D_98% value in the region isotropically enlarged by 5 mm from the gross tumor volume were significantly improved with OM on two IMPT plans and the VMAT plan. Among the organs at risk, the dose–volume indices were significantly improved with OM only in the duodenum on all plans.

Conclusion

Organ‐matching may be a better setup correction technique than BM for both photon therapy and IMPT plans. However, in some beam arrangements of IMPT, the dose distribution may be somewhat worse using OM, due to interfractional anatomical variation. Therefore, it is important to choose beam angles that are less likely to be influenced by changes in the gastrointestinal gas volume, especially in IMPT plans.

Dose assessment for patients with stage I non-small cell lung cancer receiving passive scattering carbon-ion radiotherapy using daily computed tomographic images: A prospective study

BACKGROUND AND PURPOSE

This study aimed to assess dose distributions for stage I non-small cell lung cancer (NSCLC) with passive scattering carbon-ion radiotherapy (C-ion RT) using daily computed tomography (CT) images.

MATERIALS AND METHODS

We enrolled 10 patients with stage I NSCLC and acquired a total of 40 pre-fractional CT image series under the same settings as the planning CT images. These CT images were registered with planning CT images for dose evaluation using both bone matching (BM) and tumor matching (TM). Using deformable image registration, we generated accumulated doses. Moreover, the volumetric dose parameters were compared in terms of tumor coverage and lung exposure and statistical analyses were performed.

RESULTS

Overall, 25% of 40 fractional dose distributions were unacceptable with BM, compared with 2.5% with TM (P < 0.001). Using BM, three patients' accumulated dose distributions were unacceptable; however, all were satisfactory with TM (P < 0.001). No differences were observed in water-equivalent path length (WEL). The required margins in patients with poor dose distribution were 5.9 and 4.4 mm for BM and TM, respectively.

CONCLUSIONS

This study establishes that CT image-based TM is robust compared with conventional BM for both daily and accumulated dose distributions. The effects of changes in WEL seem to be limited. Hence, daily CT alignment is recommended for patients with stage I NSCLC receiving C-ion RT.

Evaluation of Intensity- and Contour-Based Deformable Image Registration Accuracy in Pancreatic Cancer Patients

We aimed to clarify the accuracy of rigid image registration and deformable image registration (DIR) in carbon-ion radiotherapy (CIRT) for pancreatic cancer. Six patients with pancreatic cancer who were treated with passive irradiation CIRT were enrolled. Three registration patterns were evaluated: treatment planning computed tomography images (TPCT) to CT images acquired in the treatment room (IRCT) in the supine position, TPCT to IRCT in the prone position, and TPCT in the supine position to the prone position. After warping the contours of the original CT images to the destination CT images using deformation matrices from the registration, the warped delineated contours on the destination CT images were compared with the original ones using mean displacement to agreement (MDA). Four contours (clinical target volume (CTV), gross tumor volume (GTV), stomach, duodenum) and four registration algorithms (rigid image registration [RIR], intensity-based DIR [iDIR], contour-based DIR [cDIR], and a hybrid iDIR-cDIR ([hDIR]) were evaluated. The means ± standard deviation of the MDAs of all contours for RIR, iDIR, cDIR, and hDIR were 3.40 ± 3.30, 2.2 1± 2.48, 1.46 ± 1.49, and 1.46 ± 1.37 mm, respectively. There were significant differences between RIR and iDIR, and between RIR/iDIR and cDIR/hDIR. For the pancreatic cancer patient images, cDIR and hDIR had better accuracy than RIR and iDIR.

Hypofractionated carbon-ion radiotherapy for stage I peripheral nonsmall cell lung cancer (GUNMA0701): Prospective phase II study

This phase II study's aim was to confirm the efficacy and safety of hypofractionated carbon-ion radiotherapy in patients with stage I peripheral nonsmall cell lung cancer (NSCLC). The study encompassed 37 patients with histologically proven peripheral stage I NSCLC in the period June 2010-March 2015. All underwent the planned full dose of carbon-ion radiotherapy, administered with relative biological effectiveness of 52.8 Gy and 60 Gy (divided into four fractions over 1 week) for T1 and T2a tumors, respectively. The 2-year local control rate was set as the primary endpoint, while overall survival, progression-free survival, and the incidence rates of acute and late adverse events were secondary endpoints. The patients were followed up for 56.3 months overall and 62.2 months in the surviving patients, respectively. The actuarial local control rates were 91.2% after 2 years, and 88.1% after 5 years. No differences were found between the T1 and T2a tumors in the 5-year local control rate (90.9% vs 86.7%, P = .75). The actuarial overall survival rates achieved 91.9% for 2-year and 74.9% for 5-year period. T1 tumors showed actuarial 5-year overall survival rates of 80%, compared to 66.7% in T2a tumors. Two patients with T2a tumors and either severe emphysema or bronchiectasis experienced lung toxicity ≥ grade 2, in contrast to T1 patients who only experienced mild toxicities (lower than grade 2). The findings suggest that carbon-ion radiotherapy is effective and safe for peripheral stage I NSCLC; however, further clinical evaluations are needed to confirm its therapeutic efficacy. Trial registration: UMIN000003797. Registered 21 June 2010, prospectively registered.

Divided-volume matching technique for volume displacement estimation of patient positioning in radiation therapy

PURPOSE

We propose the Divided-Volume Matching (DVM) technique to visualize and estimate three-dimensional (3D) displacements of internal structures to enable more accurate patient positioning for radiation therapy.

METHODS

A CT volume is divided into a volume of interest (VOI) and a base volume (BV); 2D-3D matching is achieved using digital radiography (DR) images and digitally reconstructed radiographs (DRRs), where the DRRs are iteratively generated by changing the 3D positions and rotation angles of the separate volumes independently to identify the best match with the DR images. We demonstrate this technique with two phantom and two clinical cases.

RESULTS

3D displacements of the VOIs could be estimated independently and simultaneously with those of the BVs, with accuracies comparable to those of the conventional 2D-3D matching. The proposed technique yielded more suitable matching results when internal displacements occurred in the regions of interest (ROIs). The best matches were found when the ROI was confined to the focused structure, initial displacement values were coarsely adjusted, one volume was matched while the other was fixed, or any combination thereof.

CONCLUSIONS

The proposed technique can be used effectively for independent displacement estimations of VOIs and BVs for patient positioning in radiation therapy.

Comparison between bone matching and marker matching for evaluation of intra- and inter-fractional changes in accumulated dose of carbon ion radiotherapy for hepatocellular carcinoma

BACKGROUND AND PURPOSE

To determine whether bone matching (BM) or marker matching (MM) is the better positioning technique for carbon ion radiotherapy (CIRT) of primary hepatocellular carcinoma (HCC), we prospectively evaluated accumulated dose distributions with respect to intra- and inter-fractional anatomical changes.

MATERIALS AND METHODS

The accumulated doses in ten patients with HCC were evaluated, with the doses being calculated with respect to inter-fractional changes (InterDose) on treatment-room CT images on day 1 or day 2 of therapy (RefCT). This was accomplished by warping 3-day CT dose distributions to the RefCT through deformable registration. The accumulated doses were also calculated with respect to intra-fractional change (IntraDose) calculated by warping dose distributions for three 4DCT phases to the RefCT. Each dose was evaluated using dose-volume parameters for the clinical target volume (CTV) percentages receiving greater than 95% of the prescription dose (V₉₅).

RESULTS

The InterDose CTV V₉₅ values (mean [range]) were BM: 98.74% (95.62-100%), MM: 99.79% (98.55-100%), and the IntraDose values were BM: 99.46% (98.10-100%), MM: 99.74% (98.91-100%). Although all cases were acceptable with either matching method, MM provided better values than BM.

CONCLUSION

MM is a better positioning technique than BM for ensuring the target dose during and between fractions of CIRT. However, further analysis is required as our study included only a low number of cases.

Value of Three-Dimensional Imaging Systems for Image-Guided Carbon Ion Radiotherapy

Carbon ion radiotherapy (C-ion RT) allows excellent dose distribution because of the Bragg Peak. Compared with conventional radiotherapy, it delivers a higher dose with a smaller field. However, the dose distribution is sensitive to anatomical changes. Imaging technologies are necessary to reduce uncertainties during treatment, especially for hypofractionated and adaptive radiotherapy (ART). In-room computed tomography (CT) techniques, such as cone-beam CT (CBCT) and CT-on-rails are routinely used in photon centers and play a key role in improving treatment accuracy. For C-ion RT, there is an increasing demand for a three-dimensional (3D) image-guided system because of the limitations of the present two-dimensional (2D) imaging verification technology. This review discusses the current imaging system used in carbon ion centers and the potential benefits of a volumetric image-guided system.

Clinical outcomes of image-guided proton therapy for histologically confirmed stage I non-small cell lung cancer

Background

Two prospective phase II trials were designed to assess the efficacy and safety of image-guided proton therapy (IGPT) for either medically inoperable or operable stage I non-small cell lung cancer (NSCLC). The present study reports the interim results of these trials.

Methods

Fifty-five patients with histologically confirmed stage I NSCLC (IA in 33 patients and IB in 22 patients; inoperable in 21 patients and operable in 34 patients) who received IGPT between July 2013 and February 2017 were analyzed. The median patient age was 71 years (range: 48–88 years). IGPT with fiducial metallic marker matching was performed for suitable patients, and a respiratory gating method for motion management was used for all treatments. Peripherally located tumors were treated with 66 Gy relative biological effectiveness equivalents (Gy(RBE)) in 10 fractions (n = 49) and centrally located tumors were treated with 72.6 Gy(RBE) in 22 fractions (n = 6). Treatment associated toxicities were evaluated using Common Toxicity Criteria for Adverse Events (v.4.0).

Results

Median follow-up was 35 months (range: 12–54 months) for survivors. For all patients, the 3-year overall survival, progression-free survival, and local control rates were 87% (95% confidence interval: 73–94%), 74% (58–85%), and 96% (83–99%), respectively. Fiducial marker matching was used in 39 patients (71%). Grade 2 toxicities observed were radiation pneumonitis in 5 patients (9%), rib fracture in 2 (4%), and chest wall pain in 5 (9%). There were no grade 3 or higher acute or late toxicities.

Conclusions

IGPT appears to be effective and well tolerated for all patients with stage I NSCLC.

Trial registration

Lung-001, 13–02-09 (9), registered 11 June 2013 and Lung-002, 13–02-10 (10), registered 11 June 2013.

Technical Note: Predicting dose distribution with replacing stopping power ratio for inter-fractional motion and intra-fractional motion during carbon ion radiotherapy with passive irradiation method for stage I lung cancer

PURPOSE

We designed and evaluated a simple method for predicting the effects of intra-fractional and/or inter-fractional motion on dose distribution during carbon ion radiotherapy (CIRT) for solitary-lesion stage I lung cancer.

METHODS

The proposed method uses computed tomography (CT) images from treatment planning and intra-tumoral and/or inter-tumoral displacement. The predicted dose distribution (PDD) was calculated by replacing the current tumor region with the stopping power ratio (SPR) of the lung and replacing the moved tumor region with the SPR of the tumor. The actual dose distribution (ADD) was calculated without the replacement. Ten patients with solitary-lesion stage I lung cancer were retrospectively studied to evaluate the prediction method's accuracy. Four PDDs for intra-fractional motion (gate-in, exhalation, gate-out, inhalation phases during four-dimensional CT) and two PDDs for inter-fractional motion (CT images acquired 1-2 days before treatment) with bone- and tumor-matching methods were compared with each of six ADDs on each CT scan. Percentages of the planning/clinical target volumes (PTV/CTV) receiving >95% of the prescribed dose (V₉₅ ) and of minimum doses covering 95% of the PTV/CTV (D₉₅ ) were compared with dose volume histogram parameters.

RESULTS

The maximum tumor displacements occurred in the superior-inferior direction, with intra-fractional motion values of 3.75 and 8.97 mm for the superior and inferior directions, respectively, and inter-fractional values of 9.61 and 4.10 mm. The maximum average error for PTV V₉₅ regarding intra-fractional motion was -0.43% for the gate-out phase and -0.63% for the inhalation phase. There were no significant differences for these parameters (P = 0.541, P = 0.571). Average errors for PTV and CTV V₉₅ with inter-fractional motion with bone matching were 2.2% and 2.9%, respectively, with no significant differences (P = 0.387, P = 0.155).

CONCLUSIONS

The accuracy of the proposed method was good. Hence, it is feasible to use the proposed method during CIRT to predict dose distribution with respect to intra-fractional motion and/or inter-fractional motion of the tumor in patients with solitary-lesion stage I lung cancer.

Evaluation of the accuracy and clinical practicality of a calculation system for patient positional displacement in carbon ion radiotherapy at five sites

PURPOSE

We developed a system for calculating patient positional displacement between digital radiography images (DRs) and digitally reconstructed radiography images (DRRs) to reduce patient radiation exposure, minimize individual differences between radiological technologists in patient positioning, and decrease positioning time. The accuracy of this system at five sites was evaluated with clinical data from cancer patients. The dependence of calculation accuracy on the size of the region of interest (ROI) and initial position was evaluated for clinical use.

METHODS

For a preliminary verification, treatment planning and positioning data from eight setup patterns using a head and neck phantom were evaluated. Following this, data from 50 patients with prostate, lung, head and neck, liver, or pancreatic cancer (n = 10 each) were evaluated. Root mean square errors (RMSEs) between the results calculated by our system and the reference positions were assessed. The reference positions were manually determined by two radiological technologists to best-matching positions with orthogonal DRs and DRRs in six axial directions. The ROI size dependence was evaluated by comparing RMSEs for three different ROI sizes. Additionally, dependence on initial position parameters was evaluated by comparing RMSEs for four position patterns.

RESULTS

For the phantom study, the average (± standard deviation) translation error was 0.17 ± 0.05, rotation error was 0.17 ± 0.07, and ΔD was 0.14 ± 0.05. Using the optimal ROI size for each patient site, all cases of prostate, lung, and head and neck cancer with initial position parameters of 10 mm or under were acceptable in our tolerance. However, only four liver cancer cases and three pancreatic cancer cases were acceptable, because of low-reproducibility regions in the ROIs.

CONCLUSION

Our system has clinical practicality for prostate, lung, and head and neck cancer cases. Additionally, our findings suggest ROI size dependence in some cases.