Kiyonao Nakamura

Evaluation of different set-up error corrections on dose-volume metrics in prostate IMRT using CBCT images.

We investigated the effect of different set-up error corrections on dose–volume metrics in intensity-modulated radiotherapy (IMRT) for prostate cancer under different planning target volume (PTV) margin settings using cone-beam computed tomography (CBCT) images. A total of 30 consecutive patients who underwent IMRT for prostate cancer were retrospectively analysed, and 7–14 CBCT datasets were acquired per patient. Interfractional variations in dose–volume metrics were evaluated under six different set-up error corrections, including tattoo, bony anatomy, and four different target matching groups. Set-up errors were incorporated into planning the isocenter position, and dose distributions were recalculated on CBCT images. These processes were repeated under two different PTV margin settings. In the on-line bony anatomy matching groups, systematic error (∑) was 0.3 mm, 1.4 mm, and 0.3 mm in the left–right, anterior–posterior (AP), and superior–inferior directions, respectively. ∑ in three successive off-line target matchings was finally comparable with that in the on-line bony anatomy matching in the AP direction. Although doses to the rectum and bladder wall were reduced for a small PTV margin, averaged reductions in the volume receiving 100% of the prescription dose from planning were within 2.5% under all PTV margin settings for all correction groups, with the exception of the tattoo set-up error correction only (≥5.0%). Analysis of variance showed no significant difference between on-line bony anatomy matching and target matching. While variations between the planned and delivered doses were smallest when target matching was applied, the use of bony anatomy matching still ensured the planned doses.

Geometric and dosimetric quality assurance using logfiles and a 3D helical diode detector for Dynamic WaveArc

PURPOSE To conduct patient-specific geometric and dosimetric quality assurance (QA) for the Dynamic WaveArc (DWA) using logfiles and ArcCHECK (Sun Nuclear Inc., Melbourne, FL, USA). METHODS Twenty DWA plans, 10 for pituitary adenoma and 10 for prostate cancer, were created using RayStation version 4.7 (RaySearch Laboratories, Stockholm, Sweden). Root mean square errors (RMSEs) between the actual and planned values in the logfiles were evaluated. Next, the dose distributions were reconstructed based on the logfiles. The differences between dose-volumetric parameters in the reconstructed plans and those in the original plans were calculated. Finally, dose distributions were assessed using ArcCHECK. In addition, the reconstructed dose distributions were compared with planned ones. RESULTS The means of RMSEs for the gantry, O-ring, MLC position, and MU for all plans were 0.2°, 0.1°, 0.1 mm, and 0.4 MU, respectively. Absolute means of the change in PTV D99% were 0.4 ± 0.4% and 0.1 ± 0.1% points between the original and reconstructed plans for pituitary adenoma and prostate cancer, respectively. The mean of the gamma passing rate (3%/3 mm) between the measured and planned dose distributions was 97.7%. In addition, that between the reconstructed and planned dose distributions was 99.6%. CONCLUSIONS We have demonstrated that the geometric accuracy and gamma passing rates were within AAPM 119 and 142 criteria during DWA. Dose differences in the dose-volumetric parameters using the logfile-based dose reconstruction method were also clinically acceptable in DWA.

A pilot study of highly hypofractionated intensity-modulated radiation therapy over 3 weeks for localized prostate cancer

Abstract The purpose of this pilot study was to evaluate the feasibility of highly hypofractionated intensity-modulated radiation therapy (IMRT) in 15 fractions over 3 weeks for treating localized prostate cancer based on prostate position-based image-guided radiation therapy. Twenty-five patients with National Comprehensive Cancer Network (NCCN) very low- to unfavorable intermediate-risk prostate cancer were enrolled in this study from April 2014 to September 2015 to receive highly hypofractionated IMRT (without intraprostatic fiducial markers) delivering 54 Gy in 15 fractions over 3 weeks. Patients with intermediate-risk disease underwent neoadjuvant androgen suppression for 4–8 months. Twenty-four patients were treated with highly hypofractionated IMRT, and one was treated with conventionally fractionated IMRT because the dose constraint of the small bowel seemed difficult to achieve during the simulation. Seventeen percent had very low- or low-risk, 42% had favorable intermediate-risk, and 42% had unfavorable intermediate-risk disease according to NCCN guidelines. The median follow-up period was 31 months (range, 24–42 months). No Grade ≥3 acute toxicity was observed, and the incidence rates of Grade 2 acute genitourinary and gastrointestinal toxicities were 21% and 4%, respectively. No Grade ≥2 late toxicity was observed. Biochemical relapse was observed in one patient at 15 months, and the biochemical relapse-free survival rate was 95.8% at 2 years. A prostate-specific antigen bounce of ≥0.4 ng/ml was observed in 11 patients (46%). The highly hypofractionated IMRT regimen is feasible in patients with localized prostate cancer and is more convenient than conventionally fractionated schedules for patients and health-care providers.

Correlation between urinary dose and delayed radiation cystitis after 78 Gy intensity-modulated radiotherapy for high-risk prostate cancer: A 10-year follow-up study of genitourinary toxicity in clinical practice

Highlights • High-dose prostate IMRT was well tolerated in terms of long-term GU toxicities.• Hematuria was the most common long-term GU toxicity after high-dose IMRT.• Bladder neck dose–volume data were significantly associated with hematuria.

Recovery of Serum Testosterone Levels and Sexual Function in Patients Treated With Short-term Luteinizing Hormone-releasing Hormone Antagonist as a Neoadjuvant Therapy Before External Radiotherapy for Intermediate-risk Prostate Cancer: Preliminary Prospective Study

Introduction External beam radiation therapy (EBRT) with short‐term androgen deprivation therapy is the standard of care for intermediate‐risk prostate cancer patients. However, no study to date has evaluated the hormonal kinetics or sexual and hormonal function recovery after cessation of short‐term luteinizing hormone (LH)‐releasing hormone (LHRH) antagonist treatment. Patients and Methods Ten intermediate‐risk prostate cancer patients (mean age, 69.9 years) were included. All patients received 4 months of LHRH antagonist (degarelix) treatment followed by EBRT. The testosterone, luteinizing hormone (LH), follicle‐stimulating hormone, and prostate‐specific antigen levels were measured and Expanded Prostate Cancer Index Composite questionnaires were completed before LHRH antagonist therapy at baseline; 1, 2, 3, and 4 months after the first injection of LHRH antagonist treatment; and every 2 months thereafter until 18 months. Results The testosterone levels were at the castration level at 1 month after the first LHRH antagonist injection. The median interval to recover a normal testosterone level (> 7.2 nmol/L) was 7 months after the last LHRH antagonist administration. The LH and follicle‐stimulating hormone levels decreased but had increased more than twice above baseline at 15 months after the last LHRH antagonist injection. The sexual function and hormonal bother subdomain scores and sexual and hormonal domain scores decreased once after LHRH antagonist treatment but had significantly recovered thereafter (P < .05). Conclusion In most patients, the testosterone level had normalized within 9 months after the last LHRH administration. Sexual and hormonal function recovered after short‐term LHRH antagonist administration for neoadjuvant therapy before EBRT. Micro‐Abstract No investigation has examined the recovery of serum testosterone or sexual and hormonal function after cessation of luteinizing hormone‐releasing hormone (LHRH) antagonist administration for intermediate‐risk prostate cancer patients before external radiotherapy. The results of the present preliminary prospective study have shown that the serum testosterone level normalized within 9 months after the last LHRH antagonist treatment with gradual recovery of sexual and hormonal function.

Multivariate analysis of factors predicting prostate dose in intensity- modulated radiotherapy

We conducted a multivariate analysis to determine relationships between prostate radiation dose and the state of surrounding organs, including organ volumes and the internal angle of the levator ani muscle (LAM), based on cone-beam computed tomography (CBCT) images after bone matching. We analyzed 270 CBCT data sets from 30 consecutive patients receiving intensity-modulated radiation therapy for prostate cancer. With patients in the supine position on a couch with the HipFix system, data for center of mass (COM) displacement of the prostate and the state of individual organs were acquired and compared between planning CT and CBCT scans. Dose distributions were then recalculated based on CBCT images. The relative effects of factors on the variance in COM, dose covering 95% of the prostate volume (D95%), and percentage of prostate volume covered by the 100% isodose line (V100%) were evaluated by a backward stepwise multiple regression analysis. COM displacement in the anterior-posterior direction (COMAP) correlated significantly with the rectum volume (δVr) and the internal LAM angle (δθ; R = 0.63). Weak correlations were seen for COM in the left-right (R = 0.18) and superior-inferior directions (R = 0.31). Strong correlations between COMAP and prostate D95% and V100% were observed (R ≥ 0.69). Additionally, the change ratios in δVr and δθ remained as predictors of prostate D95% and V100%. This study shows statistically that maintaining the same rectum volume and LAM state for both the planning CT simulation and treatment is important to ensure the correct prostate dose in the supine position with bone matching.