Published papers

Postoperative radiation can cause ulcer formation, leading to the denudation of skin over alloplastic materials. The influence of backscatter radiation from fixation devices has not been investigated. The aim of this study is to evaluate backscatter dose variations for different cranial bone fixation devices in an experimental model designed to simulate postoperative radiotherapy. The authors assessed the radiation backscatter doses associated with resorbable (PLLA-PGA) and titanium plates. The samples were irradiated with 6 and 10 MV photon beams from a linear accelerator. Measurements were obtained using an ionization chamber and radiochromic films cut from the same batch. As a result, the backscatter radiation of water and PLLA-PGA proportionally decreased as the depth increased. However, the backscatter radiation of the titanium plate increased just above the plate. This depth lies in the region of the scalp. Each material showed a dose of radioactivity that was higher at 10 MV than that at 6 MV. These devices showed a significant difference, which suggested that these materials amplified the dose compared with water at 6 MV. In conclusion, it is supposed that PLLA-PGA should be used to fix the cranium to decrease the potential for radiation ulcers.

We investigated long-term treatment outcomes and the feasibility of chemoradiotherapy consisting of daily-low-dose 5-fluorouracil and cisplatin (LDFP) chemotherapy plus radiotherapy for Stage I-II squamous cell esophageal cancer. Treatment records from the 2000 through 2008 period were reviewed retrospectively. Fractionated radiotherapy was performed with a total dose of 60 Gy delivered in 2 Gy per fraction. LDFP chemotherapy, as continuous infusion of 200 mg/m2 5-fluorouracil combined with one hour infusion of 4 mg/m2 cisplatin, was administered on the same days as radiotherapy. Survival was calculated by the Kaplan-Meier method. Survival, responses, failure patterns, and toxicities were evaluated. Seventy-six (47 stage I and 29 stage II) patients were analyzed with a median follow-up of 93.6 months. The 8-year overall survival (OS), progression-free survival (PFS) and cause-specific survival (CSS) rates were 63.4%, 49.8%, and 76.7%, respectively. The 8-year OS, PFS, and CSS for stage I and stage II patients were 71.0%/56.1%/82.9% and 45.2%/40.2%/66.6%, respectively. Sixty-eight patients (89.5%) completed the treatment regimen. A complete response (CR) was achieved in 68 patients (89.5%). Twenty-five patients (36.8%) experienced recurrence after CR. The failure patterns were (overlap included): local failure (n = 12), nodal metastasis (n = 12), distant metastasis (n = 3), details unknown (n = 2). Salvage therapy was performed for local failure; endoscopic therapy (n = 7) or surgery (n = 2). Six patients remain alive without relapse after salvage endoscopic therapy. Major Grade 3 or higher acute adverse events were leukopenia (22%), anorexia (17%), and esophagitis (11%). Major late toxicities (Grade 3 or 4) involved pericardial effusion (12%), pleural effusion (4%), and esophageal stenosis (3%). Chemoradiotherapy with LDFP provided favorable long-term survival with acceptable toxicity for Stage I-II squamous cell esophageal cancer. The tumor response was excellent, but close endoscopic follow-up is essential for detecting and treating local recurrence.

Prostate-specific antigen nadir (nPSA) after radiotherapy for localized prostate cancer has been investigated as a predictor. However, nPSA usually requires several years, limiting its clinical utility. We investigated the significance of nPSA within 12 months (nPSA12) after low-dose-rate prostate brachytherapy (LDR-PB) or external beam radiotherapy (EBRT) on treatment outcomes. Between 2006 and 2014, 663 patients with prostate cancer were treated with LDR-PB or EBRT at two institutions. Four hundred and seventy-four men received LDR-PB and 189 men received EBRT, without androgen deprivation therapy. The Kaplan-Meier method was used for biochemical failure (BF)-free survival (BFFS) and distant metastasis (DM)-free survival (DMFS) analyses, and multivariable Cox regression analysis was performed. The median follow-up was 61.3 months. The median nPSA12 in the LDR-PB and EBRT cohorts was 0.7 and 1.0 ng/mL, respectively. The 7-year BFFS and DMFS rates in LDR-PB patients with nPSA12 ≤ 0.7 ng/mL were 99.1% and 99.5%, respectively; when nPSA12 was >0.7 ng/mL, they were 90.2% and 94.8%, respectively. In EBRT patients with nPSA12 ≤ 1.0 ng/mL, BFFS and DMFS rates were 85.4% and 98.5%, respectively; when nPSA12 was >1.0 ng/mL, they were 67.1% and 87.2%, respectively. nPSA12 was an independent predictor of BF and DM in both cohorts (LDR-PB, P = 0.004 and 0.020, respectively; EBRT, P = 0.005 and 0.041, respectively). The nPSA12 after LDR-PB or EBRT is significantly associated with treatment outcomes of prostate cancer. Higher nPSA12 may identify patients at high risk of relapse who might benefit from salvage treatment.

Purpose: We analyzed factors associated with rectal toxicity after iodine-125 prostate brachytherapy (BT) with or without external beam radiation therapy (EBRT). Methods and Materials: In total, 2216 prostate cancer patients underwent iodine-125 BT with or without EBRT between 2003 and 2013. The median followup was 6.9 years. Cox proportional hazards modeling was used for univariate and multivariate analyses to assess clinical and dosimetric factors associated with rectal toxicity. Dosimetric parameters from 1 day after implantation (Day 1) and 1 month after implantation (Day 30) were included in the analyses. Results: The 7-year cumulative incidence of Grade 2 or higher rectal toxicity was 5.7% in all patients. The multivariate analysis revealed that antiplatelet or anticoagulant therapy, neoadjuvant androgen deprivation therapy, treatment modality, Day 1 rectal volume receiving 100% of the prescribed dose (RV100), and the Day 30 minimal percent of the prescribed dose delivered to 30% of the rectum (RD30) were associated with rectal toxicity. Day 1 RV100 was a common predictor in both BT-alone and the BT + EBRT groups. The 5-year cumulative incidence of Grade 2 or higher rectal toxicity was 12.6%, 5.9%, and 1.7% for BT + 3-dimensional conformal radiation therapy, BT + intensity-modulated radiation therapy, and the BT-alone groups, respectively (p < 0.001). Conclusions: Rectal dosimetric parameters in BT were associated with late rectal toxicity. Although the risk of rectal toxicity was higher when EBRT was combined with BT, with proper and achievable rectal dose constraints intensity-modulated radiation therapy yielded less toxicity than 3-dimensional conformal radiation therapy.

© 2018 The Author(s). Published by S. Karger AG, Basel. We report a patient with highly advanced gastric carcinoma who was treated successfully with chemoradiotherapy (CRT) comprising S-1 and cisplatin. The patient was a 71-year-old male who was diagnosed with advanced gastric carcinoma by esophagogastroduodenoscopy (EGD) by medical examination. EGD demonstrated type 3 advanced gastric carcinoma in the posterior wall of the upper gastric body. An abdominal computed tomography (CT) scan showed that the gastric wall was thickened due to gastric primary tumor, and large lymph nodes (LNs) including the lesser curvature LN, anterosuperior LN along the common hepatic artery and some para-aortic LNs were detected. The patient was diagnosed with stage IV advanced gastric carcinoma according to the Japanese classification of gastric carcinoma (cT4a, cN3, cM1 [para-aortic LN], cStage IV). Preoperative CRT was carried out in an attempt to downstage the disease. Remarkable reduction of the primary tumor and metastatic LNs was observed after initial CRT, and radiological examination determined that a partial response had been achieved. Adverse effects included grade 2 anorexia and grade 3 ALP elevation (919 U/ml). No grade 4 or more severe adverse event was observed. After CRT, although we recommended curative surgery, the patient refused surgical treatment and opted for conservative treatment. Thus, we continued S-1 oral administration for 1 year. Five months after beginning CRT, upper endoscopy showed that the tumor had maintained regression and scar formation, in which no cancer cells were detected by endoscopic biopsy. The patient is doing well and has maintained a clinical complete response for more than 42 months without curative surgery. CRT could be considered as an option for treatment of patients with locally advanced gastric carcinoma diagnosed as unresectable, or for those who refuse surgical treatment.

© 2018, Japan Society of Clinical Oncology. Background: Investigating oncological outcomes in patients registered in the Japanese Prostate Cancer Outcome Study of Permanent Iodine-125 Seed Implantation (J-POPS) in terms of biochemical relapse-free survival (bRFS) by the Phoenix and the newly developed J-POPS definitions, exploration of predictive factors for bRFS, and preliminary verification of pitfalls of prostate-specific antigen (PSA) failure definitions. Methods: Between July 2005 and June 2007, 2316 clinically localized patients underwent permanent seed implantation. The primary endpoint was bRFS. One of the secondary endpoints was overall survival (OS). Results: The median age was 69 and performance status was 0 in 99.1% of participants. The median biologically effective dose (BED) was about 180 Gy 2 . During a median follow-up of 60.0 months, 8.4 and 5.9% had PSA failure by the Phoenix and the J-POPS definitions, respectively. The 5-year bRFSs based on the Phoenix and the J-POPS definitions were 89.1 and 91.6%, respectively. The 5-year OS was 97.3%. According to multivariate analyses, only age affected bRFS based on the Phoenix definition, whereas the risk group and BED independently affected bRFS based on the J-POPS definition. A spontaneous PSA decrease was seen in 91.1% of participants after PSA failure based on the Phoenix definition alone, but in only 22.2% after PSA failure based on the J-POPS definition alone. Conclusion: The world’s largest registration study, J-POPS, consisted of patients with longevity, and a highly quality-controlled BED resulted in excellent bRFS and OS. The high likelihood of PSA bounce by the Phoenix definition should be taken into account, especially in younger patients. Clinical trial information: NCT00534196.

© 2018 American Public Health Association Inc. All Rights Reserved. Purpose: Few studies have compared the implant quality of linked and loose seeds for prostate brachytherapy. This study aimed to evaluate and compare plan reproducibility of intraoperatively built custom linked seeds and loose seeds for prostate brachytherapy. Material and methods: Between December 2010 and March 2014, 76 localized prostate cancer patients received Iodine-125 brachytherapy with external beam radiotherapy. Linked and loose seeds were implanted in 39 and 37 patients, respectively. The primary endpoint was the mean (± standard deviation) of the absolute change in the minimum dose received by 90% of the prostate volume between intraoperative and post-operative planning (ΔD 90 ) to confirm plan reproducibility. Comparisons between the groups were evaluated using 2-sample t tests. Results: The ΔD 90 values were 6.95 ± 11.6% and -0.41 ± 8.5% for the loose and linked seed groups, respectively (p < 0.01). The linked seed group showed decreased post-operative D 90 (118.8% vs. 127.2%), V 150 (51.7% vs. 66.7%), and RV 100 (0.44 ml vs. 0.61 ml) compared to the loose seed group (p < 0.01), whereas lung migration tended to be reduced (0% vs. 8%). Conclusions: The plan reproducibility of the linked seed group was better than that of the loose seed group. Moreover, the linked seed group showed less migration and lower rectal dose.

Background: We report the feasibility and treatment outcomes of image-guided three-dimensional conformal arc radiotherapy (3D-CART) using a C-arm linear accelerator with a computed tomography (CT) on-rail system for localized prostate cancer. Methods and materials: Between 2006 and 2011, 282 consecutive patients with localized prostate cancer were treated with in-room CT-guided 3D-CART. Biochemical failure was defined as a rise of at least 2.0 ng/ml beyond the nadir prostate-specific antigen level. Toxicity was scored according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0. Results: A total of 261 patients were analyzed retrospectively (median follow-up: 61.6 months). The median prescribed 3D-CART dose was 82 Gy (2 Gy/fraction, dose range: 78-86 Gy), and 193 of the patients additionally received hormonal therapy. The 5-year overall survival rate was 93.9 %. Among low-, intermediate-, and high-risk patients, 5-year rates of freedom from biochemical failure were 100, 91.5 and 90.3 %, respectively. Rates of grade 2-3 late gastrointestinal and genitourinary toxicities were 2.3 and 11.4 %, respectively. No patient experienced late grade 4 or higher toxicity. Conclusions: In-room CT-guided 3D-CART was feasible and effective for localized prostate cancer. Treatment outcomes were comparable to those previously reported for intensity-modulated radiotherapy.

Purpose: To compare late genitourinary (GU) and gastrointestinal (GI) toxicity following different prostate cancer treatment modalities. Materials and methods: This study included 1084 consecutive prostate cancer patients treated with conventional radiotherapy, intensity-modulated radiotherapy (IMRT), permanent iodine-125 implantation (PI) alone, and PI combined with external beam radiotherapy (PI + EBRT). The effects of treatment- and patient-related factors on late grade. ≥. 2 (G2+) GU/GI toxicity risk were assessed. Results: The median follow-up was 43. months (range, 12-97. months). Compared to the PI + EBRT, there was significantly less G2+ GU toxicity in the conventional radiotherapy (hazard ratio [HR] = 0.39; 95% CI, 0.20-0.77) and the IMRT (HR = 0.45, 95% CI, 0.27-0.73). Compared to the PI + EBRT, there was significantly more G2+ GI toxicity in the IMRT (HR = 2.38; 95% CI, 1.16-4.87). In PI-related groups, prostate equivalent dose in 2. Gy fractions was a significant predictor of G2+ GU toxicity (p = 0.001), and the rectal volume receiving more than 100% of the prescribed dose was a significant predictor of G2+ GI toxicity (p = 0.001). Conclusion: The differences in the late G2+ GU/GI risk cannot be explained by the differences in treatment modalities themselves, but by the total radiation dose to the GU/GI tract, which had a causal role in the development of late G2+ GU/GI toxicity across all treatment modality groups.

Background: To evaluate the safety and efficacy of brachytherapy with permanent iodine-125 seed implantation (PI) for prostate cancer. The nationwide Japanese Prostate Cancer Outcome Study of Permanent Iodine-125 Seed Implantation (J-POPS) has continued since July 2005. This manuscript presents the rationale, J-POPS study design, and the characteristics of initial participants enrolled in this study from July 2005 to June 2007. Methods: All participants were treated with PI in accordance with the American Brachytherapy Society recommendations. The primary outcome measure was biochemical progression-free survival. Progression-free survival, overall survival, cause-specific survival, longitudinal changes in health-related quality of life, disease-specific quality of life, the International Prostate Symptom Score, and the incidence of adverse events were also investigated as secondary outcome measurements. Results: Overall, 6,927 patients were enrolled by the end of 2010, that is approximately 40 % of all cases treated around the country. During the first 2 years, 2,354 participants were enrolled and 2,339 were actually treated with PI. The age range of participants was 45 to 89 years (median 69 years) and their risk classifications were 1,037 (44.3 %) at low risk, 1,126 (48.1 %) at intermediate risk, and 134 (5.7 %) at high risk, in addition to 16 participants whose classification was unknown. Of all patients, 76.6 % were treated with PI without external beam radiation therapy and 49.3 % received neoadjuvant hormone therapy. Conclusions: The J-POPS, a nationwide prospective cohort study that enrolled approximately 40 % of all PI cases in Japan, will provide highly reliable evidence, including outcomes and quality of life, after long-term follow-up.

PURPOSE: If a prostate cancer patient treated with (125)I brachytherapy dies within 12 months after the treatment, prostate removal before cremation is recommended to avoid problems related to radioactivity in the ashes, such as inhalation of airborne particulate matter by crematorium staff or nearby residents. To provide guidance for such cases, a manual prepared under the editorial supervision of several professional associations was issued in 2008 in Japan. Herein, we investigated the incidence and causes of death, and the actions taken subsequent to death, among prostate cancer patients who died within 12 months after (125)I brachytherapy over a 10-year period in Japan; and we compared the results before and after the manual was issued.METHODS AND MATERIALS: Data extracted from the Japan Radioisotope Association database for the period from September 2003 to the end of December 2013 were used.RESULTS: Of 27,976 patients who underwent (125)I brachytherapy during the specified period, 79 died within 12 months after implantation, including 3 who died in the 2011 earthquake and tsunami. The prostate and brachytherapy source were retrieved at autopsy from 69 of the 79 patients. Autopsy could not be performed on the other 10 patients, 2 of whom died in the earthquake. Autopsy and retrieval of the brachytherapy source were significantly more common after issuance of the manual than before (22/28 cases before; 47/49 cases after; p=0.021).CONCLUSION: In most cases of early death after (125)I brachytherapy in Japan, the brachytherapy source was retrieved.

We report a case of a 21-year-old man with alveolar rhabdomyosarcoma primarily in the right hand with lymph node, lung, bone and bone marrow metastases. Complete remission was achieved after intensive chemotherapy and radiotherapy of the primary and metastatic sites, followed by allogeneic peripheral blood stem cell transplantation with reduced-intensity conditioning from a single HLA-DR locus-mismatched mother. The patient remained relapse-free for 41 months after the diagnosis. Considering that the conventional treatment for rhabdomyosarcoma with multiple risk factors (old age, bone or bone marrow involvement, unfavorable primary sites and ≥3 metastases) is associated with a poor prognosis (5% probability of a 3-year event-free survival), the graft-versus-tumor effect may have contributed to his sustained relapse-free survival. Allogeneic hematopoietic stem cell transplantation for rhabdomyosarcoma should be done by experienced clinical oncologists on properly designed controlled trials.

Background: Investigating oncological outcomes in patients registered in the Japanese Prostate Cancer Outcome Study of Permanent Iodine-125 Seed Implantation (J-POPS) in terms of biochemical relapse-free survival (bRFS) by the Phoenix and the newly developed J-POPS definitions, exploration of predictive factors for bRFS, and preliminary verification of pitfalls of prostate-specific antigen (PSA) failure definitions. Methods: Between July 2005 and June 2007, 2316 clinically localized patients underwent permanent seed implantation. The primary endpoint was bRFS. One of the secondary endpoints was overall survival (OS). Results: The median age was 69 and performance status was 0 in 99.1% of participants. The median biologically effective dose (BED) was about 180 Gy2. During a median follow-up of 60.0 months, 8.4 and 5.9% had PSA failure by the Phoenix and the J-POPS definitions, respectively. The 5-year bRFSs based on the Phoenix and the J-POPS definitions were 89.1 and 91.6%, respectively. The 5-year OS was 97.3%. According to multivariate analyses, only age affected bRFS based on the Phoenix definition, whereas the risk group and BED independently affected bRFS based on the J-POPS definition. A spontaneous PSA decrease was seen in 91.1% of participants after PSA failure based on the Phoenix definition alone, but in only 22.2% after PSA failure based on the J-POPS definition alone. Conclusion: The world’s largest registration study, J-POPS, consisted of patients with longevity, and a highly quality-controlled BED resulted in excellent bRFS and OS. The high likelihood of PSA bounce by the Phoenix definition should be taken into account, especially in younger patients. Clinical trial information: NCT00534196.

Objective: We aimed to evaluate backscatter dose variations in different cranial bone implant materials in an experimental model designed to simulate postoperative radiotherapy. Methods: We assessed the radiation backscatter doses associated with sheet- and mesh-type titanium plates and hydroxyapatite (HAP) samples (porosity: 35%, 50% and 85%). The samples were irradiated with 6- and 10-MV photon beams from a linear accelerator. Measurements were obtained using an ionization chamber and radiochromic films cut from the same batch. Results: At 6MV, the titanium sheet showed the highest peak for backscattered radiation, followed by (in decreasing order) HAP30%, HAP50%, titanium mesh and HAP85%. At 10MV, HAP30% showed the highest peak, followed by HAP50%, titanium sheet, titanium mesh and HAP85%. The peaks were at different depths in the titanium and HAP samples. The thickness of the human scalp is approximately 7mm; therefore, measurements were obtained 0-7mm above the implants to assess the likely dose on the scalp. A comparison of the maximum dose on the scalp showed the titanium sheet had the highest dose at both 6 and 10MV. Conclusion: The backscatter dose differed with the density of the material and the backscatter depth was different for each material. Advances in knowledge: Ulcer formation due to radiotherapy after brain tumour depends on not only radiation but also the implant material. Therefore, the density and type of implant material should be considered when planning radiotherapy and selecting bone reconstruction materials.

Background/Aim: We assessed the efficacy and toxicity of concurrent chemoradiotherapy (CCRT) in patients with squamous cell carcinoma of the cervical esophagus. Patients and Methods: We retrospectively analyzed 37 patients treated with definitive CCRT. The patients received radiotherapy at a fraction dose of 2 Gy (total; 60 or 70 Gy) and concurrent chemotherapy. Adjuvant chemotherapy consisted of 1 to 2 cycles of 5-fluorouracil plus cisplatin or nedaplatin. Results: The median follow-up was 119.0 months, the 10-year overall survival, progression-free survival and laryngectomy-free survival rates were 35.6, 19.9 and 30.2% respectively. In the univariate analysis, T stage (T4 vs. T1-3) was the only prognostic factor for PFS. The most common acute toxicity was leukocytopenia (Grade 3; 27%). As for late toxicities, 4 patients (11%) developed Grade 2 or 3 esophageal strictures. Conclusion: The results of this study demonstrated that CCRT yielded satisfactory clinical outcomes with acceptable toxicities.

Purpose To analyze outcomes of stereotactic body radiotherapy (SBRT) for operable patients with early-stage non-small cell lung cancer (NSCLC) and to evaluate factors associated with outcomes. Methods We retrospectively analyzed operable patients with NSCLC, staged as cT1-2N0M0, treated with SBRT between 2006 and 2015. Both biopsy-proven and clinically diagnosed NSCLC were included. Local control and survival rates were calculated and compared between subsets of patients. We investigated factors associated with outcomes. Results We identified 88 operable patients among 661 patients with cT1-2N0M0 NSCLC. The median age was 79 years (range: 55–88). The median follow-up time after SBRT was 40 months (range: 4–121). Fifty-nine patients had been pathologically diagnosed and the other 29 had been clinically diagnosed as having NSCLC. Local control, cause-specific survival (CSS) and overall survival (OS) at 3 years were 91%, 97% and 90% for T1, and 100%, 82% and 74% for T2, respectively. The CSS and OS at 3 years were 100% and 100% for GGO and 83% and 59% for solid tumors, respectively (p = 0.005). On univariate analysis, age and T stage were significantly associated with CSS, and age, the Charlson Comorbidity Index (CCI), and opacity were significantly associated with OS. On multivariate analysis, age and CCI were significantly associated with OS. As for toxicities, Grades 0, 1, 2 and 3 radiation pneumonitis occurred in 37.5%, 47.7%, 13.6% and 1.1% of patients, respectively. No Grade 4 or 5 radiation pneumonitis occurred, and no other toxicities of Grade 2 or above were observed. Conclusion Outcomes of SBRT for operable early stage NSCLC were as good as previous SBRT and surgery studies. Further investigation for selecting good SBRT candidates is warranted in high-risk operable patients.

Purpose: To analyze genitourinary toxicity by followup of the International Prostate Symptom Score (IPSS) and Overactive Bladder Symptom Score (OABSS) after prostate brachytherapy. Methods and Materials: Six hundred eighty patients were treated with iodine-125 brachytherapy for localized prostate cancer. IPSS, OABSS, and two categories of IPSS questions (storage symptom score [IPSS-S] and voiding symptom score [IPSS-V]) were evaluated. Results: The median followup was 54 months (range, 24-108). All scales showed rapid increases followed by gradual decreases. The median times to IPSS peak and resolution were 1 and 6 months, respectively. The resolution rates of IPSS, IPSS-S, IPSS-V, and OABSS at the last followup were 84.2%, 86.3%, 89.5%, and 83.0%, respectively. The difference between IPSS baseline and peak was greater for larger preimplant prostate volumes (≥25 mL, p = 0.004). The time to resolution was longer for higher biologic effective dose (BED) (≥210 Gy, p = 0.019 [IPSS]), in those with larger prostate volumes (≥25 mL, p = 0.025 [OABSS]), in younger patients (younger than 70 years, p = 0.043 [IPSS-S]), and in those with androgen deprivation therapy (ADT) use (p = 0.049 [IPSS-V]). Urge incontinence, included in the OABSS, was observed more commonly in older patients (75 years and older, p = 0.018), with ADT use (p < 0.001), and for higher BED (≥210 Gy, p = 0.006). Conclusions: The IPSS and OABSS showed similar patterns of change. Urinary symptoms improved more rapidly in those with high baseline IPSS levels. The OABSS was useful for following urinary symptoms after prostate brachytherapy. Age, ADT use, preimplant prostate volume, and BED were significantly associated with urinary outcomes.

Nippon Medical School Hospital recently developed a high dose rate superficial brachytherapy (HDR-SBT) for keloids, which has been carried out since 2008. In this treatment, Ir-192 sources are placed on the affected area through flexible tubes, which has the advantage of providing high dose concentration to complicated shapes. Obviously, unnecessary radiation exposure to high-energy gamma rays must be reduced for vital organs around the affected area. We have developed a system which can evaluate the radiation exposure of tissues and organs in a MIRD-5 phantom using the PHITS Monte Carlo code when the prescribed dose was delivered uniformly to a flat surface based on the actual geometry in HDR-SBT. In the PHITS simulation, an affected area was assumed on the chest of the MIRD-5 phantom, then the dwell time at each dwell position was optimized to deliver 6 Gy uniformly over the affected area in the actual geometry with the lead shields and the bolus. In addition, the radiation exposures of each tissue and organ in the MIRD-5 phantom during the irradiation were calculated. The biologically equivalent dose of the thymus was the highest at 1145.60 mGy followed by the heart at 236.14 mGy and the breasts at 95.32 mGy.

Purpose: Small organ subvolume irradiated by a high-dose has been emphasized to be associated with late complication after radiotherapy. Here, we demonstrate a potential use of surface-based, non-rigid registration to investigate how high-dose volume topographically correlates with the location of late radiation morbidity in a case of tracheobronchial radiation stenosis. Material and methods: An algorithm of point set registration was implemented to handle non-rigid registration between contour points on the organ surfaces. The framework estimated the global correspondence between the dose distribution and the varying anatomical structure. We applied it to an 80-year-old man who developed tracheobronchial stenosis 2 years after high-dose-rate endobronchial brachytherapy (HDR-EBT) (24 Gy in 6 Gy fractions) and external beam radiotherapy (EBRT) (40 Gy in 2 Gy fractions) for early-stage tracheal cancer. Results and conclusions: Based on the transformation function computed by the non-rigid registration, irradiated dose distribution was reconstructed on the surface of post-treatment tracheobronchial stenosis. For expressing the equivalent dose in a fractional dose of 2 Gy in HDR-EBT, α/β of linear quadratic model was assumed as 3 Gy for the tracheal bronchus. The tracheobronchial surface irradiated by more than 100 Gyαβ3 tended to develop severe stenosis, which attributed to a more than 50% decrease in the luminal area. The proposed dose reconstruction technique can be a powerful tool to predict late radiation toxicity with spatial consideration.