New ambulatory implant technique of high-dose-rate interstitial brachytherapy for prostate cancer

Purpose The aim of this study was to improve the performance status of prostate cancer patients during high-dose-rate interstitial brachytherapy (HDR-ISBT). To this end, we have developed a new ambulatory implant technique. Materials and methods Ten prostate cancer patients were treated with HDR-ISBT as monotherapy from October 2003 until March 2004. We utilized a new removable template, a flexible applicator with a nonmetallic bead and button stopper, and an inner catheter connecting the applicator and the transfer tube of the brachytherapy unit. We shortened the connector end of the flexible applicator to enable the patient to sit down and walk freely during the treatment time. Results All 10 patients could walk without any support. No problem in the application was observed. Conclusion Our new ambulatory implant technique for HDR-ISBT was able to improve the performance status of prostate cancer patients.     

Template-based high-dose-rate interstitial brachytherapy in gynecologic cancers: A single institutional experience

PurposeTo report the outcome and toxicities of radical external beam radiotherapy (EBRT) and template-based high-dose-rate interstitial brachytherapy (ISBT) in patients diagnosed with cervical cancer undergoing inadvertent surgery, vault cancers, and vaginal cancers at our institution.Methods and MaterialsBetween January 2000 and December 2008, 113 patients (37 patients of cervical cancer post-inadvertent surgery, 57 patients with vault cancers, and 19 patients with primary vaginal cancers) were treated with Martinez Universal Perineal Interstitial Template brachytherapy boost after EBRT. The median EBRT dose was 50 Gy, median ISBT dose was 20 Gy, whereas median total dose was 73 Gy equivalent dose at 2 Gy per fraction in all three groups.ResultsMedian followup of surviving patients for the whole group was 43 months (interquartile range, 19–67 months). The 3-year actuarial disease-free survival and overall survival for three groups was 61%, 61%, 59% and 64%, 64%, and 56%, respectively. Grade III/IV rectal toxicity was seen in 11 (10%) patients, bladder toxicity in 5 (4.5%) patients, whereas 7 (6%) patients developed Grade III small bowel toxicity. Residual disease at brachytherapy had significant impact on DFS and OS. Other factors such as age, disease volume, parametrial extension, and vaginal extension did not impact the survivals.ConclusionsMartinez Universal Perineal Interstitial Template–based high-dose-rate ISBT boost in gynecologic cancer results in a reasonable outcome in terms of survivals with acceptable late toxicities. The use of template-based ISBT is associated with a definite learning curve.     

Development and dosimetric assessment of a patient-specific elastic skin applicator for high-dose-rate brachytherapy

Purpose

The purpose of this study was to develop a patient-specific elastic skin applicator and to evaluate its dosimetric characteristics for high-dose-rate (HDR) brachytherapy.

Interobserver variability in rectum contouring in high-dose-rate brachytherapy for prostate cancer: A multi-institutional prospective analysis

PurposeThe aim of this study was to evaluate the interobserver variability (IOV) of rectum contouring, and its dosimetric consequences, for high-dose-rate brachytherapy in patients with prostate cancer across multiple institutions.Methods and MaterialsFive radiation oncologists contoured rectums in 10 patients on transperineal ultrasound image sets after establishing a delineation consensus. The D_0.1cc, D_1cc, and D_2cc rectum volume parameters were determined. The mean, standard deviation, and range of each dose–volume histogram parameter were evaluated for each patient. The IOV was determined using the coefficient of variation, and the dosimetric impacts on the total dose were analyzed by estimating the biologically equivalent dose (EQD_{2α/β = 3}).ResultsThe interobserver coefficients of variation (±standard deviation) for the reported D_0.1cc, D_1cc, and D_2cc were 5 ± 1.84%, 4 ± 1.26%, and 4 ± 1.33%, respectively. As for the impact on the total dose, the mean dose differences for D_0.1cc, D_1cc, and D_2cc were 10 Gy, 7.3 Gy, and 6.6 Gy, respectively.ConclusionsThe D_2cc is robust as evident by the low IOV (<5%). However, some variability ranges almost overlap with the clinical threshold level, which may present dosimetric and clinical complications. General rectal contouring guidelines for prostate high-dose-rate brachytherapy are desirable to reduce discrepancies in delineation.     

Clinical outcomes using image-guided interstitial brachytherapy for definitive cervical cancer patients with high-risk clinical target volumes greater than 30 cc

PurposeGiven the limited data using an interstitial approach with 3D-based planning for definitive cervical cancer utilizing the GEC-ESTRO defined high-risk clinical target volume (HR-CTV), we reviewed our institutional experience of cervical cancer patients with HR-CTVs ≥ 30 cc to determine whether our clinical and toxicity outcomes are acceptable.MethodsA retrospective review of 37 cervical cancer patients with high-risk clinical target volumes (HR-CTVs) ≥30 cc treated with interstitial image-guided brachytherapy (IS IGBT) was performed. All patients received external beam radiotherapy to a median dose of 45 Gy, followed by IS IGBT delivered in a single implant to a median dose of 6 Gy × 5 fractions. Median HR-CTV was 59 cc. A median HR-CTV D₉₀ of 87.44 Gy was achieved. Kaplan–Meier method was used to evaluate local control (LC), distant control, and overall survival (OS), with stratification by overall treatment time (OTT) ≤ 7 or >7 weeks.ResultsMedian followup was 17 months. The estimated 2-year LC, distant control, and OS were 77.6% (confidence interval [CI]: 63.8–94.5%), 56.8% (CI: 41.3–78.1%), and 54.4% (CI: 39.4–75%), respectively. The 2-year LC for OTT ≤7 weeks and >7 weeks were 100% and 58.3%, respectively (p = 0.026). The 2-year OS for OTT ≤7 weeks and >7 weeks were 77.8% and 38%, respectively (p = 0.021).DiscussionsIS IGBT can achieve a high D₉₀ to the HR-CTV even in the setting of large-volume disease and results in a favorable LC and toxicity profile. OTT > 7 weeks is associated with significant decrease in LC and OS.ConclusionsEfforts should be made to complete whole treatment within 7 weeks as this is associated with improved clinical outcomes.     

Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film

Purposehe purpose of this study was to study the dosimetric characterization of sonolucent material “TPX” to be used toward gynecologic high-dose-rate brachytherapy treatments using ultrasound-compatible cylinders in non–model-based dose calculation workflows.MethodsMonte Carlo simulations were performed using EGSnrc application egs_brachy in cylinders of polymethylpentene (TPX) plastic, water, and PMMA. Simulations were performed of five 192Ir sources placed longitudinally in ～3.7 cm diameter, 5.0 cm length cylinders (matching physical cylinders used in film measurements). TPX and PMMA dose distributions and percentage depth dose curves were compared relative to water.Film measurements were performed to validate egs_brachy simulations. TPX and PMMA cylinders were placed in a water tank using 3D-printed supports to position film radially and touching the surface of the cylinders. The same five 192Ir dwell positions were delivered as simulated in egs_brachy.ResultsThe egs_brachy and film percentage depth doses agreed within film uncertainties. The egs_brachy relative dose difference between TPX and water was (0.74 ± 0.09)% and between PMMA and water was (-0.79 ± 0.09)% over the dose scoring phantom. Dose differences for TPX and PMMA relative to water were less than ± 1% within 5 cm of the cylinder surface.ConclusionsIn a solid sonolucent sheath of TPX, the dosimetric differences are comparable with PMMA and other applicator materials in clinical use. No additional uncertainty to dose calculation is introduced when treating through TPX cylinders compared with current applicator materials, and therefore, it is acceptable to perform gynecologic brachytherapy treatments with a sonolucent sheath inserted during radiation delivery.     

Dosimetric and clinical outcome in image-based high-dose-rate interstitial brachytherapy for anal cancer

PurposeTo evaluate dosimetric and clinical outcome in patients of anal cancer treated with image-based interstitial high-dose-rate brachytherapy following chemoradiation.Methods and MaterialsSixteen patients with anal cancer were treated with chemoradiation followed by brachytherapy boost with image-based high-dose-rate interstitial brachytherapy from January 2007 to June 2011. Two brachytherapy dose schedules were used: 21 Gy in seven fractions and 18 Gy in six fractions depending on response to chemoradiation. CT scan was done after placement of needles for confirmation of placement and treatment planning. Target volume was contoured on CT scans. Volumetric quality indices and dose parameters were calculated.ResultsThe mean clinical target volume was 17.7 ± 4.98 cm³, and the median overall tumor size was 4.2 cm (3.4–5 cm). The mean values of coverage index, dose homogeneity index, overdose volume index, dose non-uniformity ratio, and conformal index were 0.94, 0.83, 0.21, 0.37, and 0.88, respectively. With a median followup of 41 months (range, 20–67.2 months), preservation of the anal sphincter was achieved in 14 patients. The 1- and 2-year local control rates were 93.8% and 87.5%, respectively. Treatment was well tolerated and none of the patients developed Grade 3 or higher late toxicity.ConclusionsThe combination of external beam radiotherapy with interstitial brachytherapy increases the dose to the tumor volume and limits the volume of irradiated normal tissue, thereby decreasing late toxicity. The use of image-based treatment planning provides better dose conformality with reduced toxicity and helps to prevent a geographic miss.     

High-dose-rate brachytherapy for previously irradiated patients with recurrent esophageal cancer

Purpose Our objective was to assess the feasibility, efficacy, and complications of high-dose-rate (HDR) brachytherapy for patients with recurrent esophageal cancer after external radiotherapy. Materials and methods Six patients with recurrent esophageal cancer after external radiotherapy were treated with HDR brachytherapy (Ir-192 source) from January 2003 to February 2004. The median age of the patients was 69 years. All patients had received external radiotherapy (median dose 60 Gy) before HDR brachytherapy. All patients underwent HDR brachytherapy once a week with a dose of 4 or 5 Gy per fraction in the esophageal mucosa (median total dose 20 Gy). The Kaplan-Meier method was used to calculate local control rates. Results The median overall survival period was 30.0 months. Local control was observed in five patients and residual tumor in one patient. Persistent local control was observed in two patients. No patient died of esophageal cancer, and all patients survived. We observed no severe late complications related to HDR brachytherapy. Conclusion These data suggest that HDR brachytherapy is an effective and safe treatment for patients with recurrent esophageal cancer after external radiotherapy.     

Time-driven activity-based costing of a novel form of CT-guided high-dose-rate brachytherapy intraoperative radiation therapy compared with conventional breast intraoperative radiation therapy for early stage breast cancer

IntroductionIntraoperative radiation therapy is an emerging option for adjuvant therapy for early stage breast cancer, although it is not currently considered standard of care in the United States. We applied time-driven activity-based costing to compare two alternative methods of breast intraoperative radiation therapy, including treatment similar to the techniques employed in the TARGIT-A clinical trial and a novel version with CT-guidance and high-dose-rate (HRD) brachytherapy.Methods and MaterialsProcess maps were created to describe the steps required to deliver intraoperative radiation therapy for early stage breast cancer at each institution. The components of intraoperative radiation therapy included personnel, equipment, and consumable supplies. The capacity cost rate was determined for each resource. Based on this, the delivery costs were calculated for each regimen. For comparison across centers, we did not account for indirect facilities costs and interinstitutional differences in personnel salaries.ResultsThe CT-guided, HRD form of intraoperative radiation therapy costs more to deliver ($4,126.21) than the conventional method studied in the TARGIT-A trial ($1,070.45). The cost of the brachytherapy balloon applicator ($2,750) was the primary driver of the estimated differences in costs. Consumable supplies were the largest contributor to the brachytherapy-based approach, whereas personnel costs were the largest contributor to costs of the standard form of intraoperative radiation therapy.ConclusionsWhen compared with the more established method of intraoperative radiation therapy using a portable superficial photon unit, the delivery of treatment with CT guidance and HDR brachytherapy is associated with substantially higher costs. The excess costs are driven primarily by the cost of the disposable brachytherapy balloon applicator and, to a lesser extent, additional personnel costs. Future work should include evaluation of a less expensive brachytherapy applicator to increase the anticipated value of brachytherapy-based intraoperative radiation therapy.     

Experience of high-dose-rate brachytherapy for head and neck cancer treated by a customized intraoral mold technique

Radiotherapy of head and neck cancer has become more successful with the advances in treatment modalities and use of a multidisciplinary approach. Higher quality treatment and a team approach to radiotherapy have thus been required for head and neck cancer. This study presents the clinical experience of high-dose-rate (HDR) brachytherapy for head and neck cancer treated by a customized intraoral mold technique. Two patients are reported for whom we created dental prostheses as the radiation carriers for HDR brachytherapy of their head and neck cancers. HDR brachytherapy with the dental prostheses reported here was feasible and effective for eradicating the head and neck cancer. It has been demonstrated that HDR brachytherapy using a customized intraoral technique can be a treatment option for patients who are not candidates for surgery or external irradiation. It is strongly suggested that specialized dentists are needed who are familiar with not only the anatomy and function of the head and neck region but also radiotherapy. Dental radiologists should take responsibility for constructing irradiation prostheses. If they do, they have the potential to improve the quality of life of patients who undergo radiotherapy for head and neck cancer.     

Comparison of dose-escalated,image-guided radiotherapy vs. dose-escalated,high-dose-rate brachytherapy boost in a modern cohort of intermediate-risk prostate cancer patients

PurposeWe compared outcomes in intermediate-risk prostate cancer patients treated with dose-escalated adaptive image-guided radiation therapy (IGRT) or dose-escalated high-dose-rate brachytherapy boost (HDR-B).Methods and MaterialsPatients with intermediate-risk prostate cancer by National Comprehensive Cancer Network criteria were treated with either CT-based off-line adaptive IGRT (n = 734) or HDR-B (n = 282). IGRT was delivered with 3D-conformal or intensity-modulated radiation therapy with a median dose of 77.4 Gy. For HDR-B, the whole pelvis received a median 46 Gy, and the prostate 2 implants of 9.5 Gy (n = 71), 10.5 Gy (n = 155), or 11.5 Gy (n = 56).ResultsMedian followup was 3.7 years for IGRT and 8.0 years for HDR-B (p < 0.001). Eight-year biochemical control was 86% for IGRT and 91% for HDR-B (p = 0.22), disease-free survival 67% for IGRT and 79% for HDR-B (p = 0.006), and overall survival 75% for IGRT and 86% for HDR-B (p = 0.009). Cause-specific survival (8-year, 100% vs. 99%), freedom from distant metastases (98% vs. 97%), and freedom from local recurrence (98% vs. 98%) did not differ (p > 0.50 each). A worse prognosis group was defined by percent positive prostate biopsy cores >50%, perineural invasion, or stage T2b–c, encompassing 260 (35%) IGRT and 171 (61%) HDR-B patients. These patients evidenced a 5-year biochemical control of 96% for HDR-B and 87% for IGRT (p = 0.002).ConclusionsDose-escalated IGRT and HDR-B both yield excellent clinical outcomes for patients with intermediate-risk prostate cancer. Improved biochemical control with HDR-B for patients with worse pretreatment characteristics suggests that a subgroup of intermediate-risk prostate cancer patients may benefit from dual-modality treatment.     

Improved survival for patients with prostate cancer receiving high-dose-rate brachytherapy boost to EBRT compared with EBRT alone

PurposeHigh-dose-rate (HDR) brachytherapy boost is a treatment of intermediate- to high-risk prostate cancer, but long-term clinical outcome data are sparse. We report long-term survival and toxicity data in a cohort of patients treated in a single institution.MethodsBetween 1998 and 2004, 654 patients with localized prostate cancer received either 3-dimensional conformal radiotherapy (median 46 Gy) with an HDR (median 18 Gy in three fractions) boost (“3-D conformal radiotherapy [3DCRT] + HDR”; 215 patients) or 3DCRT alone (“3DCRT”; median 70 Gy; 439 patients) with curative intent. Men with National Comprehensive Cancer Network intermediate risk were offered neoadjuvant androgen deprivation and with high risk were also offered adjuvant androgen deprivation. Data collection included patient-reported outcome measures.ResultsThe 3DCRT + HDR group was older (72.3 vs. 68.9 yrs), had higher presenting PSAs (iPSA) (15.66 and 12.57 ng/mL, respectively), higher proportion of Gleason scores >7 (15.3% vs. 12.4%), and higher proportions of extracapsular disease (29.3% vs. 25.5%). 3DCRT + HDR men had lower proportions of low-risk patients (3.3% vs. 19.4%) and higher proportions of high-risk patients (50.7% vs. 37.4%) than the 3DCRT group. The 5-, 10-, and 15-year overall survival was superior at 92%, 81%, and 67%, respectively, for the 3DCRT + HDR group, compared with 88%, 71%, and 53%, respectively, in the 3DCRT group (p < 0.001). The 5-, 10-, and 15-year cause specific survival also favored the HDR boost group with survival of 96%, 93%, and 87% (3DCRT + HDR) and 95% 88% and 79% (3DCRT), respectively (p < 0.037).ConclusionsHDR brachytherapy boost in conjunction with 3DCRT offered superior overall survival and cause-specific survival in our patient population.     

Dosimetric analysis of breast cancer tumor bed boost: An interstitial brachytherapy vs. external beam radiation therapy comparison for deeply seated tumors

PurposeTo dosimetrically compare interstitial brachytherapy (MIBT) vs. EBRT (3DCRT and high-energy electron beams) for deep-seated tumor bed boosts (depth ≥4 cm) in early-stage breast cancer.Methods and MaterialsPlanning CTs of fifteen left-side breast cancer patients previously treated with MIBT boost chosen for this study. MIBT, 3DCRT (three-field technique), and enface high-energy electron (15–18 MeV) plans retrospectively generated on these images. To minimize intrapatient target contour inconsistency, due to a technical limitation for transferring identical contours from brachytherapy to EBRT planning system, spherical volumes delineated as hypothetical CTVs (CTV-H) (depth ≥4 cm with considering the geometry of the brachytherapy implant) instead of original lumpectomy cavities (which had irregular contours). In EBRT, PTV-H=CTV-H+5 mm. To account for beam penumbra, additional PTV-H to beam-edge margins added (3DCRT = 5 mm; electron = 10 mm). Included organs at risk (OARs) were ipsilateral breast, skin, ribs, lung, and heart. Prescribed dose-fractionations were 12 Gy/3fractions (MIBT) and 16 Gy/8fractions (EBRT) (BED = 24 Gy, breast cancer Alpha/Beta = 4 Gy). Biologically equivalent DVH parameters for all techniques compared.ResultsMean CTV-H depth was 6 cm. Normal breast V_25%–V_100%; skin V_10%–V_90%; rib V_25%–V_75%; lung V_5%–V_25%; heart V_10%; mean lung dose; ribs/lung D_max were lower in MIBT vs. 3CDRT. MIBT reduced breast V_25%–V_125%; skin V_25%–V_125%; rib V_25%–V_75% and V_100%; lung V_25%–V_90%; heart V_10%–V_50%; skin/ribs/lung D_max compared to electrons. In contrast, breast V_125%–V_250% and V_175%–V_250% were increased in MIBT vs. 3DCRT and electron plans, respectively. Electron plans had the minimum mean heart dose.ConclusionsFrom a dosimetric point of view, in deeply-seated lumpectomy beds, MIBT boost better protects OARs from exposure to medium and high doses of radiation compared to 3DCRT and high energy electron beams (except more ipsilateral breast hot spots).     

The equivalent dose contribution from high-dose-rate brachytherapy to positive pelvic lymph nodes in locally advanced cervical cancer

PurposeDefinitive radiation therapy for locally advanced cervical cancer involves external beam radiation therapy (EBRT) and high-dose-rate (HDR) brachytherapy. There remains controversy and practice pattern variation regarding the optimal radiation dose to metastatic pelvic lymph nodes (LNs). This study investigates the contribution of the pelvic LN dose from HDR brachytherapy.Methods and MaterialsFor 17 patients with 36 positive pelvic LNs, each LN was contoured on a computed tomography (CT) plan for EBRT and on brachytherapy planning CTs using positron emission tomographic images obtained before chemoradiation. The mean delivered dose from each plan was recorded, and an equivalent dose in 2-Gy fractions (EQD2) was calculated. A Student's t test was performed to determine if the mean delivered dose is significantly different from the mean prescribed dose and EQD2.ResultsThe average prescribed dose from the total EBRT was 54.09 Gy. The average prescribed HDR dose to International Commission on Radiation Units point A was 26.81 Gy. The average doses delivered to the involved LNs from EBRT and brachytherapy were 54.25 and 4.31 Gy, respectively, with the corresponding EQD2 of 53.45 and 4.00 Gy. There was no statistically significant difference (p < 0.05) between the mean delivered and the prescribed doses for EBRT and between the delivered dose and the EQD2 for EBRT and brachytherapy.ConclusionsOur study shows that the HDR contribution is 7% (4.00 Gy) of the total EQD2 (57.45 Gy). The HDR contribution should be accounted for when prescribing the EBRT boost dose to pelvic LNs for the optimal therapeutic dose.     

3D打印个体化模具在子宫内膜癌术后三维后装治疗中的剂量学研究

目的 探讨3D打印个体化模具辅助子宫内膜癌术后三维后装治疗中的剂量学优势。方法 回顾性选取宁波大学附属第一医院21例早期子宫内膜癌术后患者的三维后装治疗计划,利用北京科霖众计划系统,在已实施的个体化模具组基础上,为每位患者设计虚拟单通道柱状施源器计划,所有计划均采用三维逆向模拟退火的算法。比较两组计划靶区90%、98%和100%体积接受的最低剂量(D₉₀、D₉₈、D₁₀₀)以及适形指数(CI)、均匀度(HI)、超剂量体积指数(OI);同时,对比两组危及器官膀胱、直肠、小肠和尿道的0.01、1、2以及5 cm³所接受的最大剂量(D_{0.01 cm³}、D_{1 cm³}、D_{2 cm³}以及D_{5 cm³})差异。结果 两组计划都能满足临床需求。在靶区所受剂量方面,两组计划靶区D₉₀、D₉₈、D₁₀₀没有明显差异,但是个体化模具组靶区剂量的CI、HI均优于单通道组靶区,而靶区OI指数小于单通道计划(t=-3.21、-5.99、6.25,P＜0.05)。在危及器官所受剂量方面,个体化模具组膀胱、直肠、尿道所受剂量D_{1 cm³}、D_{2 cm³}和D_{5 cm³}相比单通道组均有明显降低(t=3.18、3.21、3.77、7.97、8.92、10.92、2.54、3.46、4.28,P＜0.05);小肠由于距离靶区比较远,在两组计划中所受剂量差异不明显(P＞0.05)。结论 3D打印个体化模具在子宫内膜癌术后三维近距离治疗中靶区均匀度、适形指数更优,而且膀胱、直肠、尿道所受剂量更低,具有推广价值。     

Workflow and efficiency in MRI-based high-dose-rate brachytherapy for cervical cancer in a high-volume brachytherapy center

PurposeWe report the clinical workflow and time required for MRI-based image-guided brachytherapy (MR-IGBT) of cervical cancer patients in a high-volume brachytherapy center with 10 years of experiences to provide a practical guideline for implementing MR-IGBT into clinical use.Methods and MaterialsWe recorded the time and workflow of each procedure step within the 40 consecutive ring and tandem applicator fractions of MR-IGBT by our multidisciplinary team. We divided the entire procedure into four sections based on where the procedure was performed: (1) applicator insertion under sedation, (2) MR imaging, (3) planning, and (4) treatment delivery. In addition, we compared the current procedure time to the initial procedure time when first implementing MR-IGBT in 2007–2008 via a retrospective review.ResultsMean total procedure time was 149.3 min (SD 17.9, ranges 112–178). The multidisciplinary team included an anesthesia team, radiologist, radiation oncologist, nurses, radiation therapists, MRI technicians, dosimetrists, and physicists. The mean procedure time and ranges for each section (min) were as follows: (1) 56.2 (28.0–103.0), (2) 31.0 (19.0–70.0), (3) 44.3 (21.0–104.0), and (4) 17.8 (9.0–34.0). Under current setting, the combined mean procedure time for MR imaging and planning was 63.2 min. In comparison, the same procedure took 137.7 min in 2007–2008 period, which was significantly longer than the current workflow (p < 0.001).ConclusionsA skilled and dedicated multidisciplinary team is required for an efficient clinical workflow and delivery of MR-IGBT. Over the years, we have improved efficiency with clinical experience and continuous efforts in staff education.     

Radiobiological optimization comparison between pulse-dose-rate and high-dose-rate brachytherapy in patients with locally advanced cervical cancer

PurposeOnly scarce data are available on the possibility to include radiobiological optimization as part of the dosimetric process in cervical cancer treated with brachytherapy (BT). We compared dosimetric outcomes of pulse-dose-rate (PDR) and high-dose-rate (HDR)-BT, according to linear-quadratic model.Methods and MaterialsThree-dimensional dosimetric data of 10 consecutive patients with cervical cancer undergoing intracavitary image-guided adaptive PDR-BT after external beam radiation therapy were examined. A new HDR plan was generated for each patient using the same method as for the PDR plan. The procedure was intended to achieve the same D₉₀ high-risk clinical target volume with HDR as with PDR planning after conversion into dose equivalent per 2 Gy fractions (EQD2) following linear-quadratic model. Plans were compared for dosimetric variables.ResultsAs per study's methodology, the D₉₀ high-risk clinical target volume was strictly identical between PDR and HDR plans: 91.0 Gy (interquartile: 86.0–94.6 Gy). The median D₉₈ intermediate-risk clinical target volume was 62.9 Gy_EQD2 with HDR vs. 65.0 Gy_EQD2 with PDR (p < 0.001). The median bladder D_2cc was 65.6 Gy_EQD2 with HDR, vs. 62 Gy_EQD2 with PDR (p = 0.004). Doses to the rectum, sigmoid, and small bowel were higher with HDR plans with a median D_2cc of 55.6 Gy_EQD2 (vs. 55.1 Gy_EQD2, p = 0.027), 67.2 Gy_EQD2 (vs. S 64.7 Gy_EQD2, p = 0.002), and 69.4 Gy_EQD2 (vs. 66.8 Gy_EQD2, p = 0.014), respectively. For organs at risk (OARs), the effect of radiobiological weighting depended on the dose delivered. When OARs BT contribution to D_2cc doses was <20 Gy_EQD2, both BT modalities were equivalent. OARs EQD2 doses were all higher with HDR when BT contribution to D_2cc was ≥20 Gy_EQD2.ConclusionBoth BT modalities provided satisfactory target volume coverage with a slightly higher value with the HDR technique for OARs D2_cc while intermediate-risk clinical target volume received higher dose in the PDR plan. The radiobiological benefit of PDR over HDR was predominant when BT contribution dose to OARs was >20 Gy.     

宫颈癌二维近距离后装治疗中危及器官参考点剂量与三维体积剂量的相关性研究

目的 利用宫颈癌二维近距离后装治疗中危及器官（OARs）点剂量预测其三维体积剂量,评估在特定条件下,二维计划OARs体积剂量能否满足三维后装剂量限值要求。方法 回顾性分析基于CT图像的10例宫颈癌患者近距离后装治疗计划,将处方参考点剂量定为600 cGy,膀胱和直肠参考点剂量<360 cGy,设计并优化得到二维后装治疗计划。采用Pearson相关分析法对膀胱、直肠参考点剂量及OARs体积受量做相关性分析,利用线性回归方法得出膀胱、直肠参考点与其体积剂量的线性方程。结果 膀胱、直肠参考点剂量分别与其D_{1 cm³}、D_{2 cm³}、D_{5 cm³}和平均剂量显著正相关（r=0.559~0.668,P<0.05）;膀胱、直肠参考点剂量分别是其D_{2 cm³}的1.404和1.181倍;内外照射完成后膀胱、直肠D_{2 cm³}的相当于200 cGy分次等效生物剂量（EQD2）分别为8 410.0和6 827.0 cGy,均低于二者体积剂量限值。结论 利用膀胱、直肠参考点剂量能在一定程度上预测其体积剂量,对于满足膀胱、直肠参考点剂量低于处方剂量60%二维近距离后装计划,可将膀胱、直肠体积受量控制在相对安全的剂量范围内。而由于缺乏对小肠、乙状结肠剂量检测,二维后装计划在临床使用上仍然具有很大局限性。