High-dose gynecologic endocavitary brachytherapy. Technical and dosimetric aspects

The technical and dosimetric aspects are presented of high-dose intracavitary brachytherapy in gynecology. Fifty-five patients (203 insertions) were examined over two years with a remote loading Selectron HDR 60Co unit installed in a dedicated bunker. The dose to the rectal and bladder markers on AP and LL films was calculated before every irradiation, in order to allow the necessary corrections to be made. Uniform irradiation conditions were obtained at each treatment set-up for both tumoral target and bladder and rectal doses. High-dose intracavitary brachytherapy proved to be a safe, reliable and versatile method from the technical and dosimetric point of view both in the treatment of unoperated gynecological malignancies and in postoperative therapy.     

腮腺癌术后高危复发区放疗的不同治疗计划剂量学比较

目的 探讨腮腺癌术后高危复发区用何种照射方法可以更有效的使靶区剂量均匀及更好的保护危及器官.方法 对8例腮腺癌术后患者设计治疗计划,处方剂量为95%计划靶区(PTV)60 Gy/30次.对常规放疗、二维适形放疗(2D-CRT)、三维适形放疗(3D-CRT)和调强放疗(IMRT)等放射治疗技术的腮腺癌术后靶区进行放疗计划设计,分析比较各种治疗计划靶区适形度和在保护危及器官等方面的优劣.结果 在2D-CRT时,以计算点深度取3.5 cm,电子线能量采取12 MeV及X射线/电子射线(X/E)剂量比为1∶2时靶区的适形度和均匀度较好,危及器官的受量较低.与2D-CRT比较,常规放疗照射野能够较好地包括CT断层图像上勾画的靶区.与2D-CRT及3D-CRT相比,IMRT计划有最好的靶区适形度及均匀度,同时对危及器官有较好的保护作用.结论 X射线与电子线混合线束照射时,剂量计算点深度取3.5 cm左右、电子线能量采取12 MeV及X/E剂量比为1∶2时,靶区的适形度和均匀度较好,对正常组织的保护较好,但具体患者最好用计划系统来选择以上指标.常规放疗按解剖标志确定的照射野能够较好地包括三维靶区.IMRT计划的靶区适形度及均匀度最好,并且危及器官受量较低,在腮腺癌术后放射治疗中IMRT技术是值得推广并普及的放射治疗技术.     

Interventional procedures for biliary drainage with bilioplasty in paediatric patients: dosimetric aspects

PURPOSE: This study was undertaken to evaluate patient dose in paediatric liver transplant recipients treated by percutaneous biliary drainage and bilioplasty procedures. MATERIALS AND METHODS: Effective dose rates and entrance skin-dose (ESD) rates per minute of fluoroscopy were measured by using a plexiglas phantom (thickness 10 cm) simulating the patient and by varying the exposure parameters (type of pulsed fluoroscopy, image intensifier diameter, presence of diaphragms) to identify the technique delivering the lowest patient dose. In vivo measurements were performed during three interventional procedures. RESULTS: The effective dose rate proved to be lowest for a particular type of pulsed fluoroscopy, with maximum magnification and with field-limiting diaphragms. The in vivo measurements showed a maximum ESD value of around 50 MGY (the threshold for transient erythema is 2,000 MGY, ICRP 60). The effective dose values were in the range of 0.9-1.5 MSV. CONCLUSIONS: We established exposure parameters providing the desired image quality with the lowest dose for the equipment used and for a specific type of interventional procedure. The measured ESD values allow us to exclude the risk of deterministic effects on the skin. The effective dose values and considerations regarding the likelihood of radiation-induced cancer led to the conclusion that the radiological risk for the patient is largely justified by the benefits of these kinds of procedure.     

Multicentre dosimetric comparison of photon-junctioning techniques in head and neck radiotherapy

Because many head and neck radiotherapy treatment techniques rely on a junction between X-ray fields, it was the aim of the present study to investigate the use of different junctioning techniques and the affect on the dose across the junction. Techniques in use at nine radiotherapy centres in Australia were investigated using thermoluminescence dosimetry (TLD). The techniques could broadly be divided into two groups: (i) use of the light field to match the fields after moving the patient; and (ii) use of asymmetric collimation to create a single isocentre located in the junction. The mean dose at the junction and its reproducibility was studied in five consecutive treatments in each centre using 25 TLD chips placed throughout the junction in an anthropomorphic phantom. There was a tendency for the mono-isocentric technique to deliver a lower, more accurate mean dose at the junction (Group I: 1.22 Gy (n = 8) vs Group II: 0.96 Gy (n = 5) for 1 Gy planned, some centres contributed to both technique) with greater reproducibility (Group I: 9.6%, Group II: 5.1% of the mean dose). We conclude that a mono-isocentric treatment technique has the potential to deliver a more accurate and reproducible dose distribution at the field junction of photon beams in head and neck treatment.     

Indium-111 bleomycin complex for radiochemotherapy of head and neck cancer — dosimetric and biokinetic aspects

Bleomycin (BLM) is used for the treatment of head and neck cancer. In order to improve the effectiveness of this chemotherapeutic drug, BLM was combined with indium-111. A complex of these agents (¹¹¹In-BLMC), formed at low pH, was injected intravenously into ten head and neck cancer patients in escalating activities of 75, 175 and 375 MBq. The internally delivered dose to the tumours varied from 0.20 to 2.73 mGy at 75 MBq, from 0.33 to 2.51 mGy at 175 MBq, and from 0.87 to 31.3 mGy at the 375 MBq activity level. Uptake of radioactivity was 0.45±0.24×10^–3% ID/g in primary tumours and 0.52±0.20×l0^–3% ID/g in metastases (at 48 h). Tumour volumes varied from 0.51 to 49.0 cm³. The radioactivity half-lives in the tumours were 30±7 h. The activity distribution and penetration into tumour tissue were not affected by increasing the injected activity. There was a positive correlation between BLMC uptake and Ki-67/Mib activity as well as number of mitoses in tumour tissue. These data indicate that¹¹¹In-BLMC has potential as a radiochemotherapeutic agent in head and neck cancer and that adjuvant Auger-electron therapy is possible using^114m-In-labelled BLMC.     

Head and neck tumors: dosimetric considerations of mixed-energy photon beam therapy

The goal of sophisticated treatment planning in radiation therapy is to maximize dose to the tumor or target volume, while the integral dose is minimized, to reduce normal tissue morbidity. In the head and neck regions, the anatomic irregularities of individual patients and the critical structures that limit the administration of dose within the irradiated volumes often complicate the optimization of dosimetry. The availability of dual-energy accelerators that deliver beams of low- and high-energy photons allows the convenient administration of mixed-energy photon irradiation and facilitates the development of optimal treatment strategies for selected lesions. Highly lateralized carcinomas of the upper aerodigestive tract, in which sparing of contralateral cervicofascial tissue is desirable, are particularly well suited for this technique. Treatment plans that make use of irradiation with conventional single-energy beams and mixed-energy photon therapy are compared for representative lesions of the head and neck.     

Technical and dosimetric aspects of iodine-125 seed reimplantation in suboptimal prostate implants

Objective:

Brachytherapy employing iodine-125 seeds is an established treatment for low-risk prostate cancers. Post-implant dosimetry (PID) is an important tool for identifying suboptimal implants. The aim of this work was to improve suboptimal implants by a subsequent iodine-125 seed top-up (reimplantation), based on the PID results.

Methods:

Of 255 patients treated between 2009 and 2012, 6 were identified as having received suboptimal implants and were scheduled for seed top-up. Needle configurations and the number of top-up seeds were determined based on post-implant CT images as well as a reimplantation treatment plan. An average of 14 seeds per patient were implanted during each top-up. Dosimetric outcome was assessed via target parameters and doses received by organs at risk.

Results:

All six patients had a successful top-up, with a 67% increase in the mean dose delivered to 90% of the prostate volume and a 40% increase in the volume that receives 100% of the prescribed dose. However, the final dosimetric assessment was based on the same seed activity, as the planning system does not account for the decay of the initially implanted seeds. Although physical dosimetry is not influenced by different seed activities (doses are calculated to infinity), the radiobiological implications might be slightly different from the situation when optimal implantation is achieved with one treatment only.

Conclusion:

Seed reimplantation in suboptimal prostate implants is feasible and leads to successful clinical outcomes.

Advances in knowledge:

Suboptimal prostate implants can occur for various reasons. This work shows that seed reimplantation as salvage therapy can lead to an optimal dosimetric outcome with manageable normal tissue effects.Low dose rate (LDR) brachytherapy employing radioactive seeds is a well-established treatment for low-risk prostate cancers. In our centre, implants are conducted with iodine-125 seeds (Oncura RAPID Strand, model 6711; Oncura Inc., Arlington Heights, IL) with an average seed activity of 0.395 mCi to deliver a prescribed dose of 145 Gy (to >98% of the prostate). Treatment planning and post-implant dosimetry (PID) are completed using SPOT-PRO™ v. 3.1 (Nucletron, Utrecht, Netherlands) software based on transrectal ultrasound images (for treatment planning) and CT images (for PID).The most commonly reported parameters that are indicative of the dosimetric quality of the implant are D₉₀ (the dose delivered to 90% of the prostate volume) and V₁₀₀ (the volume that receives 100% of the prescribed dose). Several studies showed a link between the quality of implants and the biochemical outcome [1–3]. Therefore, to minimise the risk of recurrence, it is recommended to achieve a post-implant D₉₀>140 Gy and V₁₀₀>90% [1].PID is an important quantitative tool for the assessment of LDR implants; therefore, it is recommended as a routine procedure by several professional organisations [2–5]. Besides evaluating the overall quality of the implant, PID can assist in the dosimetric assessment of the organs at risk (OARs). Although the dosimetry of OARs cannot be adjusted if overdosed, the radiation oncologist can have a closer follow-up of those patients at risk of developing normal tissue sequelae.Another role of PID is to identify suboptimal implants that can arise owing to organ movement during the procedure, geographical misses of seeds or technical equipment errors. Despite all the efforts and experience of the brachytherapy team, suboptimal implants do occur and they have to be dealt with. Although several centres encounter such events, there is a lack of guidelines or even indications as to how to proceed to improve the final outcome. The major challenge is perhaps the planning, which cannot be done in a conventional way, i.e. based on the ultrasound study of the transrectal volume, owing to lack of previously implanted seed visibility [6]. Therefore, post-implant CT images are the most convenient to use for this task, as the original seeds can be seen and extra seeds can be added to cover the underdosed areas of the prostate.The aim of this work was to present our experience with iodine-125 seed reimplantation (top-up) in a cohort of six patients whose initial implant was suboptimal as identified by PID. The technical and dosimetric challenges of seed top-up implants are investigated.     

Magnetic resonance tomography of pituitary tumors

This paper presents a survey of the current status of the diagnosis of pituitary tumors by means of magnetic resonance imaging. It focuses on the clinical and practical aspects. The recommended procedure and the sequences and slice orientations for magnetic resonance imaging of the pituitary gland are presented, and the features that are essential for the diagnosis of pituitary tumors are discussed.     

Radiological treatment of male varicocele: technical, clinical, seminal and dosimetric aspects

PURPOSE: The purpose of this study was to present our experience with percutaneous treatment of male varicocele considering technical, clinical, seminal and dosimetric aspects. MATERIALS AND METHODS: At baseline and at 6 months' follow-up, 290 male patients aged between 18 and 37 (average age 27.3 years) with left (266 cases) or bilateral (24 cases) varicocele underwent clinical assessment, Doppler ultrasonography (US), laboratory testing of free and total serum testosterone, leutenising hormone (LH) and follicle stimulating hormone (FSH) gonadotropins, inhibin B and spermiogram. In 223 cases, selective catheterisation of the spermatic vein was performed with a right transfemoral approach. Two hundred and six out of 223 underwent radiological treatment of varicocele; in 194, hydroxy-poliethoxydocanol (Aetoxysclerol) was used only whereas in 12 cases (5.8%), 5 ml of absolute alcohol and a Gianturco coil (0.038-in. Cook coil, 10 mmx50 mm) were also used. In 17/223 patients (7.6%), sclerotherapy was contraindicated or not technically feasible. Sixty-seven patients refused radiological treatment and were used as a control group. In 20 patients, the following parameters were measured: dose area product, entrance surface dose, effective dose and gonad dose. RESULTS: Technical success was achieved in 206/223 cases; two phlebographic examinations (immediately following administration of the sclerosing agent and after 15-20 min) showed prethrombotic endoluminal alterations of the internal spermatic vein. At 6 months' follow-up, 172/206 patients (83.49%) showed complete resolution of the varicocele whereas 34/206 (16.5%) had only partial disengorgement of the pampiniform plexus. In these 206 patients, the spermogram showed a significant increase in sperm concentration (52.1+/-4.1 vs. 44.2+/-3.6 million/ml, p=0.002) and motility (40.5+/-2.2 vs. 33.3+/-2.0%, p=0.0001), with negligible morphological changes. In the control group and in the other 17 untreated patients, no variations in seminal parameters were observed. The following minor procedural complications were recorded: two cases of acute abdominal pain, three of vagal crisis during administration of sclerosing agent that resolved spontaneously and two of spermatic cord inflammation that resolved within days after medical therapy. We recorded no statistically significant differences with regard to testicular volume or serum hormone levels between the treated and untreated groups. Maximum effective dose and maximum gonad dose equivalent were 6.9 mSv and 0.69 mSv, respectively. DISCUSSION AND CONCLUSIONS: Percutaneous radiological treatment of varicocele is a minimally invasive technique, which is well tolerated by patients and able to significantly improve seminal parameters. The principal technical limitation to percutaneous treatment is related to difficult selective catheterisation of the spermatic vein due to anatomic alterations, spasms and intimal dissection of the vein. Moreover, when the cremasteric vein is incontinent, inguinal surgical ligation provides better results. In the majority of cases, administration of at least 3 ml sclerosing agent at 3% ensures occlusion of the gonadic vein above the abdominal collaterals, which are responsible for long-term recurrence if not treated. In the remaining cases, absolute alcohol and metallic coils can be used to complete the treatment. The positive results in seminal parameters do not, however, allow for reliable assessment of patients' fertility. Finally, we believe that radiological procedures are not indicated or justified when prolonged catheterisation with elevated gonadic irradiation is needed.     

Accelerated partial breast irradiation: a dosimetric comparison of three different techniques

PURPOSE: We report the first single-institutional dosimetric comparison of patients treated with three forms of accelerated partial breast irradiation: interstitial HDR brachytherapy, the MammoSite balloon apparatus, and 3D conformal external beam quadrant irradiation (3D-CRT). METHODS: A retrospective dosimetric comparison of interstitial HDR brachytherapy, MammoSite balloon brachytherapy, and 3D-CRT was performed. Thirty patients including 10 from each treatment technique were included for a dosimetric comparison of the dose received by the ipsilateral breast, PTV, heart, and ipsilateral lung. Interstitial patients were treated with 4 Gy in 8 fractions to 32 Gy, and the MammoSite patients were treated with 3.4 Gy in 10 fractions to 34 Gy. 3D-CRT patients were treated with 3.85 Gy in 10 fractions to 38.5 Gy using multiple isocentric beams. The CT images from simulation or implant evaluation were transferred into our 3D treatment planning software. The lumpectomy cavities were outlined for every patient, except the MammoSite patients, where the cavity was defined by the balloon edge. The PTV was constructed as a uniform expansion of 1.5 cm for all interstitial HDR patients, 1.0 cm for the MammoSite patients, and a 1.0 cm expansion in addition to the CTV expansion of 1.0 cm (n=2), and 1.5 cm (n=8) for the 3D-CRT patients. The CTV expansion for 3D-CRT and the PTV expansion for the brachytherapy patients were limited to the chest wall and skin. Normal structures including both ipsilateral lung and breast and heart for left-sided lesions were outlined. The lumpectomy cavity was subtracted from the PTV and normal breast tissue for evaluation. To evaluate dose to the ipsilateral breast and lung, PTV, and heart, a dose-volume histogram (DVH) analysis was performed. All histograms were normalized to the volume of the structure (i.e., expressed as percent volume). RESULTS: The average percentage of the breast receiving 100% and 50% of the prescribed dose (PD) was higher in the 3D-CRT group (24% and 48%, respectively) compared with the MammoSite (5% and 18%, respectively) and interstitial patients (10% and 26%, respectively). Improved coverage of the PTV was noted in the 3D-CRT plans compared with the MammoSite and interstitial HDR plans. With the interstitial HDR technique, 58% of the PTV received 100% of the PD compared with 76% with MammoSite and 100% with 3D-CRT techniques. The percentage of the PTV receiving 90% of the PD was 68%, 91%, and 100% for the interstitial HDR, MammoSite, and 3D-CRT patients, respectively. The ipsilateral lung V20 was slightly higher for 3D-CRT at 5% compared with 0% for both brachytherapy techniques. CONCLUSION: In those treated with 3D-CRT, coverage of the PTV was better with 3D-CRT but varied with the definition used. At the coverage at 90% of the PD, no difference was observed between 3D-CRT and MammoSite (which were both better than interstitial). 3D-CRT resulted in better coverage of the PTV compared with MammoSite or interstitial brachytherapy techniques. Better PTV coverage with 3D-CRT came at the cost of a higher integral dose to the remaining normal breast. Dosimetrically, the best partial breast irradiation technique appears to depend on the clinical situation. Of the brachytherapy techniques, MammoSite appears to be superior in PTV coverage. When comparing MammoSite vs. 3D-CRT PTV coverage at 90% of the PD, the difference was not significantly different.