Radiation safety consideration during intraoperative radiation therapy

Real World and Public Health Perspectives of Intraoperative Radiotherapy in Early-Stage Breast Cancer: A Multidisciplinary Analysis Beyond the Statistical Facts

Breast conservation therapy (BCT) (usually a lumpectomy plus radiotherapy (RT)) has become a standard alternative to radical mastectomy in early-stage breast cancers with equal, if not higher, survival rates. The established standard of the RT component of the BCT had been about six weeks of Monday through Friday external beam RT to the whole breast (WBRT). Recent clinical trials have shown that partial breast radiation therapy (PBRT) to the region surrounding the lumpectomy cavity with shorter courses can result in equal local control, survival, and slightly improved cosmetic outcomes. Intraoperative RT (IORT) wherein RT is administered at the time of operation for BCT to the lumpectomy cavity as a single-fraction RT is also considered PBRT. The advantage of IORT is that weeks of RT are avoided. However, the role of IORT as part of BCT has been controversial. The extreme views go from "I will not recommend to anyone" to "I can recommend to all early-stage favorable patients." These divergent views are due to difficulty in interpreting the clinical trial results. There are two modalities of delivering IORT, namely, the use of low-energy 50 kV beams or electron beams. There are several retrospective, prospective, and two randomized clinical trials comparing IORT versus WBRT. Yet, the opinions are divided. In this paper, we try to bring clarity and consensus from a highly broad-based multidisciplinary team approach. The multidisciplinary team included breast surgeons, radiation oncologists, medical physicists, biostatisticians, public health experts, nurse practitioners, and medical oncologists. We show that there is a need to more carefully interpret and differentiate the data based on electron versus low-dose X-ray modalities; the randomized study results have to be extremely carefully dissected from biostatistical points of view; the importance of the involvement of patients and families in the decision making in a very transparent and informed manner needs to be emphasized; and the compromise some women may be willing to accept between 2-4% potential increase in local recurrence (as interpreted by some of the investigators in IORT randomized studies) versus mastectomy. We conclude that, ultimately, the choice should be that of women with detailed facts of the pros and cons of all options being presented to them from the angle of patient/family-focused care. Although the guidelines of various professional societies can be helpful, they are only guidelines. The participation of women in IORT clinical trials is still needed, and as genome-based and omics-based fine-tuning of prognostic fingerprints evolve, the current guidelines need to be revisited. Finally, the use of IORT can help rural, socioeconomically, and infrastructure-deprived populations and geographic regions as the convenience of single-fraction RT and the possibility of breast preservation are likely to encourage more women to choose BCT than mastectomy. This option can also likely lead to more women choosing to get screened for breast cancer, thus enabling the diagnosis of breast cancer at an earlier stage and improving the survival outcomes.

Calculated and measured radiation dose for the low energy xoft axxent eBT X-ray source

PURPOSE

In this study, it was aimed to evaluate the functionality to deliver different prescription dose except 20 Gy for the Xoft Axxent Ebt (electronic Brachytherapy) system and analyzing the system in terms of radiation dosimetry in water and 0.9% isotonic Sodium Chloride (NaCl) solution.

MATERIALS AND METHODS

In the Xoft Axxent eBT, different prescription dose in single fraction were calculated for different balloon applicator volumes based on source position and irradiation times. EBT-XD Gafchromic film was calibrated at 6MV photon energy. A balloon applicator filled with 0.9% isotonic NaCl solution was used to deliver a radiation dose of 20 Gy, 16 Gy, 10 Gy on the applicator surface. Then the balloon applicator was filled with water and the same measurements were repeated. Finally, the balloon applicator was irradiated by positioning it at different distances in the water phantom to simulate the isodose contour.

RESULTS

At the time the balloon applicator was filled with water and 0,9% NaCl solution, the difference between the planned dose and the absorbed dose was ~ 2% vs. 15% for 30 cc, ~ 5% vs. 14% for 35 cc and ~ 3,5% vs. 10% for 40 cc respectively. Finally, the absorbed dose at a distance of 1 cm from the applicator surface was measured as 9.63 Gy.

CONCLUSION

In this study, it was showed that different prescription dose could be possible to deliver in the Xoft Axxent eBT system based on the standard plan. In addition, the absorbed dose was higher than the planned dose depending on the effective atomic number of NaCl solution comparing to water due to photoelectric effect in low energy photons. By measuring the dose distributions at different distances from the balloon applicator surface, the absorbed dose in tissue equivalent medium was determined and the isodose contours characteristics was simulated.

Feasibility of electronic brachytherapy in cervix cancer-A dosimetric comparison of different brachytherapy techniques

INTRODUCTION

This study analyzes cases in which electronic brachytherapy (eBT) led to acceptable treatment plans in cervical cancer. Findings were compared with dosimetry values obtained in ¹⁹²Ir-based treatments according to the high-risk clinical target volume (HR-CTV) and the disease stage.

MATERIAL AND METHODS

We retrospectively analyzed 48 patients with cervical cancer from two centers. The patients were treated with ¹⁹²Ir based on MRI. It was possible to use interstitial needles via an Utrecht-type applicator. Dosimetry was simulated using eBT and the parameters D90 and D98 (HR-CTV) and D2cc, D1cc, and D0.1cc (bladder, rectum, and sigmoid colon) were evaluated. The Mann-Whitney U test was used for comparison. The overall cohort of patients was analyzed, as were the sub-cohorts based on stage (FIGO stages I+IIA, IIB and III-IV). Finally, the dosimetry of the eBT plans was evaluated, and the plans obtained were classified as "good", "acceptable", or "poor".

RESULTS

Statistically significant differences were found between the eBT and ¹⁹²Ir plans for D98 (HR-CTV), D1cc and D0.1cc (bladder), and D1cc and D0.1cc (sigmoid colon). A total of 31 cases (64.6%) were considered good, seven (14.6%) were considered acceptable, and 10 (20.8%) were considered poor. For volumes <30 cc, all the plans were good or acceptable; for volumes >30 cc, 54.3% were good, and 71.4% were good or acceptable. By stage, eBT plans for patients with stage IB-IIA disease were good in 100%, whereas those for patients with stage IIB were good in 70.6% and III-IV disease were good in 50%.

CONCLUSIONS

eBT provides appropriate dosimetry for treatment of cervical cancer in selected cases.

Feasibility of interstitial stepping-source electronic brachytherapy to locally inoperable tumors

Purpose

Radiotherapy is the mainstay in the treatment of locally inoperable tumors. Interstitial electronic needle-based kilovoltage brachytherapy (EBT) could be an economic alternative to high-dose-rate (HDR) brachytherapy or permanent seed implantation (PSI). In this work, we evaluated if locally inoperable tumors treated with PSI at our institution may be suitable for EBT.

Material and methods

A total of 10 post-interventional computed tomography (CT) scans of patients, who received PSI and simulated stepping-source EBT applied with Intrabeam system and needle applicator were used. EBT treatment planning software with 3-dimensional image and projection of applicator were applied for designing trajectories and establishing dwell positions. Dwell position doses were summarized, and doses covering 90% of the target volume (D₉₀) achieved with stepping-source EBT were compared to those of PSI. Additionally, conformality of dose distributions and total irradiation time were assessed using conformation number (CN) or conformal index (COIN).

Results

In all patients, D₉₀ of EBT exceeded the prescribed dose or D₉₀ of PSI on average by 4.7% or 21.3% relative to the prescribed dose, respectively. Mean number of trajectories was 5.0 for EBT and 6.9 for PSI. Average CN/COIN for EBT was 0.69, with a mean irradiation time of 27.8 minutes for standardized dose of 13 Gy.

Conclusions

Stepping-source EBT allowed for a conformal treatment of inoperable interstitial tumors with similar D₉₀. Fewer trajectories were required for EBT in majority of cases.

A Novel Radiotherapy Approach for Keloids with Intrabeam

Background

Keloids are hard nodules or plaques formed by excessive proliferation of connective tissue. Radiotherapy, widely used in various benign and malignant skin diseases, is an effective treatment for keloids. This work evaluates Intrabeam photon radiotherapy in the management of keloids.

Methods

Fourteen patients who have undergone Intrabeam radiotherapy for a total of 15 sites of keloids were followed up. Twelve cases were first onset and the other two had recurrent diseases. Thirteen patients underwent surgical resection of keloids before radiotherapy. One relapsing patient received only 2 rounds of radiation therapy as she could not be reoperated. Radiotherapy was divided into 2 sessions on days 0 and 3 after surgery. The dose was 4 or 5 Gy each time for 3 min 14 s to 12 min 1 s. In addition, we compared our data to the recurrence of keloids in fourteen patients who had previously been exposed to electron beam using conventional accelerators.

Results

We analyzed the treatment for adverse reactions and recurrence. In the Intrabeam group, one patient developed superficial skin ulcers a month after treatment. No one experienced wound rupture, bleeding, infection, skin contractures, or obvious hyperpigmentation. None of the fourteen cases showed any recurrence so far after on median 22.5 months of follow-up. Five patients in the electron beam group relapsed 3 to 10 months after treatment.

Conclusion

Here, Intrabeam photon radiotherapy was shown to be an effective treatment for keloid scars and it is therefore recommended for management of this disease.

American College of Radiology-American Brachytherapy Society practice parameter for electronically generated low-energy radiation sources

BACKGROUND

This collaborative practice parameter technical standard has been created between the American College of Radiology and American Brachytherapy Society to guide the usage of electronically generated low energy radiation sources (ELSs). It refers to the use of electronic X-ray sources with peak voltages up to 120 kVp to deliver therapeutic radiation therapy.

MAIN FINDINGS

The parameter provides a guideline for utilizing ELS, including patient selection and consent, treatment planning, and delivery processes. The parameter reviews the published clinical data with regard to ELS results in skin, breast, and other cancers.

CONCLUSIONS

This technical standard recommends appropriate qualifications of the involved personnel. The parameter reviews the technical issues relating to equipment specifications as well as patient and personnel safety. Regarding suggestions for educational programs with regard to this parameter,it is suggested that the training level for clinicians be equivalent to that for other radiation therapies. It also suggests that ELS must be done using the same standards of quality and safety as those in place for other forms of radiation therapy.

Evaluation of the shielding in a treatment room with an electronic brachytherapy unit

Esteya® (Elekta Brachytherapy, Veenendaal, The Netherlands) is an electronic brachytherapy (eBT) system based on a 69.5 kVp x-ray source and a set of collimators of 1 to 3 cm in diameter, used for treating non-melanoma skin cancer lesions. This study aims to estimate room shielding requirements for this unit. The non-primary (scattered and leakage) ambient dose equivalent rates were measured with a Berthold LB-133 monitor (Berthold Technologies, Bad Wildbad, Germany). The latter ranges from 17 mSv h^-1 at 0.25 m distance from the x-ray source to 0.1 mSv h^-1 at 2.5 m. The necessary room shielding was then estimated following US and some European guidelines. The room shielding for all barriers considered was below 2 mmPb. The dose to a companion who, exceptionally, would stay with the patient during all treatment was estimated to be below 1 mSv if a leaded apron is used. In conclusion, Esteya shielding requirements are minimal.

Dosimetric comparison of brachytherapy sources for high-dose-rate treatment of endometrial cancer: (192)Ir, (60)Co and an electronic brachytherapy source

OBJECTIVE

To compare high-dose-rate (HDR) brachytherapy systems with (192)Ir, (60)Co and electronic brachytherapy source (EBS) for treatment of endometrial cancers.

METHODS

Two additional plans were generated per patient fraction using a (60)Co source and Xoft-EBS on 10 selected patients, previously treated with a vaginal cylinder applicator using a (192)Ir source. Dose coverage of "PTV_CYLD", a 5-mm shell surrounding the cylinder, was evaluated. Doses to the following organs at risk (OARs) the rectum, bladder and sigmoid were evaluated in terms of V35% and V50%, the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D2cm(3), the highest dose to a 2-cm(3) volume of an OAR.

RESULTS

Xoft-EBS reduces doses to all OARs in the lower dose range, but it does not always provide better sparing of the rectum in higher dose range as does evaluation using D2cm3. V150% and V200% for PTV_CYLD was up to four times greater for Xoft-EBS plans than for plans generated with (192)Ir or (60)Co. Surface mucosal (vaginal cylinder surface) doses were also 23% higher for Xoft-EBS than for (192)Ir or (60)Co plans.

CONCLUSION

Xoft-EBS is a suitable HDR source for vaginal applicator treatment with advantages of reducing radiation exposure to OARs in the lower dose range, while simultaneously increasing the vaginal mucosal dose.

ADVANCES IN KNOWLEDGE

This work presents newer knowledge in dosimetric comparison between (192)Ir or (60)Co and Xoft-EBS sources for endometrial vaginal cylinder HDR planning.

Preclinical Evaluation of Intraoperative Low-Energy Photon Radiotherapy Using Spherical Applicators in Locally Advanced Prostate Cancer

Background

Surgery plus adjuvant radiotherapy is standard care for locally advanced prostate cancer (stage pT3R1). Intraoperative low-energy photon radiotherapy offers several advantages over external beam radiotherapy, and several systems are now available for its delivery, using spherical applicators, which require only limited shielding. The aim of this study was to evaluate the feasibility of this technique for the prostate bed.

Materials and methods

Applicators were assessed using MRI image data and cadaveric dissection. In cadavers, targeted tissues, defined as a urethral section, both neurovascular bundle sections, the bladder neck and the beds of the seminal vesicles, were marked with metallic surgical clips. Distances between clips and applicator were measured using CT. A dosimetric study of the application of 12 Gy at 5 mm depth was performed using CT images of prostatectomized cadavers.

Results

Using MRI images from 34 prostate cancer patients, we showed that the ideal applicator diameter ranges from 45 to 70 mm. Using applicators of different sizes to encompass the prostate bed in nine cadavers, we showed that the distance between target tissues and applicator was <2 mm for all target tissues except the upper extremity of the seminal vesicles (19 mm). Dosimetric study showed a good dose distribution in all target tissues in contact with the applicator, with a low probability of rectum and bladder complication.

Conclusion

Intraoperative radiotherapy of the prostate bed is feasible, with good coverage of targeted tissues. Clinical study of safety and efficacy is now required.

Comparison of Axxent-Xoft, (192)Ir and (60)Co high-dose-rate brachytherapy sources for image-guided brachytherapy treatment planning for cervical cancer

OBJECTIVE

To evaluate the dosimetric differences and similarities between treatment plans generated with Axxent-Xoft electronic brachytherapy source (Xoft-EBS), (192)Ir and (60)Co for tandem and ovoids (T&O) applicators.

METHODS

In this retrospective study, we replanned 10 patients previously treated with (192)Ir high-dose-rate brachytherapy. Prescription was 7 Gy × 4 fractions to Point A. For each original plan, we created two additional plans with Xoft-EBS and (60)Co. The dose to each organ at risk (OAR) was evaluated in terms of V(35%) and V(50%), the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D(2cc), highest dose to a 2 cm(3) volume of an OAR.

RESULTS

There was no difference between plans generated by (192)Ir and (60)Co, but the plans generated using Xoft-EBS showed a reduction of up to 50% in V(35%), V(50%) and D(2cc). The volumes of the 200% and 150% isodose lines, however, were 74% and 34% greater than the comparable volumes generated with the (192)Ir source. Point B dose was on average only 16% of the Point A dose for plans generated with Xoft-EBS compared with 30% for plans generated with (192)Ir or (60)Co.

CONCLUSION

The Xoft-EBS can potentially replace either (192)Ir or (60)Co in T&O treatments. Xoft-EBS offers either better sparing of the OARs compared with (192)Ir or (60)Co or at least similar sparing. Xoft-EBS-generated plans had higher doses within the target volume than (192)Ir- or (60)Co-generated ones.

ADVANCES IN KNOWLEDGE

This work presents newer knowledge in dosimetric comparison between Xoft-EBS, (192)Ir or (60)Co sources for T&O implants.

Electronic brachytherapy--current status and future directions

In the past decade, electronic brachytherapy (EB) has emerged as an attractive modality for the treatment of skin lesions and intraoperative partial breast irradiation, as well as finding wider applications in intracavitary and interstitial sites. These miniature X-ray sources, which operate at low kilovoltage energies (<100 kV), have reduced shielding requirements and inherent portability, therefore can be used outside the traditional realms of the radiotherapy department. However, steep dose gradients and increased sensitivity to inhomogeneities challenge accurate dosimetry. Secondly, ease of use does not mitigate the need for close involvement by medical physics experts and consultant oncologists. Finally, further studies are needed to relate the more heterogeneous dose distributions to clinical outcomes. With these provisos, the practical convenience of EB strongly suggests that it will become an established option for selected patients, not only in radiotherapy departments but also in a range of operating theatres and clinics around the world.