High-dose-rate intraoperative irradiation: current status and future directions

Optimization of the regularization parameter in the Dual Annealing method used for the reconstruction of energy spectrum of electron beam generated by the AQURE mobile accelerator

INTRODUCTION

The shape of the energy spectrum is an essential component of any electron beam Monte Carlo model. Due to specialized equipment and the long measurement time for the direct methods for determining the energy spectrum, attractive alternatives are backward spectrum reconstructions from the measured data. One such approach is solving the first-degree Fredholm integral equation with appropriate regularization. It makes it possible to calculate the depth distribution as the sum of the distributions from monoenergetic beams. This study aims to determine the optimal value of the regularization parameter for the problem of determining the spectrum of the electron beam produced by a mobile accelerator used during intraoperative radiotherapy.

MATERIAL AND METHODS

The Geant4 package was used to generate the distributions of deep doses for monoenergetic beams for two models with different degrees of complexity, i.e. simple (theoretical) and full (for the mobile accelerator). The dose distributions for four different shapes of energy spectrum (for each model) were obtained similarly. They were established as the reference data for further calculations. The Dual Annealing optimization method was used to obtain the reconstructed spectrum. The multiple optimizations that differ by the regularization parameter (ranging from 0 to 1) were performed. For each reconstruction, similarity indicators of the energy spectrum and the dose distribution to the referenced data were calculated to determine the optimal regularization parameters.

RESULTS

Optimal regularization parameters determined by similarity indicators for the spectrum and the dose distribution differ for geometry models considered in the study. The regularization parameter for the simple geometry ranged from 0.03 to 0.05, while for full geometry, they were from 0.05 to 0.06. The results for conventional linear accelerators found in the literature range from 0.5 to 1.1.

CONCLUSION

The Dual Annealing optimization method can be effectively used to solve the Fredholm equation with Tikhonov regularization to reconstruct an electron beam's energy spectrum. The regularization parameter value depends on the beam-forming system. Its value for the mobile accelerator considered in the study ranges from 0.05 to 0.06, depending on the nominal beam energy value.

ACR-ABS-ASTRO practice parameter for the performance of radionuclide-based high-dose-rate brachytherapy

PURPOSE

This practice parameter aims to detail the processes, qualifications of personnel, patient selection, equipment, patient and personnel safety, documentation, and quality control and improvement necessary for an HDR brachytherapy program.

METHODS AND MATERIALS

This practice parameter was revised collaboratively by the American College of Radiology (ACR), the American Brachytherapy Society (ABS), and the American Society for Radiation Oncology (ASTRO).

RESULTS

Brachytherapy is a radiotherapeutic modality in which radionuclide or electronic sources are used to deliver a radiation dose at a distance of up to a few centimeters by surface, intracavitary, intraluminal, or interstitial application. Brachytherapy alone or combined with external beam radiotherapy plays an important role in the management and treatment of patients with cancer. High-dose-rate (HDR) brachytherapy uses radionuclides, such as iridium-192, at dose rates of ≥12 Gy/hr to a designated target point or volume, and it is an important treatment for a variety of malignant and benign conditions. Its use allows for application of high doses of radiation to defined target volumes with relative sparing of adjacent critical structures.

CONCLUSIONS

HDR brachytherapy requires detailed attention to personnel, equipment, patient and personnel safety, and continuing staff education. Coordination between the radiation oncologist and treatment planning staff and effective quality assurance procedures are important components of successful HDR brachytherapy programs.

The American College of Radiology and the American Brachytherapy Society practice parameter for the performance of radionuclide-based high-dose-rate brachytherapy

Brachytherapy is a radiation therapy method in which radionuclide sources are used to deliver a radiation dose at a distance of up to a few centimeters by surface, intracavitary, intraluminal, or interstitial application. This practice parameter refers only to the use of radionuclides for brachytherapy. Brachytherapy alone or combined with external beam therapy plays an important role in the management and treatment of patients with cancer. High-dose-rate (HDR) brachytherapy uses radionuclides such as iridium-192 at dose rates of 20 cGy per minute (12 Gy per hour) or more to a designated target point or volume. High-dose-rate (HDR) brachytherapy is indicated for treating malignant or benign tumors where the treatment volume or targeted points are defined and accessible.

Primary peritoneal clear cell carcinoma treated with IMRT and interstitial HDR brachytherapy: a case report

Primary peritoneal clear cell carcinoma (PP‐CCC), which is a rare tumor with poor prognosis, is typically managed with surgery and/or chemotherapy. We present a unique treatment approach for a patient with a pelvic PP‐CCC, consisting of postchemotherapy intensity‐modulated radiation therapy (IMRT) followed by interstitial high‐dose–rate (HDR) brachytherapy. A 54‐year‐old female with an inoperable pelvic‐supravaginal 5.6 cm T3N0M0 PP‐CCC tumor underwent treatment with 6 cycles of carboplatin and taxol chemotherapy. Postchemotherapy PET/CT scan revealed a residual 3.3 cm tumor. The patient underwent CT and MR planning simulation, and was treated with 50 Gy to the primary tumor and 45 Gy to the pelvis including the pelvic lymph nodes, using IMRT to spare bowel. Subsequently, the patient was treated with an interstitial HDR brachytherapy implant, planned using both CT and MR scans. A total dose of 15 Gy in 5 Gy fractions over two days was delivered with Ir‐192 HDR brachytherapy. The total prescribed equivalent 2 Gy dose (EQD2) to the HDR planning target volume (PTV) from both the EBRT and HDR treatments ranged between 63 and 68.8Gy2 due to differential dosing of the primary and pelvic targets. The patient tolerated radiotherapy well, except for mild diarrhea not requiring medication. There was no patient‐reported acute toxicity one month following the radiotherapy course. At four months following adjuvant radiation therapy, the patient had near complete resolution of local tumor on PET/CT without any radiation‐associated toxicity. However, the patient was noted to have metastatic disease outside of the radiation field, specifically lesions in the liver and bone. This case report illustrates the feasibility of the treatment of a pelvic PP‐CCC with IMRT followed by interstitial HDR brachytherapy boost, which resulted in near complete local tumor response without significant morbidity.

PACS number: 87.55.‐x

Prospective single-arm study of intraoperative radiotherapy for locally advanced or recurrent rectal cancer

INTRODUCTION

This study aims to evaluate the feasibility and outcomes of intraoperative radiotherapy (IORT) using high-dose-rate (HDR) brachytherapy for locally advanced or recurrent rectal cancers. Despite preoperative chemoradiation, patients with locally advanced or recurrent rectal cancers undergoing surgery remain at high risk of local recurrence. Intensification of radiation with IORT may improve local control.

METHODS

This is a prospective non-randomised study. Eligible patients were those with T4 rectal cancer or pelvic recurrence, deemed suitable for radical surgery but at high risk of positive resection margins, without evidence of metastasis. Chemoradiation was followed by radical surgery. Ten gray (Gy) was delivered to tumour bed via an IORT applicator at time of surgery.

RESULTS

There were 15% primary and 85% recurrent cancers. The 71% received preoperative chemoradiation. R0, R1 and R2 resections were 70%, 22% and 7%, respectively. IORT was successfully delivered in 27 of 30 registered patients (90% (95% confidence interval (CI) = 73-98) ) at a median reported time of 12 weeks (interquartile range (IQR) = 10-16) after chemoradiation. Mean IORT procedure and delivery times were 63 minutes (range 22-105 minutes). Ten patients (37% (95% CI = 19-58) ) experienced grade 3 or 4 toxicities (three wound, four abscesses, three soft tissue, three bowel obstructions, three ureteric obstructions and two sensory neuropathies). Local recurrence-free, failure-free and overall survival rates at 2.5 years were 68% (95% CI = 52-89), 37% (95% CI = 23-61) and 82% (95% CI = 68-98), respectively.

CONCLUSION

The addition of IORT to radical surgery for T4 or recurrent rectal cancer is feasible. It can be delivered safely with low morbidity and good tumour outcomes.

Intraoperative high-dose-rate radiotherapy in the management of locoregionally recurrent head and neck cancer

BACKGROUND

The purpose of this article was to present the Beth Israel Medical Center experience using high-dose-rate intraoperative radiotherapy (HDR-IORT) in the management of recurrent head and neck cancer.

METHODS

We conducted a retrospective review of all patients with locally or regionally recurrent head and neck cancer who underwent HDR-IORT at our institution between 2001 and 2010.

RESULTS

Seventy-six patients were identified who underwent treatment to a total of 87 sites after gross-total resection. The 2-year estimate of in-field tumor control was found to be 62%. Median overall survival was 19 months with 42% of the patients surviving at least 2 years. Significantly longer survival was found for patients achieving in-field control versus infield progression (33 months vs 17 months, respectively; p = .01).

CONCLUSION

HDR-IORT is well tolerated and associated with encouraging in-field disease control. In-field control is associated with improved survival. Further study is warranted to more fully investigate HDR-IORT in the salvage setting.

Intraoperative radiotherapy in colorectal cancer: systematic review and meta-analysis of techniques, long-term outcomes, and complications

BACKGROUND

The precise contribution of IORT to the management of locally advanced and recurrent colorectal cancer (CRC) remains uncertain. We performed a systematic review and meta-analysis to assess the value of IORT in this setting.

METHODS

Studies published between 1965 and 2011 that reported outcomes after IORT for advanced or recurrent CRC were identified by an electronic literature search. Studies were assessed for methodological quality and design, and evaluated for technique of IORT delivery, oncological outcomes, and complications following IORT. Outcomes were analysed with fixed-effect and random-effect model meta-analyses and heterogeneity and publication bias examined.

RESULTS

29 studies comprising 14 prospective and 15 retrospective studies met the inclusion criteria and were assessed, yielding a total of 3003 patients. The indication for IORT was locally advanced disease in 1792 patients and locally recurrent disease in 1211 patients. Despite heterogeneity in methodology and reporting practice, IORT is principally applied for the treatment of close or positive margins. When comparative studies were evaluated, a significant effect favouring improved local control (OR 0.22; 95% CI = 0.05-0.86; p = 0.03), disease free survival (HR 0.51; 95% CI = 0.31-0.85; p = 0.009), and overall survival (HR 0.33; 95% CI = 0.2-0.54; p = 0.001) was noted with no increase in total (OR 1.13; 95% CI = 0.77-1.65; p = 0.57), urologic (OR 1.35; 95% CI = 0.84-2.82; p = 0.47), or anastomotic complications (OR 0.94; 95% CI = 0.42-2.1; p = 0.98). Increased wound complications were noted after IORT (OR 1.86; 95% CI = 1.03-3.38; p = 0.049).

CONCLUSIONS

Despite methodological weaknesses in the studies evaluated, our results suggest that IORT may improve oncological outcomes in advanced and recurrent CRC.

Intraoperative electron beam radiotherapy for primary treatment of stage IIB cervical cancer: a retrospective study

OBJECTIVE

A retrospective study to evaluate intraoperative electron beam radiotherapy (IOERT) as a primary treatment modality for stage IIB cervical squamous cell carcinoma.

METHODS

Patients underwent treatment with IOERT (n = 78) or radical radiotherapy (RT; n = 89). Patients in the IOERT group received 20 Gy external beam radiotherapy (EBRT) in 10 fractions, intracavitary brachytherapy (7-14 Gy, in patients with tumours ≥ 4 cm in diameter) and simple hysterectomy/selective lymphadenectomy with 18 - 20 Gy IOERT. Patients in the RT group received 50 Gy EBRT in 25 fractions followed by intracavitary brachytherapy (35-40 Gy).

RESULTS

Median duration of follow-up was 92 months. IOERT resulted in significantly better 5- and 10-year overall survival, disease-free survival and local control rates, as well as fewer rectal and bladder complications, compared with RT.

CONCLUSION

IOERT is an effective primary treatment for stage IIB cervical squamous cell carcinoma.

Feasibility of flap reconstruction in conjunction with intraoperative radiation therapy for advanced and recurrent head and neck cancer

BACKGROUND

Radiation is a known risk factor for poor wound healing. Patients undergoing intraoperative radiation therapy (IORT) typically receive higher cumulative doses to their wound beds than patients treated with conventional radiation therapy. We review our experience with IORT in patients undergoing resection of head and neck cancer and flap reconstruction. Logistics of delivery and outcomes are discussed.

METHODS

A retrospective chart review was performed on all patients at Beth Israel Medical Center who underwent IORT for head and neck cancer between 2000 and 2007. Twenty-one patients receiving 22 treatments involving flap reconstruction were identified. The results of these reconstructions were evaluated for complications and functional outcome.

RESULTS

All patients had complex surgical wounds of the face, upper aerodigestive tract, or neck who received IORT in conjunction with pedicled or free flap closure. Twenty-five flaps in 21 patients were performed in the setting of IORT. All patients received between 10 and 15 Gy of IORT administered directly to the wound bed. There were no perioperative mortalities. Wound breakdown occurred in three cases, all of which were treated successfully by operative revision. Functionally, most patients did well and performed similarly to historic controls for their type of reconstruction.

CONCLUSIONS

Reconstruction using flaps in the context of IORT can be achieved with expectation of good wound healing in the majority of cases despite heavy cumulative doses of radiation to recipient wound beds.

High-dose-rate remote afterloaders for intraoperative radiation therapy

Intraoperative radiation therapy (IORT) is a treatment option that directly irradiates a surgically exposed tumor or tumor bed while preventing radiation exposure of normal tissues. This article discusses the high-dose-rate intraoperative radiation therapy (HDR-IORT) technique by reviewing the roles of IORT team members, discussing needed equipment and supplies, describing quality assurance processes, explaining the HDR-IORT treatment delivery procedure, and reviewing the post-treatment phase.

Intraoperative HDR brachytherapy for rectal cancer using a flexible intraoperative template: standard plans versus individual planning

HDR intraoperative brachytherapy (IOBT) is applied to locally advanced rectal tumors using a 5 mm thick flexible intraoperative template (FIT). To reduce the procedure time, treatment planning is performed using standard plans that neglect the curvature of the FIT. We have calculated the individual treatment plan, based on the real geometry of the FIT, and the dose at clips placed during surgery. A mean treatment dose of 9.55+/-0.21 Gy was found for the individual plan, compared to the prescribed 10 Gy (P<0.0001) The mean central dose was 10.03+/-0.10 Gy in the standard plan and 9.20+/-0.32 Gy in the individual plan (P<0.0001) The mean dose at the corners of the FIT was 10.3 Gy in the standard plan and ranged between 10.3 and 10.5 Gy in the individual plan. In 63% of the clips, the dose was larger than 15.0 Gy, which is equivalent to a gap between the FIT and the target smaller than 5 mm. In 18% of the clips, the dose was smaller than 13.0 Gy indicating that locally the gap was larger than 5 mm. Clinical practice will have to prove if these small dose deviations influence the clinical outcome.

A real-time image-guided intraoperative high-dose-rate brachytherapy system

PURPOSE

To develop a real-time, image-guided intraoperative high-dose-rate brachytherapy system.

METHODS AND MATERIALS

The surface applicator, a catheter array on a 1-mm-thick soft and semitransparent silicone rubber sheet, was directly sutured on the surgical bed. A three-dimensional video camera was then used to instantly capture images of the catheters and the surgical surface. Tracing the catheters on the images allowed us to automatically determine the dwell source positions. Dwell times in the dwell positions were optimized to minimize the dose variation and deviation from the treatment prescription. A dose-texture plot was created to quantify the dose distribution.

RESULTS

Treatment planning time was reduced from hours to a few minutes. Phantom tests have shown that the new source localization is accurate with sigma<1.5 mm. All hot spots and cold spots had been eliminated after the dwell-time optimization.

CONCLUSIONS

This real-time, image-guided planning system can provide optimal image-guided intraoperative high-dose-rate brachytherapy with geometric and dosimetric improvements and a short planning time.