IORT using high-dose-rate brachytherapy or electron beam for colorectal carcinoma

Intraoperative radiation therapy using a mobile electron linear accelerator: field matching for large-field electron irradiation

Intraoperative radiation therapy (IORT) consists of delivering a large, single-fraction dose of radiation to a surgically exposed tumour or tumour bed at the time of surgery. With the availability of a mobile linear accelerator in the OR, IORT procedures have become more feasible for medical centres and more accessible to cancer patients. Often the area requiring irradiation is larger than what the treatment applicators will allow, and therefore, two or more adjoining fields are used. Unfortunately, the divergence and scattering of the electron beams may cause significant dose variations in the region of the field junction. Furthermore, because IORT treatments are delivered in a large single fraction, the effects of underdosing or overdosing could be more critical when compared to fractionated external beam therapy. Proper matching of the fields is therefore an important technical aspect of treatment delivery. We have studied the matching region using the largest flat applicator available for three different possibilities: abutting the fields, leaving a small gap or creating an overlap. Measurements were done using film dosimetry for the available energies of 4, 6, 9 and 12 MeV. Our results show the presence of clinically significant cold spots for the low-energy beams when the fields are either gapped or abutted, suggesting that the fields should be overlapped. No fields should be gapped. The results suggest that an optimal dose distribution may be obtained by overlapping the fields at 4 and 6 MeV and simply abutting the fields at 9 and 12 MeV. However, due to uncertainties in the placement of lead shields during treatment delivery, one may wish to consider overlapping the higher energy fields as well.

Intraoperative radiation therapy using mobile electron linear accelerators: report of AAPM Radiation Therapy Committee Task Group No. 72

Intraoperative radiation therapy (IORT) has been customarily performed either in a shielded operating suite located in the operating room (OR) or in a shielded treatment room located within the Department of Radiation Oncology. In both cases, this cancer treatment modality uses stationary linear accelerators. With the development of new technology, mobile linear accelerators have recently become available for IORT. Mobility offers flexibility in treatment location and is leading to a renewed interest in IORT. These mobile accelerator units, which can be transported any day of use to almost any location within a hospital setting, are assembled in a nondedicated environment and used to deliver IORT. Numerous aspects of the design of these new units differ from that of conventional linear accelerators. The scope of this Task Group (TG-72) will focus on items that particularly apply to mobile IORT electron systems. More specifically, the charges to this Task Group are to (i) identify the key differences between stationary and mobile electron linear accelerators used for IORT, (ii) describe and recommend the implementation of an IORT program within the OR environment, (iii) present and discuss radiation protection issues and consequences of working within a nondedicated radiotherapy environment, (iv) describe and recommend the acceptance and machine commissioning of items that are specific to mobile electron linear accelerators, and (v) design and recommend an efficient quality assurance program for mobile systems.

Intraoperative radiotherapy using a mobile electron LINAC: a retroperitoneal sarcoma case

The advent of mobile LINACs for use in intraoperative radiation therapy (IORT) promises to make IORT more accessible than before and easier to deliver to patients undergoing surgery. Although mobile IORT systems have been available since 1999, few treatment centers currently use them. Here, we present the case of a typical patient undergoing IORT for retroperitoneal sarcoma to show how easy these mobile systems are to use and how adaptable they are within the operating room (OR) environment. We also discuss the roles and coordination of multidisciplinary team members during IORT and the feasibility of using mobile LINACs for IORT.

PACS number(s):

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.

Intraoperative electron beam radiotherapy in recurrent colorectal carcinoma

BACKGROUND AND OBJECTIVES

The installation of a dedicated linear accelerator in a shielded operating room in 1992 allowed us to start a feasibility study of intraoperative electron beam radiation therapy (IOERT) in colorectal carcinoma.

METHODS

From March 1992 to February 1996, 28 patients with recurrent colorectal carcinoma were treated with maximal surgical resection and IOERT to the pelvis (n = 20) or paraortics (n = 8). IOERT dose ranged from 10 to 20 Gy with electron energies of 6-15 MeV. Postoperative external beam radiation therapy (EBRT) of 45-50 Gy was planned for the previously unirradiated patients.

RESULTS

IOERT was well tolerated, but 10 (70%) of 13 patients in the previously unirradiated group did not complete the EBRT per protocol. Eight patients (29%) had some morbidity including surgically related fistula distal from IOERT sites. Two patients developed pelvic pain, which can be attributed to IOERT. Three-year local control at sites treated with IOERT was 40% (53% for previously irradiated patients and 27% for previously unirradiated patients). The 3-year actuarial overall survival was 12% (17% for previously irradiated patients and 8% for previously unirradiated patients).

CONCLUSIONS

Our initial experience showed that it was feasible to treat poor prognostic colorectal cancer patients with IOERT. The morbidity observed was mainly related to extensive surgery in high-risk patients. Poor local control was obtained in patients treated with low-dose IOERT alone. Hence, previously unirradiated patients are encouraged to complete the planned EBRT or, alternatively, are considered for EBRT preoperatively or are given a higher IOERT dose (up to 20 Gy) if EBRT will not be given. Since IORT doses >20 Gy are associated with nerve toxicity, we currently add limited dose EBRT in the previously irradiated group. Patients with disease located in multiple abdominal sites are no longer considered candidates for IOERT.

Radioimmunoguided-intraoperative radiation therapy in colorectal carcinoma: a new technique to precisely define the clinical target volume

PURPOSE

The clinical target volume (CTV) to be irradiated by intraoperative radiation therapy (IORT) after resection is generally based on the surgeon's estimation of close margins. We have developed a new technique, radioimmunoguided-intraoperative radiation therapy (RIG-IORT), that uses an intraoperative hand-held gamma-detecting probe to define areas of residual microscopic disease containing radiolabeled monoclonal antibodies to tumor associated antigen, to more precisely delineate the CTV for IORT.

METHODS AND MATERIALS

Patients were injected i.v. with 2 mCi 125I- radiolabeled CC49 antibody approximately 3 weeks before surgery. They then underwent radioimmunoguided surgery (RIGS) with maximal resection of tumor. A hand-held gamma-detecting probe (Neoprobe 1000) was used intraoperatively to detect and resect areas of high radioactivity, representing tumor. Areas with persistently high probe counts after resection were the areas of occult residual disease, and represented the CTV to be irradiated. The IORT was given with either 6-9 MeV electron beam from a dedicated linear accelerator, or with high-dose-rate brachytherapy from a remote afterloader. If all RIGS-positive tissue had been resected, or if widely disseminated disease remained, the patient was not considered for IORT.

RESULT

This technique was used in 31 patients with colorectal adenocarcinoma recurrent into the pelvis (n = 23) or paraortic nodes (n = 8). The CTV for IORT was delineated by increased RIGS count in 13 of 19 patients (68%) with microscopic residual, and in 11 of 12 patients (92%) with gross residual. In the other 7 patients, the tumor area did not accumulate the radiolabeled antibody; therefore, these tumor beds were irradiated based on the surgeon's estimation of close margins. Hence, overall, the RIG-IORT technique was used to define the tumor bed for IORT in 24 of 31 patients (77%). This technical report focuses on the development of the RIG-IORT technique and does not address the outcome results of the treated patients.

CONCLUSION

A new technique, RIG-IORT, which uses radiolabeled monoclonal antibodies to precisely determine the CTV for IORT, is described. Whether the use of this technique will lead to improved tumor control will only be known upon the outcome analysis of RIG-IORT-treated patients compared with those obtained using traditional IORT techniques.