Radiation dose perturbation in the presence of permanent vascular-access injection ports.

Injection ports are commonly used to maintain permanent vascular access in patients with malignant disease. The injection ports allow blood sampling as well as infusion or injection of chemotherapeutic agents directly into the circulation. The access catheters are usually placed in the subclavian vein with the injection port being implanted in the intraclavicular area. These injection ports are entirely self-contained underneath the skin and may have been placed in an area which subsequently requires radiation treatment. A comprehensive study of the perturbation effects of the injection ports when placed in the path of the beam was carried out. All dose measurements were performed using stainless steel and titanium injection ports. The radiation beams were 6 MV and 10 MV X rays and 6, 9, 12, 15, and 18 MeV electrons. The data indicate that the presence of injection ports significantly alters the radiation dose and dose uniformity. For example, the dose underlying a stainless steel port is reduced by 47% when 18 MeV electrons are used. This paper presents the dosimetric data, discusses the clinical significance of the results, and provides recommendations for design modifications of the ports.

Combined pre and postoperative radiation for carcinoma of the rectum.

Since 1976, a new approach to adjuvant radiation therapy in carcinoma of the rectum has been used at Thomas Jefferson University Hospital. Seventy-eight patients with biopsy-proven invasive carcinoma of the rectum have been treated with low dose preoperative radiation, 500 rad given either on the day of or the day before surgery. Following surgery, the lesions were pathologically staged according to Astler-Coller's Modification of Duke's staging. Patients with good prognostic features (Stage A or B1) were followed with no further treatment while patients with poor prognostic characteristics (Stage B2, C1 and C2) were treated with aggressive postoperative pelvic radiation, 4500 rad delivered in five weeks. All patients entered into this study received the preoperative dose of 500 rad. Fifty-six patients underwent an A-P resection, four patients underwent a low anterior resection and ten patients had a combined abdominal transsacral resection. Eight patients were found to have liver metastasis at laparotomy and underwent a colostomy followed by palliative therapy. Twenty-nine patients were found to have early disease, Stage A or B1, and were given no further therapy. Of 41 patients with Stage B2 or C, 25 patients received the full course of postoperative radiation. Sixteen patients did not receive postoperative radiation for a variety of reasons. Follow-up in these patients ranges from six months to a maximum of 48 months with a median follow-up of 18 months. Sixty-nine of the total group of 78 patients are currently alive. Two patients with early tumor (Stage A or B1) have died of metastasis. One other patient with Stage A carcinoma died of unrelated causes. Two of the 25 patients receiving postoperative radiation developed metastatic disease, but none of the patients developed local recurrence in the pelvis. Six of 16 patients who should have received postoperative radiation, but did not recurred. Four of these six recurrences have been in the pelvis. Both the incidence of failure and the pattern of recurrence between these two groups of patients who did not receive postoperative radiation is suggestive of a better effect in the PR unrelated group. Survival of patients treated with this approach appears to be improved.

Treatment of cancer of the pancreas by precision high dose (PHD) external photon beam and intraoperative electron beam therapy (IOEBT).

Twenty-five patients with a diagnosis of unresectable adenocarcinoma of the pancreas were explored in the Clement O. Miniger (COMROC) IOEBT operating amphitheater at the Medical College of Ohio. Seventeen were treated with IOEBT (20-30 Gy, 15 or 18 meV electrons) PHD external beam radiation therapy (40-60 Gy, 1.8 Gy per fraction) plus appropriate operative biliary and gastrointestinal bypass procedures. No intraoperative complications were observed. Two patients died of causes that may have been treatment-related. Two patients developed abdominocutaneous fistulae. Pain was ameliorated in eleven of twelve patients. Jaundice was relieved in all patients. Four of ten patients with weight loss showed a reversal of that trend. Patient survival was not significantly different from that of patients treated with high-dose precision therapy alone.

Biochemical and cellular effects of radiofrequency induced interstitial hyperthermia on normal canine liver.

Interstitial hyperthermia (44.0 +/- 0.5 degrees C for 40 minutes) was delivered to the livers of 16 dogs to determine acute effects of treatment on blood chemistry, histology, and cellular appearance of normal liver. SGOT in treated animals peaked immediately at 300 +/- 21 U/L (within 2 hrs) and returned to control value within 7 days. LDH levels peaked at 1 day post-treatment and again at 2 weeks (300 +/- 16 U/L and 340 +/- 25 U/L respectively) and returned to pre-treatment values by week 4. SGPT remained elevated for 6 to 7 days following hyperthermia, but returned to control value at 2 weeks. There was also a rise in alkaline phosphatase (200 +/- 14 U/L 1 day post-treatment), which returned to a pre-treatment level by week 3. Changes in serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, lactate dehydrogenase, and alkaline phosphatase were attributed to both liver parenchymal damage induced by hyperthermia and to surgery. Other deviations in the blood chemistries and hematological parameters measured were ascribed to the stress response from surgical intervention, or to the resultant hemodilution from fluids during surgery. Microscopic examination upon necropsy, performed 4 weeks post-operatively, displayed limited fibrosis with some alteration of liver architecture, generalized sinusoidal dilation and red blood cells in the space of Disse. Cellular ultrastructure changes showed an increase of myelin figures, but mitochondria and other cellular organelles remained essentially normal. Localized tissue inflammation and some loss of function occurred in response to localized hyperthermia for this volume of tissue at therapeutic temperatures. This study showed that the technique was feasible and confirmed that the parenchymal damage caused by interstitial hyperthermia did not produce the severe loss of function that might have been expected.

Treatment of cancer of the pancreas by intraoperative electron beam therapy: physical and biological aspects.

Radiation therapy has had a significant and an expanded role in the management of cancer of the pancreas during the last decade. In particular, for locally advanced disease, radiation therapy has improved the median survival of patients to 1 year. Intraoperative electron beam therapy has been applied to unresectable and resectable pancreatic cancer in an attempt to enhance local control of disease and to improve patient survival. This paper presents a survey of the role of radiation therapy in treatment of cancer of the pancreas, provides information on the radiobiological aspects of this treatment modality and details the physical and dosimetric characteristics of intraoperative radiation therapy with electrons. Presented are the design specifics of an applicator system, central axis beam data, applicator parameters, dose distribution data, shielding, treatment planning and means of verification. Emphasis is placed on the collaboration and cooperation necessary for all members of the intraoperative radiation therapy team including surgeons, radiation therapists, medical physicists, anesthesiologists, technologists, and nurses.

Intraoperative electron beam radiation therapy (IOEBRT) for carcinoma of the exocrine pancreas.

The abdominal cavities of 50 patients were explored in a specially constructed intraoperative radiotherapy operating amphitheater at the Medical College of Ohio. Twenty-six patients were treated with intraoperative and postoperative precision high dose external beam therapy, 12 with intraoperative irradiation but no external beam therapy, and 12 with palliative surgery alone. All but two patients completed the postoperative external beam radiation therapy as initially prescribed. The median survival time for patients treated with palliative surgery alone was 4 months, and that for patients treated with intraoperative radiotherapy without external beam therapy was 3.5 months. Patients undergoing intraoperative irradiation and external beam radiation therapy had a median survival time of 10.5 months. Four patients died within 30 days of surgery and two patients died of gastrointestinal hemorrhage 5 months posttreatment.

Adjuvant radiation therapy for pancreatic cancer: a 15-year experience.

PURPOSE: A retrospective analysis to determine differences in survival of patients with pancreatic adenocarcinoma treated by radical surgery with and without adjuvant radiation therapy. METHODS AND MATERIALS: Between 1980 and 1995, 249 patients with pancreatic tumors were identified at the Medical College of Ohio. Forty-four of these patients underwent radical surgical procedures with curative intent. These patients were divided into four groups according to treatment: surgery alone (n = 14), surgery plus intraoperative radiation therapy (IORT) (n = 6), surgery plus external beam radiation therapy (EBRT) (n = 14), or surgery plus both IORT and EBRT (n = 10). Outcome and survival were analyzed among the four groups. RESULTS: The median survival time of patients treated with radical surgery alone was 6.5 months. The median survival time for the surgery plus IORT group was 9 months; however, 33.3% (two of six) of these patients survived longer than 5 years. This survival pattern was borderline significantly better than that for the surgery alone group (p = 0.0765). The surgery plus EBRT and the surgery plus IORT and EBRT groups had median survival times of 14.5 and 17.5 months, respectively. These were significantly better than that of the surgery alone group (p = 0.0004 and p = 0.0002, respectively). The addition of radiation therapy did not affect the treatment complication rate. CONCLUSION: The survival of patients who were treated with radical surgery alone was significantly poorer than that of patients who received adjuvant radiation therapy. These results are consistent with other studies in the literature. Patients treated with all three modalities (surgery, IORT, and EBRT) displayed the best median survival time.

Salvage external beam radiotherapy for clinical failure after cryosurgery for prostate cancer.

PURPOSE: To investigate the role of external beam radiotherapy (EBRT) as salvage treatment of prostate cancer after cryosurgery failure. METHODS AND MATERIALS: Between 1993 and 1998, 6 patients underwent EBRT with curative intent for local recurrence of prostate cancer after cryosurgery. All 6 patients had biopsy-proven recurrence and palpable disease on digital rectal examination at the time of EBRT. The median follow-up was 34 months (range 8-46). The median prostate-specific antigen level was 2.3 ng/mL (range 0.8-4.1). No patient had evidence of metastatic disease. Two patients received hormonal therapy before beginning EBRT. No patient received hormonal therapy after EBRT completion. The median elapsed time between cryosurgery and EBRT was 3 years (range 1.5-4). The median delivered dose was 66 Gy (range 62-70.2) using a 10-MeV photon beam. An in-house-developed three-dimensional treatment planning system was used to plan delivery of the prescribed dose with conformal radiotherapy techniques. RESULTS: After EBRT, all patients had complete resolution of palpable disease. Four patients (66%) were disease free at the time of the last follow-up. Two patients developed biochemical failure as defined by the American Society for Therapeutic Radiology and Oncology consensus definition. One of these patients had a prostate-specific antigen level of 97 ng/mL before cryosurgery. No patient developed distant metastasis during follow-up. Two patients (33%) developed proctitis; 1 case resolved with Rowasa suppositories and 1 required blood transfusion. CONCLUSIONS: Our preliminary results suggest that EBRT can render a significant number of patients biochemically free of disease and can cause complete resolution of clinically palpable disease after initial cryosurgery. The results also showed that EBRT can be given without excessive morbidity. EBRT should be considered as a treatment option in these potentially curable cases.

Radiosurgical treatment compared to surgery alone for rectal cancer.

Between February 1981 and September 1989, 144 patients with rectal cancer were treated according to a radiosurgical sandwich protocol (27Gy + surgery + 18Gy) or postoperative radiotherapy (45Gy) at the University Hospital 'A. Gemelli' in Rome. This group is compared with a group of 133 patients operated on between January 1968 and January 1981, by the same team of surgeons but who received no radiotherapy. The historical group is comparable to the radiosurgical group in terms of stage, histology, and surgical procedures. The median follow-up period of the radiosurgical group is 38 months and 68% of cases have been observed longer than 2 years. At 2 years local recurrence in the historical control group was 22% versus 17% in the prospective group (p = 0.8). For Stage C disease, local recurrence dropped from 54% to 35% with adjuvant radiotherapy (p = 0.3). Metastases were observed in 22% of the control group versus 13% of the radiosurgical group (p = 0.2). For Stage C disease the incidence of distant metastases dropped from 59% to 26% at 2 years with the use of the prospective radiosurgical protocol (p = 0.05). The Kaplan-Meier survival rate at 5 years was 46% for the historical group and 72% for the radiosurgical group (p = 0.003) (Stage A 71% & 94%, Stage B 48% & 77%, and Stage C 16% & 38%, respectively). Neither serious nor late toxicity has been detected in the radiotherapy group, nor were surgical complications observed in the pre-operative radiotherapy group. The data strongly suggest a survival advantage for patients treated with the radiosurgical combination (p = 0.003).

Interstitial brachytherapy for pancreatic cancer: report of seven cases treated with 125I and a review of the literature.

Since 1975, seven groups of investigators have reported clinical results of interstitial brachytherapy (IBT) for pancreatic cancer. The reports are comprised of data from 254 patients, 21 of whom died in the postoperative period for an overall operative mortality rate of 8.7%. Operative mortality rate range from 0% to 32% in individual reports. Most patients have been treated with 125I, although 25 patients were treated with 198Au seeds. Most investigators report combining IBT with external beam radiation therapy (EBRT) +/- adjuvant chemotherapy. In general, IBT has been associated with considerable morbidity. Median patient survival time has not exceeded 15 months. This report describes an additional seven patients with locally unresectable pancreatic cancer, without distant metastases, treated primarily with 60 to 100 Gy matched peripheral dose (MPD) by 125I IBT. One patient died postoperatively of a pulmonary embolus. Four of the remaining six patients were also treated with modest doses (10.5 to 30 Gy) of EBRT late in the course of the disease for local tumor progression. One developed a pancreaticocutaneous fistula, and one developed exacerbation of pre-existing diabetes mellitus. The median patient survival time from the date of IBT was 7 months (range: 0 to 21 months). One patient is alive without clinical evidence of cancer 9 months after IBT.

Intraoperative radiation therapy of pancreatic carcinoma: a report of RTOG-8505. Radiation Therapy Oncology Group.

The Radiation Therapy Oncology Group in 1985 began a study of IORT plus external beam radiation therapy for patients with locally unresected, non-metastatic pancreatic cancer. Patients were treated with a combination of 2000 cGy of IORT and postoperative external beam radiation therapy to 5040 cGy in combination with IV 5-FU (500 mg/m2/day on the first 3 days of the external beam treatment). As patients were registered on study prior to exploration, it was expected that a number of patients would be excluded from further analysis at the time of surgery. Eighty-six patients were entered on study through 6/1/88 and analyzed through 4/90. Fifty-one patients were fully analyzable. Median survival time of the 51 patients was 9 months with an 18-month actuarial survival rate of 9%. Local control could not be adequately evaluated in this multi-institutional study. Major postoperative complications were not excessive and occurred in 12% of patients. Two patients had major late morbidity leading to death, one from duodenal bleeding and the second from biliary obstruction. Although this study does demonstrate the feasibility of IORT in a multi-institutional setting, it does not demonstrate any advantage of IORT over conventional therapy for this disease.

Flow cytometric DNA content analysis of paraffin block embedded endometrial carcinomas.

Flow cytometry is being used as an aid in planning the treatment of patients with various malignancies. We report our experience with DNA content analysis on paraffin-embedded carcinomas. Hospital, radiation therapy, clinic, and pathology records were reviewed in 139 cases of endometrial carcinoma diagnosed between December 1980 and December 1986. Patients having Stage IV tumors, endometrial sarcomas, dual primary tumors, or incomplete records were eliminated from the analysis, which left 98 evaluable patients. This report outlines our experience with the first 20 patients. Five of 20 (25%) specimens demonstrated DNA content consistent with aneuploidy, median coefficient of variance of 5.3%. The median survival time of these five patients is 55 months, with three dying of cancer and one patient dying of other causes but with metastatic disease. The median %S phase was 3.7% in the 15 patients comprising the DNA content diploid population, median coefficient of variance 5.4%. No patient whose tumor showed S-phase cells below 3.7% died of endometrial cancer. Four of 7 patients developed recurrent cancer with 3 of the 4 patients dying of disease in the high %S phase group. The median patients survival time in the DNA content diploid population was 73 (range: 17-98) months. Patients with 3.7% or below S-phase cells had a median survival time of 75 (range: 40-98) months whereas the median survival time was 48 (range: 17-89) months for patients having a %S phase fraction above 3.7%. Although the number of patients studied is small, it appears that DNA content aneuploid tumors are frequently "upstaged" at surgery. These patients may not benefit from preoperative irradiation. Accurate determination of the %S phase fraction in DNA content diploid tumors may possibly identify patients with a poorer prognosis who may benefit from adjuvant therapy.

Intraluminal brachytherapy in the treatment of pancreas and bile duct carcinoma.

PURPOSE: A new method of palliation of malignant obstructive jaundice is presented. METHODS AND MATERIALS: Twelve patients with carcinoma of the extrahepatic bile ducts (EHBD-five patients) or pancreatic head (PH-seven patients) received radiation therapy between 1988 and 1991. Percutaneous transhepatic biliary drainage was performed in four EHBD patients and an endoprosthesis was placed during endoscopic retrograde cholangiopancreatography (ERCP) in the other eight patients. All 12 received intraluminal brachytherapy (ILBT): 20-50 Gy calculated at 1 cm from the Iridium-192 (192Ir) wire. In four PH patients the source was placed in the duct of Wirsung; in the other eight patients ILBT was performed via the common bile duct. Five of the seven PH patients and one of the five EHBD patients received External Beam Radiation Therapy (EBRT): 26-50 Gy, alone or with concomitant 5-Fluorouracil (5-FU). RESULTS: Cholangitis occurred in six patients. Three PH patients treated with EBRT+ILBT developed gastrointestinal toxicities. With a minimum follow-up of 18 months, median survival times were 14 months (EHBD) and 11.5 months (PH); one of the seven PH patients is alive (29 months) and two of the EHBD patients are alive (18 and 43 months). All patients had satisfactory control of jaundice. CONCLUSIONS: The results in the EHBD patients suggest that the addition of ILBT after biliary drainage prolongs survival. Further experience is necessary to determine whether ILBT in the common bile duct and/or in the duct of Wirsung may be, in PH patients, an alternative boost technique to Interstitial Brachy-therapy (IBT) or Intraoperative Electron Beam Radiation Therapy (IOEBRT).

Predictions of blood flow from thermal clearance during regional hyperthermia.

In order to provide a method for estimation of regional blood flow during hyperthermia, a mathematical model has been developed which employs thermal clearance to measure this physiologic parameter. Limbs of mongrel dogs were heated with 2450 megaHertz microwaves to temperatures of 43 degrees C, 45 degrees C, or 47 degrees C and thermal washout was measured at five minute intervals throughout each treatment period. Calculated blood flow indicates that in response to heat challenge, normal tissue compensates by increasing regional blood flow within the treatment volume. This increase in blood flow continues to a maximum value after which the blood flow begins to decrease. Data indicate that the time for maximum increase in blood flow (induction time) decreases as treatment temperature increases. These induction times were 40 minutes, 25 minutes, and 15 minutes for treatment temperatures of 43 degrees, 45 degrees, and 47 degrees C, respectively. The data also show that the calculated value of peak blood flow is directly related to treatment temperature. Calculated peak blood flow values reached 37.8, 59.0, and 183.0 ml/minute/100 grams of tissue during 43 degrees, 45 degrees, and 47 degrees C, hyperthermia, respectively. It is suggested that a therapeutic advantage could be gained by treating tumors for a specific length of time during which the blood flow in adjacent normal tissues continues to increase. This would take maximum advantage of normal tissue's ability to compensate for increased temperature, and would exploit any decreased ability of tumor tissue to perform this same function.

Phase I-II trial of concomitant continuous carboplatin (CBDCA) infusion and radiotherapy in advanced nonsmall cell lung cancer with evaluation for surgery: final report.

PURPOSE: The goal of this trial was to determine the maximum tolerable dose when carboplatin (CBDCA) was administered in continuous infusion concurrently with radiotherapy in patients with nonsmall cell lung cancer. METHODS AND MATERIALS: From October 1989 to July 1993, 54 patients were studied (male/female ratio: 44 to 10), median age was 62 years. Two patients had Stage II cancer, 22 had Stage IIIA, 24 had Stage IIIB, and 6 had Stage IV. Carboplatin was given for 96 h, starting at a dose of 30 mg/m2/day: 13 patients received 30 mg/m2/day (group A), 12 patients received 50 mg/m2/day (group B), 12 patients received 70 mg/m2/day (group C), 10 patients received 90 mg/m2/day (group D), and 7 patients 110 mg/m2/day (group E). The radiation dose was 50.40 Gy delivered to the target volume in 5.3 weeks. RESULTS: Fifty-three of 54 patients were evaluable for toxicity and 52 out of 54 for response. Toxicity (Miller score): Myelotoxicity: in groups A and B it was almost absent; in groups C and D it was moderate (leukopenia G1-2: 45.4% patients; trombocytopenia G1-2: 22.7%, G3: 9%; anemia G1-2: 9%); only in group E was it severe (leukopenia G1 and G3 16.6% respectively; trombocytopenia G3: 33.3%, G4: 16.6%; anemia G1-2: 50%). Nephrotoxicity was present only in one patient of group E and was Grade 3. Nausea and vomiting were related to CBDCA dose. One patient in Group E died of intractable toxicity 3 days after the end of infusion; then the study was closed. The limiting toxicity dose was shown to be 110 mg/m2/day given for 96 h. Clinical response rate: Twenty-six of 52 patients had major response, 24 had minor response, and only 2 patients had progression of disease. SURGERY: Twenty-one of 52 tumors were judged resectable: 18 patients had complete tumor resection, 1 had exploratory thoracotomy, and 2 patients refused surgery. Pathological response rate: Five patients had pathologic state T0 or Tis. CONCLUSIONS: These results indicate that the maximum tolerable dose of CBDCA infusion for 96 h is 90 mg/m2/day, and this schedule seems to produce an appreciable response rate. Therefore, we have started a Phase II trial, which will permit us to define the true efficacy of this schedule.

Intraoperative electron beam radiation therapy: technique, dosimetry, and dose specification: report of task force 48 of the Radiation Therapy Committee, American Association of Physicists in Medicine.

Intraoperative radiation therapy (IORT) is a treatment modality whereby a large single dose of radiation is delivered to a surgically open, exposed cancer site. Typically, a beam of megavoltage electrons is directed at an exposed tumor or tumor bed through a specially designed applicator system. In the last few years, IORT facilities have proliferated around the world. The IORT technique and the applicator systems used at these facilities vary greatly in sophistication and design philosophy. The IORT beam characteristics vary for different designs of applicator systems. It is necessary to document the existing techniques of IORT, to detail the dosimetry data required for accurate delivery of the prescribed dose, and to have a uniform method of dose specification for cooperative clinical trials. The specific charge to the task group includes the following: (a) identify the multidisciplinary IORT team, (b) outline special considerations that must be addressed by an IORT program, (c) review currently available IORT techniques, (d) describe dosimetric measurements necessary for accurate delivery of prescribed dose, (e) describe dosimetric measurements necessary in documenting doses to the surrounding normal tissues, (f) recommend quality assurance procedures for IORT, (g) review methods of treatment documentation and verification, and (h) recommend methods of dose specification and recording for cooperative clinical trials.

Clinical fusion of three-dimensional images using Bremsstrahlung SPECT and CT.

UNLABELLED: Infusional brachytherapy for treatment of neoplasms, with colloidal 32P has been used to treat various tumors in the pancreas, liver, brain, lung, and head and neck. In performing such treatments, anatomical verification of the location of the administered 32P from the image obtained by Bremsstrahlung SPECT alone is not possible due to the lack of internal landmarks, since the radionuclide is distributed only in the tumor and does not usually accumulate in the normal organs. The purpose of this study was to provide a practical three-dimensional approach for image fusion between Bremsstrahlung SPECT and CT. METHODS: The tumors in four cancer patients were injected directly with 32P under CT guidance. A Bremsstrahlung SPECT study using 99mTc backscatter sources to obtain the body contour was then performed. SPECT images were used to generate the skin contours using a threshold detection method. A three-dimensional surface was generated from these contours using a tiling program and fused with a corresponding CT surface generated from a CT scan in the same patient through an iterative surface-fitting algorithm. The three-dimensional surface of the region of high-activity, corresponding to the infused tumor, was then generated using the Bremsstrahlung SPECT data by mapping the iso-count surfaces through a computer program. The three-dimensional image of the organ then was fused with the registered CT-SPECT datasets. RESULTS: The accuracy of fit measured as the mean distance between the SPECT and CT surfaces was in the range of 3-4 mm. CONCLUSION: The anatomical co-registration of Bremsstrahlung SPECT with CT images using the outer surface-fitting algorithm is a reliable tool. This correlation permits direct anatomic confirmation of the region of the 32P activity distribution with the anatomic site selected for injection.

Diplopia and pneumoencephalocoele after chest wall resection and intraoperative radiation therapy.

The dural sheath may be transected in the course of a posterior thoracic procedure. If air is introduced into the subarachnoid space, a cranial nerve palsy may result. Computed tomographic scanning establishes the diagnosis. The condition resolves without treatment.

Association of malignant lymphoma with pancreatic adenocarcinoma: a clinicopathologic study of three patients.

Three patients with pancreatic adenocarcinoma are studied who had a prior history of malignant lymphoma. No common predisposing factors for the development of pancreatic adenocarcinoma were identified. We conclude that patients with malignant lymphoma who have new or persistent pancreatic masses must be evaluated for the possibility of a second primary neoplasm.

Radiation contamination and leakage assessment of intraoperative electron applicators.

In intraoperative radiation therapy, it is critical to reduce the radiation contamination outside the useful field by as much as physically feasible. Additionally, a uniform dose is clinically desirable across the tumor volume. A study of the Medical College of Ohio applicators indicates that the radiation contamination outside the field can be as high as 18% of the central axis dose. The effects of the photon collimator setting on the magnitude and energy of the radiation contamination are discussed and means are presented for reducing this unwanted radiation. The dose nonuniformity across the field is found to be virtually independent of the photon collimator setting and is shown to be mostly due to the transparent applicator wall. The clinical significance of the findings is discussed.