Brachytherapy for in-stent restenosis in general interventional practice: a single institution's experience using four radiation devices

BACKGROUND

The effectiveness of brachytherapy for the treatment of in-stent restenosis (ISR) has been established in a number of large randomized controlled trials. Efficacy of this therapy in general population is less well established.

METHODS AND MATERIALS

We report our experience of 207 patients, 236 coronary lesions, treated with brachytherapy between November 2000 and November 2002. All commercially available brachytherapy devices, as well as one investigational device, were utilized. This cohort was followed over 9 months and clinical outcomes were obtained with subsequent analysis of patient and lesion-specific characteristics.

RESULTS

Average treatment age was 62.5 years; 73% were male and the most frequent presentation was unstable angina (74%). All patients had successful delivery of radiation, with no in-hospital deaths. Novoste BetaCath device was used for 163 (65%) lesions, Cordis Checkmate for 56 (24%) lesions, Interventional Therapies device in 13 (8%) lesions, and Guidant Galileo in 4 lesions (3%). At a mean follow-up of 9.1 months, 78.7% were free of major adverse cardiac event (MACE). Twenty-one patients required repeat PTCA (10.1%), 19 had CABG (9.2%), 3 had MI (1.4%), and there was 1 death (0.5%). Unadjusted MACE rates for each device were 21% for Novoste, 28% for Checkmate, 8% for Interventional Therapies, and 50% for Galileo. Lesion length, minimal lumen diameter, renal failure, diabetes, and smoking did not predict treatment failure; only age was inversely correlated with MACE (P=.002).

CONCLUSION

When applied across a spectrum of patients, lesions, and devices, brachytherapy retains its effectiveness with outcomes similar to those reported in randomized clinical trials.

A biplane angiographic study on cardiac motion of coronary artery stents: options to minimize the target volume for high-precision external beam radiotherapy of coronary artery in-stent restenosis

PURPOSE

High-precision external beam radiotherapy (EBRT) has been suggested as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis. The purpose of our study was to investigate and compare different options to define a smallest feasible target volume.

METHODS AND MATERIALS

The cardiac motion of 17 coronary artery stents in 17 patients was studied by use of biplane conventional angiography, recorded during breath-hold. Each stent was reconstructed in three dimensions by use of biplane sets of frames covering an entire cardiac cycle. The volume traversed by the stent during the entire or part of the cardiac cycle was determined. Four options to define the stent-traversed volume (STV) as a target for high-precision EBRT were investigated.

RESULTS

The mean STV during the entire cardiac cycle was 3.5 cm3; the STV represented less than 1% of the heart volume in all patients. The STV during the diastolic and systolic phase resulted in a mean reduction of 26.6% and 29.1%, respectively, compared with the STV during the entire cardiac cycle. The smallest STV, measured during a 160-ms interval within the cardiac cycle, resulted in a mean maximal reduction of 75.9% compared with the STV during the entire cardiac cycle.

CONCLUSIONS

The STV during the entire cardiac cycle represents a small potential target volume for high-precision EBRT. A significant reduction of this target volume is possible in case of definition during a selected interval within the cardiac cycle.

Intramural neovascularization and haemorrhages are major long-term effects of intravascular gamma-radiation after stenting

Structural changes that might influence the structural integrity of the vessel in response to intravascular brachytherapy (IVB) and stenting were examined, focus being on the importance of neovascularization in rabbit stented arteries. Stents were implanted in the infrarenal aortas of rabbits, immediately followed by gamma IVB or a sham radiation procedure, and the arteries harvested at 6 months. Labelling for von Willebrand factor showed an increase in adventitial and medial neovascularization in irradiated versus control arteries group (5.04+/-0.89 versus 1.51+/-0.23 mm(-2), respectively; p=0.004). Moreover, intramedial haemorrhages (free hemosiderin deposition) and inflammation (macrophages) were only observed in irradiated arteries. No significant change in expression of matrix metalloproteinase 1, 2 or 3 was observed between the irradiated and control group while collagen content decreased in the irradiated versus the control group (10.05%+/-1.48% versus 31.92%+/-3.12%, respectively; p<0.001). The study supports the hypothesis that IVB associated with stenting induces late deleterious effects on the medial layer, characterized by formation of intramural neovessels, haemorrhages and a decrease in collagen content.

[Effect of beta radiation brachytherapy in the treatment of restenosis of coronary stents]

Brachytherapy currently represents the only treatment method for in-stent restenosis (ISR) confirmed in randomised clinical studies. In a group of 46 patients, selected for brachytheraphy on the bases of clinical signs of restenosis accompanied with development or deterioration of angina pectoris and with angiography results showing significant in-stent restenosis, we used a beta radiation system BetaCath NOVOSTE. This therapy was safe. Results of acute angiography were positive in 91% of patients. Clinical restenoses within 6 month of clinical monitoring occurred in 8.6% of patients. Due to impairment of more arteries in the majority of patients from the sample, following revascularisation of nontarget vessels was necessary in 19.6% of patients. We haven't observed late thrombosis. It was probably eliminated by prolonged administration of a combination of aspirin and clopidogrel. Dosimetry results during brachytherapy showed that doses of radiation both for a surgeon and a patient corresponded to a fraction of doses received from an x-ray apparatus during fluoroscopy and acquisition. Both an edge restenosis and a diffuse restenosis were identified in stenoses of patients with in-stent restenosis. Brachytherapy with beta radiation seems to be an efficient method for treatment of coronary in-stent restenosis.

Five-Year Follow-Up After Intracoronary Gamma Radiation Therapy for In-Stent Restenosis

Background— The Washington Radiation for In-Stent Restenosis Trial is a double-blinded randomized study evaluating the effects of intracoronary radiation therapy (IRT) in patients with in-stent restenosis (ISR).

Methods and Results— One hundred thirty patients with ISR (100 native coronary and 30 vein grafts) underwent percutaneous transluminal coronary angioplasty, laser ablation, rotational atherectomy, or additional stenting (36% of lesions). Patients were randomized to either 192-Iridium IRT or placebo, with a prescribed dose of 15 Gy to a 2-mm radial distance from the center of the source. Angiographic restenosis (27% versus 56%, P =0.002) and target vessel revascularization (26% versus 68%, P <0.001) were reduced at 6 months in patients treated with IRT. Between 6 and 60 months, patients treated with IRT compared with placebo had more target lesion revascularization (IRT, 21.6% versus placebo, 4.7%; P =0.04) and target vessel revascularization (IRT, 21.5% versus placebo, 6.1%; P =0.03). At 5 years, the major adverse cardiac event rate was significantly reduced with IRT (46.2% versus 69.2%, P =0.008).

Conclusions— In the Washington Radiation for In-Stent Restenosis Trial, patients with ISR treated with IRT using 192-Iridium had a reduction in the need for repeat target lesion and vessel revascularization at 6 months and 5 years.

Efficacy and safety of endovascular intracoronary brachytherapy

Intracoronary brachytherapy has emerged as one of the novel exciting developments in the field of interventional cardiology to counteract the problem of restenosis. Restenosis is the major limitation to a full expansion of all revascularization procedures. Elastic recoil, unfavorable remodeling and a proliferative response to injury are the more importune mechanisms to restenosis. The technique of intracoronary brachytherapy involves application of locally delivered radiation or brachytherapy in the management of restenosis. Ionizing radiation has been shown to decrease the proliferative response to injury in animal models of restenosis. Subsequently, several small randomized trials have demonstrated that intracoronary brachytherapy can reduce the rates of both angiographic and clinical restenosis in patients undergoing percutaneous coronary intervention for in-stent restenosis.

Favorable effect of ?-radiation for in-stent restenosis: Effect of diabetes on angiographic and clinical outcomes

The purpose of this study was to examine the effect of vascular brachytherapy with gamma-radiation (gamma-RT) in patients with diabetes mellitus (DM) with coronary in-stent restenosis (ISR). In the Washington Radiation for In-Stent Restenosis (WRIST) trial, 130 patients with ISR were treated with (192)Ir or placebo. Of the patients enrolled, 44 (34%) had DM (18 of them treated with gamma-RT and 26 with placebo). Gamma-radiation therapy of ISR in diabetics resulted in similar procedural success and in-hospital outcome compared to nondiabetics. At 6-month follow-up, both DM and non-DM patients treated with gamma-RT had significantly lower target lesion revascularization (TLR), target vessel revascularization, and major adverse cardiac event rates compared to placebo. DM remains a powerful predictor of TLR and major adverse cardiac events even after treatment of ISR with gamma-RT.

Late intravascular ultrasound findings of patients treated with brachytherapy for diffuse in-stent restenosis

This study aimed at evaluating long-term (24-month) effects of beta-irradiation (188Re-MAG3-filled balloon) using intravascular ultrasound (IVUS) in patients with in-stent restenosis (ISR). Long-term effects of beta-irradiation on intimal hyperplasia (IH) within the stented segment and vessel and lumen dimensions of nonstented adjacent segments in patients with ISR have not been sufficiently evaluated. Two-year follow-up IVUS was performed in 30 patients with patent ISR segments at 6-month follow-up angiography. Serial IVUS images were acquired at five equidistant intrastent sites and at three different reference segment sites. IH burden (%) was defined as 100 x (IH/stent area). Mean intrastent IH area and IH burden significantly increased between 6 and 24 months, from 2.1 +/- 1.1 to 2.6 +/- 1.4 mm2 (P < 0.001) and from 26% +/- 10% to 33% +/- 14% (P < 0.001), respectively. There was a significant decrease of mean external elastic membrane (from 10.1 +/- 3.9 to 9.7 +/- 3.9 mm2; P = 0.015) and lumen area (from 5.6 +/- 2.3 to 5.1 +/- 2.3 mm2; P = 0.021) within distal reference segments between 6 and 24 months. Target lesion revascularization (TLR) was performed in six patients (20%) between 6 and 24 months after beta-irradiation therapy. There were no significant differences between TLR and non-TLR groups except for a smaller minimum lumen area at 24 months in the TLR group. Because of a small amount of late loss between 6 and 24 months, most irradiated ISR vessel segments remained stable for up to 2 years. However, quantitative evidence of late catch-up was evident in most patients and was significantly associated with 24-month TLR in some patients.

Intravascular brachytherapy: indications and management of adverse events

Intravascular brachytherapy has become the standard of care for the treatment of coronary in-stent restenosis after repeat angioplasty. More than 5000 patients have been treated as part of various clinical trials. Based on the results of the GAMMA I trial, the START ((90)Sr Treatment of Angiographic Restenosis Trial), and the INHIBIT (INtimal Hyperplasia Inhibition with Beta In-stent restenosis Trial), the Checkmate system using (192)Ir, the Betacath system using (90)Sr/Y, and the Galileo system using (32)P, have been approved for the treatment of in-stent restenosis. With a better understanding and application of radiation oncology concepts to vascular brachytherapy, problems such as edge failure are being overcome. The complication of late thrombosis has also become less significant with the elimination of restenting at the brachytherapy procedure, and the prolonged use of antiplatelet therapy. There are other competing modalities in the early phases of clinical trials. The durability of results, lack of any significant long-term complications and the confirmation of the efficacy in other sites will further consolidate the role of radiation in treating in-stent restenosis.

Clinical outcomes for sirolimus-eluting stent implantation and vascular brachytherapy for the treatment of in-stent restenosis

The purpose of this study was to compare the mid-term clinical outcome of sirolimus-eluting stent (SES) implantation and vascular brachytherapy (VBT) for in-stent restenosis (ISR). We assessed the 9-month occurrence of major adverse cardiac events (MACE) in 44 consecutive patients with ISR treated with SES implantation and 43 consecutive patients treated with VBT in the period immediately prior. Baseline clinical and angiographic characteristics of the two groups were similar. During follow-up, three patients (7%) died in the VBT group and none in the SES group. The incidence of myocardial infarction was 2.3% in both groups. Target lesion revascularization was performed in 11.6% of the VBT patients and 16.3% of the SES patients (P = NS). The 9-month MACE-free survival was similar in both groups (79.1% VBT vs. 81.5% SES; P = 0.8 by log rank). The result of this nonrandomized study suggests that sirolimus-eluting stent implantation is at least as effective as vascular brachytherapy in the treatment of in-stent restenosis.

Intracoronary beta brachytherapy as a treatment option for high-risk refractory in-stent restenosis

BACKGROUND

Vascular (VBT) has clearly been shown in multiple clinical trials to decrease restenosis rates for in-stent restenosis (ISR). However, patients enrolled in these randomized clinical trials represent a select group, and the efficacy of VBT in patients with ISR who were excluded from these controlled trials due to more complex coronary anatomy requires further investigation. This study sought to define the angiographic and clinical profile and outcomes of these high-risk patients with ISR who were excluded from the randomized clinical trials and who received VBTusing Strontium-90 (Sr-90) using the Novoste Beta-Cath System through a Compassionate Use Protocol (CUP).

METHODS

The study was designed as a single center, prospective, open label registry trial evaluating the use of VBT on complex instent restenotic lesions in patients who were excluded from the START and START 40 trials. In general, these patients included those with saphenous vein graft (SVG) lesions, long lesions (>35 mm), and patients with a history of more than three prior interventions. VBT using Sr-90 was delivered using the Novoste Beta-Cath System after successful angioplasty. The predetermined primary endpoint was freedom from target vessel revascularization (TVR) at 8 months, one and two years. The secondary endpoint was a composite of death, myocardial infarction (MI) and TVR at 8 months, one year, and two years.

RESULTS

Between September 4, 1998 and December 6, 2000, 32 patients were treated with VBT under the UCP protocol. The mean duration of follow up was 15.3 +/- 8.3 months. There were 9 major cardiac events at eight months including one death, one acute myocardial infarction and 7 TVR. Excluding the one patient who died, 33 lesions were available for follow-up. The rate of TVR in this high-risk patient population was 21.1% (n = 7/33 lesions). The method of revascularization included one bypass surgery and 6 repeat percutaneous coronary interventions.

CONCLUSIONS

This trial demonstrates that utilization of the Beta-Cath System using Sr-90 for the treatment of ISR in a patient population excluded from the randomized clinical trials due to unfavorable lesions characteristics is feasible appears to be associated TVR rates that compare favorably with the event rates of patients enrolled in other trials enrolling lower-risk groups.

Long-term follow-up of brachytherapy for treatment of allograft in-stent restenosis

The experience of brachytherapy in the treatment of in-stent restenosis of allograft arteries is limited. We present two cases of in-stent restenosis treated with brachytherapy with favorable angiographic follow-up at 10 months in one patient and at 17 months in the other.

Three-Year Clinical Follow-up Results of Intracoronary Radiation Therapy Using a Rhenium-188-Diethylene-Triamine-Penta-Acetic-Acid-Filled Balloon System

BACKGROUND

Intracoronary radiation therapy (IRT) prevents recurrent in-stent restenosis, but its long-term safety and efficacy remain uncertain. In the present study, the long-term clinical outcome of IRT using the rhenium-188 ((188)Re)-filled balloon system was evaluated.

METHODS AND RESULTS

After successful catheter-based treatment of either a de novo or restenotic lesion, 187 patients were randomly assigned to either the radiation (N=104) or the control (N=83) group. The (188)Re-filled balloon system was designed to deliver 17.6 Gy to 1.0-mm tissue depth. Angiographic restenosis was significantly reduced with IRT at 9 months (18.9% vs 45.9%, p<0.001), but the incidence of major adverse cardiac events (MACE) including death, myocardial infarction, and target-vessel revascularization (TVR) by 3 years showed no difference. Lack of clinical benefit might be related to TVR caused by geographic miss (6/22, 28.6%), balloon-induced unhealed dissection (3/22, 13.6%) and late thrombosis (2/22, 9.1%). In the restenotic subgroup (N=39), the MACE rate within 3 years was significantly reduced with IRT (14.3% vs 54.5%, p=0.01).

CONCLUSIONS

IRT using the (188)Re -filled balloon system is safe and technically feasible. Although IRT failed to show favorable outcomes for de novo lesion, the clinical benefits for restenotic lesions seem durable for 3 years. Furthermore, preventing geographic miss and dissection might improve long-term outcomes.

Gamma radiation for in-stent restenosis: effect of lesion length on angiographic and clinical outcomes

The relation between lesion length and effectiveness of gamma radiation treatment (gamma-RT) has not been well described. We evaluated the acute and long-term outcome according to baseline lesion length in 130 patients treated with (192)Ir in the Washington Radiation for In-Stent Restenosis Trial; 44 (35.5%) had baseline short in-stent restenosis (ISR) lesions (length < 15 mm) and 80 (64.5%) long ISR lesions (length > or = 15 mm). At 6-month follow-up after gamma-RT, the short ISR group had larger lumen dimensions and lower late loss than the long ISR group. Restenosis rate was significantly higher in patients with long ISR for both the placebo (74% vs. 39%; P = 0.01) and the gamma-RT arm (31% vs. 5.3%; P = 0.04). gamma-RT significantly improved the angiographic outcome in the short-lesion groups but had the more pronounced effect on the reduction of clinical events after treatment of long ISR group. Lesion length remains a powerful predictor of recurrent ISR and clinical events after treatment of ISR even with gamma-RT.

Real-world clinical practice of intracoronary radiation therapy as compared to investigational trials

Intracoronary radiation therapy (IRT) is well established in clinical practice as an effective treatment for in-stent restenosis. We aimed to determine if the 6-month clinical outcome of patients treated postapproval for marketing [commercial radiation (CR)] is equivalent to those patients enrolled in the Washington Radiation for In-Stent Restenosis Trials [Gamma WRIST and Beta WRIST; investigational radiation (IR)]. The 6-month clinical outcome of 110 consecutive patients with 125 lesions who received IRT (gamma, (192)Ir, 15-18 Gy, n = 6; or beta, (32)P, 20 Gy, n = 20; or (90)Sr/Y, 18.4-23.0 Gy, n = 99) in CR was compared with the 6-month clinical outcome of 117 patients with 117 lesions who received IRT ((192)Ir, 15 Gy, n = 65, in Gamma WRIST; and (90)Y, 20.6 Gy, n = 52, in Beta WRIST) in IR. Patients in CR were treated with wider radiation margins. The CR received antiplatelet therapy for at least 6 months and the IR for 1 month. The baseline characteristics of both groups were similar. Use of atheroablation devices was less in CR than IR (15.2% vs. 32.8%, respectively; P = 0.001). The overall major adverse cardiac events (death, Q-wave myocardial infarction, and target vessel revascularization; 18.2% vs. 29.1% in IR; P = 0.05) were significantly lower in the CR when compared with patients in the IR. The real-world clinical practice of IRT demonstrates lower events and better clinical outcomes. This is most likely a result of implementation of the lessons learned from the clinical trials such as optimizing the dosimetry by using a higher dose, treating wider margins to minimize edge effect, and administering prolonged antiplatelet therapy to abolish late thrombosis.

Impact of radiation dose on late clinical outcome after intracoronary radiation therapy: Three-year follow-up of Long WRIST

To determine the safety and efficacy, including the impact, on the late recurrence rate of an incremental gamma-radiation dose from 15 to 18 Gy, we report the 3-year clinical outcome of Washington Radiation for In-Stent Restenosis Trial for Long Lesions (Long WRIST). One hundred eighty patients with recurrent in-stent restenosis (ISR) were enrolled in the Long WRIST series and treated with (192)Ir with 1 month of antiplatelet therapy. Between 6 months and 3 years, the need for repeat revascularization was low and similar among the three groups. At 3 years, target lesion revascularization (TLR) and major adverse cardiac events (MACE) were less frequent in the 18 Gy group than in the 15 Gy group (P = 0.12 for TLR, P < 0.05 for MACE) and less frequent in the 15 Gy group as compared to the placebo group (P < 0.05 for TLR and MACE). At 3 years, a higher dose of 18 Gy with (192)Ir continues to improve the outcome of patients treated for ISR when compared to patients treated with 15 Gy or placebo.

Cutting balloon angioplasty vs. conventional balloon angioplasty in patients receiving intracoronary brachytherapy for the treatment of in-stent restenosis

The objective of this study was to evaluate the safety and efficacy of cutting balloon angioplasty (CBA) for the treatment of in-stent restenosis prior to intracoronary brachytherapy (ICB). Cutting balloon angioplasty may reduce the incidence of uncontrolled dissection requiring adjunctive stenting and may limit "melon seeding" and geographic miss in patients with in-stent restenosis who are subsequently treated with ICB. We performed a retrospective case-control analysis of 134 consecutive patients with in-stent restenosis who were treated with ICB preceded by either CBA or conventional balloon angioplasty. We identified 44 patients who underwent CBA and ICB, and 90 control patients who underwent conventional percutaneous transluminal coronary angioplasty (PTCA) and ICB for the treatment of in-stent restenosis. Adjunctive coronary stenting was performed in 13 patients (29.5%) in the CBA/ICB group and 41 patients (45.6%; P < 0.001) in the PTCA/ICB group. There was no difference in the injury length or active treatment (ICB) length. The procedural and angiographic success rates were similar in both groups. There were no statistically significant differences in the incidence of death, myocardial infarction, recurrent angina pectoris, subsequent target lumen revascularization, or the composite endpoint of all four clinical outcomes (P > 0.05). Despite sound theoretical reasons why CBA may be better than conventional balloon angioplasty for treatment of in-stent restenosis with ICB, and despite a reduction in the need for adjunctive coronary stenting, we were unable to identify differences in clinical outcome.

Comparison of the angiographic outcomes after beta versus gamma vascular brachytherapy for treatment of in-stent restenosis

This study was designed to compare the angiographic outcomes of beta versus gamma vascular brachytherapy (VBT). We reviewed the angiographic results of 636 lesions (212 that underwent beta and 212 that underwent gamma VBT, and 212 that received placebo) with native coronary in-stent restenosis matched for lesion length, vessel size, preprocedure minimum lumen diameter (MLD), and time to angiographic follow-up in the various randomized clinical trials and studies. Baseline lesion complexity was similar in these 3 groups. Final MLD was smaller in the beta VBT group than in the gamma VBT or placebo group. At follow-up, beta and gamma VBT significantly reduced both angiographic restenosis (34.4% for beta VBT, 26.4% for gamma VBT, and 50.9% in the placebo group; p <0.0001) and recurrent lesion length (9.2 mm for beta VBT, 8.4 mm for gamma VBT, and 15.5 mm placebo, p <0.0001) compared with placebo. Gamma VBT was associated with a greater reduction in restenosis outside the stent than beta VBT. By multivariable analysis, independent angiographic predictors of treated segment restenosis included beta or gamma VBT, lesion length, and vessel size. In matched lesions, beta and gamma VBT achieved similar reductions in treated segment restenosis and recurrent lesion length compared with placebo.

Extra-stent vascular remodeling in in-stent restenosis after 188Re-MAG3 radiation therapy

BACKGROUND

The effect of beta-radiation on extra-stent vascular remodeling in patients with in-stent restenosis has not been studied. The correlation between the extent of extra-stent plaque proliferation and that of intimal hyperplasia (IH) in in-stent restenosis in patients who received beta-radiation therapy as well as conventional therapy has also not been studied.

METHODS

We evaluated the extra-stent remodeling in diffuse in-stent restenosis between a beta-radiation therapy patient group (188Re-MAG3, n=50) and a control group (n=9) by applying serial intravascular ultrasound (IVUS) analysis. Matching (post-intervention and follow-up) images were acquired at the follow-up lesion site and were available in 44 of 50 patients who received radiation therapy and in seven of nine control patients.

RESULTS

There was a significant increase of the external elastic membrane (EEM) area in both groups: 16.4 +/- 3.3 mm2 post-intervention to 17.1 +/- 3.3 mm2 at follow-up, P=0.001 in the radiation therapy group, and 16.8 +/- 4.0 mm2 post-intervention to 17.4 +/- 4.1 mm2 at follow-up, P=0.008 in the control group. There were no statistically significant differences of the Delta EEM area between the two groups: 0.7 +/- 0.4 mm2 in the radiation therapy group vs. 0.6 +/- 0.4 mm2 in the control group, P=0.389. The Delta IH area correlated with the Delta EEM area in the control group (r=0.826, P=0.022), but not in the radiation therapy group (r=0.016, P=0.919).

CONCLUSIONS

The findings of this IVUS study were that positive remodeling (increased EEM area) occurred equally in both control and irradiated patients with in-stent restenosis. The extent of remodeling was directly in proportion to IH in the control group, but no such relationship existed in the irradiated patient group.

Understanding Stereotactic Radiosurgery for Intracranial Tumors, Seed Implants for Prostate Cancer, and Intravascular Brachytherapy for Cardiac Restenosis

Our 21st century has moved us into a world of technology never imagined. The aim of our article is to move oncology nurses beyond the realm of external beam radiation therapy. We chose to present 3 modalities of high precision that are infiltrating the everyday world of radiation therapy. Stereotactic radiosurgery for intracranial brain tumors and brachytherapy for prostate cancer require an expanded knowledge base for nursing to deliver excellent patient care. Cardiac patients receiving radiation seeds is new in the world of oncology nursing. These patients are unique but they are now a part of our world. Expanding our knowledge base to include a radiation procedure in cardiac care does bring us beyond the world of external beam radiation. Patients often seek information from nurses. Having an understanding of the basic principles and techniques will enable oncology nurses to educate patients. The purpose of this article is to explain the procedure of stereotactic radiosurgery, brachytherapy for prostate cancer, and intravascular brachytherapy for cardiac restenosis. Our discussion will include selection criteria, potential sides effects and risks, and nursing care.

Considerations on radiation source selection and utilization in vascular brachytherapy

Three radiation sources have been approved for commercial use in vascular brachytherapy. The beta sources ((90)Strontium and (32)Phosphorous) are more popular because of less radiation protection concerns than gamma sources. Because (90)Strontium has a longer half-life than (32)Phosphorous, it requires less frequent source exchanges. Also, because (90)Strontium is more penetrating, a similar benefit can be achieved with lower delivered doses. Based on these advantages, (90)Strontium is the preferred isotope for vascular brachytherapy.

Beta radiation in lesions > 15 mm: a START subgroup

BACKGROUND

Following conventional treatment of in-stent restenosis, clinical restenosis may be as high as 60% in long lesions. Results of the START (Stents and Radiation Therapy) trial indicate that intracoronary beta radiation yields significant reductions in the incidence of recurrent in-stent restenosis as compared with placebo.

METHODS AND RESULTS

In a subgroup of the START trial, results in patients with coronary lesions > 15 mm in length (n = 239) were analyzed to assess treatment with a 30 mm, beta radiation source train. Patients received an intracoronary catheter with (90)Strontium/(90)Yttrium (n = 128) or placebo (n = 111). Clinical and angiographic parameters were evaluated at 8 months. Patient demographics and angiographic lesion characteristics were similar between the 2 groups. The mean lesion lengths were comparable in the radiation and placebo groups (21.5 5.2 mm versus 22.1 5.5 mm, respectively; p = 0.3873). A total of 14.1% and 22.5% of patients in the radiation and placebo groups, respectively, received new stents (p = 0.09). At 8 months, radiation therapy yielded significant reductions in major adverse cardiac events (16.4% versus 29.7%; p = 0.014), target vessel revascularization (14.8% versus 28.8%; p = 0.0085) and target lesion revascularization (11.7% versus 27.9%; p = 0.0015). There was no stent thrombosis, and binary restenosis rates were significantly lower in the radiation group compared to placebo.

CONCLUSION

Intracoronary beta radiation may prevent early recurrent restenosis in long lesions. Additional study is required to determine if the reduction persists throughout mid- to long-term follow-up.

Coronary restenosis: a review of mechanisms and management

Percutaneous coronary interventions represent an attractive alternative to surgical revascularization; nevertheless, these techniques continue to be characterized by their propensity to elicit restenosis. Despite an exhaustive search for an effective pharmacotherapy to treat or prevent restenosis, hundreds of clinical trials have failed to identify an agent with proven therapeutic benefit. Recently, however, the Food and Drug Administration approved intracoronary radiation (brachytherapy) as a viable therapeutic option for in-stent stenosis. In addition, recent randomized trials have shown encouraging results for drug-eluting stents. This article reviews the pathophysiology of restenosis, along with current and future treatment options.

Treatment of in-stent restenosis in a gastroepiploic artery coronary bypass graft with brachytherapy

The pedicled right gastroepiploic artery is used as an arterial conduit in a select group of patients undergoing coronary artery bypass grafting with favorable patency and survival rates. Myocardial ischemia can occur, especially secondary to distal anastomotic stenosis. Percutaneous coronary interventions have been successful in treating these stenoses, precluding further challenging and higher risk operations. The restenosis rate of such interventions is unknown. We describe a case of distal right gastroepiploic graft anastomotic stenosis that was initially treated with percutaneous angioplasty, but later required stenting for restenosis. Subsequent in-stent restenosis was successfully treated with angioplasty and brachytherapy via the left axillary approach.

Effects of vessel geometry and catheter position on dose delivery in intracoronary brachytherapy

In-stent restenosis is commonly observed in coronary arteries after intervention. Intravascular brachytherapy has been found effective in reducing the recurrence of restenosis after stent placement. Conventional dosing models for brachytherapy with beta (beta) radiation neglect vessel geometry as well as the position of the delivery catheter. This paper demonstrates in computer simulations on phantoms and on in vivo patient data that the estimated dose distribution varies substantially in curved vessels. In simulated phantoms of 50-mm length with a shape corresponding to a 60 degrees - 180 degrees segment of a respectively sized torus, the average dose in 2-mm depth was decreased by 2.70%-7.48% at the outer curvature and increased by 2.95%-9.70% at the inner curvature as compared with a straight phantom. In vivo data were represented in a geometrically correct three-dimensional model that was derived by fusion of intravascular ultrasound (IVUS) and biplane angiography. These data were compared with a simplified tubular model reflecting common assumptions of conventional dosing schemes. The simplified model yielded significantly lower estimates of the delivered radiation and the dose variability as compared with a geometrically correct model (p < 0.001). The estimated dose in ten vessel segments of eight patients was on average 8.76% lower at the lumen/plaque and 6.52% lower at the media/adventitia interfaces (simplified tubular model relative to geometrically correct model). The differences in dose estimates between the two models were significantly higher in the right coronary artery as compared with the left coronary artery (p < 0.001).

Automated preparation of 188Re-labeled radiopharmaceuticals for endovascular radiation therapy

We have developed an automated system for the preparation of highly concentrated 188Re-perrhenate, diethylenetriamine pentaacetic acid (DTPA) and mercaptoacetyltriglycine (MAG3). The three procedural steps include concentration of 188Re-perrhanerate, chelation and purification and sterilization. The steps are operated by a small micro-controller. The eluted 188Re-perrhenate of 15 GBq/18 ml from 37 GBq 188W/188Re-generator was concentrated to 1.2 ml in 10 +/- 0.5 min with a recovery yield of 95 +/- 1.5%. We obtained the highest radiochemical yield of 95.4 +/- 2.8% and 98.5 +/- 1.2% for 188Re-DTPA and MAG3 at the oil bath temperatures of 95-97 degrees C and 93-97 degrees C, respectively.

Vascular brachytherapy using a beta emitter source in diabetic patients with in-stent restenosis: angiographic and clinical outcomes

PURPOSE

The management of diabetic patients with restenosis after percutaneous coronary intervention remains a significant challenge. Diabetic patients remain at significant risk of restenosis despite stent implantation. This retrospective analysis was performed to determine the extent to which vascular brachytherapy improves late clinical and angiographic outcomes in diabetic patients compared to conventional therapy and compared to patients' nondiabetic counterparts.

METHODS

Pooled data from two studies (START [Stents and Radiation Trial] and START-40 trials) of patients (204 diabetic, 477 nondiabetic) receiving vascular brachytherapy (VBT) with a (90)Sr/(90)Y source after conventional percutaneous coronary intervention for in-stent restenosis comprise the study population. The radiation delivery system used in both studies was the Beta-Cath system. The prescribed dose at 2 mm from the centerline of the source axis was 18.4 Gy or 23 Gy, depending on vessel diameter. The reference vessel diameter, minimal lumen diameter, and percent diameter stenosis were measured before the intervention, at the conclusion of the procedure, and at the 8-month follow-up examination. The Breslow-Day test was used to formally assess the similarity of treatment effect between diabetic and nondiabetic patients.

RESULTS

Target lesion and target vessel revascularization rates and angiographic restenosis rates in diabetic and nondiabetic patients treated with beta radiation or placebo were analyzed. Diabetic patients were more likely to have longer and more complex coronary lesions. In-hospital outcomes in diabetic and nondiabetic patients were similar, irrespective of treatment status. At 8 months, patients treated with beta radiation exhibited less target lesion revascularization (diabetic: 10.9% vs. 22.7%, p = 0.02; nondiabetic: 12.8% vs. 22.3%, p = 0.007) and less target vessel revascularization (diabetic: 14.7% vs. 25.3%, p = 0.06; nondiabetic: 16.6% vs. 23.6%, p = 0.06) compared to placebo. In-stent binary angiographic restenosis was lower in irradiated patients (diabetic: 19.4% vs. 37.3% for placebo, p = 0.01; nondiabetic: 12.9% vs. 43% for placebo, p < 0.001). However, restenosis beyond the stent site reduced the impact of VBT, regardless of diabetic status. The magnitude of the treatment effect for target lesion and target vessel revascularization rates was similar between diabetic and nondiabetic patients.

CONCLUSIONS

Previously published institutional experiences have suggested that diabetic patients benefit from the use of VBT in the management of in-stent restenosis. This analysis now provides direct evidence to support the role of beta radiation VBT in this patient population. Diabetic patients undergoing this therapy are just as likely to benefit from it as their nondiabetic counterparts.

[Past, present, and future of intracoronary brachytherapy]

Intracoronary brachytherapy has been developed as an adjunctive treatment strategy for prevention and treatment of restenosis. Two technologies, one employing radioactive stents, the other catheter-based radiation systems (beta or gamma), have been tested in several animal and human studies in both de novo and restenotic coronary lesions. In particular, intravascular ultrasound imaging studies have given great insights into the mechanisms of action of intracoronary brachytherapy and its complications. Negative results from clinical trials performed in patients with de novo coronary lesions and the encouraging results obtained with drug-eluting stents have lead intracoronary brachytherapy to be abandoned in this clinical context, while it still remains the best therapeutic tool for the treatment of patients with in-stent restenosis. In this manuscript, principles of radiation therapy, results of clinical trials, current clinical practice, and future perspectives of intracoronary brachytherapy are summarized.

Vascular brachytherapy and the strontium90 vascular brachytherapy system

Restenosis remains a vexing problem in patients undergoing percutaneous coronary interventions (PCI). This phenomenon is related to a combination of events, including elastic recoil, negative remodeling and fibrointimal tissue proliferation. While stenting (bare metal and drug eluting) has made a dramatic impact in preventing recoil and remodeling, restenosis still occurs. Once restenosis occurs, it presents its own set of challenges due to the excess tissue proliferation. Major predicators of restenosis include diabetes, small stent diameter and long stented lesions. Vascular brachytherapy is the only proven therapy associated with a significant reduction in angiographic restenosis and the need for target vessel revascularization for the treatment of in-stent restenosis.

Intracoronary radiation to treat in-stent restenosis in six cardiac transplant patients

Transplant vasculopathy significantly limits the survival of cardiac transplant patients and occurs in 50% of patients by 5 years posttransplant. We report our experience with six cardiac transplant patients who underwent intracoronary brachytherapy for in-stent restenosis. At four centers, six patients underwent intracoronary radiation for in-stent restenosis. All patients received extended antiplatelet therapy with clopidogrel and aspirin. Follow-up angiography was performed in all patients. Two of the six patients underwent subsequent target lesion revascularization. Patient 1 presented with total occlusion of her radiated lesion. She had a complex procedure requiring stenting for a dissection after the radiation dwell. Patient 2 had high-grade restenosis following brachytherapy. Patient 3 had a 50% restenotic lesion. Patients 4, 5, and 6 had follow-up angiography that showed no evidence of restenosis. There are few good options to treated accelerated transplant vasculopathy. Radiation therapy may be a viable option in this difficult patient population.

Successful brachytherapy of coronary vasospasm

Brachytherapy is a proposed treatment for in-stent restenosis and is the subject of several clinical trials and debates. The standard treatment of patients with variant angina is to eliminate vasoconstrictive factors and to administer vasodilating drugs. This is the first description of successful brachytherapy for coronary spasm.

Repeat intracoronary radiation for recurrent in-stent restenosis in patients who failed intracoronary radiation

BACKGROUND

Intracoronary radiation therapy (IRT) is the only proven treatment for in-stent restenosis (ISR). It is, however, associated with a significant failure rate. The present study evaluated the outcomes of patients who underwent repeat intracoronary radiation for recurrent ISR.

METHODS AND RESULTS

Fifty-one consecutive patients who failed a previous radiation treatment, presented with angina and angiographic evidence of ISR, and were treated with percutaneous coronary intervention (PCI) and repeat radiation to the same segment were studied. Twenty-five patients were treated with gamma radiation in a dose of 15 Gy, and 26 were treated with beta radiation doses of 18.3 to 23 Gy. The mean cumulative dose for this cohort was 39.5+/-11.9 Gy (range, 29 to 75.6 Gy). The outcomes of those patients were compared with outcomes of 299 patients who also failed initial radiation but were treated with repeat conventional PCI to a previously irradiated segment without repeat radiation. At 9 months after treatment, the repeat-IRT group had lower rates of target lesion revascularization (23.5% versus 54.6%; P<0.001) and major adverse cardiac events, including target vessel revascularization (29.4% versus 61.3%; P<0.001). At 9 months, patients with repeat IRT were free of angiographic and clinical events related to the radiation therapy.

CONCLUSIONS

Repeat gamma or beta radiation to treat failed IRT for ISR after conventional PCI is safe and effective at 9 months and should be considered as a therapeutic option for this difficult patient subset.

Experimental dosimetry of a 32P catheter-based endovascular brachytherapy source

The experimental dosimetry in a water phantom of a 32P linear source, 20 mm in length, used for the brachytherapy of coronary vessels is reported. The source content activity, A, was determined by means of a calibrated well ion-chamber and the value was compared with the contained activity reported in the manufacturer's certification. In this field of brachytherapy dosimetry, radiochromic film supplies a high enough spatial resolution. A highly sensitive radiochromic film, that presents only one active layer, was used in this work for the source dosimetry in a water phantom. The radiochromic film was characterized by electron beams produced by a clinical linac. A Monte Carlo calculation of beta spectra in water at different distances along the source transverse bisector axis allowed to take into account the low dependence of film response from the electron beam energy. The adopted experimental set-up, with the source in its catheter positioned on the film plane inside the water phantom, supplies accurate dosimetric information. The measured dose rate to water per unit of source activity at reference distance, D(r0, theta0)/A, in units of cGy s(-1) GBq(-1), was in agreement with the value reported in the manufacturer's certification within the experimental uncertainty. The radial dose function, g(r), is in good agreement with the literature data. The anisotropy function F(r, theta) is also reported. The analysis of the dose profile obtained at 2 mm from the source longitudinal axis shows that the uniformity is within 10% along 75% of the 20 mm treatment length. The adopted experimental set-up seems to be adequate for the quality control procedure of the dose homogeneity distribution in the water medium.

[Intracoronary beta-radiotherapy in high-risk in-stent restenosis. Prospective results of a single center registry]

BACKGROUND

The aim of the study was to evaluate, on single center prospective data, long-term angiographic and clinical results of intracoronary beta (32P) brachytherapy in "real world" patients with high-risk in-stent restenosis lesions.

METHODS

Sixty-nine consecutive patients (77 lesions) with high-risk in-stent restenosis (mean lesion length 30.3 +/- 16.1 mm, pattern III-IV 57.2%, diabetes 33.3%) treated with percutaneous dilation procedures and beta-radiation therapy, underwent 7-month clinical and angiographic follow-up.

RESULTS

One patient (1.4%) presented with procedural non-Q wave myocardial infarction. At a mean follow-up of 7 +/- 1.5 months, death was observed in 1 patient (1.4%) and non-Q wave myocardial infarction in 3 (4.3%) (in 2 patients, who prematurely discontinued antiplatelet therapy, caused by late coronary thrombosis). Seven-month binary angiographic restenosis occurred in 20 lesions (25.9%) (in-stent restenosis 11.6%). Target lesion and target vessel revascularization occurred in 20 (28.9%) and 21 (30.4%) patients. At follow-up only 12 (17.3%) patients presented with CCS class III-IV angina. After intracoronary beta brachytherapy angiographic restenosis occurred regardless of the vessel size, lesion length and ostial location. On the contrary a high restenosis rate was documented in obstructive lesions.

CONCLUSIONS

As applied in routine clinical practice, radiation therapy is safe and effective in the treatment of high-risk in-stent restenosis. In spite of all that, total occlusion at baseline predicts late angiographic restenosis.

Long-term follow-up of patients after gamma intracoronary brachytherapy failure (from GAMMA-I, GAMMA-II, and SCRIPPS-III)

We report the long-term outcome of 225 patients who failed gamma-brachytherapy for in-stent restenosis. Total adverse events, target vessel revascularization, and myocardial infarction were higher after repeat percutaneous coronary intervention versus coronary artery bypass grafting. Therefore, coronary artery bypass grafting may be the preferable first-line therapy in these patients until other therapies (i.e., drug-eluting stents) are available. Shorter time from brachytherapy to radiation failure and late thrombosis after brachytherapy were independent predictors of adverse events.

Complex transradial three vessel brachytherapy in a single session

BACKGROUND

We report the case of a patient who underwent transradial brachytherapy in 3 different coronary vessels during a single session. She initially presented with unstable angina 4 months after the index procedure; control angiography showed severe and diffuse in-stent restenosis in the LAD, Cx and Mg arteries.

METHODS

After successful dilatation of the three vessels, we performed vascular brachytherapy using the Novoste Beta-Rail system and a 60 mm length source train of 90Sr/Y radioactive seeds. No further stent was implanted. The patient left the hospital the next day. Follow-up angiography revealed widely patent vessels with no restenosis.

CONCLUSION

Transradial multivessel brachytherapy can be done during the same session.

Effects of beta-radiation using a holmium-166 coated balloon on neointimal hyperplasia in a porcine coronary stent restenosis model

Brachytherapy is a promising method of preventing and treating coronary stent restenosis. The present study was designed to observe the therapeutic effects of a radioactive balloon loaded with Holmium-166 ((166)Ho) in a porcine coronary stent restenosis model. A radioisotope of (166)Ho was coated onto the balloon surface using polyurethane (20 Gy at 0.5 mm depth). Stent overdilation injuries were induced in 2 coronary arteries in each pig (n=8). Four weeks after the injury, control balloon dilation was performed in one coronary artery (Group I) and radiation therapy using the (166)Ho coated balloon in the other coronary artery (Group II) in each pig. Follow-up coronary angiography and histopathologic assessment were performed at 4 weeks after the radiation therapy or the control balloon dilations. With regard to complete blood cell counts, liver function tests, lipid profiles and coagulation tests, there were no differences between the baseline and after radiation. On quantitative coronary angiographic analysis, reference and target artery diameter showed no differences between the 2 groups before, or 4 and 8 weeks after stenting. On histopathologic analysis of groups I and II, the injury score was 1.34+/-0.09 and 1.32+/-0.10, the area of internal elastic lamina was 4.99+/-0.17 mm(2) and 4.82+/-0.20 mm(2), and the luminal area was 3.20+/-0.10 mm(2) and 3.45+/-0.14 mm(2), respectively (p=NS). The neointimal area was 1.78+/-0.11 mm(2) in group I and 1.36+/-0.12 mm(2) in group II (p=0.017), and the histopathologic area of stenosis was 35.1+/-1.6% in group I and 27.6+/-1.9% in group II (p=0.005). In conclusion, beta-radiation of the stented porcine coronary artery using a radioactive (166)Ho coated balloon inhibited stent restenosis without any side effects.

Additional stenting promotes intimal proliferation and compromises the results of intravascular radiation therapy: an intravascular ultrasound study

BACKGROUND

Vascular brachytherapy (VBT) reduces in-stent restenosis (ISR). However, additional stenting at the time of radiation may be associated with a worse outcome.

METHODS AND RESULTS

Intravascular ultrasound (IVUS) was performed after VBT and at 6 months follow-up in 79 native artery ISR patients treated with gamma-radiation who participated in the Washington Radiation for In-Stent restenosis Trial (WRIST), Gamma-1, and Angiorad Radiation Technology for In-Stent restenosis Trial in Coronaries (ARTISTIC) trials. Patients were treated with (192)Ir at 14 or 15 Gy at 2 mm from the source. Additional stents were used to treat the ISR lesions in 45 patients; these patients were then compared with the 34 patients treated without restenting. Paired measurements included stent, lumen, and intimal hyperplasia volumes. After the VBT procedure, intimal hyperplasia volume was smaller in the group treated with additional stents (54 +/- 33 mm(3) vs 34 +/- 33 mm(3), P =.012), but minimal lumen area was similar between the 2 groups (4.3 +/- 1.5 mm(2) vs 4.7 +/- 1.4 mm(2) respectively, P = NS). Between the time of the VBT procedure and follow-up, intimal hyperplasia volume increased by 27 +/- 19 mm(3) in the restented group and by 9 +/- 21 mm(3) in the group treated without additional stents (P =.014). At 6 months, intimal volume was similar in the 2 groups, but minimal lumen area was slightly smaller in the group treated with additional stents (3.4 +/- 1.8 mm(2) vs 4.2 +/- 1.7 mm(2), P =.053). Patients treated with additional stents had more target lesion revascularizations than the group treated without additional stents (38% vs 15%, P =.02).

CONCLUSIONS

Additional stenting reduces intimal hyperplasia within the stents acutely. However, it compromises the benefit of VBT by promoting higher intimal regrowth within months after radiation.

Dose distributions in bifurcated coronary vessels treated with catheter-based photon and beta emitters in intravascular brachytherapy

The dose distributions in the bifurcated vessels treated with intravascular brachytherapyline sources are complicated and depend on the bifurcation geometry consisting of a main and a branch vessel at different angles. To investigate the dosimetric effects at the bifurcation, calculations were performed on branching vessels of various bifurcation angles ranging from 20 degrees to 90 degrees. Two catheter based delivery systems were considered in the calculations using a 40 mm long radioactive sources of 192Ir or 90Sr/Y. It was assumed that the bifurcated vessel was treated in twoseparate source insertions, once for the main vessel and later for the branch vessel. Calculations were performed for different values of source gap from 0 to 9 mm, at the junction of main and branch vessels. Our results indicate that main vessel always receives a higher dose (up to 200%) when the branch vessel is also treated. Hot spots at portions of the main vessel near the junction cannot be totally avoided without severely underdosing the branch vessel. For bifurcation angle greater than 45 degrees, a 4 mm source gap can almost ensure that overdosing of the main vessel does not exceed 60% and underdosing of the branch vessel does not exceed 10% for 192Ir. However, for 90Sr/Y, the same is not possible unless the bifurcation angle is larger than 70 degrees. Dose heterogeneity using 90Sr/Y is more sensitive to the value of source gap than 192Ir because 90Sr/Y source provides a sharper dose-fall-off than 192Ir. For both photon and beta emitters, there is no acceptable solution for bifurcation angles less than 30 degrees, where the activity of the line source has a uniform distributions. Appropriate choice of gap at the junction can only help to reduce either overdosing of the main vessel or underdosing of the branch vessel, but not both.

Intracoronary beta-irradiation with a rhenium-188-filled balloon catheter: a randomized trial in patients with de novo and restenotic lesions

BACKGROUND

Restenosis requiring reintervention is the main limitation of coronary angioplasty. Intracoronary irradiation reduces neointimal proliferation. We studied the efficacy of a self-centering liquid rhenium-188-filled balloon catheter for coronary beta-brachytherapy.

METHODS AND RESULTS

After successful coronary angioplasty with or without stenting, 225 patients (71% de novo lesions) were randomly assigned to receive 22.5 Gy intravascular beta-irradiation in 0.5-mm tissue depth (n=113) or to receive no additional intervention (n=112). Clinical and procedural data did not differ between the groups except a higher rate of stenting in the control group (63%) compared with the rhenium-188 group (45%, P<0.02). After 6 months of follow-up, late loss was significantly lower in the irradiated group compared with the control group, both of the target lesion (0.11+/-0.54 versus 0.69+/-0.81 mm, P<0.0001) and of the total segment (0.22+/-0.67 versus 0.70+/-0.82 mm, P<0.0001). This was also evident in the subgroup of patients with de novo lesions and independent from stenting. Binary restenosis rates were significantly lower at the target lesion (6.3% versus 27.5%, P<0.0001) and of the total segment (12.6% versus 28.6%, P<0.007) after rhenium-188 brachytherapy compared with the control group. Target vessel revascularization rate was significantly lower in the rhenium-188 (6.3%) compared with the control group (19.8%, P=0.006).

CONCLUSIONS

Intracoronary beta-brachytherapy with a rhenium-188 liquid-filled balloon is safe and efficiently reduces restenosis and revascularization rates after coronary angioplasty.

GAF film dosimetry of a tandem positioned beta-emitting intravascular brachytherapy source train

Coronary artery brachytherapy may require treatment of lesions longer than a single source length. A treatment option is tandem positioning of the single source. This study presents relative dosimetric measurements of a cardiovascular brachytherapy source and the dosimetric characteristics in the junction region of tandem treatments. Measurements were carried out using a Novoste Beta Cath 90Sr/90Y 40 mm beta source in a plastic water phantom. Radiochromic MD-55-2 film, calibrated using both 6 MV photon and 6 MeV electron beams from a linear accelerator, was used as the dosimeter. Dose distributions around a single source and in the junction region of tandem irradiation were measured. Measurements of the near field dose as close as 1.2 mm from the source are presented. Significant over- or underdoses in the junction region of tandem irradiation were quantified. At a radial distance of 2 mm from the longitudinal axis of the source, the dose value in the middle of the junction region, normalized to the dose at 2 mm midline single source, was about 182% for a 2-seed overlap and 16% for a 2-seed gap, respectively. Dose distributions in the junction region as a function of source overlap and radial distance have fairly high gradients and exhibit characteristic patterns. The fraction of prescription dose was found to have a sigmoidal dependence on overlap size, for radial distances ranging between 1.2 and 3 mm. The parameters of these sigmoids, quantified as functions of radial distance, could be used to provide quick and reasonable over/underdose estimates, given any potential overlap or gap in the junction area, with an uncertainty within 10%.