PErsonalized TReatment for Endometrial Carcinoma (PETREC): study design and methods of a prospective Finnish multicenter trial.

BACKGROUND: Endometrial carcinomas can be classified into four molecular subgroups - mismatch repair deficient (MMRd), p53 abnormal (p53abn), polymerase-ϵ (POLE) ultramutated, and 'no specific molecular profile' (NSMP). Retrospective data imply that the response to adjuvant therapies may depend on the molecular subgroup. These findings emphasize the need for adjuvant therapy trials where patients are randomized to treatment arms separately within each molecular subgroup. PRIMARY OBJECTIVE: The PErsonalized TReatment for Endometrial Carcinoma (PETREC) trial clarifies the value of molecular classification in the determination of adjuvant therapies of high-intermediate risk and early-stage high-risk endometrial carcinoma. STUDY HYPOTHESIS: Compared with vaginal brachytherapy, the utilization of whole pelvic radiotherapy may result in improved outcomes for either MMRd or NSMP high-intermediate risk carcinomas. Early-stage high-risk p53abn and nonendometrioid carcinomas are postulated to gain benefits from chemoradiotherapy, as opposed to chemotherapy alone. POLE ultramutated carcinomas harboring high-intermediate or high-risk clinicopathologic features are speculated to have favorable prognosis without any adjuvant therapy. TRIAL DESIGN: This prospective, multicenter, phase 3 trial compares the efficacy of vaginal brachytherapy vs whole pelvic radiotherapy in high-intermediate risk MMRd and NSMP molecular subgroups, and chemotherapy vs chemoradiotherapy in early-stage high-risk p53abn subtype and nonendometrioid carcinomas. Eligible women who consent to participation in the trial are randomly allocated (1:1) to treatment arms. MAJOR INCLUSION/EXCLUSION CRITERIA: Women with stages I-II molecular integrated high-intermediate risk or high-risk endometrial carcinoma will be included. PRIMARY ENDPOINT: The primary endpoint is the 5 year cumulative incidence of disease recurrence. SAMPLE SIZE: A total sample size of 294 patients (49 subjects in each treatment arm of the three subgroups intended for randomization) was estimated to be sufficient. ESTIMATED DATES FOR COMPLETING ACCRUAL AND PRESENTING RESULTS: Patient recruitment will be completed in 2025, and follow-up will be completed in 2030. TRIAL REGISTRATION: NCT05655260.

Dose-volume effects of breast cancer radiation therapy on the risk of second oesophageal cancer.

PURPOSE: To investigate the relationship between oesophagus dose-volume distribution and long-term risk of oesophageal cancer after radiation therapy for breast cancer. MATERIALS AND METHODS: In a case-control study nested within a cohort of 289,748 ≥5-year survivors of female breast cancer treated in 1943-2003 in five countries, doses to the second primary cancer (DSPC) and individual dose-volume histograms (DVH) to the entire oesophagus were reconstructed for 252 oesophageal cancer cases and 488 matched controls (median follow-up time: 13, range: 5-37 years). Using conditional logistic regression, we estimated excess odds ratios (EOR) of oesophageal cancer associated with DVH metrics. We also investigated whether DVH metrics confounded or modified DSPC-related -risk estimates. RESULTS: Among the DVH metrics evaluated, median dose (Dmedian) to the entire oesophagus had the best statistical performance for estimating risk of all histological types combined (EOR/Gy = 0.071, 95% confidence interval [CI]: 0.018 to 0.206). For squamous cell carcinoma, the most common subtype, the EOR/Gy for Dmedian increased by 31% (95% CI: 3% to 205%) for each increment of 10% of V30 (p = 0.02). Adjusting for DVH metrics did not materially change the EOR/Gy for DSPC, but there was a borderline significant positive interaction between DSPC and V30 (p = 0.07). CONCLUSION: This first study investigating the relationship between oesophagus dose-volume distribution and oesophageal cancer risk showed an increased risk per Gy for Dmedian with larger volumes irradiated at high doses. While current techniques allows better oesophagus sparing, constraints applied to Dmedian and V30 could potentially further reduce the risk of oesophageal cancer.

Randomised comparison of 1.1 GBq and 3.7 GBq radioiodine to ablate the thyroid in the treatment of low-risk thyroid cancer: a 13-year follow-up.

Purpose: The optimal activity of radioiodine (I-131) administered for ablation therapy in papillary and follicular thyroid cancer after thyroidectomy remains unknown in a long-term (> 10 year) follow-up. Some, shorter follow-up studies suggest that activities 1.1 GBq and 3.7 GBq are equally effective. We evaluated the long-term outcomes after radioiodine treatment to extend current knowledge about the optimal ablative dose of I-131.Methods: One hundred and sixty consecutive adult patients (129 females, 31 males; mean age 46 ± 14 y, range 18-89 y) diagnosed with histologically confirmed differentiated thyroid cancer, were randomised in a prospective, phase III, open-label, single-centre study, to receive either 1.1 GBq or 3.7 GBq of I-131 after thyroidectomy. At randomisation, patients were stratified according to the histologically verified cervical lymph node status and were prepared for ablation using thyroid hormone withdrawal. No uptake in the whole-body scan with I-131 and serum thyroglobulin concentration less than 1 ng/mL at 4-8 months after treatment was considered successful ablation.Results: Median follow-up time was 13.0 years (mean 11.0 ± 4.8 y; range 0.3-17.1 y). Altogether 81 patients received 1.1 GBq with successful ablation in 45 (56%) patients. In the original study, thirty-six patients (44%) needed one or more extra administrations to replete the ablation. Of these, 4 (8.9%) and 5 (14%) patients relapsed during the follow-up, respectively. Of the 79 patients treated with 3.7 GBq 45 (57%) had successful ablation after one administration of radioiodine and 34 (43%) needed several treatments. Of these, 2 (4.4%) and 9 (26.5%) patients relapsed, respectively. The groups did not differ in the proportion of patients relapsing (p = .591).Conclusion: During follow-up of median 13 years, 3.7 GBq is not superior to 1.1 GBq in the radioiodine treatment after thyroidectomy in papillary and follicular thyroid cancer.

TEDDI: radiotherapy delivery in deep inspiration for pediatric patients - a NOPHO feasibility study.

BACKGROUND: Radiotherapy (RT) delivered in deep inspiration breath-hold (DIBH) is a simple technique, in which changes in patient anatomy can significantly reduce the irradiation of the organs at risk (OARs) surrounding the treatment target. DIBH is routinely used in the treatment of some adult patients to diminish the risk of late effects; however, no formalized studies have addressed the potential benefit of DIBH in children. METHODS/DESIGN: TEDDI is a multicenter, non-randomized, feasibility study. The study investigates the dosimetric benefit of RT delivered in DIBH compared to free breathing (FB) in pediatric patients. Also, the study aims to establish the compliance to DIBH and to determine the accuracy and reproducibility in a pediatric setting. Pediatric patients (aged 5-17 years) with a tumor in the mediastinum or upper abdomen with the possible need of RT will be included in the study. Written informed consent is obligatory. Prior to any treatment, patients will undergo a DIBH training session followed by a diagnostic PET/CT- or CT-staging scan in both DIBH and FB. If the patient proceeds to RT, a RT planning CT scan will be performed in both DIBH and FB and two separate treatment plans will be calculated. The superior treatment plan, i.e. equal target coverage and lowest overall dose to the OARs, will be chosen for treatment. Patient comfort will be assessed daily by questionnaires and by adherence to the respiratory management procedure. DISCUSSION: RT in DIBH is expected to diminish irradiation of the OARs surrounding the treatment target and thereby reduce the risk of late effects in childhood cancer survivors. TRIAL REGISTRATION: The Danish Ethical Committee (H-16035870, approved November 24th 2016, prospectively registered). The Danish Data Protection Agency (2012-58-0004, approved January 1st 2017, prospectively registered). Registered at clinicaltrials.gov ( NCT03315546 , October 20th  2017, retrospectively registered).

Stomach Cancer Following Hodgkin Lymphoma, Testicular Cancer and Cervical Cancer: A Pooled Analysis of Three International Studies with a Focus on Radiation Effects.

To further understand the risk of stomach cancer after fractionated high-dose radiotherapy, we pooled individual-level data from three recent stomach cancer case-control studies. These studies were nested in cohorts of five-year survivors of first primary Hodgkin lymphoma (HL), testicular cancer (TC) or cervical cancer (CX) from seven countries. Detailed data were abstracted from patient records and radiation doses were reconstructed to the site of the stomach cancer for cases and to the corresponding sites for matched controls. Among 327 cases and 678 controls, mean doses to the stomach were 15.3 Gy, 24.7 Gy and 1.9 Gy, respectively, for Hodgkin lymphoma, testicular cancer and cervical cancer survivors, with an overall mean dose of 10.3 Gy. Risk increased with increasing radiation dose to the stomach cancer site (P < 0.001) with no evidence of nonlinearity or of a downturn at the highest doses (≥35 Gy). The pooled excess odds ratio per Gy (EOR/Gy) was 0.091 [95% confidence interval (CI): 0.036-0.20] with estimates of 0.049 (95% CI: 0.007-0.16) for Hodgkin lymphoma, 0.27 (95% CI: 0.054-1.44) for testicular cancer and 0.096 (95% CI: -0.002-0.39) for cervical cancer (P homogeneity = 0.25). The EOR/Gy increased with time since exposure (P trend = 0.004), with an EOR/Gy of 0.38 (95% CI: 0.12-1.04) for stomach cancer occurring ≥20 years postirradiation corresponding to odds ratios of 4.8 and 10.5 at radiation doses to the stomach of 10 and 25 Gy, respectively. Of 111 stomach cancers occurring ≥20 years after radiotherapy, 63.8 (57%) could be attributed to radiotherapy. Our findings differ from those based on Japanese atomic-bomb survivors, where the overall EOR/Gy was higher and where there was no evidence of an increase with time since exposure. By pooling data from three studies, we demonstrated a clear increase in stomach cancer risk over a wide range of doses from fractionated radiotherapy with the highest risks occurring many years after exposure. These findings highlight the need to directly evaluate the health effects of high-dose fractionated radiotherapy rather than relying on the data of persons exposed at low and moderate acute doses.

Increased pancreatic cancer risk following radiotherapy for testicular cancer.

BACKGROUND: Pancreatic cancer risk is elevated among testicular cancer (TC) survivors. However, the roles of specific treatments are unclear. METHODS: Among 23 982 5-year TC survivors diagnosed during 1947-1991, doses from radiotherapy to the pancreas were estimated for 80 pancreatic cancer patients and 145 matched controls. Chemotherapy details were recorded. Logistic regression was used to estimate odds ratios (ORs). RESULTS: Cumulative incidence of second primary pancreatic cancer was 1.1% at 30 years after TC diagnosis. Radiotherapy (72 (90%) cases and 115 (80%) controls) was associated with a 2.9-fold (95% confidence interval (CI) 1.0-7.8) increased risk. The OR increased linearly by 0.12 per Gy to the pancreas (P-trend<0.001), with an OR of 4.6 (95% CI 1.9-11.0) for ⩾25 Gy vs <25 Gy. Radiation-related risks remained elevated ⩾20 years after TC diagnosis (P=0.020). The risk increased with the number of cycles of chemotherapy with alkylating or platinum agents (P=0.057), although only one case was exposed to platinum. CONCLUSIONS: A dose-response relationship exists between radiation to the pancreas and subsequent cancer risk, and persists for over 20 years. These excesses, although small, should be considered when radiotherapy with exposure to the pancreas is considered for newly diagnosed patients. Additional data are needed on the role of chemotherapy.

VMAT technique enables concomitant radiotherapy of prostate cancer and pelvic bone metastases.

BACKGROUND: Prostate cancer (PCa) patients with metastatic disease often suffer from skeletal pain and urinary retention impairing their quality of life. Prophylactic radiotherapy to bone metastases planned concomitantly with primary PCa radiotherapy could enable more precise control of combined dose in healthy tissues when compared to sequential palliative treatment. MATERIALS AND METHODS: Volumetric modulated arc therapy (VMAT) was planned for 14 PCa patients with primary bone metastases. The bone planning target volume (PTVbone) was contoured together with the PTVs of prostate (pr), pelvic lymph nodes (ln) and seminal vesicles (sv). Another virtual plan was calculated excluding PTVbone for dose volume histogram (DVH) comparison. DVHs were additionally compared to a set of actual VMAT treatment plans of a control cohort of 13 high risk PCa patients treated with PTVpr, PTVsv and PTVln. The prescribed doses varied between 42 and 76 Gy for PTVbone. RESULTS: Recommended healthy tissue tolerances (Quantec) were not exceeded except for one patient's rectum V50Gy value. Rectum doses did not increase significantly due to the inclusion of PTVbone. For bladder, there was a slight increase for V65Gy and V50Gy (2.7% and 7.4%). The DVHs of metastatic and non-metastatic patients were comparable. There were no differences in the PTVpr DVH parameters, while mean PTVln dose increased by 3.7 Gy-4.4 Gy due to the increased treatment volume related to PTVbone. All side effects were

Stomach cancer risk after treatment for hodgkin lymphoma.

PURPOSE: Treatment-related stomach cancer is an important cause of morbidity and mortality among the growing number of Hodgkin lymphoma (HL) survivors, but risks associated with specific HL treatments are unclear. PATIENTS AND METHODS: We conducted an international case-control study of stomach cancer nested in a cohort of 19,882 HL survivors diagnosed from 1953 to 2003, including 89 cases and 190 matched controls. For each patient, we quantified cumulative doses of specific alkylating agents (AAs) and reconstructed radiation dose to the stomach tumor location. RESULTS: Stomach cancer risk increased with increasing radiation dose to the stomach (Ptrend < .001) and with increasing number of AA-containing chemotherapy cycles (Ptrend = .02). Patients who received both radiation to the stomach ≥ 25 Gy and high-dose procarbazine (≥ 5,600 mg/m(2)) had strikingly elevated stomach cancer risk (25 cases, two controls; odds ratio [OR], 77.5; 95% CI, 14.7 to 1452) compared with those who received radiation < 25 Gy and procarbazine < 5,600 mg/m(2) (Pinteraction < .001). Risk was also elevated (OR, 2.8; 95% CI, 1.3 to 6.4) among patients who received radiation to the stomach ≥ 25 Gy but procarbazine < 5,600 mg/m(2); however, no procarbazine-related risk was evident with radiation < 25 Gy. Treatment with dacarbazine also increased stomach cancer risk (12 cases, nine controls; OR, 8.8; 95% CI, 2.1 to 46.6), after adjustment for radiation and procarbazine doses. CONCLUSION: Patients with HL who received subdiaphragmatic radiotherapy had dose-dependent increased risk of stomach cancer, with marked risks for patients who also received chemotherapy containing high-dose procarbazine. For current patients, risks and benefits of exposure to both procarbazine and subdiaphragmatic radiotherapy should be weighed carefully. For patients treated previously, GI symptoms should be evaluated promptly.

Radiation dose and subsequent risk for stomach cancer in long-term survivors of cervical cancer.

PURPOSE: To assess the dose-response relationship for stomach cancer after radiation therapy for cervical cancer. METHODS AND MATERIALS: We conducted a nested, matched case-control study of 201 cases and 378 controls among 53,547 5-year survivors of cervical cancer diagnosed from 1943 to 1995, from 5 international, population-based cancer registries. We estimated individual radiation doses to the site of the stomach cancer for all cases and to corresponding sites for the matched controls (overall mean stomach tumor dose, 2.56 Gy, range 0.03-46.1 and after parallel opposed pelvic fields, 1.63 Gy, range 0.12-6.3). RESULTS: More than 90% of women received radiation therapy, mostly with external beam therapy in combination with brachytherapy. Stomach cancer risk was nonsignificantly increased (odds ratio 1.27-2.28) for women receiving between 0.5 and 4.9 Gy to the stomach cancer site and significantly increased at doses ≥ 5 Gy (odds ratio 4.20, 95% confidence interval 1.41-13.4, Ptrend=.047) compared with nonirradiated women. A highly significant radiation dose-response relationship was evident when analyses were restricted to the 131 cases (251 controls) whose stomach cancer was located in the middle and lower portions of the stomach (Ptrend=.003), whereas there was no indication of increasing risk with increasing dose for 30 cases (57 controls) whose cancer was located in the upper stomach (Ptrend=.23). CONCLUSIONS: Our findings show for the first time a significant linear dose-response relationship for risk of stomach cancer in long-term survivors of cervical cancer.

Axillary and supraclavicular recurrences are rare after axillary lymph node dissection in breast cancer.

BACKGROUND: This study was designed to evaluate the incidence of and risk factors for axillary recurrence (AR) and supraclavicular recurrence (SR) in breast cancer patients with axillary lymph node dissection. METHODS: The study was based on 1,180 patients with unilateral invasive breast cancer operated between January 2000 and December 2003. The median duration of follow-up was 78 months. RESULTS: The 7-year AR incidence was 0.7% and SR incidence was 1.3%. Twelve of the 14 SR patients and 4 of the 8 AR patients had concomitant distant recurrences. No risk factors for AR were identified. Histological tumor grade III as well as estrogen and progesterone negativity were risk factors for SR. SR, but not AR, was an independent risk factor for poor breast cancer-specific survival [hazard ratio, 10.116; P < 0.0001]. Among N1 patients, the extent of radiotherapy (RT) had no influence on regional recurrences. Among N2-N3 patients, the 7-year regional recurrence rates were 34.3% in patients without RT, 0% in patients with local RT, and 1.2% in patients with locoregional RT (P < 0.0001). CONCLUSIONS: AR and SR are rare events that often are detected concomitantly with distant metastases. SRs are associated with aggressive disease and poor survival. Our results also suggest that regional RT reduces regional recurrences in N2-N3 patients but not in N1 patients, but the retrospective, nonrandomized study setting renders this conclusion as uncertain.

Patterns of relapse following surgery and postoperative intensity modulated radiotherapy for oral and oropharyngeal cancer.

BACKGROUND: To investigate the patterns of relapse following intensity modulated radiotherapy (IMRT) given after radical surgery for oral and oropharyngeal squamous cell cancer. PATIENTS AND METHODS: One hundred and two patients with oral or oropharyngeal cancer were treated with radical surgery followed by IMRT up to a mean total dose of 60 Gy between years 2001 and 2007. Thirty-nine of the patients (%) also received concomitant weekly cisplatin. Forty of the patients had oral and 62 had oropharyngeal cancer. Data on the tumour, patient and treatment factors were collected. Following therapy the patients were followed by clinical examination, endoscopy and MRI/CT at 2- to 3-months interval up to 2 years and thereafter at 6-month intervals. RESULTS: The mean follow-up time of the patients was 55 months (range, 26-106 months). The rate for local tumour control for the whole cohort was 92.2%: 87.5% for oral cancer patients and 96.7% for oropharyngeal cancer patients. The 5-year disease specific survival was 90.2% and 5-year overall survival 84.3%. During the follow-up eight locoregional recurrences were observed, three at the primary tumour site and one at regional nodal site and four at both sites. The mean time to primary tumour recurrence was seven months (range, 2-10 months) and to nodal recurrence seven months (range, 2-12 months). Distant metastasis occurred in six (6%) patients. The factors associated with poor prognosis were the primary tumour size and tumour site with oral cancers having worse outcome. The treatment was well tolerated with no unexpected toxicities. The most frequent late toxicity was dysphagia necessitating permanent PEG in five patients. This was correlated with the advanced primary tumour size and resulting in wide tumour excision and reconstruction. CONCLUSIONS: Surgery combined with postoperative radiotherapy given as IMRT results in low level of tumour recurrence.

Patterns of relapse following definitive treatment of head and neck squamous cell cancer by intensity modulated radiotherapy and weekly cisplatin.

Eighty-three patients with oropharyngeal, hypopharyngeal or laryngeal cancer were treated with concomitant cisplatin 40 mg/m(2) once a week during the radiotherapy and IMRT up to a total dose of 70 Gy. The 2-year rate of local control, overall survival and disease specific survival were 84%, 82% and 89%, respectively. The corresponding 5-year Kaplan-Meier estimates were 79%, 69% and 76%.

[Towards more conservative surgical and radiation therapy of breast cancer]. / Kohti rintasyövän säästävämpää leikkaus- ja sädehoitoa.

Surgery and radiation therapy in breast cancer aim to minimize the risk of disease relapse in the breast, chest wall or lymph node regions. Relapses cause distress for the patients and worsen the survival rates. The risk of relapse has decreased considerably during the last ten years. The improved standard of surgical treatment brought about by centralized care, new techniques of radiotherapy as well as the more widely applied and more effective adjuvant drug therapy underlie this favorable development. The extent of surgical therapy and indications of radiotherapy require continuous evaluation in order to avoid prolonged morbidity.

[Long-term morbidity caused by breast cancer therapy]. / Rintasyövän hoidon aiheuttama pitkäaikainen sairastavuus.

All forms of breast cancer therapies are associated with both acute adverse effects and manifold long-term morbidity. Due to the common occurrence and favorable prognosis of breast cancer, the number of those suffering from complications worsening the quality of life is considerable. In a significant proportion, the long-term adverse effects caused by the therapy can be alleviated. The importance of follow-up visits of a breast cancer patient is not limited to diagnosing or excluding of relapses. During these visits, the elucidation of long-term adverse effects and their treatment alternatives and even discussing the symptoms and supporting the patient are important with respect to the quality of life.

Linac-based isocentric electron-photon treatment of radically operated breast carcinoma with enhanced dose uniformity in the field gap area.

BACKGROUND AND PURPOSE: Isocentric treatment technique is a standard method in photon radiotherapy with the primary advantage of requiring only a single patient set-up procedure for multiple fields. However, in electron treatments the size of the standard applicators does not generally allow to use an isocentric treatment technique. In this work we have modified and dosimetrically tested electron applicators for isocentric treatments in combination with photons. An isocentric treatment technique with photons and electrons for postmastectomy radiation therapy (PMRT) has been developed with special emphasis on improving the dose uniformity in the field gap area. MATERIALS AND METHODS: Standard electron applicators of two Varian Clinac 2100CD linear accelerators were shortened by 10cm allowing isocentric treatments of 90cm

The effect of intensity-modulated radiotherapy and high dose rate brachytherapy on acute and late radiotherapy-related adverse events following chemoradiotherapy of anal cancer.

BACKGROUND AND PURPOSE: To investigate acute and late radiotherapy-related adverse events following intensity-modulated radiotherapy (IMRT) and high dose rate (HDR) brachytherapy of anal cancer. MATERIALS AND METHODS: Fifty-nine consecutive patients treated by chemoradiotherapy for anal squamous cell cancer were evaluated for acute and late radiotherapy-related adverse events. Twenty patients were treated by IMRT and 39 by conventional 3D-radiotherapy. In 29 patients, the boost dose to the primary tumour was given by HDR brachytherapy: 30 patients were treated only by external radiotherapy. RESULTS: A significant reduction in skin and mucosal eruptions in the female genital area (P=0.04) and in radiotherapy-associated > grade 2 diarrhoea (P=0.004) was observed in patients treated by IMRT. The difference in unplanned gaps during the radiotherapy was highly significant (P=0.004). A correlation between the equivalent dose in 2Gy fractions (EQD2) at the wall of anal canal opposite to the tumour and radiation proctitis was observed. In patients that received the final boost dose to the primary tumour by HDR brachytherapy, a trend towards lower incidence of radiation proctitis was observed (P=0.065). CONCLUSIONS: IMRT significantly reduces acute radiotherapy-associated adverse events in patients treated by chemoradiotherapy for anal cancer. A combination of external radiotherapy and HDR brachytherapy may reduce the risk of late radiation proctitis.

Low vs. high radioiodine activity to ablate the thyroid after thyroidectomy for cancer: a randomized study.

BACKGROUND: Radioactive iodine is commonly administered following thyroidectomy for differentiated thyroid carcinoma to ablate the thyroid remnant. The optimal administered activity of radioiodine is unknown. METHODOLOGY/PRINCIPAL FINDINGS: Adult subjects (n = 160) diagnosed with papillary or follicular thyroid carcinoma were randomly allocated to receive either 1100 MBq (30 mCi) or 3700 MBq (100 mCi) activity of radioiodine ((131)I) following thyroidectomy. The study participants were prepared for ablation using thyroid hormone withdrawal. Ablation was considered successful when serum thyroglobulin concentration was less than 1 ng/mL and no uptake was present in (131)I scan. Ablation was successful following one administration of radioiodine in 42 (52%; 95% CI, 41% to 63%) of the 81 evaluable study participants who received 1100 MBq, and in 43 (56%, 45% to 67%) of the 77 subjects who received 3700 MBq activity (P = .61). There was no difference between the groups in the numbers of repeat radioiodine treatments needed to complete ablation (P = .27). The higher activity was associated with more nausea and taste disturbances, and a longer stay in a radioprotected isolation unit. None of the participants died from thyroid cancer during a median follow up of 51 months; three subjects in the 3700 MBq group and none in the 1100 MBq group were diagnosed with distant metastases during follow-up. In a meta-analysis of four randomized studies that compared the 1100 and 3700 MBq activities, the 1100 MBq activity tended to be associated with a higher risk of unsuccessful ablation (relative risk 1.148, 95% CI 0.974 to 1.353, P = .10). CONCLUSIONS/SIGNIFICANCE: The results provide no conclusive evidence that 3700 MBq activity is more effective for ablation of the thyroid remnant than 1100 MBq activity. The 3700 MBq activity is associated with more adverse effects. TRIAL REGISTRATION: ClinicalTrials.gov NCT00115895.