Comparison of contralateral breast doses from 1/2 beam block and isocentric treatment techniques for patients treated with primary breast irradiation with 60CO

The risk of carcinogenesis in breast tissue subject to low to moderate radiation doses may be of concern to the clinical radiotherapist. With earlier diagnosis, more women, and especially younger women, are electing breast preservation radiation therapy. During therapy, tissue outside the treatment field is exposed to leakage and scattered radiation. Such exposure could lead to significant doses of radiation resulting in carcinogenesis. Therefore, reduction of contralateral breast dose may be an important factor to consider when selecting a treatment technique. This study measured dose in the contralateral breast on 15 patients treated with 60Co gamma rays with the source to skin distance (SSD), 1/2 beam block, and the source to axis distance (SAD), no 1/2 beam block, techniques. Thermoluminescent dosimeters (TLD), with 0.5 cm of superflab used as build-up material, were placed on the contralateral breast to measure dose from the medial tangential beam and from the lateral tangential beam. Dose measurements were done on patients in the treatment position and do not represent phantom or formula calculation of dose to the opposite breast. Our results indicated that total opposite breast dose ranged from 325-650 cGy for SSD treatments as opposed to 200-450 cGy for SAD treatments, in patients receiving a total prescribed dose of 5,040 cGy in 28 fractions to the involved breast. This paper points out that a simple solution for reduction of opposite breast dose for patients treated with 60Co may be utilization of the modified SAD treatment technique.     

乳腺癌调强放射治疗和常规切线野治疗的三维剂量学研究

背景与目的:乳房保留治疗已在早期乳腺癌患者中逐渐推广应用,其中全乳根治性放疗的标准技术通常采用常规切线野技术。调强放射治疗(intensity-modulatedradiotherapy,IMRT)技术有望在保障相同疗效的同时进一步减少放疗并发症,提高生活质量。本研究利用三维计划系统评价全乳IMRT的剂量学优势与适应证。方法:选择10例接受保乳手术的Tis～2N0M0早期乳腺癌病例,利用三维治疗计划系统为每例患者设计两种全乳放射治疗计划,切线野常规计划与IMRT计划,处方剂量均为5000cGy。用剂量体积直方图(dosevolumehistograms,DVH)来比较各种计划中计划靶体积(planningtargetvolume,PTV)、危及器官(organsatrisks,OARs)的剂量学差异。结果:靶区覆盖率在两种计划中相似,分别为98.3%和97.7%。与常规计划比较,IMRT计划的PTV接受<95%处方剂量与>103%处方剂量的体积百分比之和(inhomogeneityindex,IHI)从29.9%减少到2.9%,PTV接受至少105%处方剂量照射的体积百分比(V105%)从28.2%减少到0.6%;IMRT计划改善IHI和减少V105%的平均值在PTV较大的患者中优势更明显。左侧患者中冠状动脉的最大剂量(Dmax)以及心脏的平均剂量(Dmean)分别从5057.1cGy减少到4832.9cGy和从629.8cGy到450.7cGy;右侧患者肝脏的Dmean从283.9cGy减少到172.0cGy;所有患者中同侧肺的Dmean、至少接受20Gy照射的体积百分比(V20)分别从925.2cGy减少到765.9cGy,从16.0%到15.3%,Dmean与V20的平均值在IMRT计划中减少的百分比在不同射野中心肺厚度(centrallungdistance,CLD)亚组中分别是14.7%与20.9%,7.0%与12.9%;对侧乳腺和对侧肺的Dmean也分别从75.4cGy减少到20.3cGy和从30.9cGy到16.1cGy。结论:全乳IMRT的剂量学优势主要在于保证靶区覆盖率的前提下,显著改善靶区的剂量分布均匀性并一定程度上降低OARs的受照剂量与容积。乳房体积和CLD较大的病例可以通过IMRT技术获得更好的剂量学结果。     

Radiotherapy of nonfunctional adenomas of the pituitary gland. Results with long-term follow-up

A total of 112 patients with the diagnosis of nonfunctional pituitary adenoma received radiation therapy at the University of Pittsburgh between 1964 and 1987. Postoperative radiation therapy was administered in 87 patients. Actuarial progression-free survival (tumor control) at 5, 10, 15, and 20 years was 97%, 89%, 87%, and 76%, respectively. Radiation prescribed to the 95% isodose ranged from 35.72 Gy to 62.32 Gy. Multivariate analysis showed decreased tumor control to be significantly associated with increasing field size (P = .036). No improvement in tumor control could be detected with increasing total radiation dose or nominal standard dose (NSD). One patient developed optic neuropathy and another developed a glioblastoma after doses in both patients of 4750 cGy in 25 fractions. External beam radiotherapy for nonfunctional pituitary adenomas was found to be effective and safe when doses less than 4750 cGy in 25 fractions were used.     

Comparison of contralateral breast dose for various tangential field techniques in clinical radiotherapy

Contralateral breast (CLB) cancer is a rare but serious concern in radiotherapy. In this study, the CLB dose was measured using MOSFET dosimeter in 49 patients who underwent breast conservation surgery treated by different radiotherapy tangential field techniques, which included enhanced dynamic wedge (EDW), physical wedge, and intensity modulated radiation therapy (IMRT). The mean percent of the prescribed dose received by the contralateral areola in treatment technique using physical wedge (Cobalt), physical wedge (Linac), EDW, and IMRT were 4.27% (SD: 0.65), 3.61% (SD: 0.60), 3.38% (SD: 0.58), and 1.65% (SD: 0.24), respectively. There was a 29% CLB dose reduction at 3 cm from the medial tangential field border with IMRT compared to other wedged tangential field techniques. The study shows that the CLB dose could be reduced with IMRT or reducing or avoiding the medial wedge in conventional tangential field planning for breast cancer.     

Comparision of Different Radiotherapy Planning Techniques for Breast Cancer after Breast Conserving Surgery

Objectives:To compare different radiotherapy planning techniques for breast cancer after breast conserving surgery.Materials and methods: Eighteen patients with breast cancer who underwent breast conserving surgery were selected.For each patient four different whole breast irradiation techniques including Tan, fIMRT, iIMRT and VMAT werecompared to the conventional tangential technique (Tan). Results: Mean maximum point dose (Dmax) for Tan, fIMRT,iIMRT and VMAT were 110.17% (±1.87), 105.89% (±1.13), 106.47% (±0.92) and 106.99% (±1.16) (p<0.001). Meanminimum point dose (Dmin) from Tan was 84.02% (±3.68) which was significantly higher than those from fIMRT,iIMRT and VMAT which were 76.57% (±11.4), 67.69 %( ±19.20) and 80.69% (±7.06) (p<0.001). Only the meanV95 of fIMRT was significantly less than Tan (p=0.01). Mean percentage of volume receiving ≥ 20 Gy (V20Gy) andmean doses of the ipsilateral lung were 17.09% and 953.05 cGy, 16.60% and 879.20 cGy, 14.79% and 772.26 cGy,15.32% and 984.34 cGy for Tan, fIMRT, iIMRT and VMAT. Only iIMRT had a significantly lower mean V20Gy andthe mean dose to ipsilateral lung in comparison with Tan. Significantly, high mean doses to the contralateral breast(498.07 cGy, p<0.001) were observed in VMAT. Conclusion: The conventional tangential technique provides adequatedose coverage but resulted in high dose-volumes. The iIMRT and fIMRT had significantly smaller high dose-volumesand better conformity. VMAT demonstrated excellent dose homogeneity and conformity but an increased low-dosevolume outside the target should be of concern.     

A comparison of Monte Carlo and Fermi-Eyges-Hogstrom estimates of heart and lung dose from breast electron boost treatment

PURPOSE: Electrons are commonly used in the treatment of breast cancer primarily to deliver a tumor bed boost. We compared the use of the Monte Carlo (MC) method and the Fermi-Eyges-Hogstrom (FEH) algorithm to calculate the dose distribution of electron treatment to normal tissues. METHODS AND MATERIALS: Ten patients with left-sided breast cancer treated with breast-conservation therapy at the University of California, San Francisco, were included in this study. Each patient received an electron boost to the surgical bed to a dose of 1,600 cGy in 200 cGy fractions prescribed to 80% of the maximum. Doses to the left ventricle (LV) and the ipsilateral lung (IL) were calculated using the EGS4 MC system and the FEH algorithm implemented on the commercially available Pinnacle treatment planning system. An anthromorphic phantom was irradiated with radiochromic film in place to verify the accuracy of the MC system. RESULTS: Dose distributions calculated with the MC algorithm agreed with the film measurements within 3% or 3 mm. For all patients in the study, the dose to the LV and IL was relatively low as calculated by MC. That is, the maximum dose received by up to 98% of the LV volume was < 100 cGy/day. Less than half of the IL received a dose in excess of 30 cGy/day. When compared with MC, FEH tended to show reduced penetration of the electron beam in lung, and FEH tended to overestimate the bremsstrahlung dose in regions well beyond the electron practical range. These differences were clinically likely to be of little significance, comprising differences of less than one-tenth of the LV and IL volume at doses > 30 cGy and differences in maximum dose of < 35 cGy/day to the LV and 80 cGy/day to the IL. CONCLUSIONS: From our series, using clinical judgment to prescribe the boost to the surgical bed after breast-conserving treatment results in low doses to the underlying LV and IL. When calculated dose distributions are desired, MC is the most accurate, but FEH can still be used.     

Multifractionated image-guided and stereotactic intensity-modulated radiotherapy of paraspinal tumors: a preliminary report

PURPOSE: The use of image-guided and stereotactic intensity-modulated radiotherapy (IMRT) techniques have made the delivery of high-dose radiation to lesions within close proximity to the spinal cord feasible. This report presents clinical and physical data regarding the use of IMRT coupled with noninvasive body frames (stereotactic and image-guided) for multifractionated radiotherapy. METHODS AND MATERIALS: The Memorial Sloan-Kettering Cancer Center (Memorial) stereotactic body frame (MSBF) and Memorial body cradle (MBC) have been developed as noninvasive immobilizing devices for paraspinal IMRT using stereotactic (MSBF) and image-guided (MBC) techniques. Patients were either previously irradiated or prescribed doses beyond spinal cord tolerance (54 Gy in standard fractionation) and had unresectable gross disease involving the spinal canal. The planning target volume (PTV) was the gross tumor volume with a 1 cm margin. The PTV was not allowed to include the spinal cord contour. All treatment planning was performed using software developed within the institution. Isocenter verification was performed with an in-room computed tomography scan (MSBF) or electronic portal imaging devices, or both. Patients were followed up with serial magnetic resonance imaging every 3-4 months, and no patients were lost to follow-up. Kaplan-Meier statistics were used for analysis of clinical data. RESULTS: Both the MSBF and MBC were able to provide setup accuracy within 2 mm. With a median follow-up of 11 months, 35 patients (14 primary and 21 secondary malignancies) underwent treatment. The median dose previously received was 3000 cGy in 10 fractions. The median dose prescribed for these patients was 2000 cGy/5 fractions (2000-3000 cGy), which provided a median PTV V100 of 88%. In previously unirradiated patients, the median prescribed dose was 7000 cGy (5940-7000 cGy) with a median PTV V100 of 90%. The median Dmax to the cord was 34% and 68% for previously irradiated and never irradiated patients, respectively. More than 90% of patients experienced palliation from pain, weakness, or paresthesia; 75% and 81% of secondary and primary lesions, respectively, exhibited local control at the time of last follow-up. No cases of radiation-induced myelopathy or radiculopathy have thus far been encountered. CONCLUSIONS: Precision stereotactic and image-guided paraspinal IMRT allows the delivery of high doses of radiation in multiple fractions to tumors within close proximity to the spinal cord while respecting cord tolerance. Although preliminary, the clinical results are encouraging.     

A dosimetric evaluation of conventional helmet field irradiation versus two-field intensity-modulated radiotherapy technique

PURPOSE: To compare dosimetric differences between conventional two-beam helmet field irradiation (external beam radiotherapy, EBRT) of the brain and a two-field intensity-modulated radiotherapy (IMRT) technique. METHODS AND MATERIALS: Ten patients who received helmet field irradiation at our institution were selected for study. External beam radiotherapy portals were planned per usual practice. Intensity-modulated radiotherapy fields were created using the identical field angles as the EBRT portals. Each brain was fully contoured along with the spinal cord to the bottom of the C2 vertebral body. This volume was then expanded symmetrically by 0.5 cm to construct the planning target volume. An IMRT plan was constructed using uniform optimization constraints. For both techniques, the nominal prescribed dose was 3,000 cGy in 10 fractions of 300 cGy using 6-MV photons. Comparative dose-volume histograms were generated for each patient and analyzed. RESULTS: Intensity-modulated radiotherapy improved dose uniformity over EBRT for whole brain radiotherapy. The mean percentage of brain receiving >105% of dose was reduced from 29.3% with EBRT to 0.03% with IMRT. The mean maximum dose was reduced from 3,378 cGy (113%) for EBRT to 3,162 cGy (105%) with IMRT. The mean percent volume receiving at least 98% of the prescribed dose was 99.5% for the conventional technique and 100% for IMRT. CONCLUSIONS: Intensity-modulated radiotherapy reduces dose inhomogeneity, particularly for the midline frontal lobe structures where hot spots occur with conventional two-field EBRT. More study needs to be done addressing the clinical implications of optimizing dose uniformity and its effect on long-term cognitive function in selected long-lived patients.     

Multileaf field-in-field forward-planned intensity-modulated dose compensation for whole-breast irradiation is associated with reduced contralateral breast dose: a phantom model comparison.

PURPOSE: Static multileaf collimated field-in-field forward-planned intensity-modulated radiation treatment (FiF-IMRT) has been shown to improve dose homogeneity compared to conventional wedged fields. However, a direct comparison of the scattered dose to the contralateral breast resulting from wedged and FiF-IMRT plans remains to be documented. METHODS: The contralateral scattered breast dose was measured in a custom-designed anthropomorphic breast phantom in which 108 thermoluminescent dosimeters (TLDs) were volumetrically placed every 1-2cm. The target phantom breast was treated to a dose of 50Gy using three dose compensation techniques: No medial wedge and a 30-degree lateral wedge (M0-L30), 15-degree lateral and medial wedges (M15-L15), and FiF-IMRT. TLD measurements were compared using analysis of variance. RESULTS: For FiF-IMRT, the mean doses to the medial and lateral quadrants of the contralateral breast were 112cGy (range 65-226cGy) and 40cGy (range 18-91 cGy), respectively. The contralateral breast doses with FiF-IMRT were on average 65% and 82% of the doses obtained with the M15-L15 and M0-L30 techniques, respectively (p<0.001). Compared to the M15-L15 technique, the maximum dose reduction obtained with FiF-IMRT was 115cGy (range 13-115cGy). CONCLUSIONS: The dose to the contralateral breast is significantly reduced with FiF-IMRT compared to wedge-compensated techniques. Although long-term follow-up is needed to establish the clinical relevance of this finding, these results, along with the previously reported improvement in ipsilateral dose homogeneity, support the use of FiF-IMRT if resources permit.     

Phase I/II study of treatment of locally advanced (T3T4) non-oat cell lung cancer with high dose radiotherapy (rapid fractionation): Radiation Therapy Oncology Group Study

The Radiation Therapy Oncology Group (RTOG) completed a pilot study to test the feasibility of high dose of radiation therapy and its impact on tumor control and survival. From April 1, 1983 through May 1985, a total of 56 patients were treated on this protocol. All patients had locally advanced disease without distant metastases. The treatment regimen consisted of delivering 7500 cGy in 28 fractions over 5.5 weeks to the tumor, while the nodal bearing areas received 5040 cGy in the same period (daily dose to the mediastinum was 180 cGy; daily dose to gross tumor was 268 cGy). This is a considerably higher dose, with a TDF of 142 compared with a TDF of 92 (conventional fractionation of 6000 cGy in 6 weeks), which is the highest dose used in previous RTOG studies. Doses in this protocol (7500 cGy) was corrected for lung transmission whereas doses in prior RTOG protocols (6000 cGy) were uncorrected. Thus, after correction dose of 6600 cGy was calculated and coded for comparison. All short-term toxicities were acceptable, and the only major toxicity was one third-degree esophagitis in a patient with a follow-up of 12 months. Forty-four out of fifty-six patients received prescribed dose of irradiation. There were 17 complete responders and 15 partial responders, with an overall response rate of 32 out of 44 (72.7%). At the time of this report, there were 9 patients alive (NED); 5 died without tumor; and the remainder died of tumor or unknown.     

CT Based 3-Dimensional Treatment Planning of Intracavitary Brachytherapy for Cancer of the Cervix : Comparison between Dose-Volume Histograms and ICRU Point Doses to the Rectum and Bladder

Background: CT based brachytherapy allows 3-dimensional (3D) assessment of organs at risk (OAR) doses with dose volume histograms (DVHs). The purpose of this study was to compare computed tomography (CT) based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the cervix treated with high-dose-rate (HDR) intracavitary brachytherapy (ICBT). Materials and Methods: Between March2011 and May 2012, 20 patients were treated with 55 fractions of brachytherapy using tandem and ovoids and underwent post-implant CT scans. The external beam radiotherapy (EBRT) dose was 48.6Gy in 27 fractions. HDR brachytherapy was delivered to a dose of 21 Gy in three fractions. The ICRU bladder and rectum point doses along with 4 additional rectal points were recorded. The maximum dose (DMax) to rectum was the highest recorded dose at one of these five points. Using the HDRplus 2.6 brachyhtherapy treatment planning system, the bladder and rectum were retrospectively contoured on the 55 CT datasets. The DVHs for rectum and bladder were calculated and the minimum doses to the highest irradiated 2cc area of rectum and bladder were recorded (D2cc) for all individual fractions. The mean D2cc of rectum was compared to the means of ICRU rectal point and rectal DMax using the Student’s t-test. The mean D2cc of bladder was compared with the mean ICRU bladder point using the same statistical test .The total dose, combining EBRT and HDR brachytherapy, were biologically normalized to the conventional 2 Gy/fraction using the linear-quadratic model. (α/β value of 10 Gy for target, 3 Gy for organs at risk). Results: The total prescribed dose was 77.5 Gyα/β10. The mean dose to the rectum was 4.58±1.22 Gy for D2cc, 3.76±0.65 Gy at DICRU and 4.75±1.01 Gy at DMax. The mean rectal D2cc dose differed significantly from the mean dose calculated at the ICRU reference point (p<0.005); the mean difference was 0.82 Gy (0.48 -1.19Gy). The mean EQD2 was 68.52±7.24 Gyα/β3 for D2cc, 61.71±2.77 Gyα/β3 at DICRU and 69.24±6.02Gyα/β3 at DMax. The mean ratio of D2cc rectum to DICRU rectum was 1.25 and the mean ratio of D2cc rectum to DMax rectum was 0.98 for all individual fractions. The mean dose to the bladder was 6.00±1.90 Gy for D2cc and 5.10±2.03 Gy at DICRU. However, the mean D2cc dose did not differ significantly from the mean dose calculated at the ICRU reference point (p=0.307); the mean difference was 0.90 Gy (0.49-1.25Gy). The mean EQD2 was 81.85±13.03 Gyα/β3 for D2cc and 74.11±19.39 Gyα/β3 at DICRU. The mean ratio of D2cc bladder to DICRU bladder was 1.24. In the majority of applications, the maximum dose point was not the ICRU point. On average, the rectum received 77% and bladder received 92% of the prescribed dose. Conclusions: OARs doses assessed by DVH criteria were higher than ICRU point doses. Our data suggest that the estimated dose to the ICRU bladder pointmay be a reasonable surrogate for the D2cc and rectal DMax for D2cc. However, the dose to the ICRU rectal point does not appear to be a reasonable surrogate for the D2cc.     

Comparison between CT-based volumetric calculations and ICRU reference-point estimates of radiation doses delivered to bladder and rectum during intracavitary radiotherapy for cervical cancer

PURPOSE: To compare CT-based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the uterine cervix treated with definitive low-dose-rate intracavitary radiotherapy (ICRT). METHODS AND MATERIALS: Between November 2001 and March 2003, 60 patients were prospectively enrolled in a pilot study of ICRT with CT-based dosimetry. Most patients underwent two ICRT insertions. After insertion of an afterloading ICRT applicator, intraoperative orthogonal films were obtained to ensure proper positioning of the system and to facilitate subsequent planning. Treatments were prescribed using standard two-dimensional dosimetry and planning. Patients also underwent helical CT of the pelvis for three-dimensional reconstruction of the radiation dose distributions. The systems were loaded with 137Cs sources using the Selectron remote afterloading system according to institutional practice for low-dose-rate brachytherapy. Three-dimensional dose distributions were generated using the Varian BrachyVision treatment planning system. The rectum was contoured from the bottom of the ischial tuberosities to the sigmoid flexure. The entire bladder was contoured. The minimal doses delivered to the 2 cm3 of bladder and rectum receiving the highest dose (DBV2 and DRV2, respectively) were determined from dose-volume histograms, and these estimates were compared with two-dimensionally derived estimates of the doses to the corresponding ICRU reference points. Results: A total of 118 unique intracavitary insertions were performed, and 93 were evaluated and the subject of this analysis. For the rectum, the estimated doses to the ICRU reference point did not differ significantly from the DRV2 (p = 0.561); the mean (+/- standard deviation) difference was 21 cGy (+/- 344 cGy). The median volume of the rectum that received at least the ICRU reference-point dose was 2.1 cm3. In 66 (71%) of 93 cases, <5 cm3 was treated to this dose. However, for the bladder, the estimated doses to the ICRU reference point were significantly lower than the D(BV2) (p <0.001); the mean difference was 680 cGy (+/- 543 cGy). The median volume of the bladder that received at least the ICRU reference-point dose was 13.0 cm3. CONCLUSIONS: Our data suggest that the estimated dose to the ICRU rectal point may be a reasonable surrogate for the DRV2. However, this result may not be applicable to other treatment guidelines and ICRT applicator systems. In contrast, the dose to the ICRU bladder point does not appear to be a reasonable surrogate for the DBV2. Correlation with late complications are needed to define the role of three-dimensional dosimetry in treatment planning.     

Transperineal injection of hyaluronic acid in anterior perirectal fat to decrease rectal toxicity from radiation delivered with intensity modulated brachytherapy or EBRT for prostate cancer patients

PURPOSE: Rectal toxicity remains a serious complication affecting quality of life for prostate cancer patients treated with radiotherapy. We began an investigational trial injecting hyaluronic acid (HA) in the perirectal fat to increase the distance between the prostate and the anterior rectal wall. This is the first report using HA injection in oncology. METHODS AND MATERIALS: This is a trial of external beam radiation therapy with HDR brachytherapy boosts in prostate cancer. During the two high-dose-rate (HDR) fractions, thermoluminescent dosimeter dosimeters were placed in the urethra and in the rectum. Before the second HDR fraction, 3-7 mL (mean, 6 mL) of HA was injected under transrectal ultrasound guidance in the perirectal fat to systematically create a 1.5-cm space. Urethral and rectal HDR doses were calculated and measured. Computed tomography and magnetic resonance imaging were used to assess the stability of the new space. RESULTS: Twenty-seven patients enrolled in the study. No toxicity was produced from the HA or the injection. In follow-up computed tomography and magnetic resonance imaging, the HA injection did not migrate or change in mass/shape for close to 1 year. The mean distance between rectum and prostate was 2.0 cm along the entire length of the prostate. The median measured rectal dose, when normalized to the median urethral dose, demonstrated a decrease in dose from 47.1% to 39.2% (p < 0.001) with or without injection. For an HDR boost dose of 1150 cGy, the rectum mean Dmax reduction was from 708 cGy to 507 cGy, p < 0.001, and the rectum mean Dmean drop was from 608 to 442 cGy, p < 0.001 post-HA injection. CONCLUSION: The new 2-cm distance derived from the HA injection significantly decreased rectal dose in HDR brachytherapy. Because of the several-month duration of stability, the same distance was maintained during the course of external beam radiation therapy.     

Fetal Dose Evaluation During Breast Cancer Radiotherapy

Purpose: The aim of the work was to estimate the radiation dose delivered to the fetus in a pregnant patient irradiated for breast cancer.Methods and Materials: A 45-year woman was treated for left breast cancer using a 6 MV photon beam with two isocentric opposing tangential unwedged fields. Daily dose was 2.3 Gy at 95% isodose line given by two fields/day, 5 days/week. A total dose of 46 Gy was given in 20 fractions over a 4-week period. Pregnancy confirmed during the second therapeutic week. Treatment lasted between the second and sixth gestation week. Radiation dose to fetus was estimated from in vivo and phantom measurements using thermoluminescence dosimeters and an ionization chamber. In vivo measurements were performed by inserting either a catheter with TL dosimeters or ionization chamber into the patient’s rectum. Phantom measurements were performed by simulating the treatment conditions on an anthropomorphic phantom.Results: TLD measurements (in vivo and phantom) revealed fetal dose to be 0.085% of the tumor dose, corresponding to a cumulative fetal dose of 3.9 cGy for the entire treatment of 46 Gy. Chamber measurements (in vivo and phantom) revealed a fetal dose less than the TLD result: 0.079 and 0.083% of the tumor dose corresponding to cumulative fetal dose of 3.6 cGy and 3.8 cGy for in vivo and phantom measurement, respectively.Conclusions: It was concluded that the cumulative dose delivered to the unshielded fetus was 3.9 cGy for a 46 Gy total tumor dose. The estimated fetal dose is low compared to the total tumor dose given due to the early stage of pregnancy, the large distance between fundus-radiation field, and the fact that no wedges and/or lead blocks were used. No deterministic biological effects of radiation on the live-born embryo are expected. The lifetime risk for radiation-induced fatal cancer is higher than the normal incidence, but is considered as inconsequential.     

Radiation therapy of esophageal cancer: role of high dose rate brachytherapy.

Fifty untreated cases of squamous cell carcinoma arising from the middle one-third of the esophagus, with no apparent extraesophageal spread on a computed tomography (CT) scan and with a Karnofsky performance status of over 70, were treated by external beam irradiation to a dose of 3500 cGy/15 fractions/3 weeks. Twenty-five patients (Group A) received treatment with further external beam irradiation to a dose of 2000 cGy/10 fractions/2 weeks. Another group of 25 patients (Group B) received treatment with high dose rate intracavitary irradiation to a dose of 1200 cGy delivered in two sessions of 600 cGy each a week apart. All patients were assessed symptomatically, endoscopically, and radiologically every 3 months. There was marked difference at the end of 1 year in relief of dysphagia (37.5% in Group A vs. 70.6% in Group B), local control (25% in group A vs. 70.6% in group B) although the results were statistically insignificant (p greater than 0.05) and actuarial survival (44% in group A vs. 78% in group B) which was, however, significant statistically (z = 2.83). The cumulative radiation effect (CRE) by external beam irradiation was 1729 reu and by external beam and intracavitary irradiation 1741 reu, but the biological dose effect was better with external beam and intracavitary irradiation. Eight percent of patients treated by external beam and intracavitary irradiation had strictures in contrast to 4% treated by external beam irradiation alone. Moderate doses of external beam and intracavitary irradiation can give a better local response than external beam irradiation alone for the same biological dose in the treatment of esophageal carcinoma.     

Dosimetry of the breast for determining carcinogenic risk in mantle irradiation

Development of secondary malignancies following treatment of Hodgkin's disease with radiation (central axis midline dose of 3600-4500 cGy) is a recognized risk, and the incidence in breast cancer has been reported to increase by a factor of 4.3 (95% confidence level 2.0 to 8.4) for patients treated with mantle irradiation. Increased incidence of breast cancer has also been shown in atomic bomb survivors, women who underwent multiple fluoroscopic examinations, and women treated for postpartum mastitis. The dose response, however, for radiation dose above 1000 cGy is virtually unknown. Quantitative analysis of carcinogenesis after radiation is exacerbated by the large dose gradient across the breast (300-4200 cGy for midline doses of 4000 cGy), large individual variation in breast size and treatment field position. We have developed differential dose volume histograms calculated using a 3-dimensional (Eg TAR) algorithm as a potential tool for retrospective and prospective epidemiological evaluation. The breast volume forms a bimodal distribution with respect to dose and with further analysis other quantities, such as mean dose and integral dose, can be calculated from the histograms. Using the mean dose, the linear model for carcinogenesis predicts an increased incidence of secondary breast cancer by a factor of 11.6 and 9.6 for the left and right breast, respectively. The dose calculations has been corrected for inhomonogenities 3-dimensionally and test of the accuracy has been included.     

Lack of radiation dose response for patients with low-risk clinically localized prostate cancer: a retrospective analysis

The need for dose escalation for patients with low-risk clinically localized prostate cancer remains controversial. In this study, we report our pooled institutional experience of low-risk patients treated with a range of “standard” radiation doses to assess outcome in regard to biochemical failure and to determine whether a dose-response relationship exists within this conventional dose range.

Patients with low-risk clinically localized prostate cancer (T1 or T2a, Gleason grade ≤6, and prostate-specific antigen ≤10 ng/mL) treated at Joint Center for Radiation Therapy-affiliated institutions between October 1989 and September 1997 were retrospectively analyzed for freedom from biochemical failure. The dose was prescribed volumetrically with 95% normalization to between 5760 and 6900 cGy (6100 and 7300 cGy ICRU reference point dose). Patients were stratified into 3 groups with relatively equal numbers of patients (<6660, 6660, and >6660 cGy). To ensure that any differences in biochemical failure between patients at the lower and higher ends of the dose range used were not masked by analysis of the entire cohort, patients receiving ≤6500 cGy or ≥6800 cGy were subsequently analyzed separately. Biochemical failure was defined per the ASTRO consensus definition. The log-rank test was used to assess for differences in follow-up and time to biochemical failure. A Kaplan-Meier plot of time to biochemical failure for the initial 3 subgroups was generated.

A total of 264 patients were identified. Sixteen patients whose dose was not recorded in the database were excluded from analysis. The median follow-up was 35 months. No significant differences were found in baseline prostate-specific antigen, Gleason grade, or clinical stage among the groups. The overall actuarial rate of 5-year freedom from biochemical failure was 80.2%. By dose level, the 5-year biochemical failure-free rate was 79.2%, 78.4%, and 84.5% for <6660 cGy, 6660 cGy, and >6660 cGy, respectively. These differences were not significant. Subsequently, 45 patients receiving ≤6500 cGy were compared with 23 patients receiving ≥6800 cGy. The difference between these groups was not significant. The 5-year freedom from biochemical failure rate for the patients receiving ≤6500 cGy was 89.9%.

Within a range of doses considered standard for treatment of low-risk clinically localized prostate cancer during an 8-year period, no improvement in biochemical freedom from failure was noted with the higher doses. The overall 5-year rate of freedom from biochemical failure is consistent with that reported by others with standard and escalated external beam doses used in this low-risk population. A prospective randomized study is necessary to define the optimal dose in this patient population.     

The Doses Received by the Breast During Mantle Radiotherapy

Purpose: To accurately measure the dose received by the breast during mantle radiotherapy.Methods and Materials: A phantom containing lung-equivalent material was used to measure the doses received by the breast during mantle radiotherapy given by anterior and posterior opposing fields. These were measured using thermoluminescent dosimeters and compared with point dose calculations obtained by computer planning.Results: Most of the breast lies under the lung shields or inferior to the mantle field, but the upper outer quadrant of the breast remains unshielded. In the unshielded areas of the breast, the average dose measured was nearly 13% higher than the dose prescribed at the central axis. In the shielded parts of the breast, the average measured dose was nearly 10% of the dose prescribed at the central axes, decreasing from 18% superiorly to 4% inferiorly. The posterior field contributed 45% to the dose in the breast, even though doses were prescribed at the midplane. The computer calculations systematically varied from measured doses by up to 35%, becoming less accurate towards the inferior edge of the field.Conclusions: In a conventional course of mantle radiotherapy (for example, 36 Gy in 20 fractions), most of the breast is shielded but will receive a dose of 3–4 Gy, higher than expected largely due to internally scattered radiation passing through the lungs from the posterior field. Computer dose calculations may poorly reflect actual off-axis doses in large fields with complex shielding, containing inhomogeneous tissue.