Radiation-induced second cancers: the impact of 3D-CRT and IMRT

Papillary thyroid cancer: medical management and follow-up

The incidence of epithelial derived thyroid cancer (papillary thyroid cancer and follicular thyroid cancer, known collectively as differentiated thyroid cancer) is rising. About 80% of patients with thyroid cancer have PTC and are best treated with thyroidectomy and functional lymph node dissection, followed by radioiodine ablation or therapy and performance of a posttreatment whole-body scan, followed by thyroid stimulating hormone (TSH) suppression. One year after radioiodine administration, the use of sensitive thyroglobulin (Tg) assays can separate the vast majority of patients with persistent disease from those who are free of disease and unlikely to have recurrent disease all without the need for repeat whole-body radioiodine imaging. Patients with detectable serum Tg during TSH suppression (Tg-on) or Tg that rises above 2 ng/mL after TSH stimulation (TSH-Tg) are highly likely to harbor residual tumor. TSH stimulation can be achieved using either thyroid hormone withdrawal or recombinant human TSH (rhTSH). Highly skilled screening neck ultrasonography can identify a few additional patients with subcentimeter residual neck lymph node metastases not detected by TSH-Tg. However, ultrasonography and chest computed tomography (CT) are most critical for tumor localization in those patients with Tg values that suggest residual disease or in those patients with persistent antithyroglobulin antibodies (TgAb) that falsely lower Tg measurement. TgAb quantitative titers typically resolve steadily over just a few years in patients free of disease after initial therapy. Another paradigm shift is the recognition that most patients who eventually achieve freedom from disease do so by surgery with fewer patients cured by repetitive radioiodine treatments, and even fewer cured with external beam radiation. Patients who appear to be free of disease require a lifetime of follow-up to optimize levothyroxine treatment, and they will undergo periodic stimulation testing because some will still manifest recurrent disease. Patients with persistent disease despite negative ultrasonography, chest CT, and whole-body radioiodine imaging may have a tumor identified by fluorodeoxyglucose positron emission tomography, optimally performed with combined TSH stimulation and image fusion with CT or magnetic resonance imaging. Patients with metastatic disease who are unresponsive to conventional treatment are encouraged to participate in increasingly available thyroid cancer-specific clinical trials using targeted experimental oral or intravenous chemotherapeutic agents to address this tumor that has historically proven resistant to conventional chemotherapeutic agents.

Does electron and proton therapy reduce the risk of radiation induced cancer after spinal irradiation for childhood medulloblastoma? A comparative treatment planning study

The aim of this treatment planning comparison study was to explore different spinal irradiation techniques with respect to the risk of late side-effects, particularly radiation-induced cancer. The radiotherapy techniques compared were conventional photon therapy, intensity modulated x-ray therapy (IMXT), conventional electron therapy, intensity/energy modulated electron therapy (IMET) and proton therapy (IMPT).CT images for radiotherapy use from five children, median age 8 and diagnosed with medulloblastoma, were selected for this study. Target volumes and organs at risk were defined in 3-D. Treatment plans using conventional photon therapy, IMXT, conventional electron therapy, IMET and IMPT were set up. The probability of normal tissue complication (NTCP) and the risk of cancer induction were calculated using models with parameters-sets taken from published data for the general population; dose data were taken from dose volume histograms (DVH). Similar dose distributions in the targets were achieved with all techniques but the absorbed doses in the organs-at-risk varied significantly between the different techniques. The NTCP models based on available data predicted very low probabilities for side-effects in all cases. However, the effective mean doses outside the target volumes, and thus the predicted risk of cancer induction, varied significantly between the techniques. The highest lifetime risk of secondary cancers was estimated for IMXT (30%). The lowest risk was found with IMPT (4%). The risks associated with conventional photon therapy, electron therapy and IMET were 20%, 21% and 15%, respectively. This model study shows that spinal irradiation of young children with photon and electron techniques results in a substantial risk of radiation-induced secondary cancers. Multiple beam IMXT seems to be associated with a particularly high risk of secondary cancer induction. To minimise this risk, IMPT should be the treatment of choice. If proton therapy is not available, advanced electron therapy may provide a better alternative.

Cancer Survivorship—Genetic Susceptibility and Second Primary Cancers: Research Strategies and Recommendations

Cancer survivors constitute 3.5% of the United States population, but second primary malignancies among this high-risk group now account for 16% of all cancer incidence. Although few data currently exist regarding the molecular mechanisms for second primary cancers and other late outcomes after cancer treatment, the careful measurement and documentation of potentially carcinogenic treatments (chemotherapy and radiotherapy) provide a unique platform for in vivo research on gene-environment interactions in human carcinogenesis. We review research priorities identified during a National Cancer Institute (NCI)-sponsored workshop entitled "Cancer Survivorship--Genetic Susceptibility and Second Primary Cancers." These priorities include 1) development of a national research infrastructure for studies of cancer survivorship; 2) creation of a coordinated system for biospecimen collection; 3) development of new technology, bioinformatics, and biomarkers; 4) design of new epidemiologic methods; and 5) development of evidence-based clinical practice guidelines. Many of the infrastructure resources and design strategies that would facilitate research in this area also provide a foundation for the study of other important nonneoplastic late effects of treatment and psychosocial concerns among cancer survivors. These research areas warrant high priority to promote NCI's goal of eliminating pain and suffering related to cancer.

The risk of second primary tumors in patients with nasopharyngeal carcinoma after definitive radiotherapy

BACKGROUND

Second primary tumors (SPTs) have a substantial impact on survival in cancer patients. However, risk factors for SPTs have not been documented well, especially in nasopharyngeal carcinoma (NPC). The objective of this retrospective analysis was to evaluate such risks in patients with NPC after they received definitive radiation treatment.

METHODS

Three hundred twenty-six consecutive patients with pathologically confirmed, nonmetastatic, undifferentiated NPC who received treatment between January 1, 1994 and December 30, 1995 were analyzed. All patients were restaged in accordance with the 2002 American Joint Committee on Cancer staging classification. There were 18 patients (5.5%) with Stage I NPC, 152 patients (46.6%) with Stage II NPC, 101 patients (31.0%) with Stage III NPC, and 55 patients (16.9%) with Stage IVA or IVB NPC at initial diagnosis. All patients received definitive radiotherapy with either Cobalt-60 or megavoltage therapy. High-dose-rate brachytherapy was given to 23 patients either as part of their primary treatment or as adjuvant treatment for residual lesions.

RESULTS

The median follow-up for all patients was 5.6 years (range, 1.0-8.0 years). Seventeen patients (5.2%) developed SPTs, for an average annual rate of 1.0%, and the 5-year cumulative incidence was 5.8%. Six SPTs were located within the radiation field. The cumulative incidence of in-field SPTs was 0.35% at 3 years and 1.2% at 5 years, and the average annual rate was 0.35%. Eleven patients (64.7%) had tumors of the upper aerodigestive tract (UADT). Among the 14 SPTs that occurred within 5 years after radiotherapy, only 3 tumors (21.4%) occurred within the radiation field. In contrast, all 3 SPTs that occurred >5 years after radiotherapy occurred within the radiation field (P = .029). Multivariate analysis showed that age was the only independent risk factor for developing SPTs after RT for NPC. Advanced age (age >or=50 years) was associated with a 37% increased risk of developing SPTs (relative risk, 1.367; 95% confidence interval, 1.067-1.1753; P = .014). Other factors, including gender, tumor or lymph node classification, chemotherapy, total radiation dose to the nasopharynx, reirradiation, and adjuvant brachytherapy did not influence the risk of SPTs.

CONCLUSIONS

SPTs in patients with NPC occurred preferentially in the UADT and tended to develop within the irradiated field >5 years after patients received radiation. Older patients with NPC (age >or=50 years) may be at increased risk. Further studies with larger samples and longer follow-up will be needed to confirm these findings.

Dosimetric issues in radiation protection of radiotherapy patients

As life expectancy increases, thanks to improving general medical practices, cancer treatments for the ageing population become evermore necessary. Radiation therapy is increasingly a treatment of choice, promoted by continuing improvements in dose delivery technologies. Some techniques, collectively referred to as intensity-modulated radiation therapy, are encountering widespread acceptance and implementation, promoted by reports of superior tumour control and reduced toxicity. However, these new techniques pose new challenges in terms of radiation protection of patients, as they cause a more extensive low-dose exposure of normal tissues compared with conventional radiation therapy. The related dosimetric challenges and the methods available to tackle them are reviewed in this paper, which also emphasises the need for standard radiation protection dosimetry procedures so that information may be consistently gathered for a comparative evaluation of the different treatment modalities.

Intensity modulated radiotherapy: advantages, limitations and future developments

Intensity modulated radiotherapy (IMRT) is widely used in clinical applications in developed countries, for the treatment of malignant and non-malignant diseases. This technique uses multiple radiation beams of non-uniform intensities. The beams are modulated to the required intensity maps for delivering highly conformal doses of radiation to the treatment targets, while sparing the adjacent normal tissue structures. This treatment technique has superior dosimetric advantages over 2-dimensional (2D) and conventional 3-dimensional conformal radiotherapy (3DCRT) treatments. It can potentially benefit the patient in three ways. First, by improving conformity with target dose it can reduce the probability of in-field recurrence. Second, by reducing irradiation of normal tissue it can minimise the degree of morbidity associated with treatment. Third, by facilitating escalation of dose it can improve local control. Early clinical results are promising, particularly in the treatment of nasopharyngeal carcinoma (NPC). However, as the IMRT is a sophisticated treatment involving high conformity and high precision, it has specific requirements. Therefore, tight tolerance levels for random and systematic errors, compared with conventional 2D and 3D treatments, must be applied in all treatment and pre-treatment procedures. For this reason, a large-scale routine clinical implementation of the treatment modality demands major resources and, in some cases, is impractical. This paper will provide an overview of the potential advantages of the IMRT, methods of treatment delivery, and equipment currently available for facilitating the treatment modality. It will also discuss the limitations of the equipment and the ongoing development work to improve the efficiency of the equipment and the treatment techniques and procedures.

Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose-response relationships

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED(rad-ther)) in the irradiated organs. The OED(rad-ther) concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose-response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose-response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin's disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin's disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.

Technology insight: Proton beam radiotherapy for treatment in pediatric brain tumors

Tumors of the central nervous system are the most common solid tumor in childhood. Treatment options for childhood brain tumors include radiation therapy, surgery and chemotherapy, often given in combination. Radiation therapy regularly has a pivotal role in treatment, and technological advancements during the past quarter of a century have dramatically improved the ability to deliver radiation in a more focused manner. Improvements in imaging and computing ability led to better targeting of tumor tissue using conventional X-ray therapy. These advances have been harnessed for proton radiation therapy. Proton radiotherapy has special physical characteristics that allow normal tissues to be spared better than even the most conformal photon radiation, and it will reduce the complications from treatment. This review discusses the characteristics of proton radiation, and describes examples of pediatric brain tumor patients who would benefit most from this form of treatment.

Ionizing radiation and tobacco use increases the risk of a subsequent lung carcinoma in women with breast cancer: case-only design

PURPOSE

To analyze the risk of lung cancer in women treated with radiotherapy for breast cancer. We accessed the lung dose in relation to different radiotherapy techniques, provided the excess relative risk (ERR) estimate for radiation-associated lung cancer, and evaluated the influence of tobacco use.

PATIENTS AND METHODS

The Swedish Cancer Registry was used to identify 182 women diagnosed with breast and subsequent lung cancers in Stockholm County during 1958 to 2000. Radiotherapy was administered to 116 patients. Radiation dose was estimated from the original treatment charts, and information on smoking history was searched for in case records and among relatives. The risk of lung cancer was assessed in a case-only approach, where each woman contributed a pair of lungs.

RESULTS

The average mean lung dose to the ipsilateral lung was 17.2 Gy (range, 7.1 to 32.0 Gy). A significantly increased relative risk (RR) of a subsequent ipsilateral lung cancer was observed at > or = 10 years of follow-up (RR = 2.04; 95% CI, 1.24 to 3.36). Squamous cell carcinoma (RR = 4.00; 95% CI, 1.50 to 10.66) was the histopathologic subgroup most closely related to ionizing radiation. The effect of radiotherapy was restricted to smokers only (RR = 3.08; 95% CI, 1.61 to 5.91). The ERR/Gy for women with latency > or = 10 years after exposure was 0.11 (95% CI, 0.02 to 0.44).

CONCLUSION

Radiotherapy for breast cancer significantly increases the risk of lung carcinoma more than 10 years after exposure in women who smoked at time of breast cancer.

Radiation-induced osteosarcomas in the pediatric population

PURPOSE

Radiation-induced osteosarcomas (R-OS) have historically been high-grade, locally invasive tumors with a poor prognosis. The purpose of this study was to perform a comprehensive literature review and analysis of reported cases dealing with R-OS in the pediatric population to identify the characteristics, prognostic factors, optimal treatment modalities, and overall survival of these patients.

METHODS AND MATERIALS

A MEDLINE/PubMed search of articles written in the English language dealing with OSs occurring after radiotherapy (RT) in the pediatric population yielded 30 studies from 1981 to 2004. Eligibility criteria included patients <21 years of age at the diagnosis of the primary cancer, cases satisfying the modified Cahan criteria, and information on treatment outcome. Factors analyzed included the type of primary cancer treated with RT, the radiation dose and beam energy, the latency period between RT and the development of R-OS, and the treatment, follow-up, and final outcome of R-OS.

RESULTS

The series included 109 patients with a median age at the diagnosis of primary cancer of 6 years (range, 0.08-21 years). The most common tumors treated with RT were Ewing's sarcoma (23.9%), rhabdomyosarcoma (17.4%), retinoblastoma (12.8%), Hodgkin's disease (9.2%), brain tumor (8.3%), and Wilms' tumor (6.4%). The median radiation dose was 47 Gy (range, 15-145 Gy). The median latency period from RT to the development of R-OS was 100 months (range, 36-636 months). The median follow-up after diagnosis of R-OS was 18 months (1-172 months). The 3- and 5-year cause-specific survival rate was 43.6% and 42.2%, respectively, and the 3- and 5-year overall survival rate was 41.7% and 40.2%, respectively. Variables, including age at RT, primary site, type of tumor treated with RT, total radiation dose, and latency period did not have a significant effect on survival. The 5-year cause-specific and overall survival rate for patients who received treatment for R-OS involving chemotherapy alone, surgery alone, and surgery plus chemotherapy was 17.3% and 17.3%, 56.6% and 50.3%, and 71.0% and 68.3%, respectively (p < 0.0001, log-rank test).

CONCLUSION

The type of treatment for R-OS was the most significant factor for cause-specific and overall survival. Patients who develop R-OS should be aggressively treated, because the outcome is not as dismal as once thought.

Diagnosis and Management of Synovial Sarcoma

Synovial sarcoma is a unique tumor with substantial promise for biologically targeted therapy. Although it demonstrates moderate chemosensitivity, with approximately 50% response rates to ifosfamide- and doxorubicin-containing regimens, it has a diagnostic translocation and a potentially informative chimeric protein product. Although surgical management remains the cornerstone to effect local control, therapeutic advancements are unlikely to occur by continuing to include advanced cases of synovial sarcomas in trials with other soft tissue sarcomas. Rather, attention should be turned toward prospective molecular targets and development of novel agents to exploit them. Research should be directed at understanding the fusion protein of the X,18 translocation and further validating the role of overexpressed proteins in synovial sarcoma. Meanwhile, carefully designed clinical trials of these agents, with translational correlates, will provide in vivo data to complement the preclinical experience.

A feasibility study for image guided radiotherapy using low dose, high speed, cone beam X-ray volumetric imaging

BACKGROUND AND PURPOSE

Image Guidance of patient set-up for radiotherapy can be achieved by acquiring X-ray volumetric images (XVI) with Elekta Synergy and registering these to the planning CT scan. This enables full 3D registration of structures from similar 3D imaging modalities and offers superior image quality, rotational set-up information and a large field of view. This study uses the head section of the Rando phantom to demonstrate a new paradigm of faster, lower dose XVI that still allows registration to high precision.

MATERIALS AND METHODS

One high exposure XVI scan and one low exposure XVI scan were performed with a Rando Head Phantom. The second scan was used to simulate ultra low dose, fast acquisition, full and half scans by discarding a large number of projections before reconstruction. Dose measurements were performed using Thermo Luminescent Dosimeters (TLD) and an ion chamber. The reconstructed XVI scans were automatically registered with a helical CT scan of the Rando Head using the volumetric, grey-level, cross-correlation algorithm implemented in the Syntegra software package (Philips Medical Systems). Reproducibility of the registration process was investigated.

RESULTS

In both XVI scans the body surface, bone-tissue and tissue air interfaces were clearly visible. Although the subjective image quality of the low dose cone beam scan was reduced, registration of both cone beam scans with the planning CT scan agreed within 0.1 mm and 0.1 degrees . Dose to the patient was reduced from 28mGy to less than 1mGy and the equivalent scan speed reduced to one minute or less.

CONCLUSIONS

Automatic 3D registration of high speed, ultra low dose XVI scans with the planning CT scan can be used for precision 3D patient set-up verification/image guidance on a daily basis with out loss of accuracy when compared to higher dose XVI scans.

Is intensity-modulated radiotherapy better than conventional radiation treatment and three-dimensional conformal radiotherapy for mediastinal masses in patients with Hodgkin's disease, and is there a role for beam orientation optimization and dose constraints assigned to virtual volumes?

PURPOSE

To evaluate the role of beam orientation optimization and the role of virtual volumes (VVs) aimed at protecting adjacent organs at risk (OARs), and to compare various intensity-modulated radiotherapy (IMRT) setups with conventional treatment with anterior and posterior fields and three-dimensional conformal radiotherapy (3D-CRT).

METHODS AND MATERIALS

Patients with mediastinal masses in Hodgkin's disease were treated with combined modality therapy (three to six cycles of adriamycin, bleomycin, vinblastine, and dacarbazine [ABVD] before radiation treatment). Contouring and treatment planning were performed with Somavision and CadPlan Helios (Varian Systems, Palo Alto, CA). The gross tumor volume was determined according to the prechemotherapy length and the postchemotherapy width of the mediastinal tumor mass. A 10-mm isotropic margin was added for the planning target volume (PTV). Because dose constraints assigned to OARs led to unsatisfactory PTV coverage, VVs were designed for each patient to protect adjacent OARs. The prescribed dose was 40 Gy to the PTV, delivered according to guidelines from International Commission on Radiation Units and Measurements Report No. 50. Five different IMRT treatment plans were compared with conventional treatment and 3D-CRT.

RESULTS

Beam orientation was important with respect to the amount of irradiated normal tissues. The best compromise in terms of PTV coverage and protection of normal tissues was obtained with five equally spaced beams (5FEQ IMRT plan) using dose constraints assigned to VVs. When IMRT treatment plans were compared with conventional treatment and 3D-CRT, dose conformation with IMRT was significantly better, with greater protection of the heart, coronary arteries, esophagus, and spinal cord. The lungs and breasts in women received a slightly higher radiation dose with IMRT compared with conventional treatments. The greater volume of normal tissue receiving low radiation doses could be a cause for concern.

CONCLUSIONS

The 5FEQ IMRT plan with dose constraints assigned to the PTV and VV allows better dose conformation than conventional treatment and 3D-CRT, notably with better protection of the heart and coronary arteries. Of concern is the "spreading out" of low doses to the rest of the patient's body.

Intensity-modulated radiation therapy use in the U.S., 2004

BACKGROUND

Intensity-modulated radiation therapy (IMRT) is a novel approach to the planning and delivery of radiation therapy. The prevalence of IMRT use among radiation oncologists in the U.S. appears to be increasing, despite limited data evaluating its risks and benefits.

METHODS

A random sample of radiation oncologists in the U.S., including a cohort of 441 physicians who were surveyed in 2002, was surveyed regarding IMRT use. IMRT users were questioned regarding their frequency of use, clinical applications, and reasons for adopting IMRT. IMRT nonusers were asked their reasons for not using IMRT, whether they planned to use it in the future, and reasons for wanting to adopt IMRT. Differences in responses between 2002 and 2004 were compared.

RESULTS

The survey was conducted between July 1, 2004 and August 31, 2004. Of 368 evaluable participants, 239 physicians (64.9%) responded. The proportion of respondents who used IMRT was 73.2% (175 physicians), compared with 32.0% in 2002. The adoption rate of IMRT among nonusers from 2002 to 2004 was 62.7% (95% confidence interval, 51.9-73.5%). Many IMRT users (81.0%) had used IMRT to deliver higher than conventional doses of radiation, predominantly in patients with genitourinary and head and neck tumors. Major reasons cited for IMRT adoption were permitting normal tissue sparing (88.0%), dose escalation (85.1%), and economic competition (62.4%). Ninety-one percent of nonusers planned to adopt IMRT in the future.

CONCLUSIONS

IMRT use among radiation oncologists in the U.S. has increased significantly since 2002. Standardized guidelines and careful, prospective analyses evaluating its risks and benefits are needed.

Solid tumor risks after high doses of ionizing radiation

There is increasing concern regarding radiation-related second-cancer risks in long-term radiotherapy survivors and a corresponding need to be able to predict cancer risks at high radiation doses. Although cancer risks at moderately low radiation doses are reasonably understood from atomic bomb survivor studies, there is much more uncertainty at the high doses used in radiotherapy. It has generally been assumed that cancer induction decreases rapidly at high doses due to cell killing. However, recent studies of radiation-induced second cancers in the lung and breast, covering a very wide range of doses, contradict this assumption. A likely resolution of this disagreement comes from considering cellular repopulation during and after radiation exposure. Such repopulation tends to counteract cell killing and accounts for the large discrepancies between the current standard model for cancer induction at high doses and recent second-cancer data. We describe and apply a biologically based minimally parameterized model of dose-dependent cancer risks, incorporating carcinogenic effects, cell killing, and, additionally, proliferation/repopulation effects. Including stem-cell repopulation leads to risk estimates consistent with high-dose second-cancer data. A simplified version of the model provides a practical and parameter-free approach to predicting high-dose cancer risks, based only on data for atomic bomb survivors (who were exposed to lower total doses) and the demographic variables of the population of interest. Incorporating repopulation effects provides both a mechanistic understanding of cancer risks at high doses and a practical methodology for predicting cancer risks in organs exposed to high radiation doses, such as during radiotherapy.

Energy modulated electron therapy using a few leaf electron collimator in combination with IMRT and 3D-CRT: Monte Carlo-based planning and dosimetric evaluation

Energy modulated electron therapy (EMET) based on Monte Carlo dose calculation is a promising technique that enhances the treatment planning and delivery of superficially located tumors. This study investigated the application of EMET using a novel few-leaf electron collimator (FLEC) in head and neck and breast sites in comparison with three-dimensional conventional radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) techniques. Treatment planning was performed for two parotid cases and one breast case. Four plans were compared for each case: 3D-CRT, IMRT, 3D-CRT in conjunction with EMET (EMET-CRT), and IMRT in conjunction with EMET (EMET-IMRT), all of which were performed and calculated with Monte Carlo techniques. For all patients, dose volume histograms (DVHs) were obtained for all organs of interest and the DVHs were used as a means of comparing the plans. Homogeneity and conformity of dose distributions were calculated, as well as a sparing index that compares the effect of the low isodose lines. In addition, the whole-body dose equivalent (WBDE) was estimated for each plan. Adding EMET delivered with the FLEC to 3D-CRT improves sparing of normal tissues. For the two head and neck cases, the mean dose to the contralateral parotid and brain stem was reduced relative to IMRT by 43% and 84%, and by 57% and 71%, respectively. Improved normal tissue sparing was quantified as an increase in sparing index of 47% and 30% for the head and neck and the breast cases, respectively. Adding EMET to either 3D-CRT or IMRT results in preservation of target conformity and dose homogeneity. When adding EMET to the treatment plan, the WBDE was reduced by between 6% and 19% for 3D-CRT and by between 21% and 33% for IMRT, while WBDE for EMET-CRT was reduced by up to 72% when compared with IMRT. FLEC offers a practical means of delivering modulated electron therapy. Although adding EMET delivered using the FLEC results in perturbation of target conformity when compared to IMRT, it significantly improves normal tissue sparing while offering enhanced target conformity to the 3D-CRT planning. The addition of EMET systematically leads to a reduction in WBDE especially when compared with IMRT.

New insights on cell death from radiation exposure

Ionising radiation has been an important part of cancer treatment for almost a century, being used in external-beam radiotherapy, brachytherapy, and targeted radionuclide therapy. At the molecular and cellular level, cell killing has been attributed to deposition of energy from the radiation in the DNA within the nucleus, with production of DNA double-strand breaks playing a central part. However, this DNA-centric model has been questioned because cell-death pathways, in which direct relations between cell killing and DNA damage diverge, have been reported. These pathways include membrane-dependent signalling pathways and bystander responses (when cells respond not to direct radiation exposure but to the irradiation of their neighbouring cells). New insights into mechanisms of these responses coupled with technological advances in targeting of cells in experimental systems with microbeams have led to a reassessment of the model of how cells are killed by ionising radiation. This review provides an update on these mechanisms.

[Radiation-induced infiltrating transitional cell carcinoma]

INTRODUCTION

The increased risk of developing a transitional cell carcinoma (TCC) among patients irradiated for other pathologies in a known fact, but many times forgotten due to its low incidence. Our aim is to review the association between radiotherapy (RT) and muscle-infiltrating TCC among our patients.

MATERIAL AND METHODS

Clinical survey among our muscle-infiltrating TCC data base since 1975. Descriptive analysis of found cases.

RESULTS

We found 5 patients who developed muscle-infiltrating TCC with a mean time of 19.2 years since radiotherapy (three of them more than 20 years and the other two less than 10 years). Three patients also developed other tumours or pathologies related to radiotherapy. Two of them had an upper tract muscle-infiltrating TCC and required nephroureterectomy. All of them had high risk TCC of the bladder and one developed distant metastasis.

CONCLUSIONS

Patients under abdomino-pelvic RT and a prolongued follow-up, can be considered a risk group for developing muscle-infiltrating TCC. Thus, either micro or macrohaematuria or irritative symptoms should lead us to think in this possibility, demanding complete and exhaustive study to rule out TCC in all the urothelium.

Importance of protocol target definition on the ability to spare normal tissue: An IMRT and 3D-CRT planning comparison for intraorbital tumors

PURPOSE

We selected five intraorbital tumor sites that are frequently found in clinical practice in children diagnosed with orbital rhabdomyosarcoma and performed three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated photon radiotherapy (IMRT) planning. Results of target coverage and doses to critical structures were compared. The goal of this study was to evaluate and to document realistic expectations as to organ-sparing capabilities of modern radiation therapy planning technologies with a focus on lens-sparing irradiation. Furthermore, we investigated potential added benefits of IMRT compared with 3D-CRT and the influence of protocol volume criteria definitions on the ability to obtain normal tissue dose sparing using the orbit as an example of a complex anatomic site.

METHODS AND MATERIALS

The five intraorbital tumor sites were placed retrobulbar, temporal, nasal, in the upper inner and upper outer quadrant, the latter two more complex in shape. Gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV) were defined in image-fused computed tomography and magnetic resonance data sets. 3D-CRT and IMRT photon plans, using equal beam angles and collimation for direct comparison, were designed to 45 Gy prescription dose according to Intergroup Rhabdomyosarcoma Study Group-D9602 (IRSG-D9602) protocol (Intergroup Rhabdomyosarcoma Study V [IRS-V] protocol) for Stage I, Clinical Group 3 orbital rhabdomyosarcoma. To compare the impact of changed target definitions in IMRT planning, additional IMRT plans were generated using modified volume and dose coverage criteria. The minimum dose constraint (95%) of the PTV was substituted by a required minimum volume coverage (95%) with the prescribed dose. Dose-volume histograms (DVHs) were obtained, including target volumes, lens, optic nerves, optic chiasm, lacrimal gland, bony orbit, pituitary gland, frontal and temporal lobes.

RESULTS

Protocol target volume coverage criteria were fulfilled in all cases (5/5) with 3D-CRT and IMRT. Using the protocol criteria, lens sparing was achieved only for two tumor sites (retrobulbar and lateral position) with either planning technique. Mean lens doses were 8.5 and 10.4 Gy for 3D-CRT and 7.5 and 13.2 Gy for IMRT, respectively. The mean lens doses for the other three tumor locations averaged 26.8 Gy. IMRT plans reduced the lens dose in four of five cases by an average of 2.6 Gy compared with 3D-CRT. Modified target protocol prescription markedly reduced mean lens doses by 23-50% and by as much as 18 Gy. Recorded mean lens doses after protocol modification were 26% lower using IMRT plans compared with 3D-CRT. The cold spot as a result of the relaxed volume coverage requirements was within 2% of the original protocol criteria and located at the edge of the PTV, outside the CTV. Compared with 3D-CRT, IMRT resulted in an increase of brain volume receiving 10% (V10) and 20% (V20) of the prescribed dose.

CONCLUSION

Strict adherence to IRS-V protocol criteria prohibits at present lens sparing within compliance criteria for the majority of intraorbital tumor locations because of protocol-specific CTV and PTV target definitions. Changing protocol definitions by prescribing to the volume rather than to a dose constraint, IMRT planning significantly reduced lens doses. This was not accomplished to the same degree with 3D-CRT. Our study underlines the importance of appropriate selection of planning objectives to maximize the specific capabilities and advantages of IMRT in terms of sufficient target coverage and simultaneous sparing of critical structures. Our results can add to the ongoing discussion in the design of future 3D-CRT/IMRT protocols.

Helical tomotherapy radiation leakage and shielding considerations

Leakage radiation and room shielding considerations increase significantly for intensity-modulated radiation therapy (IMRT) treatments due to the increased beam-on time to deliver modulated fields. Tomotherapy, with its slice by slice approach to IMRT, further exacerbates this increase. Accordingly, additional shielding is used in tomotherapy machines to reduce unwanted radiation. The competing effects of the high modulation and the enhanced shielding were studied. The overall room leakage radiation levels are presented for the continuous gantry rotations, which are always used during treatments. The measured leakage at 4 m from the isocenter is less than 3 x 10(-4) relative to calibration output. Primary radiation exposure levels were investigated as well. The effect of forward-directed leakage through the beam-collimation system was studied, as this is the leakage dose the patient would receive in the course of a treatment. A 12-min treatment was calculated to produce only 1% patient leakage dose to the periphery region. Longer treatment times might yield less patient dose if the field width selected is correspondingly narrower. A method for estimating the worst-case leakage dose a patient would receive is presented.

Risk factors for developing a second upper aerodigestive cancer after radiotherapy with or without chemotherapy in patients with head-and-neck cancers: An exploratory outcomes analysis

PURPOSE

The objective was to assess the influence of treatment-related and patient-related factors on the risk of developing a second primary tumor (SPT) of the upper aerodigestive tract (UADT) in patients with locoregionally advanced nonmetastatic carcinomas of the head-and-neck region.

METHODS AND MATERIALS

The data of 521 patients with a minimum follow-up of 1 year were pooled: 224 patients from the Swiss Group for Clinical Cancer Research (SAKK) 10/94 trial, treated with 1.2 Gy b.i.d. to 74.4 Gy, and randomized to receive or not to receive simultaneous chemotherapy with cisplatin (excluding nasopharyngeal and maxillary sinus carcinomas); and 297 patients from Geneva, all treated with accelerated radiotherapy with concomitant boost to 69.9 Gy and predominantly cisplatin-based concomitant chemotherapy in 33% of patients (including 21 patients with nasopharyngeal carcinomas). An exploratory analysis using competing risk methodology was performed.

RESULTS

A total of 65 SPT of the UADT were observed after a median observation time of 4.7 years. The overall risk of experiencing an SPT of the UADT at 10 years in the presence of all other possible events was estimated to be 33%. There were no SPTs after treatment for nasopharyngeal carcinoma. In a multivariate logistic regression analysis, there was no difference in occurrence of SPT at 3 years with respect to the administration of chemotherapy (p = 0.31), age (p = 0.62), performance status (p = 0.61), gender (p = 0.27), presence of nodal disease (p = 0.51), or T stage (p = 0.72). However, patients treated with concomitant boost had fewer SPTs (p = 0.0093).

CONCLUSIONS

Our data do not suggest that addition of chemotherapy to radiotherapy influences the incidence of second cancers in patients with head-and-neck cancer. The difference in the incidence of SPT between the two radiotherapy schedule groups merits further exploration.

BLADDER CANCER RISK FOLLOWING PRIMARY AND ADJUVANT EXTERNAL BEAM RADIATION FOR PROSTATE CANCER

PURPOSE

Increased rates of secondary bladder malignancies have been reported after external beam radiation therapy (EBRT) for gynecological malignancies with relative risks of 2 to 4. This study was designed to determine if there was an increase in bladder cancer after EBRT for prostate cancer.

MATERIALS AND METHODS

We retrospectively reviewed the Mayo Clinic Cancer Registry for patients who received EBRT for prostate cancer (1980 to 1998). Patients diagnosed with bladder cancer were identified. Comparative incidence rates were obtained from the national Surveillance, Epidemiology and End Results database. Subset analysis included patients treated with adjuvant radiation and those residing locally. Medical histories of patients with bladder cancer were reviewed.

RESULTS

A total of 1,743 patients received EBRT for prostate cancer at our institution. In more than 12,353 man-years of followup no increase in bladder cancer risk was encountered. Subset analysis of men who received adjuvant radiation demonstrated that the relative risk of bladder cancer was increased but was not statistically significant. When the analysis was restricted to patients residing in the local area, the number of patients in whom subsequent bladder cancer developed was similar to Surveillance, Epidemiology and End Results rates. However, in the adjuvant radiation subset there was a statistically significant increase in subsequent bladder cancer. Patients in whom bladder cancer develops after EBRT often present with low grade disease but many have recurrence and progression.

CONCLUSIONS

This retrospective review suggests there is not evidence of increased risk of bladder cancer after radiation therapy, assuming unbiased followup and complete ascertainment of cases. The natural history of bladder cancer in this population does not seem to be altered by a history of radiation.

Feasibility of cranio-spinal axis radiation with the Hi-Art tomotherapy system

BACKGROUND AND PURPOSE

Helical tomotherapy can eliminate the need for junction lines. The goal of this study is to evaluate tomotherapy in the delivery of CSA radiation and measurement of plan quality using physical parameters in comparing conventional (CSA-RT) and helical tomotherapy (CSA-TOMO) plans.

PATIENTS AND METHODS

CSA-TOMO and CSA-RT plans were created for dosimetric comparison. Integral dose values were calculated. The ratios D50% (dose received by 50% of the organ at risk's volume) and D10% (dose received by 10% of the organ at risk's volume) were calculated representing large volumes and small volumes of organs at risk receiving significant dose.

RESULTS

When considering D50% and D10%, CSA-TOMO has a dosimetric advantage over CSA-RT for most organs at risk. The body integral dose was higher for the CSA-TOMO plan by approximately 6.5%.

CONCLUSIONS

Tomotherapy is a feasible alternative for treatment of CSA. Analysis shows that tomotherapy improves dose ratios over conventional radiation for most organs at risk. The impact of a small increase in whole body integral dose is unknown. Long-term follow-up will be needed to answer this question as others have argued of the possibility of increased risk of secondary malignancies due to delivery of radiotherapy with IMRT.

The calculated risk of fatal secondary malignancies from intensity-modulated radiation therapy

PURPOSE

Out-of-field radiation doses to normal tissues may be associated with an increased risk of secondary malignancies, particularly in long-term survivors. Step-and-shoot intensity-modulated radiation therapy (IMRT), an increasingly popular treatment modality, yields higher out-of-field doses than do conventional treatments, because of an increase in required monitor units (beam-on time).

METHODS

We used published risk coefficients (NRCP Report 116) and out-of-field dose equivalents to multiple organ sites to estimate a conservative maximal risk of fatal secondary malignancy associated with 6 IMRT approaches and 1 conventional external-beam approach for prostate cancer.

RESULTS

Depending on treatment energy, the IMRT treatments required 3.5-4.9 times as many monitor units to deliver as did the conventional treatment. The conservative maximum risk of fatal second malignancy was 1.7% for conventional radiation, 2.1% for IMRT using 10-MV X-rays, and 5.1% for IMRT using 18-MV X-rays. Intermediate risks were associated with IMRT using 6-MV X-rays: 2.9% for treatment with the Varian accelerator and 3.7% for treatment with the Siemens accelerator, as well as using 15-MV X-rays: 3.4% (Varian) and 4.0% (Siemens).

CONCLUSION

The risk of fatal secondary malignancy differed substantially between IMRT and conventional radiation therapy for prostate cancer, as well as between different IMRT approaches. Perhaps this risk should be considered when choosing the optimal treatment technique and delivery system for patients who will undergo prostate radiation.

Intensity-modulated radiation therapy: emerging cancer treatment technology

The use of intensity-modulated radiation therapy (IMRT) is rapidly advancing in the field of radiation oncology. Intensity-modulated radiation therapy allows for improved dose conformality, thereby affording the potential to decrease the spectrum of normal tissue toxicities associated with IMRT. Preliminary results with IMRT are quite promising; however, the clinical data is relatively immature and overall patient numbers remain small. High-quality IMRT requires intensive physics support and detailed knowledge of three-dimensional anatomy and patterns of tumour spread. This review focuses on basic principles, and highlights the clinical implementation of IMRT in head and neck and prostate cancer.

Proton radiotherapy for orbital rhabdomyosarcoma: clinical outcome and a dosimetric comparison with photons

BACKGROUND

Over 85% of pediatric orbital rhabdomyosarcoma (RMS) are cured with combined chemotherapy and radiation. However, the late effects of photon radiation compromise function and cosmetic outcome. Proton radiation can provide excellent tumor dose distributions while sparing normal tissues better than photon irradiation.

METHODS AND MATERIALS

Conformal 3D photon and proton radiotherapy plans were generated for children treated with proton irradiation for orbital RMS at Massachusetts General Hospital. Dose-volume histograms (90%, 50%, 10%) were generated and compared for important orbital and central nervous system structures. Average percentages of total dose prescribed were calculated based on the 3 dose-volume histogram levels for normal orbital structures for both the proton and photon plans. The percent of normal tissue spared by using protons was calculated.

RESULTS

Seven children were treated for orbital rhabdomyosarcoma with proton irradiation and standard chemotherapy. The median follow-up is 6.3 years (range, 3.5-9.7 years). Local and distant controls compare favorably to those in other published accounts. There was an advantage in limiting the dose to the brain, pituitary, hypothalamus, temporal lobes, and ipsilateral and contralateral orbital structures. Tumor size and location affect the degree of sparing of normal structures.

CONCLUSIONS

Fractionated proton radiotherapy is superior to 3D conformal photon radiation in the treatment of orbital RMS. Proton therapy maintains excellent tumor coverage while reducing the radiation dose to adjacent normal structures. Proton radiation therapy minimizes long-term side effects.

Radiation as a Nervous System Toxin

Neurotoxicity from radiation can range widely and produce effects that may include (1) small absolute increases in cancer risks, (2) subtle effects on higher level functioning in some individuals, (3) severe cognitive impairment in some individuals, (4) severe focal injury tat may include necrosis or irreversible loss of function, and (5) overwhelming and rapidly fatal diffuse injury associated with high-dose, whole-body exposures. An understanding of the implications of nervous system exposure to radiation can guide efforts in radiation protection and aid in the optimization of the medical uses of radiation.

IMRT with the sliding window: comparison of the static and dynamic methods. Dosimetric and spectral analysis

BACKGROUND AND PURPOSE

Aim of the study is the critical appraisal of the two delivery techniques for intensity-modulated treatments commonly known as dynamic and static step and shoot, in the framework of a sliding window multileaf sequencing method.

METHODS

The study was performed using the solution commercialised by Varian with the Eclipse treatment planning system (TPS) and the Clinac accelerator. For a set of intensity modulated fluences, the calculated dose maps and the dose delivered to films were compared for the static and dynamic modes to verify the capability of the TPS to accurately model both the delivery modes. For these investigations, the gamma concept of Low et al. [Low D, Harms W, Mutic S, Purdy J. A technique for the quantitative evaluation of dose distributions. Med Phys 1998;25: 656-60] was applied demonstrating, in general, optimal modeling for both static and dynamic tests. Optimal and actual fluences, were analysed to ascertain the degree of the TPS accuracy in converting 'ideal' maps into realistic leaf motions.

RESULTS

Among the methods used, the Webb's Modulation Index [Webb S. Use of a quantitative index of beam modulation to characterize dose conformality: illustration by a comparison of full beamlet IMRT, few-segment IMRT and conformal unmodulated radiotherapy. Phys Med Biol. 2003;48: 2051-2062] proved to be useful. Also, dose volume histogram analysis was applied on deliverable plans using more clinical tools.

CONCLUSION

The dynamic delivery method seems to offer a more reliable agreement with the optimal calculations and, clinically, a slightly superior performance in terms of target coverage.

Improving IMRT delivery efficiency using intensity limits during inverse planning

Inverse planned intensity modulated radiotherapy (IMRT) fields can be highly modulated due to the large number of degrees of freedom involved in the inverse planning process. Additional modulation typically results in a more optimal plan, although the clinical rewards may be small or offset by additional delivery complexity and/or increased dose from transmission and leakage. Increasing modulation decreases delivery efficiency, and may lead to plans that are more sensitive to geometrical uncertainties. The purpose of this work is to assess the use of maximum intensity limits in inverse IMRT planning as a simple way to increase delivery efficiency without significantly affecting plan quality. Nine clinical cases (three each for brain, prostate, and head/neck) were used to evaluate advantages and disadvantages of limiting maximum intensity to increase delivery efficiency. IMRT plans were generated using in-house protocol-based constraints and objectives for the brain and head/neck, and RTOG 9406 dose volume objectives in the prostate. Each case was optimized at a series of maximum intensity ratios (the product of the maximum intensity and the number of beams divided by the prescribed dose to the target volume), and evaluated in terms of clinical metrics, dose-volume histograms, monitor units (MU) required per fraction (SMLC and DMLC delivery), and intensity map variation (a measure of the beam modulation). In each site tested, it was possible to reduce total monitor units by constraining the maximum allowed intensity without compromising the clinical acceptability of the plan. Monitor unit reductions up to 38% were observed for SMLC delivery, while reductions up to 29% were achieved for DMLC delivery. In general, complicated geometries saw a smaller reduction in monitor units for both delivery types, although DMLC delivery required significantly more monitor units in all cases. Constraining the maximum intensity in an inverse IMRT plan is a simple way to improve delivery efficiency without compromising plan objectives.

Intensity-modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation: initial report

PURPOSE

This study was designed to compare the dose received by the contralateral breast during primary breast irradiation using intensity-modulated radiotherapy with the dose received via conventional tangential field techniques.

METHODS/MATERIALS

Between March 2003 and March 2004, 44 patients with breast carcinoma were treated using 6-, 10-, or mixed 6/18-MV photons(36 with tangential intensity-modulated radiotherapy technique and eight with three-dimensional technique using tangential fields with wedges) for primary breast irradiation after breast-conserving surgery. Paired thermoluminescent dosimeters were placed on each patient's contralateral breast, 4 cm from the center of the medial border of the tangential field. The thermoluminescent dosimeters were left on the patient during a single fraction and then measured 24 hours later.

RESULTS

The mean dose delivered with photons to the primary breast for all patients was 4998 cGy [SD = 52], and the mean single fraction dose was 200 cGy [SD = 9]. The mean percent of the prescribed dose to the contralateral breast was 7.74% (SD = 2.35) for patients treated with intensity-modulated radiotherapy, compared with 9.74% [SD = 2.04] for the patients treated with conventional tangential field techniques. This represented a 20% reduction in the mean dose to the contralateral breast with the use of intensity-modulated radiotherapy when compared with the dose received via the three-dimensional technique, a result that was statistically significant.

CONCLUSION

Primary breast irradiation with tangential intensity-modulated radiotherapy technique significantly reduces the dose to the contralateral breast when compared with conventional tangential techniques.

Estimation of radiation-induced cancer from three-dimensional dose distributions: Concept of organ equivalent dose

PURPOSE

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional dose distributions for each individual patient. These data open up new possibilities for more precise estimates of secondary cancer incidence rates in the irradiated organs. We report a new method to estimate organ-specific radiation-induced cancer incidence rates. The concept of an organ equivalent dose (OED) for radiation-induced cancer assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer incidence.

METHODS AND MATERIALS

The two operational parameters of the OED concept are the organ-specific cancer incidence rate at low doses, which is taken from the data of the atomic bomb survivors, and cell sterilization at higher doses. The effect of cell sterilization in various organs was estimated by analyzing the secondary cancer incidence data of patients with Hodgkin's disease who were treated with radiotherapy in between 1962 and 1993. The radiotherapy plans used at the time the patients had been treated were reconstructed on a fully segmented whole body CT scan. The dose distributions were calculated in individual organs for which cancer incidence data were available. The model parameter that described cell sterilization was obtained by analyzing the dose and cancer incidence rates for the individual organs.

RESULTS

We found organ-specific cell radiosensitivities that varied from 0.017 for the mouth and pharynx up to 1.592 for the bladder. Using the two model parameters (organ-specific cancer incidence rate and the parameter characterizing cell sterilization), the OED concept can be applied to any three-dimensional dose distribution to analyze cancer incidence.

CONCLUSION

We believe that the concept of OED presented in this investigation represents a first step in assessing the potential risk of secondary cancer induction after the clinical application of radiotherapy.

Radiotherapy for nasopharyngeal carcinoma--transition from two-dimensional to three-dimensional methods

This review describes the clinical background that underlies the transition from two-dimensional to three-dimensional (3D) planning techniques in the treatment of nasopharyngeal cancer (NPC). A systematic search of the Medline was performed using 'nasopharyngeal carcinoma', 'radiotherapy', '3-dimensional conformal radiotherapy', 'stereotactic radiosurgery/radiotherapy' and 'intensity-modulated radiotherapy' as keywords. Citing evidence from the published literature and their own institutional experience, the authors critically examined the positive impact of 3D methods--with emphasis on intensity-modulated radiotherapy (IMRT)--on target coverage and geometric accuracy, sparing of normal organs, and dosimetric homogeneity. Potential problems related to the widespread practice of IMRT such as quality assurance, utilization of medical resources and the risk of developing radiation-induced secondary cancers were highlighted. Application of IMRT within the context of altered fractionation, dose escalation and concurrent chemotherapy were discussed. The article concluded with a suggested treatment approach and research direction for different stages of NPC.

Hybrid IMRT plans—concurrently treating conventional and IMRT beams for improved breast irradiation and reduced planning time

PURPOSE

To evaluate a hybrid intensity modulated radiation therapy (IMRT) technique as a class solution for treatment of the intact breast.

METHODS AND MATERIALS

The following five plan techniques were compared for 10 breast patients using dose-volume histogram analysis: conventional wedged-field tangents (Tangents), forward-planned field-within-a-field tangents (FIF), IMRT-only tangents (IMRT tangents), conventional open plus IMRT tangents (4-field hybrid), and conventional open plus IMRT tangents with 2 anterior oblique IMRT beams (6-field hybrid).

RESULTS

The 4-field hybrid and FIF achieved dose distributions better than Tangents and IMRT tangents. The volume of tissue outside the planning target volume receiving > or =110% of prescribed dose was largest for IMRT tangents (average 158 cc) and least for 6-field hybrid (average 1 cc); the FIF and 4-field hybrid were comparable (average 15 cc). Heart volume > or =30 Gy averaged 13 cc for all techniques, except Tangents, for which it was 32 cc. Average total lung volume > or =20 Gy was 7% for all. Contralateral breast doses were < 3% for all. Planning time for hybrid techniques was significantly less than for conventional FIF technique.

CONCLUSIONS

The 4-field hybrid technique is a viable class solution. The 6-field hybrid technique creates the most conformal dose distribution at the expense of more normal tissue receiving low dose.

Dose volume histogram comparison between ADAC Pinnacle and Nomos Corvus systems for IMRT

This paper compares dose volume histograms (DVHs) generated by the ADAC Pinnacle and the Nomos Corvus planning systems. Seven prostate cases and seven head and neck cases were selected for review. Plans computed on both systems possessed exactly the same anatomical contours and IMRT segments. The Pinnacle system used the collapsed cone convolution superposition, while Corvus employed a finite size pencil beam (FSPB) convolution. Prostate DVH results demonstrated similar DVH curves from both systems. For each structure, the ratio of Pinnacle dose value divided by Corvus value was calculated. The high dose structures (which might contain tumour) had ratios close to unity, while the low dose structures (the critical organs) had ratios farther away from unity. Almost all ratios were less than unity, indicating a systematic difference that Pinnacle calculated doses were lower than Corvus ones. Head and neck data provided similar findings. A possible cause for this discrepancy could be the beam modelling. The difference in DVH parameters that we discovered between the two systems was about the same order of magnitude as the measurement-computation difference. When low dose is critical, such difference may affect the clinical planning decision.

Intensity Modulated Radiation Therapy in Head and Neck Squamous Cell Carcinoma: state of the art and future challenges

Intensity-modulated radiation therapy (IMRT) for head and neck (HN) tumors refers to a new approach to the whole treatment procedure from patient immobilization to beam delivery. Implementation of IMRT thus requires knowledge of setup uncertainties, adequate selection and delineation of target volumes based on clinical examination and optimal imaging modalities, appropriate specification and dose prescription regarding dose-volume constraints, and ad hoc quality control of both the clinical and physical aspects of the whole procedure. A large number of issues still need to be resolved and/or further refined, such as the optimal selection and delineation of the target volume in particular, with the introduction of functional imaging, and a better integration of improved dose distribution into the fractionation strategy. IMRT is associated with a potentially increased incidence of carcinogenesis, although in the HN area this risk is relative to the intrinsic risk of co-morbidity and secondary cancer associated with the patient's lifestyle. Currently, the implementation of IMRT into routine clinical practice for HN cancers may not be a straightforward matter, and should probably be restricted to selected patients and selected institutions with adequate resources and experience. This review emphasizes the above aspects and provides some recommendations for the future use of IMRT in patients with HN tumors.

Theragnostic imaging for radiation oncology: dose-painting by numbers

Theragnostic imaging for radiation oncology is the use of molecular and functional imaging to prescribe the distribution of radiation in four dimensions-the three dimensions of space plus time-of radiotherapy alone or combined with other treatment modalities in an individual patient. Several new imaging targets for positron-emission tomography, single-photon-emission CT, and magnetic resonance spectroscopy allow variations in microenvironmental or cellular phenotypes that modulate the effect of radiation to be mapped in three dimensions. Dose-painting by numbers is a strategy by which the dose distribution delivered by inverse planned intensity-modulated radiotherapy is prescribed in four dimensions. This approach will revolutionise the way that radiotherapy is prescribed and planned and, at least in theory, will improve the therapeutic outcome in terms of local tumour control and side-effects to unaffected tissue.

[Intensity modulated radiotherapy (IMRT) of head and neck tumors. Increased biological effectiveness in high-risk situations by "integrated boost" therapy]

Primary tumors of the paranasal sinuses are rare entities which, because of precarious localization and frequently diffuse propagation into neighbouring cavities and the skull base, pose a significant therapeutic problem. Even after complete surgical resection, local relapses are frequent. Postoperative radiotherapy is therefore usually indicated. Intensity modulated radiotherapy (IMRT) is a new technique that helps creating dose distributions that conform closely to the target volume while maximally sparing the organs at risk. This results in the possibility of applying escalated doses to the target while still keeping the incidence of side effects low. What is especially appealing is the possibility of shaping the dose distribution within the target in such a way that areas with a presumably high tumor cell load receive increased doses, a concept which is best described by the term "integrated boost". We present the case of a patient with a sinunasal carcinoma and describe the implications of the clinical implementation of this technique.

A simple dose-response relationship for modeling secondary cancer incidence after radiotherapy* *Parts of this work were presented at the 15th annual NASA space radiation health investigators' workshop; May 2004, Port Jefferson, USA

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. There is great uncertainty concerning the dose-response relationship for radiation-induced carcinogenesis at doses higher than 4 Gy. The purpose of this report is to determine a simple dose-response relationship for secondary cancer incidence after radiotherapy treatment which can be used for comparative treatment planning. In this report a simple one-parameter model to estimate the complication probability of secondary cancer was fitted to literature data on secondary cancer incidence after radiotherapy. The results showed a linear dose-response relationship in the low-dose part and an exponentially decreasing one after a maximum at around 10 Gy. The observed dose-response relationship and the literature data used to fit the dose-response indicate that cell death effects are important for the explanation of secondary cancer incidence. Even using a dose and dose-rate effectiveness factor (DDREF) of two (instead of one), a cancer incidence maximum is observed at around 10 Gy, with decreasing incidence at higher doses.

Biologic comparison of partial breast irradiation protocols

PURPOSE

To analyze the dose/fractionation schedules currently used in ongoing clinical trials of partial breast irradiation (PBI) by comparing their biologically effective dose (BED) values to those of three standard whole breast protocols commonly used after segmental mastectomy in the treatment of breast cancer.

METHODS AND MATERIALS

The BED equation derived from the linear-quadratic model for radiation-induced cell killing was used to calculate the BEDs for three commonly used whole breast radiotherapy regimens, in addition to a variety of external beam radiotherapy, as well as high-dose-rate and low-dose-rate brachytherapy, PBI protocols.

RESULTS

The BED values of most PBI protocols resulted in tumor control BEDs roughly equivalent to a 50-Gy standard treatment, but consistently lower than the BEDs for regimens in which the tumor bed receives a total dose of either 60 Gy or 66 Gy. The BED values calculated for the acute radiation responses of erythema and desquamation were nearly all lower for the PBI schedules, and the late-response BEDs for most PBI regimens were in a similar range to the BEDs for the standard treatments.

CONCLUSION

Biologically effective dose modeling raises the concern that inadequate doses might be delivered by PBI to ensure optimal in-field tumor control.

Protons versus photons: A status assessment at the beginning of the 21st century

At present modern photon delivery techniques permit high dose isodose conformality similar to protons in many cases. However, a proton advantage appears to still be present for target volumes of higher degrees of complexity and concavity. Also, for selected histologies and sites, notably skull base tumors, protons have established a "gold standard" and photon data have yet to duplicate those proton results in clinical practice. Proton radiation therapy offers superior dose distribution by reduced low-dose integral irradiated volume. The avoidance of functional and cosmetic side effects in children by protons is at present acknowledged by the radiation oncology community and is expected to gain similar recognition in adult patients. This advantage of protons and disadvantage for photons constitutes an "inherent physical gap" that will likely be long lasting. Although the priorities of proton irradiation advantages have shifted over the decades, clinical advantages remain and are of sufficient significance and importance to justify further development and installation of proton radiation facilities worldwide.

Late effects from hadron therapy

Successful cancer patient survival and local tumor control from hadron radiotherapy warrant a discussion of potential secondary late effects from the radiation. The study of late-appearing clinical effects from particle beams of protons, carbon, or heavier ions is a relatively new field with few data. However, new clinical information is available from pioneer hadron radiotherapy programs in the USA, Japan, Germany and Switzerland. This paper will review available data on late tissue effects from particle radiation exposures, and discuss its importance to the future of hadron therapy. Potential late radiation effects are associated with irradiated normal tissue volumes at risk that in many cases can be reduced with hadron therapy. However, normal tissues present within hadron treatment volumes can demonstrate enhanced responses compared to conventional modes of therapy. Late endpoints of concern include induction of secondary cancers, cataract, fibrosis, neurodegeneration, vascular damage, and immunological, endocrine and hereditary effects. Low-dose tissue effects at tumor margins need further study, and there is need for more acute molecular studies underlying late effects of hadron therapy.

New radiation techniques in gynecological cancer

Radiation therapy has been a major therapeutic modality for eradicating malignant tumors over the past century. In fact, it was not long after the discovery of radium that the first woman with cervical cancer underwent intracavitary brachytherapy. Progress in the way that this cytotoxic agent is manipulated and delivered has seen an explosive growth over the past two decades with technological developments in physics, computing capabilities, and imaging. Although radiation oncologists are educated in and familiar with the wealth of new revolutionary techniques, it is not easy for other key members of the team to keep up with the rapid progress and its significance. However, to fully exploit these enormous gains and to communicate effectively, medical and gynecological oncologists are expected to be aware of state-of-the-art radiation oncology. Here, we elucidate and illustrate contemporary techniques in radiation oncology, with particular attention paid to the external beam radiotherapy used for adjuvant and primary definitive management of malignancies of the female pelvis.

Intensity-modulated radiation therapy in gynecologic malignancies

Radiation therapy occupies an important role in the treatment of gynecologic malignancies. Unfortunately, traditional approaches result in the irradiation of large volumes of normal tissues exposing patients to many toxicities and precluding dose escalation in select patients. A novel approach to the planning and delivery of radiation therapy, known as intensity-modulated radiation therapy (IMRT), has been introduced. Unlike conventional approaches, IMRT conforms the prescription dose to the shape of the target in three dimensions, thus sparing the surrounding normal tissues. Multiple studies have demonstrated the clear superiority of IMRT planning in these patients in terms of normal tissue sparing. Promising clinical results have also been published, suggesting that IMRT reduces the incidence of acute and chronic toxicity in these women. Ongoing studies are focusing on tumor control and patient outcome. Although further work is needed, these results suggest that IMRT may represent a major advancement in the planning and delivery of radiation therapy in patients with gynecologic malignancies.

Radiation-induced malignancies following radiotherapy for breast cancer

With advances in diagnosis and treatment, breast cancer is becoming an increasingly survivable disease resulting in a large population of long-term survivors. Factors affecting the quality of life of such patients include the consequences of breast cancer treatment, which may have involved radiotherapy. In this study, we compare the incidence of second primary cancers in women who received breast radiotherapy with that in those who did not (non-radiotherapy). All women studied received surgery for their first breast cancer. Second cancers of the lung, colon, oesophagus and thyroid gland, malignant melanomas, myeloid leukaemias and second primary breast cancers were studied. Comparing radiotherapy and non-radiotherapy cohorts, elevated relative risks (RR) were observed for lung cancer at 10–14 years and 15 or more (15+) years after initial breast cancer diagnosis (RR 1.62, 95% confidence interval [CI] 1.05–2.54 and RR 1.49, 95% CI 1.05–2.14, respectively), and for myeloid leukaemia at 1–5 years (RR 2.99, 95% CI 1.13–9.33), for second breast cancer at 5–10 years (RR 1.34, 95% CI 1.10–1.63) and 15+ years (RR 1.26, 95% CI 1.00–1.59) and oesophageal cancer at 15+ years (RR 2.19, 95% CI 1.10–4.62).

Conformal radiation therapy for childhood CNS tumors

Radiation therapy plays a central role in the management of many childhood brain tumors. By combining advances in brain tumor imaging with technology to plan and deliver radiation therapy, pediatric brain tumors can be treated with conformal radiation therapy. Through conformal radiation therapy, the radiation dose is targeted to the tumor, which can minimize the dose to normal brain structures. Therefore, by limiting the radiation dose to normal brain tissues, conformal radiation therapy offers the possibility of limiting the long-term side effects of brain irradiation.In this review, we describe different approaches to conformal radiation therapy for pediatric central nervous system tumors including: A) three-dimensional conformal radiation therapy; B) stereotactic radiation therapy with arc photons; C) intensity-modulated radiation therapy; and D) proton beam radiation therapy. We discuss the merits and limitations of these techniques and describe clinical scenarios in which conformal radiation therapy offers advantages over conventional radiation therapy for treating pediatric brain tumors.