Radiation Therapy Techniques and Dose Selection in the Treatment of Prostate Cancer

A dose response for local control of cancer of the prostate is shown, and normal tissue irradiated volume and complications are diminished with conformal radiation therapy techniques in prostate cancer. Refinements in techniques and technology, as well as phase II trials are underway. Should these studies prove dose escalation to be safe, a phase III trial comparing standard techniques and dose with conformal high dose radiotherapy is warranted for patients with adenocarcinoma of the prostate. If a phase III study is positive, then it will confirm that local control of prostate cancer can be improved with conformal therapy techniques without increasing the morbidity of treatment. However, if this is proven to be true only for institutions with highly specialized equipment, then this finding will have very little impact on the total treatment of prostate cancer or consequences of this disease. A truly successful trial will produce results that can be duplicated in modern radiation therapy centers that have conscientiously maintained current, but not necessarily esoteric technology; it is in the best interests of our patients and our colleagues to develop treatment technologies that can be implemented at all institutional strata.     

Uncertainties in radiation therapy: target volume definition in prostate cancer

Accurate definition of target volumes and pelvic organs at risk is critical to improve the outcome in patients treated with irradiation for localized carcinoma of the prostate. Precise delineation of these structures will assist in more rational therapeutic decisions and optimized radiation therapy treatment planning and delivery. Increased conformity in radiation dose distribution allows delivery of higher doses of irradiation and dose escalation studies and results in improved tumor control, lower incidence of distant metastasis, improved survival and better quality of life. Multiple imaging methods are available and significant advances have been made in image fusion to enhance target volume definition. An exhaustive review of the literature is presented.     

New radiotherapy technologies

Conventional radiation therapy has had limited success in curing inoperable lung cancer due to poor local control. There is evidence to suggest that higher doses of radiation will improve local control. In order to safely deliver higher doses of thoracic radiation, advanced treatment techniques are required. Different biologic indices have been utilized to determine whether dose escalation can be safely accomplished, and the results have been reported from many institutions. Tumor motion control aids in treatment since it allows radiation oncologists to more accurately target tumors and therefore to spare more normal tissue from the radiation field. The imaging information from 18-FDG-PET scans also improves target delineation. Advanced treatment delivery techniques, such as three-dimensional conformal radiation therapy, intensity modulated radiation therapy, and stereotactic radiosurgery are also being used to safely escalate the radiation dose. This article explores the current literature on these issues and other advanced radiation therapy techniques.     

Intensity modulated radiation therapy planning for patients with a metal hip prosthesis based on class solutions

PurposeWith the aging of the population, an increasing number of patients with metallic hip implants are referred for radiotherapy treatment. Class solutions for intensity modulated radiation therapy (IMRT) treatment planning are generally not applicable for these patients due to the required avoidance of dose delivery through prostheses. In this work a new approach for IMRT planning is presented, allowing the use of a default beam setup.Methods and MaterialsFor IMRT planning, Monaco (Elekta; CMS Software, Maryland Heights, MO) was used. In addition to the target and organs at risk, so-called prosthesis avoidance volumes (PAVs) were delineated in the beam's eye view projection for beams in which the prosthesis was partially in front of the target. By putting strict constraints on these virtual organs at risk, entrance dose delivery through a prosthesis is avoided while exit dose delivery is allowed. In this way, uncertainties in the dose delivery to the target and organs at risk, as derived by the treatment planning system, are largely minimized. To show the advantages of this IMRT-PAV technique, for 2 prostate cancer patients, 1 with bilateral and the other with unilateral metallic hip prostheses, obtained IMRT plans were compared with conventional IMRT plans using a prosthesis-avoiding beam setup.ResultsFor both IMRT techniques a similar planning target volume coverage was achieved, but with the IMRT-PAV technique the mean doses to the bladder and the rectum were reduced by up to 25%. While the IMRT-PAV technique required more time for delineation, the time for treatment planning reduced because the default beam setup could be applied. The number of segments needed for dose delivery was comparable for both techniques.ConclusionsWith the new IMRT-PAV technique IMRT class solutions can safely be applied for cancer patients with metallic hip prostheses, generally yielding a reduced dose delivery to organs at risk or improved target coverage.     

Small Cell Lung Cancer: The Influence of Dose and Treatment Volume on Outcome

The treatment of small cell lung cancer is clearly enhanced by the addition of radiation therapy. Survival increases modestly while local thoracic failure as first site of progression is reduced from approximately 60% when chemotherapy alone is used to 30% after combined modality therapy. The variables of radiation dose and treatment volume seem to be important in the successful management of this disease. Local chest control appears to increase as doses are escalated from low levels (25 Gy) to moderate levels (45 to 50 Gy(. With about one third of patients experiencing local chest progression, one can speculate that higher radiation doses might be of value. However, at this time there is no proof that increased dose or dose intensity bears out this promise. Indeed, increasing dose intensity of radiotherapy, eg, twice-daily treatment, increases esophagitis, perhaps reduces local failure, but has not improved overall survival. Using larger total doses or altered fraction schemes must still be considered to be under investigation. To increase dose in a safe manner, reduction in the volume covered by radiation portals will likely need to take place. Modern trials suggest that prophylactic treatment of the radiographically or clinically negative contralateral hilum and/or supraclavicular nodal regions may not be necessary for survival or local control. Importantly, reducing treatment volumes may permit increasing doses without exceding normal tissue tolerance. Also, reduced volumes pave the way for further clinical trials that improve radiation dose delivery by better target definition and more conformal therapy.     

Feasibility of the partial-single arc technique in RapidArc planning for prostate cancer treatment

The volumetric modulated arc therapy(VMAT)technique,in the form of RapidArc,is widely used to treat prostate cancer.The full-single arc(f-SA)technique in RapidArc planning for prostate cancer treatment provides efficient treatment,but it also delivers a higher radiation dose to the rectum.This study aimed to compare the dosimetric results from the new partial-single arc(p-SA)technique with those from the f-SA technique in RapidArc planning for prostate cancer treatment.In this study,10 patients with lowrisk prostate cancer were selected.For each patient,two sets of RapidArc plans(f-SA and p-SA)were created in the Eclipse treatment planning system.The f-SA plan was created using one full arc,and the p-SA plan was created using planning parameters identical to those of the f-SA plan but with anterior and posterior avoidance sectors.Various dosimetric parameters of the f-SA and p-SA plans were evaluated and compared for the same target coverage and identical plan optimization parameters.The f-SA and p-SA plans showed an average difference of±1%for the doses to the planning target volume(PTV),and there were no clear differences in dose homogeneity or plan conformity.In comparison to the f-SA technique,the p-SA technique reduced the doses to the rectum by approximately 6.1%to 21.2%,to the bladder by approximately 10.3%to 29.5%,and to the penile bulb by approximately 2.2%.In contrast,the dose to the femoral heads,the integral dose,and the number of monitor units were higher in the p-SA plans by approximately 34.4%,7.7%,and 9.2%,respectively.In conclusion,it is feasible to use the p-SA technique for RapidArc planning for prostate cancer treatment.For the same PTV coverage and identical plan optimization parameters,the p-SA technique is better in sparing the rectum and bladder without compromising plan conformity or target homogeneity when compared to the f-SA technique.     

Technological advances in radiotherapy for the treatment of localised prostate cancer

There is good evidence that radiation dose escalation in localised prostate cancer is associated with increased cell kill. The traditional two-dimensional (2D) technique of treatment planning and delivery is limited by normal tissue toxicity, such that the dose that can be safely delivered to the prostate by external beam radiotherapy is 65-70 Gy. Several technological advances over the last 20 years have enhanced the precision of external beam radiotherapy (EBRT), and have resulted in improved outcomes. The three-dimensional conformal radiotherapy (3D-CRT) approach reduces the dose-limiting late side-effect of proctitis and has allowed for dose escalation to the whole prostate to 78 Gy. More recently, intensity modulated radiotherapy (IMRT), an advanced form of conformal therapy, has resulted in reduced rectal toxicity when using doses greater than 80 Gy. In addition, IMRT can potentially escalate the dose to specific parts of the prostate where there are resistant subpopulations of tumour clonogens, or can be used to extend the high-dose region to pelvic lymph nodes. The addition of androgen deprivation to conventional radiotherapy has an impact on survival and local control. Initial hormone therapy causes cytoreduction of the prostate cancer allowing for a reduction in radiotherapy volume as well as an additive effect on cell kill. Long-term adjuvant androgen deprivation has been shown to improve overall survival in more advanced tumours. Prostate brachytherapy is now a recognised treatment for those with low-risk disease. It achieves similar long-term outcome to other treatment modalities. Brachytherapy can be used as monotherapy for localised disease, or as boost treatment following conventional EBRT for locally advanced disease. New techniques are available to improve the precision of both target definition and treatment verification. This so-called image-guided radiotherapy will help to enhance the accuracy of dose delivery by correcting both for inter-fraction positional variation and for intra-fraction movement of the prostate in real-time and will allow for tighter tumour margins and avoidance of normal tissues, thereby enhancing the safety of treatment.     

Innovative strategies for image-guided proton treatment of prostate cancer

Proton beam therapy has a proven track record of treating non-metastatic prostate cancer with excellent disease-free survival results when using homogeneous doses between 75 and 82 CGE (Cobalt Gray Equivalent) to the prostate target volume. In clinically organ-confined prostate cancer, it may be possible, in principle, to further improve outcomes by reducing the margins of the high-dose planning target volume to the gross tumor volume and by covering the clinical target volume with a dose sufficient to control microscopic extensions of the tumor. This would allow further dose escalation without increasing the risk of acute and late effects. In this paper, we undertake a careful review of existing histopathological data that support this view and discuss technical possibilities to this approach utilizing the highly conformal characteristics of proton beams and combining them with modern 4D imaging and treatment techniques.     

Dose escalation in locally advanced carcinoma of the prostate

Radiotherapeutic management of advanced prostate cancer is challenging. Several retrospective analyses showed a dose response for local tumor control before the availability of conformal radiation therapy. Attempts to escalate dose without the benefit of modern treatment planning was commonly fraught with high rates of bowel or bladder complications. The advent of image-guided or computed tomography-based treatment planning has allowed safe delivery of high-dose radiation therapy in men with prostate cancer with an acceptable rate of side effects and complications. Several prospective clinical trials have been conducted both at single institutions and in the cooperative group setting. Early evidence suggests that patients with high-risk factors such as advanced clinical stage, high initial prostate-specific antigen, or poorly differentiated tumors may benefit from high-dose 3-dimensional conformal radiation therapy with improved biochemical and local tumor control. A published randomized trial with conformal radiation therapy shows that a modest escalation of radiation dose leads to improved biochemical disease-free survival for a select group of patients. A confirmatory trial within the Radiation Therapy Oncology Group is underway to determine if dose escalation will improve overall survival in men without compromising quality of life. Copyright Elsevier Inc. All rights reserved.     

前列腺癌的外照射放疗进展

外照射放疗作为前列腺癌的主要治疗手段之一,随着放疗技术的进步、靶区认识的统一,已进入精确放疗时代.高剂量放疗的准确实施,使前列腺癌的疗效显著提高.而影像引导的放射治疗、质子放疗和低分割放疗则是疗效进一步提高的研究方向.     

Comparison of 2-Dimensional and 3-Dimensional Conformal Treatment Plans in Gastric Cancer Radiotherapy

Background: Postoperative chemoradiotherapy is accepted as standard treatment for stage IB-IV, M0 gastric cancer. Radiotherapy (RT) planning of gastric cancer is important because of the low radiation tolerance of surrounding critical organs. The purpose of this study was to compare the dosimetric aspects of 2-dimensional (2D) and 3-dimensional (3D) treatment plans, with the twin aims of evaluating the adequacy of 2D planning fields on coverage of planning target volume (PTV) and 3D conformal plans for both covering PTV and reducingthe normal tissue doses. Materials and Methods: Thirty-six patients with stage II-IV gastric adenocarcinoma were treated with adjuvant chemoradiotherapy using 3DRT. For each patient, a second 2D treatment plan was generated. The two techniques were compared for target volume coverage and dose to normal tissues using dose volume histogram (DVH) analysis. Results: 3DRT provides more adequate coverage of the target volume. Comparative DVHs for the left kidney and spinal cord demonstrate lower radiation doses with the 3D technique.Conclusions: 3DRT produced better dose distributions and reduced radiation doses to left kidney and spinal cord compared to the 2D technique. For this reason it can be predicted that 3DRT will result in better tumor control and less normal tissue complications.     

Dose-escalated 3D conformal radiotherapy in prostate cancer

3D conformal radiotherapy involves the delivery of radiation to a defined 3D tumor volume while minimizing doses to adjacent critical tissues. The use of sophisticated imaging tools and advanced treatment planning software have allowed for better target definition enabling the oncologist to conform or shape radiation volume more closely around the target while minimizing dose to the rectum and bladder. 3D conformal radiotherapy has resulted in dramatic reductions in acute and late toxicity of radiation treatment in prostate cancer. It has also allowed for safe escalation of radiation dose with improved tumor control compared with conventional dose radiotherapy. Long-term tumor control rates with 3D conformal radiotherapy are comparable with results using radical prostatectomy.     

Dose-escalated 3D conformal radiotherapy in prostate cancer

3D conformal radiotherapy involves the delivery of radiation to a defined 3D tumor volume while minimizing doses to adjacent critical tissues. The use of sophisticated imaging tools and advanced treatment planning software have allowed for better target definition enabling the oncologist to conform or shape radiation volume more closely around the target while minimizing dose to the rectum and bladder. 3D conformal radiotherapy has resulted in dramatic reductions in acute and late toxicity of radiation treatment in prostate cancer. It has also allowed for safe escalation of radiation dose with improved tumor control compared with conventional dose radiotherapy. Long-term tumor control rates with 3D conformal radiotherapy are comparable with results using radical prostatectomy.     

Constrained‐beam inverse planning for intensity‐modulated radiation therapy of prostate cancer patients with bilateral hip prostheses

Hip prostheses present a technical challenge in the planning of curative external beam radiation treatment for patients with prostate cancer. Bilateral prostheses compel planners to compromise between target coverage and avoidance of beam entry through the prostheses. Inverse planning systems given objectives to avoid dose to prostheses are overly restricted from allowing exit dose to them. We report a novel inverse planning technique for intensity‐modulated radiation therapy of patients with prostate cancer and bilateral hip prostheses, by constraining beam characteristics rather than dose in the inverse planning process.     

Report from the Radiation Oncology Committee of the Southwest Oncology Group (SWOG): Research Objectives Workshop 2003

To achieve the ultimate goal of cancer treatment, which is 100% cancer control with negligible toxicity, the therapeutic window must be enlarged, allowing for higher doses of beneficial treatments with reduced toxicity. The advent of image- and metabolism-guided therapy offers the best opportunity to date for combining modern radiation targeting and imaging techniques. Indeed, for the first time, it is reasonable to locally target metastatic disease with the goal of sterilization. Combining these focal radiation techniques with novel targeted antiproliferative agents and full-dose classic cytotoxic chemotherapy will become more effective as we learn to use these compounds in a less systemically toxic manner and as radiation fields become more defined. In addition, increasing numbers of biologic modifiers of normal tissue response are becoming available, and they suggest great promise for decreasing the normal tissue toxicity resulting from both radiation and chemotherapy treatments. Thus, radiation metastectomy for gross metastases, used together with systemic control of micrometastatic disease, may yield improved survival rates. This hypothesis is ready for testing in cancers of the breast, prostate, colon, and in sarcomas. Enlarging the therapeutic window is a major goal that would allow for an increasingly favorable therapeutic gain.     

Proton-beam therapy for prostate cancer

The treatment options for prostate cancer include prostatectomy, external-beam irradiation, brachytherapy, cryosurgery, focused ultrasound, hormonal therapy, watchful waiting, and various combinations of these modalities. Because the prostate abuts the bladder and rectum, the dose distributions of external-beam irradiations and the accuracy of their placement play crucial roles in the probability of tumor cure and the incidence of posttreatment complications. Principal among the newer radiation technologies is proton-beam therapy (PBT), whose dose distributions make it possible to deliver higher tumor doses and smaller doses to surrounding normal tissues than from x-ray systems. However, as the 10-year cause-specific survival for early-stage disease treated by radiation therapy now exceeds 90%, and with severe late toxicities in the range of 2% to 3%, randomized clinical trials provide the only means to demonstrate improved outcomes from PBT. Short of the data provided by such trials, the efficacy of PBT can be gleaned only from reports in the clinical literature, and, to date, these reports are equivocal. In view of the current health care crisis and the higher costs of PBT for prostate cancer, it is reasonable to assess the viability of this in-vogue but not-so-new technology.     

Intensity-modulated radiation therapy: supportive data for prostate cancer

Since its introduction into clinical use in the mid-1990s, intensity-modulated radiation therapy (IMRT) has emerged as the most effective and widely used form of external-beam radiotherapy for localized prostate cancer. Multiple studies have confirmed the importance of delivering sufficiently high doses to the prostate to achieve cure. The dosimetric superiority of IMRT over conventional techniques to produce conformal dose distributions that allow for organ sparing has been shown. A growing number of reports have confirmed that IMRT is the safest way to deliver high doses of external-beam irradiation to the prostate and the regional lymph nodes. Advances in imaging and onboard verification systems continue to advance the capabilities of IMRT and have potential implications with regards to further dose escalation and hypofractionated regimens. The clinical data in support of IMRT and the associated technical aspects of IMRT treatment planning and implementation are highlighted in this review.