1
|
Marks LB, Tepper JE, Kim HJ, Hauer-Jensen M. Don't CUT: Respecting the Potency of Radiation. Int J Radiat Oncol Biol Phys 2024; 119:724-726. [PMID: 38851273 DOI: 10.1016/j.ijrobp.2024.03.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2024] [Revised: 03/07/2024] [Accepted: 03/13/2024] [Indexed: 06/10/2024]
Affiliation(s)
| | | | - Hong Jin Kim
- Surgical Oncology, Department of Surgery, University of North Carolina School of Medicine, Chapel Hill, North Carolina
| | - Martin Hauer-Jensen
- Pharmaceutical Sciences, Surgery, and Pathology, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| |
Collapse
|
2
|
Khaleghi G, Mahdavi H, Mahdavi SR, Khajetash B, Nikoofar A, Hosntalab M, Sadeghi M, Reiazi R. Investigating dose homogeneity in radiotherapy of oral cancers in the presence of a dental implant system: an in vitro phantom study. Int J Implant Dent 2021; 7:90. [PMID: 34486092 PMCID: PMC8419140 DOI: 10.1186/s40729-021-00372-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Accepted: 06/27/2021] [Indexed: 11/17/2022] Open
Abstract
Background Materials with high atomic numbers are part of the composition of dental implant systems. In radiotherapy of oral cavity cancers, an implant can cause dose perturbations that affect target definition, dose calculation, and dose distribution. In consequence, this may result in poor tumor control and higher complications. In this study, we evaluated dose homogeneity when a dental implant replaced a normal tooth. We also aimed to evaluate the concordance of dose calculations with dose measurements. Materials and methods In this study, 2 sets of planning CT scans of a phantom with a normal tooth and the same phantom with the tooth replaced by a Z1 TBR dental implant system were used. The implant system was composed of a porcelain-fused-to-metal crown and titanium with a zirconium collar. Three radiotherapy plans were designed when the density of the implant material was corrected to match their elements, or when all were set to the density of water, or when using the default density conversion. Gafchromic EBT-3 films at the level of isocenter and crowns were used for measurements. Results At the level of crowns, upstream and downstream dose calculations were reduced when metal kernels were applied (M-plan). Moreover, relatively measured dose distribution patterns were most similar to M-plan. At this level, relative to the non-implanted phantom, mean doses values were higher with the implant (215.93 vs. 192.25), also, new high-dose areas appeared around a low-dose streak forward to the implant (119% vs. 95%). Conclusions Implants can cause a high dose to the oral cavity in radiotherapy because of extra scattered radiation. Knowledge of the implant dimensions and defining their material enhances the accuracy of calculations.
Collapse
Affiliation(s)
- Goli Khaleghi
- Medical Radiation Engineering Department, Science and Research Branch, Islamic Azad University, Daneshgah Blvd., Simon Bolivar Blvd., P.O. Box: 14515-775, Tehran, Iran
| | - Hoda Mahdavi
- Radiation Biology Research Center, Iran University of Medical Sciences, Shahid Hemmat Highway, P.O. Box: 14665-354, Tehran, Iran. .,Radiation Oncology Department, Iran University of Medical Sciences, Firoozgar hospital, Beh-Afarin St., Karimkhane-Zand Blvd., P.O. Box: 1593747811, Tehran, Iran.
| | - Seied Rabi Mahdavi
- Radiation Biology Research Center, Iran University of Medical Sciences, Shahid Hemmat Highway, P.O. Box: 14665-354, Tehran, Iran.,Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Shahid Hemmat Highway, P.O. Box: 14155-6183, Tehran, Iran
| | - Benyamin Khajetash
- Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Shahid Hemmat Highway, P.O. Box: 14155-6183, Tehran, Iran
| | - Alireza Nikoofar
- Radiation Oncology Department, Iran University of Medical Sciences, Firoozgar hospital, Beh-Afarin St., Karimkhane-Zand Blvd., P.O. Box: 1593747811, Tehran, Iran
| | - Mohammad Hosntalab
- Medical Radiation Engineering Department, Science and Research Branch, Islamic Azad University, Daneshgah Blvd., Simon Bolivar Blvd., P.O. Box: 14515-775, Tehran, Iran
| | - Mahdi Sadeghi
- Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Shahid Hemmat Highway, P.O. Box: 14155-6183, Tehran, Iran
| | - Reza Reiazi
- Princess Margaret Cancer Center, University Health Network, 101 College Street, P.O. Box: M5G 1L7, Ontario, Toronto, Canada
| |
Collapse
|
3
|
Xu M, Zang J, Luo S, Wang J, Li X. Long-term survival outcomes and adverse effects of nasopharyngeal carcinoma patients treated with IMRT in a non-endemic region: a population-based retrospective study. BMJ Open 2021; 11:e045417. [PMID: 34341036 PMCID: PMC8330594 DOI: 10.1136/bmjopen-2020-045417] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
OBJECTIVES To evaluate the long-term survival outcomes and adverse effects of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) and to summarise the experiences of IMRT in NPC in the past few decades in non-endemic northwest China. DESIGN A population-based retrospective study. SETTING An experience of using IMRT in non-endemic region of China. PARTICIPANTS The study included 792 newly diagnosed and non-metastatic NPC patients who received IMRT from January 2006 to September 2018 in Xijing Hospital. OUTCOME MEASURES The survival outcomes, adverse effects and failure patterns were evaluated by univariate, multivariate and subgroup analyses. RESULTS With a median follow-up time of 46.2 months, the 5-year local recurrence-free survival, regional recurrence-free survival, distant metastasis-free survival, disease-free survival (DFS) and overall survival (OS) rates were 90.8%, 97.0%, 82.8%, 69.6% and 78.0%, respectively. Multivariate analysis showed that age, N stage, clinical stage, pathological type and primary tumour volume of more than 23 cm3 were the independent prognosis factors for DFS (all p<0.05); age, N stage, pathological type, cervical lymph node necrosis, and anaemia were significantly associated with OS (all p<0.05). The most common acute toxicities of IMRT were dermatitis, mucositis and dysphagia. Xerostomia and hearing impairment were the top two late toxicities. The main failure patterns were distant metastasis and local and/or regional relapses. CONCLUSIONS Similar survival, toxicities and failure patterns have been observed in patients treated with IMRT in a non-endemic area of China when compared with that in endemic areas. Induction chemotherapy combined with concurrent chemoradiotherapy may benefit locally advanced NPC in non-endemic areas of China.
Collapse
Affiliation(s)
- Man Xu
- Department of Gengral Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, China
- Department of Radiation Oncology, Xi'an Gaoxin Hospital, Xi'an, Shaanxi, China
| | - Jian Zang
- Department of Radiation Oncology, Air Force Medical University Xijing Hospital, Xian, Shaanxi, China
| | - Shanquan Luo
- Department of Radiation Oncology, Air Force Medical University Xijing Hospital, Xian, Shaanxi, China
| | - Jianhua Wang
- Department of Radiation Oncology, Air Force Medical University Xijing Hospital, Xian, Shaanxi, China
| | - Xuqi Li
- Department of Gengral Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, China
| |
Collapse
|
4
|
Cheung FWK, Law MYY. A novel conformity index for intensity modulated radiation therapy plan evaluation. Med Phys 2012; 39:5740-56. [PMID: 22957639 DOI: 10.1118/1.4742848] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Intensity modulated radiation therapy (IMRT) has gained popularity in the treatment of cancers. Manual evaluation of IMRT plans for head-and-neck cancers has been especially challenging necessitating efficient and objective assessment tools. In this work, the authors address this issue by developing a personalized conformity index (CI) for comparison of IMRT plans for head-and-neck cancers and evaluating its plan quality discerning power in comparison with other widely used CIs. METHODS A two-dimensional CI with dose and distance incorporated (CI(DD)) was developed using the MATLAB program language, to quantify the planning target volume (PTV) coverage. Valuable information contained in the digital imaging and communication in medicine (DICOM) RT objects were harvested for computation of each of the CI(DD) components. Apart from the dose penalty factor, a distance-based exponential function was employed by varying the penalty weight associated with the location of cold spots within the PTV. With the goal of deriving a customized penalty factor, the distances between individual pixel and its nearest PTV boundary was found. Using the exponential function, the impact of distance penalty was substantially larger for cold spots closer to the PTV centroid but petered out quickly wherever they were situated in the vicinity of PTV border. In order to evaluate the CI(DD) scoring system, three CT image data sets of nasopharyngeal carcinoma (NPC) patients were collected. Ten IMRT plans with degrading qualities were generated from each dataset and were ranked based on CI(DD) and other existing indices. The coefficient of variance was calculated for each dataset to compare the degree of variation. RESULTS The CI(DD) scoring system that considered spatial importance of each voxel within the PTV was successfully developed. The results demonstrated that the CI(DD) including four discrete factors could provide accurate rankings of plan quality by examining the relative importance of each cold spot within the PTVs. Apart from the dose penalty factor, a distance-based exponential function was employed taking the specific tumor geometry into account. Compared with other commonly used CIs, the CI(DD) resulted in the largest coefficient of variance among the ten IMRT plans for each dataset, indicating that its discerning power was the best among the CIs being compared. CONCLUSIONS The CI(DD) scoring system was successfully developed to incorporate patient-specific spatial dose information and provide a geometry-based physical index for comparison of IMRT plans for head-and-neck cancers. By taking individual tumor geometry into account, the superiority of CI(DD) in plan discerning power was demonstrated. The use of CI(DD) could provide an effective means of benchmarking performance, reducing treatment plan variability, and advancing the quality of current IMRT planning.
Collapse
Affiliation(s)
- Fion W K Cheung
- Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong.
| | | |
Collapse
|
5
|
Abstract
PURPOSE To describe the frequency distribution for the number of residual subclinical metastatic tumor cells after removal of the primary cancer. MATERIALS AND METHODS Previously obtained autopsy, surgical pathological and laboratory data were used to characterize the size and number distributions for hematogenous and lymphatic metastases. Monte Carlo simulations were used to estimate the numbers of residual tumor cells based upon the assumption of a lognormal distribution for the sizes of metastases and Poisson, Poisson negative binomial, or negative binomial distributed numbers of metastases (corresponding to lymphatic metastases within individuals, hematogenous metastases within individuals, and lymphatic metastases within populations, respectively). RESULTS In each of the scenarios the resultant distribution for the numbers of subclinical tumor cells was unimodal and positively skewed, with a tail extending to the higher numbers of metastases. When plotted with equal sized counting bins and according the logarithm of the number of tumor cells, the distributions showed deviations from the normal form no greater than several percentage points--a result considered acceptable given the variabilities inherent to metastasis data. CONCLUSIONS The distribution for the number of residual subclinical metastases may be extrapolated from data and models derived from the size and number distributions for metastases. In the absence of a closed form description for this distribution, the lognormal distribution could provide a crude, but practical, approximation for cases limited to occult microscopic residual disease. These analyses will facilitate the definition of the dose-response for the adjuvant therapy of subclinical metastases.
Collapse
Affiliation(s)
- Wayne S Kendal
- Division of Radiation Oncology, The Ottawa Hospital Regional Cancer Centre, Ottawa, Ontario, Canada.
| |
Collapse
|
6
|
Søvik A, Malinen E, Bruland ØS, Bentzen SM, Olsen DR. Optimization of tumour control probability in hypoxic tumours by radiation dose redistribution: a modelling study. Phys Med Biol 2006; 52:499-513. [PMID: 17202629 DOI: 10.1088/0031-9155/52/2/013] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Tumour hypoxia is a known cause of clinical resistance to radiation therapy. The purpose of this work was to model the effects on tumour control probability (TCP) of selectively boosting the dose to hypoxic regions in a tumour, while keeping the mean tumour dose constant. A tumour model with a continuous oxygen distribution, incorporating pO(2) histograms published for head and neck patients, was developed. Temporal and spatial variations in the oxygen distribution, non-uniform cell density and cell proliferation during treatment were included in the tumour modelling. Non-uniform dose prescriptions were made based on a segmentation of the tumours into four compartments. The main findings were: (1) Dose redistribution considerably improved TCP for all tumours. (2) The effect on TCP depended on the degree of reoxygenation during treatment, with a maximum relative increase in TCP for tumours with poor or no reoxygenation. (3) Acute hypoxia reduced TCP moderately, while underdosing chronic hypoxic cells gave large reductions in TCP. (4) Restricted dose redistribution still gave a substantial increase in TCP as compared to uniform dose boosts. In conclusion, redistributing dose according to tumour oxygenation status might increase TCP when the tumour response to radiotherapy is limited by chronic hypoxia. This could potentially improve treatment outcome in a subpopulation of patients who respond poorly to conventional radiotherapy.
Collapse
Affiliation(s)
- Aste Søvik
- Department of Medical Physics and Technology, The Norwegian Radium Hospital, and Department of Physics, University of Oslo, 0316 Oslo, Norway
| | | | | | | | | |
Collapse
|
7
|
Spirydovich S, Papiez L, Moskvin V, Desrosiers P. Evaluation of underdosage in the external photon beam radiotherapy of glottic carcinoma: Monte Carlo study. Radiother Oncol 2006; 78:159-64. [PMID: 16360226 DOI: 10.1016/j.radonc.2005.11.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2005] [Revised: 08/04/2005] [Accepted: 11/22/2005] [Indexed: 11/26/2022]
Abstract
PURPOSE Underdosage in the human larynx may be the true factor behind the decrease in local control rates. PATIENTS AND METHODS To evaluate underdosage with Monte Carlo a CT-based geometrical model of the patient's neck (mathematical neck) was created. Dose was calculated for a pair of 6 Me V parallel-opposed photon beams modulated with 15 degree steel wedges. RESULTS At least 5% of volume of 3.5 cm(3) hypothetical tumor near the air wall of the larynx receives less than 86% of the maximum tumor dose. The same volume received less than 91% of the maximum tumor dose when the mathematical neck had no air cavities. CONCLUSIONS We conclude the significant underdosage at the air-tissue interface in the larynx occurs in traditional radiotherapy treatments, especially in the glottic part of the larynx.
Collapse
Affiliation(s)
- Siarhei Spirydovich
- Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN 46202-5289, USA.
| | | | | | | |
Collapse
|
8
|
Pedraza Muriel V. The impact on oncology of the interaction of radiation therapy and radiobiology. Clin Transl Oncol 2006; 8:83-93. [PMID: 16632421 DOI: 10.1007/s12094-006-0163-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The quantitative analysis of the cell dose-survival curves, the randomness of cell killing by radiation, the probabilistic basis of the response to irradiation of tumors and normal tissues, the understanding of the biological mechanisms underlying to this response, the rationale for dose-time and fractionation in radiotherapy, the introduction of the concepts of tumor control probability (TCP) and biologically effective dose (BED), the relationships TCP-dose, BED-alpha/beta BED-fraction size and BED-treatment time, the problems associated with the accelerated regeneration of surviving tumor clonogens during the course of fractionated radiotherapy, the new demands of knowledge on oncology and radiation biology derived from heterogeneous dose distributions in conformal radiation therapy programs and the definition of the biological basis of normal tissues tolerance to reirradiation are, probably, the most important contributions of radiobiology to clinical radiotherapy in the last twenty five years. Radiotherapy is today a scientific discipline based on the interplay of mathematics, physics, biology and oncology. The knowledge of the basic concepts of radiobiology is essential for daily radiotherapy practices and for all oncologists. The most efficient use of multimodality treatments in cancer therapy cannot be done without a clear understanding of these principles.
Collapse
|
9
|
Abstract
Radiosurgery offers patients with brain metastases an effective and minimally invasive treatment modality. Radiosurgery provides local tumor control and prolongs survival in select patients with brain metastases. This review will discuss numerous aspects of radiosurgery, including the various delivery techniques and radiobiology. Treatment recommendations will be outlined in view of the available clinical data. Although surgery or radiosurgery with whole-brain radiotherapy remains an important option for patients with a solitary brain metastasis, radiosurgery with or without whole-brain radiotherapy should be considered in patients with a limited number of small tumors and a good prognosis.
Collapse
Affiliation(s)
- Michael W McDermott
- Department of Neurosurgery, University of California, San Francisco, San Francisco, California 94143, USA.
| | | |
Collapse
|
10
|
Miften MM, Das SK, Su M, Marks LB. A dose-volume-based tool for evaluating and ranking IMRT treatment plans. J Appl Clin Med Phys 2004; 5:1-14. [PMID: 15738916 PMCID: PMC5723521 DOI: 10.1120/jacmp.v5i4.1981] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
External beam radiotherapy is commonly used for patients with cancer. While tumor shrinkage and palliation are frequently achieved, local control and cure remain elusive for many cancers. With regard to local control, the fundamental problem is that radiotherapy‐induced normal tissue injury limits the dose that can be delivered to the tumor. While intensity‐modulated radiation therapy (IMRT) allows for the delivery of higher tumor doses and the sparing of proximal critical structures, multiple competing plans can be generated based on dosimetric and/or biological constraints that need to be considered/compared. In this work, an IMRT treatment plan evaluation and ranking tool, based on dosimetric criteria, is presented. The treatment plan with the highest uncomplicated target conformity index (TCI+) is ranked at the top. The TCI+ is a dose‐volume‐based index that considers both a target conformity index (TCI) and a normal tissue‐sparing index (NTSI). TCI+ is designed to assist in the process of judging the merit of a clinical treatment plan. To demonstrate the utility of this tool, several competing lung and prostate IMRT treatment plans are compared. Results show that the plan with the highest TCI+ values accomplished the competing goals of tumor coverage and critical structures sparing best, among rival treatment plans for both treatment sites. The study demonstrates, first, that dose‐volume‐based indices, which summarize complex dose distributions through a single index, can be used to automatically select the optimal plan among competing plans, and second, that this dose‐volume‐based index may be appropriate for ranking IMRT dose distributions. PACS numbers: 87.53.‐j, 87.53.Tf
Collapse
Affiliation(s)
- Moyed M. Miften
- Department of Radiation OncologyDuke University Medical CenterDurhamNorth Carolina27710U.S.A.
| | - Shiva K. Das
- Department of Radiation OncologyDuke University Medical CenterDurhamNorth Carolina27710U.S.A.
| | - Min Su
- Department of Radiation OncologyDuke University Medical CenterDurhamNorth Carolina27710U.S.A.
| | - Lawrence B. Marks
- Department of Radiation OncologyDuke University Medical CenterDurhamNorth Carolina27710U.S.A.
| |
Collapse
|
11
|
Haworth A, Ebert M, Waterhouse D, Joseph D, Duchesne G. Prostate implant evaluation using tumour control probability—the effect of input parameters. Phys Med Biol 2004; 49:3649-64. [PMID: 15446795 DOI: 10.1088/0031-9155/49/16/012] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In this paper, we examine the effect of treatment parameters in a model used to evaluate permanent prostate implants. The model considers the prostate to be composed of 12 sub-sections, each sub-section is assigned a cell density based on the probability of finding cancer foci in that sub-section. Wasted dose as a result of the dose rate from the implant falling below a level adequate to counteract repopulation was found to vary by 2-16% over the range of radiosensitivity and repopulation rates considered. Within the model, applied to five dose distributions, the uncertainty in the tumour control probability (TCP) values calculated for each sub-section as a result of differences in the model parameters, was found to be less than 12% in most cases for the good quality implants. The difference in TCP values was much larger for the poor quality implant. Substituting a heterogeneous distribution of alpha for a single mean value resulted in generally lower TCP values though introducing a cutoff value with a Gaussian distribution had a profound effect on the calculated values. Despite uncertainties in the parameters, the model was able to identify sub-sections at risk of local recurrence but as a result of these uncertainties, the TCP values can only be considered in the relative rather than absolute sense.
Collapse
Affiliation(s)
- Annette Haworth
- Department of Radiation Oncology, Sir Charles Gairdner Hospital Nedlands, WA, Australia.
| | | | | | | | | |
Collapse
|
12
|
Paganetti H. Significance and implementation of RBE variations in proton beam therapy. Technol Cancer Res Treat 2004; 2:413-26. [PMID: 14529306 DOI: 10.1177/153303460300200506] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Key to radiation therapy is to apply a high tumor-destroying dose while protecting healthy tissue, especially near organs at risk. To optimize treatment for ion therapy not the dose but the dose multiplied by the relative biological effectiveness (RBE) is decisive. Proton therapy has been based on the use of a generic RBE, which is applied to all treatments independent of dose/fraction, position in the spread-out Bragg peak (SOBP), initial beam energy or the particular tissue. Dependencies of the RBE on various physical and biological properties are disregarded. The variability of RBE in clinical situations is believed to be within 10-20%. This is in the same range of effects that receive high attention these days, i.e., patient set-up uncertainties, organ motion effects, and dose calculation accuracy all affecting proton as well as conventional radiation therapy. Elevated RBE values can be expected near the edges of the target, thus probably near critical structures. This is because the edges show lower doses and, depending on the treatment plan, may be identical with the beam's distal edge, where dose is deposited in part by high-LET protons. We assess the rationale for the continued use of a generic RBE and whether the magnitude of RBE variation with treatment parameters is small relative to our abilities to determine RBE's. Two aspects have to be considered. Firstly, the available information from experimental studies and secondly, our ability to calculate RBE values for a given treatment plan based on parameters extracted from such experiments. We analyzed published RBE values for in vitro and in vivo endpoints. The values for cell survival in vitro indicate a substantial spread between the diverse cell lines. The average value at mid SOBP over all dose levels is approximately 1.2 in vitro and approximately 1.1 in vivo. Both in vitro and in vivo data indicate a statistically significant increase in RBE for lower doses per fraction, which is much smaller for in vivo systems. The experimental in vivo data indicate that continued employment of a generic RBE value of 1.1 is reasonable. At present, there seems to be too much uncertainty in the RBE value for any human tissue to propose RBE values specific for tissue, dose/fraction, etc. There is a clear need for prospective assessments of normal tissue reactions in proton irradiated patients and determinations of RBE values for several late responding tissues in animal systems, especially as a function of dose in the range of 1-4 Gy. However, there is a measurable increase in RBE over the terminal few mm of the SOBP, which results in an extension of the bio-effective range of the beam of a few mm. This needs to be considered in treatment planning, particularly for single field plans or for an end of range in or close to a critical structure. To assess our ability to calculate RBE values we studied two approaches, which are both based on the track structure theory of radiation action. RBE calculations are difficult since both the physical input parameters, i.e., LET distributions, and, even more so, the biological input parameters, i.e., local cellular response, have to be known with high accuracy. Track structure theory provides a basis for predicting dose-response curves for particle irradiation. However, designed for heavy ion applications the models show weaknesses in the prediction of proton radiation effects. We conclude that, at present, RBE modeling in treatment planning involves significant uncertainties. To incorporate RBE variations in treatment planning there has to be a reliable biological model to calculate RBE values based on the physical characteristics of the radiation field and based on well-known biological input parameters. In order to do detailed model calculations more experimental data, in particular for in vivo endpoints, are needed
Collapse
Affiliation(s)
- H Paganetti
- Massachusetts General Hospital, Department of Radiation Oncology & Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA.
| |
Collapse
|
13
|
Abstract
Losses in tumor control are estimated for cold spots of various "sizes" and degrees of "cold dose." This question is important in the context of intensity modulated radiotherapy where differential dose-volume histograms (DVHs) for targets that abut a critical structure often exhibit a cold dose tail. This can be detrimental to tumor control probability (TCP) for fractions of cold volumes even as small as 1%, if the cold dose is lower than the prescribed dose by substantially more than 10%. The Niemierko-Goitein linear-quadratic algorithm with gamma50 slope 1-3 was used to study the effect of cold spots of various degrees (dose deficit below the prescription dose) and size (fractional volume of the cold dose). A two-bin model DVH has been constructed in which the cold dose bin is allowed to vary from a dose deficit of 1%-50% below prescription dose and to have volumes varying from 1% to 90%. In order to study and quantify the effect of a small volume of cold dose on TCP and effective uniform dose (EUD), a four-bin DVH model has been constructed in which the lowest dose bin, which has a fractional volume of 1%, is allowed to vary from 10% to 45% dose deficit below prescription dose. The highest dose bin represents a simultaneous boost. For fixed size of the cold spot the calculated values of TCP decreased rapidly with increasing degrees of cold dose for any size of the cold spot, even as small as 1% fractional volume. For the four-subvolume model, in which the highest dose bin has a fractional volume of 80% and is set at a boost dose of 10% above prescription dose, it is found that the loss in TCP and EUD is moderate as long as the cold 1% subvolume has a deficit less than approximately 20%. However, as the dose deficit in the 1% subvolume bin increases further it drives TCP and EUD rapidly down and can lead to a serious loss in TCP and EUD. Since a dose deficit to a 1% volume of the target that is larger than 20% of the prescription dose may lead to serious loss of TCP, even if 80% of the target receives a 10% boost, particular attention has to be paid to small-volume cold regions in the target. The effect of cold regions on TCP can be minimized if the EUD associated with the target DVH is constrained to be equal to or larger than the prescription dose.
Collapse
Affiliation(s)
- Wolfgang A Tomé
- Department of Human Oncology, University of Wisconsin Medical School, CSC, Madison 53792, USA.
| | | |
Collapse
|
14
|
Kim GE, Lim J, Park HC, Keum KC, Kim YB, Moon SR, Lee CG, Seong J, Suh CO. A feasibility study using three-dimensional conformal boost technique in locally advanced carcinoma of the nasopharynx. Acta Oncol 2002; 40:582-7. [PMID: 11669329 DOI: 10.1080/028418601750444114] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
To investigate the feasibility and efficacy of dose escalation using three-dimensional (3-D) conformal boost technique, 21 patients with stage III or IV nasopharyngeal cancer were enrolled in a prospective protocol. All patients with node metastases initially received external radiotherapy by conventional technique up to 70.2 Gy, followed by 3-D conformal radiotherapy (3-D CRT) to the boost part up to 79.2 Gy with 9 Gy increments (daily fraction of 1.8 Gy for 5 days). A modified technique with the same dose escalation of 9 Gy using 3-D CRT was applied to 7 patients without node metastases, who were treated by conventional technique up to 54 Gy, followed by 3-D CRT to boost up to a basic dose of 70.2 Gy, and then finally with dose escalation of 9 Gy. The protocol was relatively well tolerated by the majority of patients. Acute complications during the dose escalation schedule was low, with rare occurrences of grade 3 or 4 toxicity. Although late radiation-induced complications also appeared limited, 1 patient developed a temporal lobe necrosis and 2 patients suffered from sensory-neural hearing loss. There were no radiation-induced fatal complications. At a median follow-up of 48 months, only 3 patients experienced local failure and 2 patients developed distant metastases. The 5-year overall actuarial survival rate and recurrence-free survival rate for all patients were 68% and 85%, respectively. On the basis of acceptable morbidity and encouraging treatment results, we conclude that the dose escalation in 9 Gy increments using a 3-D conformal boost technique is relatively safe and efficacious, enough to be used routinely for locally advanced nasopharyngeal cancers.
Collapse
Affiliation(s)
- G E Kim
- Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University, College of Medicine, Seoul, Korea.
| | | | | | | | | | | | | | | | | |
Collapse
|