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Biologically effective dose distribution based on the linear quadratic model and its clinical relevance (ASTRO Research Fellowship)
197
Proceedings of the 36th Annual ASTRO Meeting
77 BIOLOGICALLY EFFECTIVE DOSE DISTB.IBUTION (ASTRO Research Fellowship) CLINICAL RELEVANCE Steve
P. Lee, Min Y. Leu, James
Department
of Radiation
B. Smathers,
Oncology,
Robert
UCLA School
BASED
G. Parker,
of Medicine,
ON THE LINEAR
H. Rodney Los Angeles,
QUADRATIC
MODEL
AND
ITS
Withers CA 90024
Purpose/Objective: Radiotherapy plans based on physical dose distributions do not necessarily reflect entirely the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model. Materials & Methods: A computer program which converts a physical dose distribution calculated by a commercially available treatment planning system to a biologically effective dose (BED) distribution has been developed and verified against theoretical calculations. This software accepts a user’s input of biological parameters for each structure of interest (linear and quadratic dose-response and repopulation kinetic parameters), as well as treatment scheme factors (number of fractions, fractional dose, and treatment time). It then presents a two-dimensional BED display in conjunction with anatomical structures. With this tool and the parameters extracted from the literature, selected scenarios of clinical treatments were studied for the variations in tissue BED under different treatment schemes. Results: The following sample case serves to illustrate the application of our tool in clinical practice. For a typical four-field, evenly weighted prostate treatment using 10 MV X-ray beams, physical dosimetry predicted a comparable dose at the femoral heads between an alternate a-field/day and 4-field/day set-ups. However, our calculations revealed an approximate 25% higher BED for the 2-field/day scheme. This overdose to the femoral heads can be eliminated if the treatment is delivered with a 3 : 2 @P/PA : bilateral) dose weighting. Similar BED results of the above set-ups were seen with higher energy beams (such as 24 MV X-rays). With Co-60 beams, the increase of BED with alternate a-field/day, 1:l set-up was even more pronounced (34%). Conclusion: We have demonstrated the feasibility to construct a biologically oriented dose distribution for clinical practice of radiotherapy. The discordance between physical dose distributions and the biological counterparts based on the given treatment schemes were quantified. The computerized display of BED at non-prescription points greatly enhanced the versatility of this tool. While the routine use of this implementation in clinical radiotherapy should be cautiously done, depending largely on the accuracy of the published biological parameters, it may nevertheless help the clinicians derive an optimal treatment plan with a particular fractionation scheme or use it as a quantitative tool for outcome analysis in clinical research.
78 THE ROLE OF 3-DIMENSIONAL FUNCTIONAL LUNG IMAGING IN TREATMENT PLANNING: THE FUNCTIONAL DVH LB Marks, GW Sherouse, DP Spencer, G Bentel, R Clough, K Vann, R Jaszczak, E Coleman, MA Anscher, LR Prusnitz Department of Radiation Oncology and Nuclear Medicine, Duke University Medical Center, Durham, NC 27710 w: During thoracic XRT, it is common to design fields thatattemptto minimize the volume of non-tumor containing lung included. Generally, one does not consider functional heterogeneities within the lung. The 3-D functional information provided by single photon emission computed tomography (SPECT) lung perfusion scans might be useful in designing beams that minimize incidental irradiation of functioning lung tissue. We herein review the pre-treatment SPECT scans in 86 patients to determine which patients are likely to benefit from this technology. Methm: Prior to thoracic XRT, SPECT scans were obtained following the intravenous injection of = 4 mCi of 99mTc-labeled macroaggregated albumin. The presence of functional heterogeneities, their location relative to the tumor, and the clinical usefulness of their recognition were scored. Patients were grouped and compared (2-tailed chi sq) based on clinical factors. Conventional Dose-Volume Histograms (DVH’s) and Functional DVH’s (DVFH’S) are calculated based on the dose distribution throughout the CT-defined lung and SPECTdefined perfused lung, respectively.
Proceedings of the 36th Annual ASTRO Meeting
77 BIOLOGICALLY EFFECTIVE DOSE DISTB.IBUTION (ASTRO Research Fellowship) CLINICAL RELEVANCE Steve
P. Lee, Min Y. Leu, James
Department
of Radiation
B. Smathers,
Oncology,
Robert
UCLA School
BASED
G. Parker,
of Medicine,
ON THE LINEAR
H. Rodney Los Angeles,
QUADRATIC
MODEL
AND
ITS
Withers CA 90024
Purpose/Objective: Radiotherapy plans based on physical dose distributions do not necessarily reflect entirely the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model. Materials & Methods: A computer program which converts a physical dose distribution calculated by a commercially available treatment planning system to a biologically effective dose (BED) distribution has been developed and verified against theoretical calculations. This software accepts a user’s input of biological parameters for each structure of interest (linear and quadratic dose-response and repopulation kinetic parameters), as well as treatment scheme factors (number of fractions, fractional dose, and treatment time). It then presents a two-dimensional BED display in conjunction with anatomical structures. With this tool and the parameters extracted from the literature, selected scenarios of clinical treatments were studied for the variations in tissue BED under different treatment schemes. Results: The following sample case serves to illustrate the application of our tool in clinical practice. For a typical four-field, evenly weighted prostate treatment using 10 MV X-ray beams, physical dosimetry predicted a comparable dose at the femoral heads between an alternate a-field/day and 4-field/day set-ups. However, our calculations revealed an approximate 25% higher BED for the 2-field/day scheme. This overdose to the femoral heads can be eliminated if the treatment is delivered with a 3 : 2 @P/PA : bilateral) dose weighting. Similar BED results of the above set-ups were seen with higher energy beams (such as 24 MV X-rays). With Co-60 beams, the increase of BED with alternate a-field/day, 1:l set-up was even more pronounced (34%). Conclusion: We have demonstrated the feasibility to construct a biologically oriented dose distribution for clinical practice of radiotherapy. The discordance between physical dose distributions and the biological counterparts based on the given treatment schemes were quantified. The computerized display of BED at non-prescription points greatly enhanced the versatility of this tool. While the routine use of this implementation in clinical radiotherapy should be cautiously done, depending largely on the accuracy of the published biological parameters, it may nevertheless help the clinicians derive an optimal treatment plan with a particular fractionation scheme or use it as a quantitative tool for outcome analysis in clinical research.
78 THE ROLE OF 3-DIMENSIONAL FUNCTIONAL LUNG IMAGING IN TREATMENT PLANNING: THE FUNCTIONAL DVH LB Marks, GW Sherouse, DP Spencer, G Bentel, R Clough, K Vann, R Jaszczak, E Coleman, MA Anscher, LR Prusnitz Department of Radiation Oncology and Nuclear Medicine, Duke University Medical Center, Durham, NC 27710 w: During thoracic XRT, it is common to design fields thatattemptto minimize the volume of non-tumor containing lung included. Generally, one does not consider functional heterogeneities within the lung. The 3-D functional information provided by single photon emission computed tomography (SPECT) lung perfusion scans might be useful in designing beams that minimize incidental irradiation of functioning lung tissue. We herein review the pre-treatment SPECT scans in 86 patients to determine which patients are likely to benefit from this technology. Methm: Prior to thoracic XRT, SPECT scans were obtained following the intravenous injection of = 4 mCi of 99mTc-labeled macroaggregated albumin. The presence of functional heterogeneities, their location relative to the tumor, and the clinical usefulness of their recognition were scored. Patients were grouped and compared (2-tailed chi sq) based on clinical factors. Conventional Dose-Volume Histograms (DVH’s) and Functional DVH’s (DVFH’S) are calculated based on the dose distribution throughout the CT-defined lung and SPECTdefined perfused lung, respectively.