- Email: [email protected]
Reply to the comments of Dr Lee
210
Letter to the Editor / Radiotherapy and Oncology 70 (2004) 207–212
[2] Stock RG, Stone NN, Tabert A, Iannuzzi C, DeWyngaert JK. A dose–response study for I-125 prostate implants. Int J Radiat Oncol Biol Phys 1998;41(1):101– 8. [3] Stock RG, Kao J, Stone NN. Penile erectile function after permanent radioactive seed implantation for treatment of prostate cancer. J Urol 2001;165(2):436–9.
W. Robert Lee Department of Radiation Oncology, School of Medicine, Medical Center Boulevard, Wake Forest University, Winston-Salem, NC 27157-1030, USA
0167-8140/$ - see front matter q 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2003.11.012
Received 22 September 2003; accepted 17 November 2003
Reply to the comments of Dr Lee To the Editor We appreciate receiving the thoughtful comments of Dr Lee regarding our recent article, and welcome the opportunity to address his concerns about our conclusion. First and most importantly, we stand by the conclusion that the use of higher activity sources yielded significantly better dosimetric coverage in our study. While in the case of an individual patient we concur with Dr Lee’s assessment that “it is not at all clear… that a D90 of 99% (mean for low activity group) is ‘worse’ than a D90 of 108% (mean for high activity group)”, we would like to point out that the same cannot be said for our two groups of patients. The reason is that the D90 values in each group are distributed about their respective mean values to an extent quantified by their standard deviations, and so different numbers can be expected to fall below the D90 cutoff at 90% [3,4]. Our D90 values are approximately normally distributed (small patient numbers result in histograms with a rough shape), and indicate 5/20 patients below the cutoff for the low activity group (D90 ¼ 78.0%, 78.5%, 80.9%, 85.6%, 89.6%), and 2/20 for the high activity group (D90 ¼ 85.1%, 88.6%). Consequently, dosimetric coverage is better for the high activity group. Given that radiation-induced morbidity also needs to be minimized, the cautionary note sounded by Dr Lee that “more is not necessarily better and may be worse” is entirely appropriate. However, the specific finding of the Mt. Sinai group presented in support of this position, namely that more sexual morbidity is observed with D90 . 160 Gy [5], is open to question insofar as I-125 implants are concerned. As Table 3 in Ref. [5] indicates, the reported effect arises entirely from a difference for Pd-103 implants; potency rates at 6 years for I-125 implant patients above and below the 160 Gy cut point are identical. Additional guidance regarding appropriate high-dose limits
can be obtained by focusing on site-specific structures. In separate studies, the Schiffler group found no relationship between radiation dose to the neurovascular bundles (which averaged 209% of the prescribed dose for the study population) and postbrachytherapy impotence [1], and a predictive relationship between dose to the bulb of the penis (quantified by bulb D50) and brachytherapy-induced erectile dysfunction [2]. Secondly, while our clinical data may appear to suggest that short term urinary morbidity (as measured by urinary catheterization) is greater in the high activity group, the difference is not statistically significant. More importantly, a patient’s urinary status prior to implant is correlated with a need for catheterization afterwards; consequently the reported difference in catheterization rates (3/20 in the high activity group vs. 1/20 in the low) can be explained in terms of the random nature of predisposing symptom presentation for small groups of patients. This latter interpretation has been borne out by our clinical experience subsequent to completing the study. We agree with Dr Lee that dosimetric objectives for prostate brachytherapy will continue to evolve as new clinical data are reported, and appreciate the opportunity to clarify the interpretation of our own data. References [1] Merrick GS, Wallner K, Butler WM, Lief JH, Sutlief S. Short-term sexual function after prostate brachytherapy. Int J Cancer 2001;96(5): 313– 9. [2] Merrick GS, Butler WM, Wallner KE, Lief JH, Anderson RL, Smeiles BJ, Galbreath RW, Benson ML. The importance of radiation dose to the penile bulb vs. crura in the development of postbrachytherapy erectile dysfunction. Int J Radiat Oncol Biol Phys 2002;54(4): 1055–62. [3] Potters L, Cao Y, Calugaru E, Torre T, Fearn P, Wang XH. A comprehensive review of CT-based dosimetry parameters and biochemical control in patients treated with permanent prostate brachytherapy. Int J Radiat Oncol Biol Phys 2001;50(3): 605– 14. [4] Stock RG, Stone NN, Tabert A, Iannuzzi C, DeWyngaert JK. A doseresponse study for I-125 prostate implants. Int J Radiat Oncol Biol Phys 1998;41(1):101– 8. [5] Stock RG, Kao J, Stone NN. Penile erectile function after permanent radioactive seed implantation for treatment of prostate cancer. J Urol 2001;165(2):436– 9.
Ron S. Sloboda Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alta., Canada T6G 1Z2
0167-8140/$ - see front matter q 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2003.11.020
Received 13 November 2003; accepted 17 November 2003
Letter to the Editor / Radiotherapy and Oncology 70 (2004) 207–212
[2] Stock RG, Stone NN, Tabert A, Iannuzzi C, DeWyngaert JK. A dose–response study for I-125 prostate implants. Int J Radiat Oncol Biol Phys 1998;41(1):101– 8. [3] Stock RG, Kao J, Stone NN. Penile erectile function after permanent radioactive seed implantation for treatment of prostate cancer. J Urol 2001;165(2):436–9.
W. Robert Lee Department of Radiation Oncology, School of Medicine, Medical Center Boulevard, Wake Forest University, Winston-Salem, NC 27157-1030, USA
0167-8140/$ - see front matter q 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2003.11.012
Received 22 September 2003; accepted 17 November 2003
Reply to the comments of Dr Lee To the Editor We appreciate receiving the thoughtful comments of Dr Lee regarding our recent article, and welcome the opportunity to address his concerns about our conclusion. First and most importantly, we stand by the conclusion that the use of higher activity sources yielded significantly better dosimetric coverage in our study. While in the case of an individual patient we concur with Dr Lee’s assessment that “it is not at all clear… that a D90 of 99% (mean for low activity group) is ‘worse’ than a D90 of 108% (mean for high activity group)”, we would like to point out that the same cannot be said for our two groups of patients. The reason is that the D90 values in each group are distributed about their respective mean values to an extent quantified by their standard deviations, and so different numbers can be expected to fall below the D90 cutoff at 90% [3,4]. Our D90 values are approximately normally distributed (small patient numbers result in histograms with a rough shape), and indicate 5/20 patients below the cutoff for the low activity group (D90 ¼ 78.0%, 78.5%, 80.9%, 85.6%, 89.6%), and 2/20 for the high activity group (D90 ¼ 85.1%, 88.6%). Consequently, dosimetric coverage is better for the high activity group. Given that radiation-induced morbidity also needs to be minimized, the cautionary note sounded by Dr Lee that “more is not necessarily better and may be worse” is entirely appropriate. However, the specific finding of the Mt. Sinai group presented in support of this position, namely that more sexual morbidity is observed with D90 . 160 Gy [5], is open to question insofar as I-125 implants are concerned. As Table 3 in Ref. [5] indicates, the reported effect arises entirely from a difference for Pd-103 implants; potency rates at 6 years for I-125 implant patients above and below the 160 Gy cut point are identical. Additional guidance regarding appropriate high-dose limits
can be obtained by focusing on site-specific structures. In separate studies, the Schiffler group found no relationship between radiation dose to the neurovascular bundles (which averaged 209% of the prescribed dose for the study population) and postbrachytherapy impotence [1], and a predictive relationship between dose to the bulb of the penis (quantified by bulb D50) and brachytherapy-induced erectile dysfunction [2]. Secondly, while our clinical data may appear to suggest that short term urinary morbidity (as measured by urinary catheterization) is greater in the high activity group, the difference is not statistically significant. More importantly, a patient’s urinary status prior to implant is correlated with a need for catheterization afterwards; consequently the reported difference in catheterization rates (3/20 in the high activity group vs. 1/20 in the low) can be explained in terms of the random nature of predisposing symptom presentation for small groups of patients. This latter interpretation has been borne out by our clinical experience subsequent to completing the study. We agree with Dr Lee that dosimetric objectives for prostate brachytherapy will continue to evolve as new clinical data are reported, and appreciate the opportunity to clarify the interpretation of our own data. References [1] Merrick GS, Wallner K, Butler WM, Lief JH, Sutlief S. Short-term sexual function after prostate brachytherapy. Int J Cancer 2001;96(5): 313– 9. [2] Merrick GS, Butler WM, Wallner KE, Lief JH, Anderson RL, Smeiles BJ, Galbreath RW, Benson ML. The importance of radiation dose to the penile bulb vs. crura in the development of postbrachytherapy erectile dysfunction. Int J Radiat Oncol Biol Phys 2002;54(4): 1055–62. [3] Potters L, Cao Y, Calugaru E, Torre T, Fearn P, Wang XH. A comprehensive review of CT-based dosimetry parameters and biochemical control in patients treated with permanent prostate brachytherapy. Int J Radiat Oncol Biol Phys 2001;50(3): 605– 14. [4] Stock RG, Stone NN, Tabert A, Iannuzzi C, DeWyngaert JK. A doseresponse study for I-125 prostate implants. Int J Radiat Oncol Biol Phys 1998;41(1):101– 8. [5] Stock RG, Kao J, Stone NN. Penile erectile function after permanent radioactive seed implantation for treatment of prostate cancer. J Urol 2001;165(2):436– 9.
Ron S. Sloboda Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alta., Canada T6G 1Z2
0167-8140/$ - see front matter q 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2003.11.020
Received 13 November 2003; accepted 17 November 2003