Medium-dose-rate brachytherapy of cancer of the cervix: preliminary results of a prospectively designed schedule based on the linear-quadratic model

Treatment outcome of medium-dose-rate intracavitary brachytherapy for carcinoma of the uterine cervix: comparison with low-dose-rate intracavitary brachytherapy

PURPOSE

To evaluate and compare the efficacy of medium-dose-rate (MDR) and low-dose-rate (LDR) intracavitary brachytherapy (ICBT) for uterine cervical cancer.

METHODS AND MATERIALS

We evaluated 419 patients with squamous cell carcinoma of the cervix who were treated by radical radiotherapy with curative intent at Tokyo Women's Medical University from 1969 to 1999. LDR was used from 1969 to 1986, and MDR has been used since July 1987. When compared with LDR, fraction dose was decreased and fraction size was increased (1 or 2 fractions) for MDR to make the total dose of MDR equal to that of LDR. In general, the patients received a total dose of 60 to 70 Gy at Point A with external beam radiotherapy combined with brachytherapy according to the International Federation of Gynecology and Obstetrics stage. In the LDR group, 32 patients had Stage I disease, 81 had Stage II, 182 had Stage III, and 29 had Stage IVA; in the MDR group, 9 patients had Stage I disease, 19 had Stage II, 55 had Stage III, and 12 had Stage IVA.

RESULTS

The 5-year overall survival rates for Stages I, II, III, and IVA in the LDR group were 78%, 72%, 55%, and 34%, respectively. In the MDR group, the 5-year overall survival rates were 100%, 68%, 52%, and 42%, respectively. No significant statistical differences were seen between the two groups. The actuarial rates of late complications Grade 2 or greater at 5 years for the rectum, bladder, and small intestine in the LDR group were 11.1%, 5.8%, and 2.0%, respectively. The rates for the MDR group were 11.7%, 4.2%, and 2.6%, respectively, all of which were without statistical differences.

CONCLUSION

These data suggest that MDR ICBT is effective, useful, and equally as good as LDR ICBT in daytime (about 5 hours) treatments of patients with cervical cancer.

21 years of biologically effective dose

In 1989 the British Journal of Radiology published a review proposing the term biologically effective dose (BED), based on linear quadratic cell survival in radiobiology. It aimed to indicate quantitatively the biological effect of any radiotherapy treatment, taking account of changes in dose-per-fraction or dose rate, total dose and (the new factor) overall time. How has it done so far? Acceptable clinical results have been generally reported using BED, and it is in increasing use, although sometimes mistaken for "biologically equivalent dose", from which it differs by large factors, as explained here. The continuously bending nature of the linear quadratic curve has been questioned but BED has worked well for comparing treatments in many modalities, including some with large fractions. Two important improvements occurred in the BED formula. First, in 1999, high linear energy transfer (LET) radiation was included; second, in 2003, when time parameters for acute mucosal tolerance were proposed, optimum overall times could then be "triangulated" to optimise tumour BED and cell kill. This occurs only when both early and late BEDs meet their full constraints simultaneously. New methods of dose delivery (intensity modulated radiation therapy, stereotactic body radiation therapy, protons, tomotherapy, rapid arc and cyberknife) use a few large fractions and obviously oppose well-known fractionation schedules. Careful biological modelling is required to balance the differing trends of fraction size and local dose gradient, as explained in the discussion "How Fractionation Really Works". BED is now used for dose escalation studies, radiochemotherapy, brachytherapy, high-LET particle beams, radionuclide-targeted therapy, and for quantifying any treatments using ionising radiation.

Effects of oxygen on intrinsic radiation sensitivity: A test of the relationship between aerobic and hypoxic linear-quadratic (LQ) model parameters

The poor treatment prognosis for tumors with high levels of hypoxia is usually attributed to the decreased sensitivity of hypoxic cells to ionizing radiation. Mechanistic considerations suggest that linear quadratic (LQ) survival model radiosensitivity parameters for hypoxic (H) and aerobic (A) cells are related by alphaH = alphaA/oxygen enhancement ratio (OER) and (alpha/beta)H=OER(alpha/beta)A. The OER parameter may be interpreted as the ratio of the dose to the hypoxic cells to the dose to the aerobic cells required to produce the same number of DSBs per cell. The validity of these expressions is tested against survival data for mammalian cells irradiated in vitro with low- and high-LET radiation. Estimates of hypoxic and aerobic radiosensitivity parameters are derived from independent and simultaneous least-squares fits to the survival data. An external bootstrap procedure is used to test whether independent fits to the survival data give significantly better predictions than simultaneous fits to the aerobic and hypoxic data. For low-LET radiation, estimates of the OER derived from the in vitro data are between 2.3 and 3.3 for extreme levels of hypoxia. The estimated range for the OER is similar to the oxygen enhancement ratios reported in the literature for the initial yield of DSBs. The half-time for sublethal damage repair was found to be independent of oxygen concentration. Analysis of patient survival data for cervix cancer suggests an average OER less than or equal to 1.5, which corresponds to a pO2 of 5 mm Hg (0.66%) in the in vitro experiments. Because the OER derived from the cervix cancer data is averaged over cells at all oxygen levels, cells irradiated in vivo under extreme levels of hypoxia (<0.5 mm Hg) may have an OER substantially higher than 1.5. The reported analyses of in vitro data, as well as mechanistic considerations, provide strong support for the expressions relating hypoxic and aerobic radiosensitivity parameters. The formulas are also useful for the analysis of clinical data because the number of radiosensitivity parameters that need to be determined is reduced from four to three without a substantial decrease in the ability of the LQ to accurately predict the surviving faction. The relationships among radiosensitivity parameters imply that the dose to the hypoxic subvolume of the tumor needs to be escalated by a factor of the OER to achieve the same level of tumor control as in well oxygenated tumor regions.

Intracavitary brachytherapy for carcinoma of the uterine cervix—Comparison of HDR (Ir-192) and MDR (Cs-137)—

PURPOSE

To compare the results of high dose rate (HDR) (Ir-192) and medium dose rate (MDR) (Cs-137) intracavitary brachytherapy (ICRT) for carcinoma of the uterine cervix.

MATERIALS AND METHODS

Between May 1991 and March 2001, a total of 206 patients with Stage I-IVA previously untreated cervical cancer were treated with ICRT combined with external beam radiotherapy (EBRT). HDR was administered to a total of 135 patients: 22 patients in Stage I, 49 in Stage II, 56 in Stage III, and eight in Stage IVA. MDR was administered to a total of 71 patients: six patients in Stage I, 27 in Stage II, 33 in Stage III, and five in Stage IVA. The MDR at point A was 30 Gy/hour for HDR and 1.7 Gy/hour for MDR treatment, and the corresponding median follow-up periods for survivors were 55 and 68 months.

RESULTS

For the HDR group, 5-year cause-specific survival rates were 90%, 78%, 53% and 33% for Stages I, II, III, and IVA, respectively. For the MDR group, the corresponding rates were 100%, 76%, 51%, and 40%. In the HDR group, 19 patients (14%) developed Grade 2 or higher late complications, and, in the MDR group, four patients (6%) did.

CONCLUSIONS

There was no statistically significant difference in cause-specific survivals between the results of HDR and MDR brachytherapy for cervical cancer. The incidence of late complications tended to be higher for the HDR group than for the MDR group, but did not show a statistically significant difference (p=0.07).

Prospective study of HDR (192Ir) versus MDR (137Cs) intracavitary brachytherapy for carcinoma of the uterine cervix

PURPOSE

The aim of this study was to compare the results of high-dose rate (HDR) and medium-dose rate (MDR) intracavitary brachytherapy for carcinoma of the uterine cervix on the basis of a prospective study and to determine the dose rate conversion factor (DRCF) from low-dose rate (LDR) to MDR via HDR, because a DRCF of 0.54 from LDR to HDR has been widely accepted.

MATERIALS AND METHODS

Between August 1991 and July 1999, 104 patients were entered into this trial to compare results between HDR (n=54) and MDR (n=50). Three patients were excluded from this study, leaving 54 HDR patients and 47 MDR patients eligible. Method and dose of external beam radiotherapy were the same for both groups. For HDR intracavitary brachytherapy, point A dose was adjusted to 32 Gy/4 fractions for stages I and II, to 30 Gy/4 fractions for stage III, and to 22.5 Gy/3 fractions for stage IV. The corresponding values for MDR were 35.6 Gy/4 fractions, 34 Gy/4 fractions, and 25.5 Gy/3 fractions. The average dose rate at point A was 30 Gy/hour (9.0-65.2) for HDR and 1.7 Gy/hour (1.3-2.2) for MDR. We assumed a DRCF of 0.9 from MDR to HDR.

RESULTS

The 3-year cause-specific survival rates for HDR were 85%, 83%, 75%, and 0% for stages I, II, III, and IV, respectively. The corresponding figures for MDR were 100%, 82%, 58%, and 40%. Six of the HDR patients (11%) and 2 of the MDR patients (4%) developed Kottmeier's grade 2 or 3 late complications. A DRCF of 0.6 from LDR to MDR could be derived from a DRCF of 0.9 from MDR to HDR and one of 0.54 from LDR to HDR.

CONCLUSIONS

There were no statistically significant differences in cause-specific survival and incidence of late complications between HDR and MDR. A DRCF of 0.6 from LDR to MDR could be determined. However, because the results of this trial were preliminary, a further study is needed.

Compensation for changes in dose-rate in radical low-dose-rate brachytherapy: a radiobiological analysis of a randomised clinical trial

BACKGROUND AND PURPOSE

This study reanalysed the results of the Cs-137 low-dose-rate brachytherapy trials for stage I and II cervix carcinoma at the Christie Hospital, Manchester, UK, in order to quantify the clinical outcome as a function of dose, and to extract radiobiological parameter values by modelling the data for local control and morbidity.

PATIENTS AND METHODS

Kaplan-Meier survival curves and Cox regression analyses were used to analyse the time to event data. Linear-quadratic (LQ) analysis was also used in a mixture model, incorporating a half-time for repair, a time factor, and a heterogeneity function between patients. Full 5-year follow-up data were available for 339 patients receiving Cs-137 doses between 60 and 75 Gy delivered at 1.4-1.8 Gy/h, and 178 patients receiving a Ra-226 dose of 75 Gy at 0.5 Gy/h, using two insertions 7-10 days apart.

RESULTS

With the increased dose-rate, a dose reduction between 20 and 25% was required to achieve a similar morbidity rate. This reduction had a detrimental effect on tumour control, by about 15% points. Unexpectedly, this loss in local control did not lead to a decrease in cancer-specific survival. For both tumour control and complications a high alpha/beta and short half-time for repair best fitted the data, suggesting that consequential late reactions may be responsible for much of the bowel and urinary morbidity after these short treatments. The variability in response between patients was greater (CV 40%) for morbidity than for tumour control (CV 17%), probably reflecting the greater variation in dose at the target tissue. There was no significant dependence on overall treatment time detected over the 7-10-day range of these treatments.

CONCLUSIONS

The therapeutic ratio was somewhat less for the higher dose-rate, in agreement with radiobiological expectations, although cancer-specific survival was inexplicably unchanged. The LQ-parameter analysis suggests that high alpha/beta ratios and/or short repair half-times are applicable for both tumour and normal tissue responses in these treatments.

The irradiation tolerance dose of the proximal vagina

PURPOSE

The purpose of this investigation was to determine the irradiation tolerance level and complication rates of the proximal vagina to combined external irradiation and low dose rate (LDR) brachytherapy. Also, the mucosal tolerance for fractionated high dose rate (HDR) brachytherapy is further projected based on the biological equivalent dose (BED) of LDR for an acceptable complication rate.

MATERIALS AND METHODS

Two hundred seventy-four patients with stages I-IV cervical carcinoma treated with irradiation therapy alone from 1987 to 1997 were retrospectively reviewed for radiation-associated late sequelae of the proximal vagina. All patients received LDR brachytherapy and 95% also received external pelvic irradiation. Follow-up ranged from 15 to 126 months (median, 43 months). The proximal vagina mucosa dose from a single ovoid (single source) or from both ovoids plus the tandem (all sources), together with the external irradiation dose, were used to derive the probability of a complication using the maximum likelihood logistic regression technique. The BED based on the linear-quadratic model was used to compute the corresponding tolerance levels for LDR or HDR brachytherapy.

RESULTS

Grades 1 and 2 complications occurred in 10.6% of patients and Grade 3 complications occurred in 3.6%. There were no Grade 4 complications. Complications occurred from 3 to 71 months (median, 7 months) after completion of irradiation, with over 60% occurring in the first year. By logistic regression analysis, both the mucosal dose from a single ovoid or that from all sources, combined with the external irradiation dose, demonstrate a statistically significant fit to the dose response complication curves (both with P=0.016). The single source dose was highly correlated with the all source dose with a cross-correlation coefficient 0.93. The all source dose was approximately 1.4 times the single source dose. Over the LDR brachytherapy dose rate range, the complication rate was relatively stable to small variations of the underlying tumor biological characteristics and the dose rate. The complication rates change approximately an absolute 1% over the range of the alpha-beta ratio (alpha/beta) from 2 to 4 Gy and repair constant (mu) of 0.46/h to 0.60/h. The complication rates increased an absolute 2% over the mucosa dose rate from 1.75 to 3.50 Gy/h. They markedly increased as the dose rate increased above 3.00 Gy/h as in HDR brachytherapy. The projected HDR Grade 3 tolerance varied from 25 Gy for one fraction to 57 Gy for six fractions in addition to 20 Gy external irradiation for nominal 3-5% complication rates. The traditional LDR tolerance dose of 150 Gy was shown to yield nominal 11% and 4% Grades 1 and 2 and Grade 3 sequelae, respectively.

CONCLUSIONS

The traditional 150 Gy LDR tolerance dose (single source plus external irradiation) can be relaxed to 175 Gy or equivalently a full mucosal dose of 238 Gy (all sources plus external irradiation) for a nominal 5% Grade 3 complication rate. Higher fractionation is necessary with four to six fractions in HDR therapy for similar rates of sequelae. The mucosal surface dose from a single ovoid, which can be readily computed, remains a convenient tolerance check for treatment planning purposes.

The optimal fraction size in high-dose-rate brachytherapy: dependency on tissue repair kinetics and low-dose rate

BACKGROUND AND PURPOSE

Indications of the existence of long repair half-times on the order of 2-4 h for late-responding human normal tissues have been obtained from continuous hyperfractionated accelerated radiotherapy (CHART). Recently, these data were used to explain, on the basis of the biologically effective dose (BED), the potential superiority of fractionated high-dose rate (HDR) with large fraction sizes of 5-7 Gy over continuous low-dose rate (LDR) irradiation at 0.5 Gy/h in cervical carcinoma. We investigated the optimal fraction size in HDR brachytherapy and its dependency on treatment choices (overall treatment time, number of HDR fractions, and time interval between fractions) and treatment conditions (reference low-dose rate, tissue repair characteristics).

METHODS AND MATERIALS

Radiobiologic model calculations were performed using the linear-quadratic model for incomplete mono-exponential repair. An irradiation dose of 20 Gy was assumed to be applied either with HDR in 2-12 fractions or continuously with LDR for a range of dose rates. HDR and LDR treatment regimens were compared on the basis of the BED and BED ratio of normal tissue and tumor, assuming repair half-times between 1 h and 4 h.

RESULTS

With the assumption that the repair half-time of normal tissue was three times longer than that of the tumor, hypofractionation in HDR relative to LDR could result in relative normal tissue sparing if the optimum fraction size is selected. By dose reduction while keeping the tumor BED constant, absolute normal tissue sparing might therefore be achieved. This optimum HDR fraction size was found to be largely dependent on the LDR dose rate. On the basis of the BED(NT/TUM) ratio of HDR over LDR, 3 x 6.7 Gy would be the optimal HDR fractionation scheme for replacement of an LDR scheme of 20 Gy in 10-30 h (dose rate 2-0.67 Gy/h), while at a lower dose rate of 0.5 Gy/h, four fractions of 5 Gy would be preferential, still assuming large differences between tumor and normal tissue repair half-times and equal overall treatment time. For the same fraction size, an even larger normal tissue sparing can be obtained by prolongation of the HDR overall treatment time.

CONCLUSION

Radiobiologic model calculations presented here aim to demonstrate that hypofractionation in HDR might have its opportunities for widening the therapeutic window, but definitely has its limits. For each specific combination of the parameters, a theoretical optimal HDR fraction size with regard to relative or absolute normal tissue sparing can be estimated, but because of uncertainty in the biologic parameters, these hypofractionation schemes cannot be generalized for all HDR brachytherapy indications.

High-dose-rate brachytherapy at 14 Gy per hour to point A: preliminary results of a prospectively designed schedule for cancer of the cervix based on the linear-quadratic model

The objective of this study was to describe the results and complications of a prospectively designed high-dose-rate (HDR) brachytherapy schedule for early-stage cancer of the cervix, at 14 Gy/h to point A, based on the linear-quadratic model and our clinical experience. We used a combination of brachytherapy and external beam pelvic and parametrial irradiation in 88 consecutively seen patients with stage IB1-IIB treated by irradiation alone (1995-1998). The modeled HDR schedule consisted of three insertions on three treatment days separated by 10 days, with six 7 Gy planned brachytherapy fractions to point A, at 14 Gy/h, two on each treatment day with an interfraction interval of 6 h, plus an 18 Gy external whole-pelvic dose followed by additional parametrial irradiation. The calculated biologically effective dose (BED) was 92 Gy10 for tumor and 110 Gy3 for the rectum, equivalent to 77 and 66 Gy in 2 Gy fractions, respectively. The median overall treatment time was 41 days. The actuarial 4-year central recurrence-free rate, pelvic control, and disease-free survival rate were 97%, 93%, and 88% for stages IB-IIA and 79%, 75%, and 75% for stage IIB. The actuarial 4-year late complication rate for grades 2-3 was 4.7% (scale 0-3). We conclude that preliminary results of this HDR brachytherapy schedule for early-stage disease at a median follow-up of 52 months are as effective as the previously used low dose rate (LDR) at 0.44 Gy/h at point A. They are also as effective as medium-dose-rate schedules (MDR) at 1.6-1.5 Gy/h at this institution and do not require a further increase in fractionation of intracavitary treatments or in the whole-pelvic external beam irradiation dose common to standard HDR schedules. In addition, more patients per machine can be treated per day compared with MDR. Longer follow-up is required for a complete assessment of late complications.

Office hours pulsed brachytherapy boost in breast cancer

BACKGROUND AND PURPOSE

Radiobiological studies suggest equivalent biological effects between continuous low dose rate brachytherapy (CLDR) and pulsed brachytherapy (PB) when pulses are applied without interruption every hour. However, radiation protection and institute-specific demands requested the design of a practical PB protocol substituting the CLDR boost in breast cancer patients. An office hours scheme was designed, considering the CLDR dose rate, the overall treatment time, pulse frequency and tissue repair characteristics. Radiobiological details are presented as well as the logistics and technical feasibility of the scheme after treatment of the first 100 patients.

MATERIALS AND METHODS

Biologically effective doses (BEDs) were calculated according to the linear quadratic model for incomplete repair. Radiobiological parameters included an alpha/beta value of 3 Gy for normal tissue late effects and 10 Gy for early normal tissue or tumour effects. Tissue repair half-time ranged from 0.1 to 6 h. The reference CLDR dose rate of 0.80 Gy/h was obtained retrospectively from analysis of patients' data. The treatment procedure was evaluated with regard to variations in implant characteristics after treatment of 100 patients.

RESULTS

A PB protocol was designed consisting of two treatment blocks separated by a night break. Dose delivery in PB was 20 Gy in two 10 Gy blocks and, for application of the 15 Gy boost, one 10 Gy block plus one 5 Gy block. The dose per pulse was 1.67 Gy, applied with a period time of approximately 1.5 h. An inter-patient variation of 30% (1 SD) was observed in the instantaneous source strength. Taking also the spread in implant size into account, the net variation in pulse duration amounted to 38%.

CONCLUSION

An office hours PB boost regimen was designed for substitution of the CLDR boost in breast-conserving therapy on the basis of the BED. First treatment experience shows the office hour regimen to be convenient to the patients and no technical perturbations were encountered.

[Curietherapy in uterine cervix cancers: what therapeutic trends?]

Brachytherapy is a fundamental step in the treatment of patients with cervical cancer. Brachytherapy allows a significant increase in the local control rate as well as the survival rate. Brachytherapy has to be performed as soon as possible after external irradiation in order to maintain the overall treatment time below 53 days. Technical and dosimetric data characterizing low dose-rate brachytherapy using ICRU 38 recommendations have led to an improvement in local control and a decrease in complications. Data are less well known for other dose rates. The role of interstitial brachytherapy is not clearly defined and its potential benefit is probably balanced by an increase in severe complications. Concomitant brachy-chemotherapy requires further clinical investigations, even if concomitant radio-chemotherapy has become a standard in advanced cervical cancers.