Pitfalls in estimating the influence of overall treatment time on local tumor control

Lack of a Time-Factor in Alternating Chemoradiotherapy for Advanced Head and Neck Squamous Cell Carcinoma

Purpose

To assess whether a radiotherapy time factor exists also for patients affected by head and neck squamous cell carcinoma and receiving combined chemoradiotherapy.

Methods and materials

From 1989 to 1997, of 121 patients affected by stage III or IV head and neck squamous cell carcinoma who underwent alternating chemotherapy and radiotherapy according to the Merlano regimen at our institution, 59 were selected for time factor analysis. Until 1995, if chemotherapy had to be delayed because of bone marrow toxicity, radiotherapy was also delayed accordingly. Since January 1996 in order to avoid treatment-free gaps, radiotherapy was delivered continuously until it was possible to resume chemotherapy. Potential predictive factors of local-regional control were included in univariate and multivariate models. The median follow-up is 26 months (5-121 months).

Results

As a result of change in treatment policy, mean radiotherapy duration was shorter for 25 patients treated after 1995 (group A, 8.4 weeks) than for those treated during 1995 or before (group B, 9.4 weeks) (t test, P = 0.0012). In contrast, as expected, mean chemotherapy duration remained relatively unchanged through the years (10.9 vs 10.7 weeks for groups B and A, respectively, t test, P = 0.77). At 2 years, the actuarial local-regional control rate was 53 ± 7% for the whole population. The estimated rates of local-regional control at 2 years were 49 ± 10% and 56 ± 9% for patients belonging to groups A and B, respectively. At univariate and multivariate analyses, treatment group was not predictive of local-regional control.

Conclusions

Our attempt to prospectively limit radiotherapy overall treatment time failed to improve outcome. The data, although obtained on a relatively limited number of patients, suggest that tumor cell repopulation during radiotherapy may not be clinically relevant when chemotherapy is part of the treatment for advanced head and neck squamous cell carcinoma.

Onset time of tumor repopulation for cervical cancer: first evidence from clinical data

PURPOSE

Accelerated tumor repopulation has significant implications in low-dose rate (LDR) brachytherapy. Repopulation onset time remains undetermined for cervical cancer. The purpose of this study was to determine the onset time of accelerated repopulation in cervical cancer, using clinical data.

METHODS AND MATERIALS

The linear quadratic (LQ) model extended for tumor repopulation was used to analyze clinical data and magnetic resonance imaging-based three-dimensional tumor volumetric regression data from 80 cervical cancer patients who received external beam radiotherapy (EBRT) and LDR brachytherapy. The LDR dose was converted to EBRT dose in 1.8-Gy fractions by using the LQ formula, and the total dose ranged from 61.4 to 99.7 Gy. Patients were divided into 11 groups according to total dose and treatment time. The tumor control probability (TCP) was calculated for each group. The least χ(2) method was used to fit the TCP data with two free parameters: onset time (T(k)) of accelerated repopulation and number of clonogens (K), while other LQ model parameters were adopted from the literature, due to the limited patient data.

RESULTS

Among the 11 patient groups, TCP varied from 33% to 100% as a function of radiation dose and overall treatment time. Higher dose and shorter treatment duration were associated with higher TCP. Using the LQ model, we achieved the best fit with onset time T(k) of 19 days and K of 139, with uncertainty ranges of (11, 22) days for T(k) and (48, 1822) for K, respectively.

CONCLUSION

This is the first report of accelerated repopulation onset time in cervical cancer, derived directly from clinical data by using the LQ model. Our study verifies the fact that accelerated repopulation does exist in cervical cancer and has a relatively short onset time. Dose escalation may be required to compensate for the effects of tumor repopulation if the radiation therapy course is protracted.

Monte Carlo radiotherapy simulations of accelerated repopulation and reoxygenation for hypoxic head and neck cancer

OBJECTIVE

A temporal Monte Carlo tumour growth and radiotherapy effect model (HYP-RT) simulating hypoxia in head and neck cancer has been developed and used to analyse parameters influencing cell kill during conventionally fractionated radiotherapy. The model was designed to simulate individual cell division up to 10(8) cells, while incorporating radiobiological effects, including accelerated repopulation and reoxygenation during treatment.

METHOD

Reoxygenation of hypoxic tumours has been modelled using randomised increments of oxygen to tumour cells after each treatment fraction. The process of accelerated repopulation has been modelled by increasing the symmetrical stem cell division probability. Both phenomena were onset immediately or after a number of weeks of simulated treatment.

RESULTS

The extra dose required to control (total cell kill) hypoxic vs oxic tumours was 15-25% (8-20 Gy for 5 × 2 Gy per week) depending on the timing of accelerated repopulation onset. Reoxygenation of hypoxic tumours resulted in resensitisation and reduction in total dose required by approximately 10%, depending on the time of onset. When modelled simultaneously, accelerated repopulation and reoxygenation affected cell kill in hypoxic tumours in a similar manner to when the phenomena were modelled individually; however, the degree was altered, with non-additive results. Simulation results were in good agreement with standard linear quadratic theory; however, differed for more complex comparisons where hypoxia, reoxygenation as well as accelerated repopulation effects were considered.

CONCLUSION

Simulations have quantitatively confirmed the need for patient individualisation in radiotherapy for hypoxic head and neck tumours, and have shown the benefits of modelling complex and dynamic processes using Monte Carlo methods.

Clinical significance of cumulative biological effective dose and overall treatment time in the treatment of carcinoma cervix

The purpose of this retrospective study is to report the radiotherapy treatment response of, and complications in, patients with cervical cancer on the basis of cumulative biologic effective dose (BED) and overall treatment time (OTT).

Sixty-four (stage II - 35/64; stage III - 29/64) patients of cervical cancer were treated with combination of external beam radiotherapy (EBRT) and low dose rate intracavitary brachytherapy (ICBT). The cumulative BED was calculated at Point A (BED₁₀); and bladder, rectal reference points (BED_2,5) using the linear-quadratic BED equations.

The local control (LC) rate and 5-year disease-free survival (DFS) rate in patients of stage II were comparable for BED₁₀ <84.5 and BED₁₀ >84.5 but were much higher for BED₁₀ >84.5 than BED₁₀ <84.5 (P< 0.01) in stage III patients. In the stage II patients, The LC rate and 5-year DFS rate were comparable for OTT <50 days and for OTT >50 days but were much higher in stage III patients with OTT < 50 than OTT >50 days (P< 0.001). It was also observed that patients who received BED_2.5 <105 had lesser rectal (P< 0.001) and bladder complications than BED_2.5 >105. Higher rectal complication-free survival (CFS_R) rate, bladder complication-free survival (CFS_B) rate and all-type late complication-free survival rate were observed in patients who received BED_2.5 < 105 than BED_2.5 >105.

A balanced, optimal and justified radiotherapy treatment schedule to deliver higher BED₁₀ (>84.5) and lower BED_2.5 (< 105) in lesser OTT (< 50 days) is essential in carcinoma cervix to expect a better treatment outcome in all respects.

Developments in radiotherapy

A systematic assessment of radiotherapy for cancer was conducted by The Swedish Council on Technology Assessment in Health Care (SBU) in 2001. The assessment included a review of future developments in radiotherapy and an estimate of the potential benefits of improved radiotherapy in Sweden. The conclusions reached from this review can be summarized as: Successively better knowledge is available on dose-response relationships for tumours and normal tissues at different fractionation schedules and treated volumes. Optimization of dose levels and fractionation schedules should improve the treatment outcome. Improved treatment results may be expected with even more optimized fractionation schedules. The radiosensitivity of the tumour is dependent on the availability of free oxygen in the cells. The oxygen effect has been studied for a long time and new knowledge has emerged, but there is still no consensus on the best way to minimize its negative effect in the treatment of hypoxic tumours. Development in imaging techniques is rapid, improving accuracy in outlining targets and organs at risk. This is a prerequisite for advanced treatment planning. More accurate treatment can be obtained using all the computer techniques that are successively made available for calculating dose distributions, controlling the accelerator and multileaf collimator (MLC) and checking patient set-up. Optimized treatment plans can be achieved using inverse dose planning and intensity modulation radiation therapy (IMRT). Optimization algorithms based on biological data from clinical trials could be a part of future dose planning. New genetic markers might be developed that give a measure of the radiation responsiveness of tumours and normal tissue. This could lead to more individualized treatments. New types of radiation sources may be expected: protons, light ions, and improved beams (and compounds) for boron neutron capture therapy (BNCT). Proton accelerators with scanned-beam systems and energy modulation give good dose distribution. The results reported with carbon ions from Japan and Germany are promising. An interesting development is to verify the dose and position for the irradiated volume with PET on line. Safer margins are obtained and the treatment volume can thus be limited. Very large accelerators are needed to accelerate the carbon ions. Still, it should be possible to keep the costs per patient at the same level as those for other types of advanced radiotherapy, since far fewer treatments per patient are needed. It might also be possible to treat new groups of patients. Increased resources are needed to introduce all the currently available techniques. New types of particle accelerators require large investments and a new structure of radiotherapy in Sweden.

The effects of delays in radiotherapy treatment on tumour control

There is often a considerable delay from initial tumour diagnosis to the start of radiotherapy treatment, which may be due to factors such as waiting lists and referral delays. This paper uses widely published models and clinical parameters to calculate the effect of delays in treatment on local tumour control for four different types of tumour-squamous cell carcinoma (head and neck), breast, cervix and prostate. The Poisson model for tumour control probability (TCP), an exponential function for tumour growth and the linear quadratic model of cell kill are used to calculate the change in TCP for delays between diagnosis and treatment of up to 100 days. Typical values of the clinical parameters have been taken from the literature; these include alpha and beta, sigma(alpha), tumour size at diagnosis, pre-treatment doubling time, delay in onset of accelerated repopulation and doubling time during treatment. It is acknowledged that there are limitations in the reliability of these data for predicting absolute values of tumour control, but models are still useful for predicting how changes in treatment parameters are likely to affect the outcome. It is shown that for fast-growing tumours a delay of 1-2 months can have a significant adverse effect on the outcome, whereas for slow-growing tumours such as Ca prostate a delay of a few months does not significantly reduce the probability of tumour control. These calculations show the importance of ensuring that delays from diagnosis through to treatment are minimized, especially for patients with rapidly proliferating tumours.