Early and late injuries in mouse rectum after fractionated X-ray and neutron irradiation

Hypofractionated Intensity-Modulated Simultaneous Integrated Boost and Image-Guided Radiotherapy in the Treatment of High-Risk Prostate Cancer Patients: A Preliminary Report on Acute Toxicity

Aims and background

To evaluate acute toxicity of hypofractionated intensity-modulated radiotherapy with simultaneous integrated boost and image-guided radiotherapy in the treatment of high-risk prostate cancer patients.

Methods

Between November 2009 and March 2012, 59 patients with high-risk prostate cancer were enrolled. The eclipse inverse planning system (Varian) was used to calculate an IMRT plan with simultaneous integrated boost, delivering 68.75 Gy (2.75 Gy per fraction) to the prostate, 55 Gy (2.2 Gy per fraction) to the seminal vesicles and positive nodes, and 45 Gy (1.8 Gy per fraction) to the pelvis, 4 fractions per week, 25 fractions. Prior to each treatment, patients underwent a kilo-voltage cone-beam CT performing an image-guided radiation therapy (IGRT). All patients were submitted to neoadjuvant, concomitant and adjuvant hormone therapy.

Results

The median follow-up for all patients was 13 months (range, 3–28). At the last follow-up, no grade 3 or 4 side effect was observed. Toxicity occurred as follows during the treatment: grade 1 and 2 gastrointestinal toxicity 5.2% and 6.9%, respectively; grade 1 and 2 genitourinary toxicity 24.1% and 1.7%, respectively. Only 1.7% of the patients developed grade 3 genitourinary toxicity. No grade 3 gastrointestinal toxicity was observed.

Conclusions

The present study demonstrated that 4/w hypofractionated intensity-modulated radiotherapy with simultaneous integrated boost and image-guided radiotherapy in patients with high-risk prostate cancer is feasible and safe. Low acute toxicity rates were verified. Longer follow-up is needed to evaluate the outcomes in terms of late toxicity and survival.

The contribution of women to radiobiology: Marie Curie and beyond

Marie Sklodowska-Curie, an extraordinary woman, a Polish scientist who lived and worked in France, led to the development of nuclear energy and the treatment of cancer. She was the laureate of two Nobel Prizes, the first woman in Europe who obtained the degree of Doctor of Science and opened the way for women to enter fields which had been previously reserved for men only. As a result of her determination and her love of freedom, she has become an icon for many female scientists active in radiation sciences. They are successors of Maria Curie and without the results of their work, improvement in radiation oncology will not be possible. Many of them shared some elements of Maria Curie's biography, like high ethical and moral standards, passionate dedication to work, strong family values, and scientific collaboration with their husbands. The significance of Tikvah Alper, Alma Howard, Shirley Hornsey, Juliana Denekamp, Helen Evans, Eleanor Blakely, Elizabeth L. Travis, Fiona Stewart, Andree Dutreix, Catharine West, Peggy Olive, Ingela Turesson, Penny Jeggo, Irena Szumiel, Eleonor Blakely, Sara Rockwell and Carmel Mothersill contribution to radiation oncology is presented. All the above mentioned ladies made significant contribution to the development of radiotherapy (RT) and more efficient cancer treatment. Due to their studies, new schedules of RT and new types of ionizing radiation have been applied, lowering the incidence of normal tissue toxicity. Their achievements herald a future of personalized medicine.

Image guided intensity modulated hypofractionated radiotherapy in high-risk prostate cancer patients treated four or five times per week: analysis of toxicity and preliminary results

Background

To evaluate efficacy and toxicity of hypofractionated intensity-modulated simultaneous integrated boost (IMRT-SIB) and image-guided (IGRT) radiotherapy in the treatment of high-risk prostate cancer patients.

Methods

Eighty-two patients with high-risk prostate cancer were analysed. An IMRT treatment was planned delivering 68.75 Gy to the prostate, 55 Gy to the seminal vesicles and positive nodes and 45 Gy to the pelvis in 25 fractions. The first 59 patients received 4 weekly fractions whereas the last 23 patients received 5 weekly fractions. All patients were submitted to hormonal therapy.

Results

The median follow-up was 31 months. Acute grade 1–2 gastrointestinal (GI) toxicity rates were 13.4%. Grade 1–2 and grade 3 genitourinary (GU) toxicity rates were 22% and 1.2%, respectively.

Grade 1 and 2 GI late toxicity rates were 1.2%. No grade ≥3 toxicity was recorded. Grade 1 GU late toxicity rate was 2.4%. No grade ≥2 toxicity was recorded.

No significant difference was calculated in terms of acute and late toxicity between the group treated 4 or 5 times weekly.

The actuarial 3-years Overall survival and Freedom from biochemical failure were 98.6% and 91.3%, respectively.

Conclusions

The present study demonstrated that hypofractionated IGRT-IMRT-SIB in patients with high-risk prostate cancer is efficient with acceptable toxicity profile. Outcome in terms of survival are promising, but longer follow-up is needed.

Stereotactic body radiation therapy for prostate cancer

Stereotactic body radiation therapy (SBRT) is a promising treatment option for prostate cancer. Hypofractionation regimens, such as SBRT, may be more advantageous compared with conventional regimens because low α:β ratio of prostate cancer has high sensitivity to dose per fraction. In addition, a smaller and tighter margin with SBRT is expected to provide a low toxicity rate without reducing tumor control. The purpose of this article is to examine radiobiological, technical and clinical aspects of SBRT for prostate cancer.

Estimation of α/β for late rectal toxicity based on RTOG 94-06

PURPOSE

To estimate α/β, the parameter ratio from the linear-quadratic (LQ) model, for Grade ≥2 late rectal toxicity among patients treated on Radiation Therapy Oncology Group (RTOG) protocol 94-06; and to determine whether correcting the rectal dose-volume histogram (DVH) for differences in dose per fraction, based on the LQ model, significantly improves the fit to these data of the Lyman-Kutcher-Burman (LKB) normal-tissue complication probability (NTCP) model.

METHODS AND MATERIALS

The generalized LKB model was fitted to the Grade ≥2 late rectal toxicity data in two ways: by using DVHs representing physical dose to rectum, and by using a modified approach in which dose bins in the rectal DVH were corrected for differences in dose per fraction using the LQ model, with α/β estimated as an additional unknown parameter. The analysis included only patients treated with the same treatment plan throughout radiotherapy, so that the dose per fraction to each voxel of rectum could be determined from the DVH. The likelihood ratio test was used to assess whether the fit of the LQ-corrected model was significantly better than the fit of the LKB model based on physical doses to rectum.

RESULTS

The analysis included 509 of the 1,084 patients enrolled on RTOG 94-06. The estimate of α/β from the LQ-corrected LKB model was 4.8 Gy, with 68% confidence interval 0.6 Gy to 46 Gy. The fit was not significantly different from the fit of the LKB model based on physical dose to rectum (p = 0.236).

CONCLUSIONS

The estimated fractionation sensitivity for Grade ≥2 late rectal toxicity is consistent with values of α/β for rectum found previously in human beings and in rodents. However, the confidence interval is large, and there is no evidence that LQ correction of the rectal DVH significantly changes the fit or predictions of the LKB model for this endpoint.

Acute toxicity in high-risk prostate cancer patients treated with androgen suppression and hypofractionated intensity-modulated radiotherapy

PURPOSE

To report acute toxicity resulting from radiotherapy (RT) dose escalation and hypofractionation using intensity-modulated RT (IMRT) treatment combined with androgen suppression in high-risk prostate cancer patients.

METHODS AND MATERIALS

Sixty patients with a histological diagnosis of high-risk prostatic adenocarcinoma (having either a clinical Stage of > or =T3a or an initial prostate-specific antigen [PSA] level of > or =20 ng/ml or a Gleason score of 8 to 10 or a combination of a PSA concentration of >15 ng/ml and a Gleason score of 7) were enrolled. RT prescription was 68 Gy in 25 fractions (2.72 Gy/fraction) over 5 weeks to the prostate and proximal seminal vesicles. The pelvic lymph nodes and distal seminal vesicles concurrently received 45 Gy in 25 fractions. The patients were treated with helical TomoTherapy-based IMRT and underwent daily megavoltage CT image-guided verification prior to each treatment. Acute toxicity scores were recorded weekly during RT and at 3 months post-RT, using Radiation Therapy Oncology Group acute toxicity scales.

RESULTS

All patients completed RT and follow up for 3 months. The maximum acute toxicity scores were as follows: 21 (35%) patients had Grade 2 gastrointestinal (GI) toxicity; 4 (6.67%) patients had Grade 3 genitourinary (GU) toxicity; and 30 (33.33%) patients had Grade 2 GU toxicity. These toxicity scores were reduced after RT; there were only 8 (13.6%) patients with Grade 1 GI toxicity, 11 (18.97%) with Grade 1 GU toxicity, and 5 (8.62%) with Grade 2 GU toxicity at 3 months follow up. Only the V60 to the rectum correlated with the GI toxicity.

CONCLUSION

Dose escalation using a hypofractionated schedule to the prostate with concurrent pelvic lymph node RT and long-term androgen suppression therapy is well tolerated acutely. Longer follow up for outcome and late toxicity is required.

Dosimetry and preliminary acute toxicity in the first 100 men treated for prostate cancer on a randomized hypofractionation dose escalation trial

PURPOSE

The alpha/beta ratio for prostate cancer is postulated to be between 1 and 3, giving rise to the hypothesis that there may be a therapeutic advantage to hypofractionation. The dosimetry and acute toxicity are described in the first 100 men enrolled in a randomized trial.

PATIENTS AND METHODS

The trial compares 76 Gy in 38 fractions (Arm I) to 70.2 Gy in 26 fractions (Arm II) using intensity modulated radiotherapy. The planning target volume (PTV) margins in Arms I and II were 5 mm and 3 mm posteriorly and 8 mm and 7 mm in all other dimensions. The PTV D95% was at least the prescription dose.

RESULTS

The mean PTV doses for Arms I and II were 81.1 and 73.8 Gy. There were no differences in overall maximum acute gastrointestinal (GI) or genitourinary (GU) toxicity acutely. However, there was a slight but significant increase in Arm II GI toxicity during Weeks 2, 3, and 4. In multivariate analyses, only the combined rectal DVH parameter of V65 Gy/V50 Gy was significant for GI toxicity and the bladder volume for GU toxicity.

CONCLUSION

Hypofractionation at 2.7 Gy per fraction to 70.2 Gy was well tolerated acutely using the planning conditions described.

Clinical effects in a cohort of cancer patients overexposed during external beam pelvic radiotherapy

PURPOSE

To evaluate the clinical outcome of 28 overexposed cancer patients in a cohort of 153 treated with pelvic irradiation and to correlate the outcome with the doses received.

METHODS AND MATERIALS

Between August 2000 and March 2001, 153 patients were treated at the Instituto Oncológico Nacional of Panama with radiotherapy for cancers of the cervix, uterus, endometrium, prostate, and rectum using conventional techniques. In 56 patients, irradiated with partially blocked teletherapy fields, the treatment times were determined using a treatment planning system that generated isodose distributions. The absorbed doses received by the patients were calculated and the biologically effective doses (BEDs) and 2-Gy equivalent doses derived. The clinical outcome was evaluated using the Radiation Therapy Oncology Group (RTOG) and late effects on normal tissues-subjective, objective, management, analytic scales (LENT/SOMA). The relationships between clinical outcome and dose were investigated and compared with published data.

RESULTS

Of the 56 patients for whom treatment times were generated with the treatment planning system, 28 received some doses per fraction approximately double those prescribed. Using an alpha/beta = 10 Gy, the tumor BED(10) values ranged from 77 to 225 Gy. The rest of the patients received doses within 10% of the prescribed values. Seventeen of the 28 overexposed patients died 35 days to 21 months after treatment; 13 of the fatalities were caused by rectal complications. Survival was longer in those patients who had undergone colostomy. Bladder complications were less enhanced. The nonoverexposed patients with cervical cancer exhibited a greater incidence of treatment failures than generally reported in other centers.

CONCLUSION

This study provides the clinical outcome after high doses of pelvic radiotherapy in a range not previously well documented. For cervical cancer patients receiving both tele- and brachytherapy, some deaths in this overexposure cohort occurred from assumed consequential rectal injury within 2 years, when the BED(10) values exceeded 70-80 Gy. The incidence was asymptotic to 100% fatalities at >150 Gy. This confirmed and extended other data in the literature.

What hypofractionated protocols should be tested for prostate cancer?

PURPOSE

Recent analyses of clinical results have suggested that the fractionation sensitivity of prostate tumors is remarkably high; corresponding point estimates of the alpha/beta ratio for prostate cancer are around 1.5 Gy, much lower than the typical value of 10 Gy for many other tumors. This low alpha/beta value is comparable to, and possibly even lower than, that of the surrounding late-responding normal tissue in rectal mucosa (alpha/beta nominally 3 Gy, but also likely to be in the 4-5 Gy range). This lower alpha/beta ratio for prostate cancer than for the surrounding late-responding normal tissue creates the potential for therapeutic gain. We analyze here possible high-gain/low-risk hypofractionated protocols for prostate cancer to test this suggestion.

METHODS AND MATERIALS

Using standard linear-quadratic (LQ) modeling, a set of hypofractionated protocols can be designed in which a series of dose steps is given, each step of which keeps the late complications constant in rectal tissues. This is done by adjusting the dose per fraction and total dose to maintain a constant level of late effects. The effect on tumor control is then investigated. The resulting estimates are theoretical, although based on the best current modeling with alpha/beta parameters, which are discussed thoroughly.

RESULTS

If the alpha/beta value for prostate is less than that for the surrounding late-responding normal tissue, the clinical gains can be rather large. Appropriately designed schedules using around ten large fractions can result in absolute increases of 15% to 20% in biochemical control with no evidence of disease (bNED), with no increase in late sequelae. Early sequelae are predicted to be decreased, provided that overall times are not shortened drastically because of a possible risk of acute or consequential late reactions in the rectum. An overall time not shorter than 5 weeks appears advisable for the hypofractionation schedules considered, pending further clinical trial results. Even if the prostate tumor alpha/beta ratio turns out to be the same (or even slightly larger than) the surrounding late-responding normal tissue, these hypofractionated regimens are estimated to be very unlikely to result in significantly increased late effects.

CONCLUSIONS

The hypofractionated regimens that we suggest be tested for prostate-cancer radiotherapy show high potential therapeutic gain as well as economic and logistic advantages. They appear to have little potential risk as long as excessively short overall times (<5 weeks) and very small fraction numbers (<5) are avoided. The values of bNED and rectal complications presented are entirely theoretical, being related by LQ modeling to existing clinical data for approximately intermediate-risk prostate cancer patients as discussed in detail.

Radiation-induced rectal complications are not influenced by age: a dose fractionation study in the rat

Radiation-induced complications of the rectum are an important dose-limiting factor in radiotherapy of pelvic malignancies. In general, animal studies demonstrated no differences in acute and late normal tissue toxicity with age, but little is known about rectal complications in relation to age. For this purpose, an extensive histological and dose fractionation study was carried out on the rectum of young (12 weeks) and older (77-80 weeks) rats. In this paper, the results of dose fractionation are presented in relation to age at the time of irradiation. Young and older animals were irradiated with single and fractionated doses. After irradiation, rectal complications could lead to occlusion and stenosis, eventually resulting in the clinical symptoms of a megacolon and a possible fistula. For each dose group, cumulative survival rates were obtained with Kaplan-Meier analysis, from which dose-effect curves and the associated LD(50) values for a megacolon/fistula were calculated. The majority of responders died between 8 and 24 weeks after irradiation, irrespective of age. For both age groups, only the fractionation data showed a reduction in the mean latency with increasing dose. In the older age group, 39% of the responders developed a fistula compared to 26% for the younger animals. The LD(50) values increased from around 30 Gy after single doses to nearly 65 Gy after 10 fractions. The increases in LD(50) values with the number of fractions were independent of the age of the rats. For each of the dose fractionation schedules, log-rank testing indicated no significant differences in cumulative survival rates between younger and older animals (P > 0.10). The high alpha/beta ratios obtained for both the young and older animals strongly suggested that the late rectal complications were a consequence of early epithelial injury. Associated histological findings indicated that blood vessel damage, which was already evident at a high incidence at 4 weeks after irradiation, could also play a significant role in the occurrence of consequential late injuries. In conclusion, data obtained for the latent period of rectal occlusion, for the dose-effect curves, for the log-rank testing of cumulative survival rates, and for the alpha/beta ratios strongly support the hypothesis that the incidence of radiation-induced rectal complications is independent of age. Late rectal complications could be a consequence of radiation-induced acute injury.

The assessment of RBE effects using the concept of biologically effective dose

PURPOSE

To modify existing linear-quadratic (LQ) equations in order to take account of relative biological effectiveness (RBE) using the concept of biologically effective dose (BED).

METHODS AND MATERIALS

Clinically useful forms of the LQ model have been modified to incorporate RBE effects in such a way as to allow comparison between high- and low-LET (linear energy transfer) radiations in terms of similar biological dose units. The new parameter in the formulation is RBEM, the intrinsic (or maximum) RBE at zero dose. The principal assumption (following Kellerer and Rossi; ref. 1) is that high-LET radiation modifies the alpha-coefficient of damage while leaving the beta-coefficient unaltered.

RESULTS

The equations allow a quantitative estimation of how the apparent RBE will change with changes in dose/fraction or dose-rate and of how the magnitude and rate of change is governed by the low-LET alpha/beta ratio of the irradiated tissue. The modifications are applicable to all types of radiotherapy (fractionated, continuous low dose-rate, therapy with decaying sources, etc.). In cases where the normal tissue RBEM is greater than that for the tumor, the revised formulation helps explain why there will be situations where therapeutic index will be adversely affected by use of high-LET radiation. Such clinical advantages as have been observed are more likely to result from favorable geometrical sparing of critical normal tissues and/or the fact that slowly growing tumors may have alpha/beta values more typical of late-responding normal tissues.

CONCLUSIONS

The incorporation of RBE into existing LQ methodology allows quantitative assessment of clinical applications of high-LET radiations via an examination of the associated BEDs. On the basis of such assessments high-LET radiations are shown to confer few advantages.

Fractionation and therapeutic ratio with neutron therapy

Dose-response relationships of most tumours and normal tissues after neutron irradiation are characterized by relatively high alpha/beta ratios. Late reacting tissues are not as protected by low doses per fraction as they are after low linear energy transfer (LET) irradiation. Using the linear-quadratic (LQ) model with the time factor (when needed), we have calculated the therapeutic ratio (TR) as the ratio of the effect on a tumour (or an acutely responding tissue) over that on late reacting tissue. Hypothetical cases are given as well as a case derived from LQ parameters obtained experimentally in animals. It is shown that X-ray fractionation schemes that lead to a high TR will lead to a low neutron TR. For epithelial tumours, a neutron gain factor, GF (ratio of TR) is possible if neutron fractionation is compared to hypofractionated X-irradiation. Neutron treatment over conventional overall times of rapidly proliferating tumours carries a low TR and offers no GF. Neutron therapy for tumours with low alpha/beta ratios offer a potential advantage compared to tumours with high alpha/beta ratios.

Chronic radiation damage in the rat rectum: an analysis of the influences of fractionation, time and volume

PURPOSE

Analysis of four different sets of experiments performed by the G.S.F. group in Munich investigating the late tolerance of the rat rectum to external or intracavitary irradiation.

MATERIAL AND METHODS

The endpoint was late rectal stenosis in female Wistar rats. The raw data were fitted to the linear-quadratic model by means of a likelihood maximization method (Direct Analysis). The model was altered to allow for repopulation, incomplete repair, and varying irradiated lengths of the rectum.

RESULTS

Fractionation sensitivity was high or intermediate (alpha/beta ratio values [95% confidence limits] ranging from 2.67 [0.86, 4.80] to 6.65 [2.21, 11.73] Gy). Significant repopulation occurred when treatments were longer than 5 days (Dprolif equal to 0.61 [0.20, 1.47] and 1.08 [0.58, 1.90] Gy/day, in fractions of 4 Gy). Another interpretation is that radiosensitivity changed during treatment. Repair half-time estimates ranged between 1.84 [1.52, 2.34] and 5.02 [2.83, 21.7] h. Finally, the present analysis indicated that the smallest surviving compartment capable of tissue rescue was about 1/50 to 1/100 of a 1 cm high cylinder of the rectum wall.

CONCLUSIONS

The radiobiological features of late stenosis in the rats are consistent with combined injuries of early and late responding components of the rectal wall. This raises some concerns about the possible danger of hyperfractionated treatments, where the beneficial impact of fraction size reduction may be obviated for interfraction intervals that are too short. Also, accelerated irradiation may result in more late complications because of increased early reactions.

LQ-based model for biological radiotherapy planning

Despite the increasing accumulation of radiobiological data, radiotherapy planning does not take into account the alpha/beta values of normal irradiated tissues. The importance of the fact that the dose per fraction outside the 100% isodose area is not at all identical to the one inside the tumor area is also underestimated. Altered fractionation regimens further complicate the reliability of the conventional radiotherapy plans. In this study we report a theoretical application of the Macejewski's concept of "normalised total dose" that could make feasible the integration of alpha/beta and dose per fraction values in everyday radiotherapy practice. The concept of cumulative normalised total dose permits the preparing of radiotherapy plans with normalised isodose areas (the cumulative isodose area maps) for chosen ranges of radiation normalised doses. The effect of overall treatment time and interfraction interval is also taken into account. The present study suggests some guidelines that could be of value for the elaboration of a computer program for biological radiotherapy planning.