Protons to replace photons in external beam radiation therapy?

Protons provide the basis for superior distribution of radiation dose due to the physical characteristics of protons. Proton beams used in radiation therapy can be designed to yield a uniform dose across the target and then virtually zero deep to the target and lower dose proximal to the target (for non-superficial lesions). Such beams can be employed in comparable number, direction, weighting, angulation, intensity modulation as is feasible for photon beams. The result is a smaller treatment volume, and hence a lower incidence and frequency of treatment-related morbidity. Importantly, the reduction in treatment volume permits a higher dose to the tumour. This means an improved tumour control probability and lower normal tissue complication probability. Clinical gains appear to have been realized in the treatment of patient with uveal melanoma, skull-base sarcoma, para-nasal sinus carcinomas, selected stages of lung carcinoma and hepatocellular carcinoma. There are now three proton therapy centres with gantry systems with seven more being built. Further, there are seven additional centres in active planning. At present, prospective clinical evaluations are in progress for tumours at many anatomical sites.

Predictive value of histologic tumor necrosis after radiation.

Postsurgical evaluation of histologic changes of tumors after preoperative chemotherapy and/or radiotherapy has been a routine clinical practice of pathologists and oncologists. There appears to be secure evidence that the extent of tumor necrosis vs. viable tumor cells postchemotherapy is a clinically useful predictor of outcome. The significance of histologic tumor necrosis after radiotherapy, however, has not been clearly established and deserves further investigation. We investigated the correlation between histological extent of tumor necrosis, survival of tumor transplants, and radiation doses in an experimental model using three human tumor xenografts. Three human tumor cell lines were investigated: STS-26, SCC-21, and HGL-21. Tumors were grown subcutaneously in athymic nude mice and received external beam radiation of different doses. Tumors were excised 2 weeks postirradiation. One-half of the tumor was divided into 1-mm(3) fragments and transplanted to naive mice. The other half was examined for histologic tumor necrosis. Transplant survival was strongly correlated with radiation dose, TCD(p) (radiation dose that results in local tumor control in proportion, p, to irradiated tumors). In contrast, there was no clear association between transplant survival rate and the extent of tumor necrosis. The experimental model demonstrated a strong inverse correlation between radiation doses and tumor transplant survival. Histologic tumor necrosis did not correlate well with radiation doses or transplant survival rates. Despite common practices in histologic examination of tumors posttherapy, clinical interpretations and implications of histologic tumor necrosis after radiotherapy should be considered with caution.

Long-term results of intraoperative electron beam radiotherapy for primary and recurrent retroperitoneal soft tissue sarcoma.

PURPOSE: This study assesses the long-term outcome of patients with retroperitoneal sarcoma treated by preoperative external beam radiotherapy, resection, and intraoperative electron beam radiation (IOERT). METHODS AND MATERIALS: From 1980 to 1996, 37 patients were treated with curative intent for primary or recurrent retroperitoneal soft tissue sarcoma. All patients underwent external beam radiotherapy with a median dose of 45 Gy. This was followed by laparotomy, resection, and IOERT, if feasible. Twenty patients received 10-20 Gy of IOERT with 9-15 MeV electrons. These patients were compared to a group of 17 patients receiving preoperative irradiation without IOERT. RESULTS: The 5-yr actuarial overall survival (OS), disease-free survival, local control (LC), and freedom from distant disease of all 37 patients was 50%, 38%, 59%, and 54%, respectively. After preoperative irradiation, 29 patients (78%) underwent gross total resection. For 16 patients undergoing gross total resection and IOERT, OS and LC were 74% and 83%, respectively. In contrast, these results were less satisfactory for 13 patients undergoing gross total resection without IOERT. For these patients, OS and LC were 30% and 61%, respectively. Four patients experienced treatment-related morbidity. CONCLUSIONS: In selected patients, IOERT results in excellent local control and disease-free survival with acceptable morbidity.

Vascular endothelial growth factor receptor-2-blocking antibody potentiates radiation-induced long-term control of human tumor xenografts.

Antiangiogenic therapy can enhance radiation-induced tumor growth inhibition. However, the effects of combined antiangiogenic and radiation therapy on long-term tumor control and normal tissue response have not been reported. We treated mice bearing two different human tumor xenografts with anti-vascular endothelial growth factor receptor-2 antibody (DC101) and five dose fractions of local radiation and followed them for at least 6 months. DC101 significantly decreased the dose of radiation necessary to control 50% of tumors locally. The decrease was 1.7- and 1.3-fold for the moderately radiosensitive small cell lung carcinoma 54A and the highly radioresistant glioblastoma multiforme U87, respectively. In contrast to tumors, no increase in skin radiation reaction by the antibody was detected. Surprisingly, 44% of mice bearing 54A tumor developed clear ascites after DC101 treatment at its highest dose; this was fatal to 20% of mice. This adverse effect was seen only in mice that received whole-body irradiation 1 day before tumor implantation. The encouraging results on two human tumor xenografts suggest that vascular endothelial growth factor receptor-2 blockade merits further investigation to assess its potential as an enhancer of radiation therapy in the clinic.

Anti-Vascular endothelial growth factor treatment augments tumor radiation response under normoxic or hypoxic conditions.

Recent studies in experimental animals have shown that combining antiangiogenic therapy with radiation can enhance tumor response. Whether this enhancement is mainly attributable to angiogenesis inhibition, endothelial cell radiosensitivity, tumor cell apoptosis, or a decrease in the number of hypoxic cells (improved oxygenation) is not known. We designed this study to discern the role of tumor oxygenation. We chose an anti-vascular endothelial growth factor (anti-VEGF) monoclonal antibody (mAb) which has a known target, human VEGF. We also measured interstitial fluid pressure (IFP) to test the hypothesis that the decreased vascular permeability induced by the anti-VEGF mAb can lower IFP. The effect of anti-VEGF mAb on vascular density, partial oxygen tension (pO2), and apoptosis was also measured. Athymic NCr/Sed nu/nu mice bearing 6-mm xenograft of the human glioblastoma multiforme (U87), or colon adenocarcinoma (LS174T) were treated with anti-VEGF mAb injected i.p. on alternate days for a total of six injections at a dosage of 100 microg/injection/mouse. For combined anti-VEGF and radiation, single radiation doses were given under normal blood flow (20 and 30 Gy) or clamped hypoxic conditions (30 and 40 Gy) 24 h after the sixth injection of mAb. The inhibition of the growth of U87 and LS174T tumors by the anti-VEGF mAb was associated with a significant reduction in tumor vascular density and a relatively small increase in the number of apoptotic cells. Compared with size-matched controls, IFP decreased by 74% in LS174T, and 73% in U87 in mice treated with anti-VEGF mAb. After antibody treatment PO2 increased significantly in U87, but did not change in LS174T tumors. Combined treatment induced in U87 tumors a tumor-growth delay (TGD) which was greater than additive; in LS174T except for the 40-Gy hypoxic group, the effect was only additive. In both U87 and LS174T the TGD induced by the antibody was independent of oxygen levels in the tumor at the time of radiation. The fact that the increase in TGD occurred under both normoxic and hypoxic conditions suggests that anti-VEGF mAb treatment can compensate for the resistance to radiation induced by hypoxia.

Long-term results of combined modality therapy in primary bone lymphomas.

PURPOSE: To report the Massachusetts General Hospital experience in the management of patients with primary bone lymphoma (PBL) treated with combined modality therapy (CMT). METHODS AND MATERIALS: Records from 37 eligible patients were reviewed. Two patients were treated with complete resection of the tumor, while 35 patients underwent radiation therapy with a median total dose of 54 Gy (range 38.35-66.5). All patients received combination chemotherapy, which contained doxorubicin in 33 cases. We compared the current data with our previous experience in patients treated with local measures only. RESULTS: Actuarial disease-free survival (DFS) at 5 and 10 years is 78% and 73%, respectively, while overall survival (OS) is 91% and 87%, respectively. No local failures were seen. Pathologic fracture at presentation influenced DFS (p = 0.005) and OS (p = 0.017) adversely. OS was compromised in patients older than 60 years (p = 0.059) and DFS in patients with pelvic primaries (p = 0.015). CMT was associated with improved DFS (p = 0.0008) and OS p = 0.0001) compared to our historical controls. Ten patients (27%) developed complications requiring orthopedic procedures following completion of therapy at a median of 25.5 months (range 4-228). CONCLUSION: Patients with PBL have a favorable outcome with CMT, which appears superior to radiation therapy alone. Late complications can be seen, especially in weight-bearing bones.

Megavoltage radiation therapy for axial and inoperable giant-cell tumor of bone.

BACKGROUND: Treatment of giant-cell tumor of bone generally involves wide en bloc resection of the lesion and the surrounding bone or curettage with or without bone-grafting or the use of cement. Radiation therapy has been used for patients who cannot be operated on for medical reasons or who have a tumor that is technically difficult to resect or that cannot be resected because of its location. We performed the present study to evaluate the efficacy of megavoltage radiation in terms of lack of tumor progression and treatment-related morbidity. METHODS: Twenty patients who had giant-cell tumor of bone were managed with a single course of megavoltage radiation (forty to seventy gray administered at 1.8 to 2.0 gray per fraction with an average total duration of treatment of five to seven weeks) between March 1973 and March 1992. We used megavoltage photons, 160-megaelectron-volt proton beams, or a combination of the two. RESULTS: After a median duration of follow-up of 9.3 years, the tumor had not progressed in seventeen of the twenty patients. Thus, the actuarial ten-year rate for lack of progression was 85 percent. Local regrowth was evident in one patient who had received radiation alone and in two of the thirteen patients who had been managed with partial resection and radiation. Operative treatment was successful in the three patients in whom the radiation treatment had failed. No radiation-induced tumors were observed in our series. CONCLUSIONS: We concluded that giant-cell tumor of bone was effectively treated with megavoltage radiation in our series of twenty patients in whom operative resection would have been difficult or was not feasible. The rate of tumors that did not progress with this regimen of radiation is similar to that reported by investigators from several other centers. Furthermore, these results closely rival those obtained with modern curettage procedures. Malignant sarcomatous transformation was not observed in our series. A longer duration of follow-up of a larger group of patients is necessary to provide a better estimate of the risk of malignant transformation.

Taxane-induced apoptosis decompresses blood vessels and lowers interstitial fluid pressure in solid tumors: clinical implications.

Elevated tumor interstitial fluid pressure (IFP) is partly responsible for the poor penetration and distribution of therapeutic agents in solid tumors. The etiology of tumor interstitial hypertension is poorly understood. We have postulated that the solid stress generated by tumor cells growing in a confined space compresses blood vessels and increases tumor microvascular pressure and IFP. To test the hypothesis that neoplastic cell loss would decompress blood vessels and lower IFP, we induced apoptosis in tumors with paclitaxel and docetaxel. Taxanes inhibited the growth of the murine mammary carcinoma (MCa-IV) and of the human soft tissue sarcoma (HSTS-26T). Taxanes induced apoptosis and reduced the density of intact neoplastic cells in both MCa-IV and HSTS-26T. To determine whether neoplastic cell loss decompressed blood vessels, we measured the diameter of tumor vessels in HSTS-26T tumors implanted in transparent dorsal skin fold chambers. At 48 and 96 h after paclitaxel, the diameter of tumor vessels was significantly increased. The increase in vascular diameters was associated with reductions in microvascular pressure and IFP. The changes in neoplastic cell density and IFP were also correlated. In the human glioblastoma U87, which is resistant to paclitaxel, the IFP and cellular density were not modified by paclitaxel treatment. Collectively, these results support the hypothesis that solid stress generated by neoplastic cell proliferation increases vascular resistance and IFP. The increase in vessel diameter induced by paclitaxel and docetaxel suggests that taxanes could improve tumor response by increasing the vascular surface area for delivery of therapeutic agents.

Individualizing management of aggressive fibromatoses.

PURPOSE: To examine prognostic indicators in aggressive fibromatoses that may be used to optimize case-specific management strategy. METHODS AND MATERIALS: One hundred and seven fibromatoses presenting between 1971 and 1992 were analyzed. The following treatment modalities were utilized: (a) surgery alone for 51 tumors; (b) radiation alone for 15 tumors; and (c) radiation and surgery (combined modality) for 41 tumors. Outcome analysis was based on 5-year actuarial local control rates. RESULTS: Control rates among surgery, radiation therapy, and combined modality groups were 69%, 93%, and 72%. Multivariate analysis identified age < 18 years, recurrent disease, positive surgical margins, and treatment with surgery alone as predictors for failure. Patients treated with surgery alone had control rates of 50% (3 of 6) for gross residual, 56% for microscopically positive margins, and 77% for negative margins. Radiation and surgery resulted in rates of 59% for gross residual, 78% for microscopically positive margins, and 100% (6 of 6) for negative margins. For recurrent vs. primary tumors, control was achieved in 48% vs. 77%, 90% vs. 100% (5 of 5), and 67% vs. 79% in the Surgery, Radiation, and Combined modality Groups, respectively. Patients presenting with multiple disease sites tended to have aggressive disease. A radiation dose-control relation to > 60 Gy was seen in patients with unresected or gross residual disease. Of the patients, 23 with disease involving the plantar region had a control rate of 62%, with significantly worse outcomes in children. CONCLUSIONS: These results are consistent with those found in the relevant literature. They support primary resection with negative margins when feasible. Radiation is a highly effective alternative in situations where surgery would result in major functional or cosmetic defects. When negative surgical margins are not achieved in recurrent tumors, radiation is recommended. Perioperative radiation should be considered in other high-risk groups (recurrent disease, positive margins, and plantar tumors in young patients). Doses of 60-65 Gy for gross disease and 50-60 Gy for microscopic residual are recommended. Observation may be considered for primary tumors with disease remaining in situ when they are located such that progression would not cause significant morbidity. Although plantar lesions in children may represent a group at high risk for recurrence or aggressive behavior, the greater potential for radiation-induced morbidity in this group must also temper its use. Given the inconsistent nature and treatment response of this tumor, it is fundamental that treatment recommendations should be made based on the risk:benefit analysis for the individual patient, dependent on tumor characteristics and location, as well as patient characteristics and preferences.

Repopulation capacity during fractionated irradiation of squamous cell carcinomas and glioblastomas in vitro.

PURPOSE: Determination of clonogenic cell proliferation of three highly malignant squamous cell carcinomas (SCC) and two glioblastoma cell lines during a 20-day course of fractionated irradiation under in vitro conditions. METHODS AND MATERIALS: Tumor cells in exponential growth phase were plated in 24-well plastic flasks and irradiated 24 h after plating with 250 kV x-rays at room temperature. Six fractions with single doses between 0.6 and 9 Gy were administered in 1.67, 5, 10, 15, and 20 days. Colony growth was monitored for at least 60 days after completion of irradiation. Wells with confluent colonies were considered as "recurrences" and wells without colonies as "controlled." The dose required to control 50% of irradiated wells (WCD50) was estimated by a logistic regression for the different overall treatment times. The effective doubling time of clonogenic cells (T[eff]) was determined by a direct fit using the maximum likelihood method. RESULTS: The increase of WCD50 within 18.3 days was highly significant for all tumor cell lines accounting for 7.9 and 12.0 Gy in the two glioblastoma cell lines and for 12.7, 14.0, and 21.7 Gy in the three SCC cell lines. The corresponding T(eff)s were 4.4 and 2.0 days for glioblastoma cell lines and 2.4, 4.2, and 1.8 days for SCC cell lines. Population doubling times (PDT) of untreated tumor cells ranged from 1.0 to 1.9 days, showing no correlation with T(eff)s. T(eff) was significantly longer than PDT in three of five tumor cell lines. No significant differences were observed comparing glioblastomas and SCC. Increase of WCD50 with time did not correlate with T(eff) but with T(eff) InSF2 (surviving fraction at 2 Gy). CONCLUSION: The intrinsic ability of SCC and glioblastoma cells to repopulate during fractionated irradiation could be demonstrated. Repopulation induced dose loss per day depends on T(eff) and intrinsic radiation sensitivity. Proliferation during treatment was decelerated compared to pretreatment PDT in the majority of cell lines. Pretreatment cell kinetics did not predict for tumor cell proliferation during treatment.

Prognostic factors for local control of sarcomas of the soft tissues managed by radiation and surgery.

During the past decade, local control of primary sarcomas of the extremities by radiation and conservative surgery has supplanted more radical compartmental resections or amputations. Reviews of others and our published data show that the probability of achieving local control is highly dependent on achieving negative surgical margins. Other factors, such as pathological grade and size, histopathology, and concomitant chemotherapy may also affect local control, to a much lesser extent, although these are strongly correlated with the likelihood of distant metastatic disease. Appreciation of the importance of these different prognostic factors has been fundamental to the development of the current rationale for sarcoma management.

Interlaboratory variation in oxygen tension measurement by Eppendorf "Histograph" and comparison with hypoxic marker.

BACKGROUND AND OBJECTIVES: The median of pO2 values in tumor measured by Eppendorf "Histograph" with a needle-type electrode has been used as a prognostic indicator in cancer patients. However, it is not established that a pretreatment measured pO2 value can be used as a universal predictor of local control probability, because the variation in pO2 values, especially in hypoxic tissue, among institutes may not allow comparison of measured "absolute pO2 values." The purpose of this study was to examine the variation in oxygen tension measurement by Eppendorf "Histograph" among six laboratories using a single batch of mice and tumors and the same detailed protocol. These results were also compared to the immunohistochemical staining of 2-nitromidazole adducts. METHODS: C3H mice bearing FSaII murine fibrosarcoma subcutaneously were shipped to all laboratories, and the oxygen status in tumors and in normal subcutis was examined using Eppendorf "Histograph" and immunohistochemical hypoxic marker. RESULTS: All laboratories showed that the FSaII tumor was hypoxic with at least 77% of measured points under 10 mmHg in pO2 and with a median pO2 value less than that of normal subcutis. These results were further confirmed immunohistochemically. These findings are interpreted as evidence that the pO2 values measured by Eppendorf "Histograph" can be useful. However, the median values of tumor pO2 varied from 1.5 mmHg to 5.6 mmHg among the laboratories, and pO2 of normal subcutis also varied from 28 mmHg to 38 mmHg. There were also significant differences in hypoxic fraction, defined as the fraction under a given oxygen partial pressure (i.e., under 2.5, 5, or 10 mmHg), among institutes. CONCLUSIONS: Caution needs to be exercised in using the absolute, median, or distribution of pO2 values measured by the Eppendorf "Histograph" to compare the data between laboratories or to predict the radiation response in an individual subject.

The potential role of proton beams in radiation oncology.

Historically, major gains in the local control of large, deep-seated tumors treated with radiation have occurred whenever dose distributions have become more localized to the tumor. Better dose localization permits the delivery of higher tumor doses while delivering less dose to dose-limiting normal tissues. High-energy protons, because they stop abruptly in tissue at the end of their range and deposit most of their energy there, provide dose distributions that are superior to x-rays when used in comparable beam configurations. The installation of a hospital-based proton therapy facility at the Massachusetts General Hospital in Boston, MA, and the existing facility at Loma Linda University Medical Center, Loma Linda, CA, provide a potential for achieving higher rates of local control in tumors throughout the body.