Conformal proton beam therapy of prostate cancer--update on the Loma Linda University medical center experience

Proton therapy - Present and future

In principle, proton therapy offers a substantial clinical advantage over conventional photon therapy. This is because of the unique depth-dose characteristics of protons, which can be exploited to achieve significant reductions in normal tissue doses proximal and distal to the target volume. These may, in turn, allow escalation of tumor doses and greater sparing of normal tissues, thus potentially improving local control and survival while at the same time reducing toxicity and improving quality of life. Protons, accelerated to therapeutic energies ranging from 70 to 250MeV, typically with a cyclotron or a synchrotron, are transported to the treatment room where they enter the treatment head mounted on a rotating gantry. The initial thin beams of protons are spread laterally and longitudinally and shaped appropriately to deliver treatments. Spreading and shaping can be achieved by electro-mechanical means to treat the patients with "passively-scattered proton therapy" (PSPT) or using magnetic scanning of thin "beamlets" of protons of a sequence of initial energies. The latter technique can be used to treat patients with optimized intensity modulated proton therapy (IMPT), the most powerful proton modality. Despite the high potential of proton therapy, the clinical evidence supporting the broad use of protons is mixed. It is generally acknowledged that proton therapy is safe, effective and recommended for many types of pediatric cancers, ocular melanomas, chordomas and chondrosarcomas. Although promising results have been and continue to be reported for many other types of cancers, they are based on small studies. Considering the high cost of establishing and operating proton therapy centers, questions have been raised about their cost effectiveness. General consensus is that there is a need to conduct randomized trials and/or collect outcomes data in multi-institutional registries to unequivocally demonstrate the advantage of protons. Treatment planning and plan evaluation of PSPT and IMPT require special considerations compared to the processes used for photon treatment planning. The differences in techniques arise from the unique physical properties of protons but are also necessary because of the greater vulnerability of protons to uncertainties, especially from inter- and intra-fractional variations in anatomy. These factors must be considered in designing as well as evaluating treatment plans. In addition to anatomy variations, other sources of uncertainty in dose delivered to the patient include the approximations and assumptions of models used for computing dose distributions for planning of treatments. Furthermore, the relative biological effectiveness (RBE) of protons is simplistically assumed to have a constant value of 1.1. In reality, the RBE is variable and a complex function of the energy of protons, dose per fraction, tissue and cell type, end point, etc. These uncertainties, approximations and current technological limitations of proton therapy may limit the achievement of its true potential. Ongoing research is aimed at better understanding the consequences of the various uncertainties on proton therapy and reducing the uncertainties through image-guidance, adaptive radiotherapy, further study of biological properties of protons and the development of novel dose computation and optimization methods. However, residual uncertainties will remain in spite of the best efforts. To increase the resilience of dose distributions in the face of uncertainties and improve our confidence in dose distributions seen on treatment plans, robust optimization techniques are being developed and implemented. We assert that, with such research, proton therapy will be a commonly applied radiotherapy modality for most types of solid cancers in the near future.

Range, Range Modulation, and Field Radius Requirements for Proton Therapy of Prostate Cancer

The Loma Linda University Proton Treatment Facility has treated over 5,000 patients for prostate cancer. Other institutions may find information regarding field size and range requirements for this population of patients useful for designing new proton beamlines. The maximum range, range modulation, and maximum field radius for 240 fields of prostate patients undergoing treatment were sampled and analyzed. Most fields required a range less than 290 mm of water, a modulation width less than or equal to 120 mm, and a radius less than 75 mm.

Acute toxicity of combined photon IMRT and carbon ion boost for intermediate-risk prostate cancer - acute toxicity of 12C for PC

BACKGROUND

Carbon ion ((12)C) therapy in the treatment of prostate cancer (PC) might result in an improved outcome as compared to low linear energy transfer irradiation techniques. In this study, we present the first interim report of acute side effects of the first intermediate-risk PC patients treated at the GSI (Gesellschaft für Schwerionenforschung) and the University of Heidelberg in an ongoing clinical phase I/II trial using combined photon intensity modulated radiation therapy (IMRT) and (12)C carbon ion boost.

MATERIAL AND METHODS

Fourteen patients (planned accrual: 31 pts) have been treated within this trial so far. IMRT is prescribed to the median PTV at a dose of 30 × 2 Gy; (12)C boost is applied to the prostate (GTV) at a dose of 6 × 3 GyE using raster scan technique. Safety margins added to the clinical target volume were determined individually for each patient based on five independent planning computed tomography (CT)-scans. Acute gastrointestinal (GI) and genitourinary (GU) toxicity was assessed and documented according to the CTCAE Version 3.0.

RESULTS

Radiotherapy was very well tolerated without any grade 3 or higher toxicity. Acute anal bleeding grade 2 was observed in 2/14 patients. Rectal tenesmus grade 1 was reported by three other patients. No further GI symptoms have been observed. Most common acute symptoms during radiotherapy were nocturia and dysuria CTC grade 1 and 2 (12/14). There was no severe acute GU toxicity.

CONCLUSION

The combination of photon IMRT and carbon ion boost is feasible in patients with intermediate-risk PC. So far, the treatment has been well tolerated. Acute toxicity rates were in good accordance with data reported for high dose IMRT alone.

Proton therapy - a systematic review of clinical effectiveness

BACKGROUND AND PURPOSE

Proton therapy is an emerging treatment modality for cancer that may have distinct advantages over conventional radiotherapy. This relates to its ability to confine the high-dose treatment area to the tumour volume and thus minimizing radiation dose to surrounding normal tissue. Several proton facilities are currently operating or under planning world-wide - in the United States, Asia and Europe. Until now no systematic review assessing the clinical effectiveness of this treatment modality has been published.

MATERIALS AND METHODS

A systematic review of published studies that investigated clinical efficacy of proton therapy of cancer.

RESULTS

We included 54 publications: 4 randomized controlled trials (RCTs) reported in 5 publications, 5 comparative studies and 44 case series. Two RCTs addressed proton irradiation as a boost following conventional radiation therapy for prostate cancer, where one demonstrated improved biochemical local control for the highest dose group without increased serious complication rates. Proton therapy has been used to treat a large number of patients with ocular tumours, but except for one low quality RCT, no proper comparison with other treatment alternatives has been undertaken. Proton therapy offers the option to deliver higher radiation doses and/or better confinement of the treatment of intracranial tumours in children and adults, but reported studies are heterogeneous in design and do not allow for strict conclusions.

CONCLUSION

The evidence on clinical efficacy of proton therapy relies to a large extent on non-controlled studies, and thus is associated with low level of evidence according to standard heath technology assessment and evidence based medicine criteria.

Optimization of radiobiological effects in intensity modulated proton therapy

Today, inverse treatment planning for intensity modulated proton therapy (IMPT) usually employs a constant relative biological effectiveness (RBE). In this paper, the potential clinical relevance of RBE variations for scanning techniques in IMPT is investigated, and a new strategy to include the RBE into the inverse planning process is presented. Three-dimensional RBE distributions are calculated based on a phenomenological model that describes the RBE as a function of dose, linear energy transfer (LET) and tissue type in the framework of the linear-quadratic model. This RBE model is integrated into the optimization loop of inverse planning by using a modified version of the standard quadratic objective function, where the physical dose is replaced by the biological effect. This system for "biological optimization" was implemented into a research version of the inverse planning software KonRad and allows the direct optimization of the product of RBE and physical dose. Several treatment plans for a prostate case are presented, which compare the biological with the conventional physical dose optimization for IMPT scanning techniques, in particular distal edge tracking (DET) and the full three-dimensional (3D) modulation of beam spots. Mainly due to their different LET distributions, the RBE effects for these two techniques are quite different: while the RBE distribution was more or less homogeneous in the planning target volume (PTV) for 3D modulation, considerable RBE variations within the PTV were observed for DET. These unfavorable effects could be compensated for by employing the new biological objective function, which led to a more homogeneous distribution of the product of RBE and physical dose in the PTV. The computation time increased by a factor of 2 compared to the optimization of the physical dose. In conclusion, the proposed method allows the simultaneous multifield optimization of the biological effect in a reasonable time, and is therefore well suited for studying the influence of a variable RBE in IMPT as well as for minimizing potentially adverse effects.

Medical aspects of the national centre for oncological hadrontherapy (CNAO — Centro nazionale adroterapla oncologica) in Italy

More than 20 hadrontherapy centres are active in the world and about 40,000 patients have been treated, almost 4000 with ions. Physical selectivity and high relative biologic efficiency (RBE) represent the rationale for using ions in the treatment of tumours. The clinical results are very promising and justify the construction of new centres. We present the main characteristics of CNAO (Centro Nazionale Adroterapia Oncologica) and its possible integration in a nationwide network. The Italian project started in 1991 thanks to the activity of the TERA Foundation and was financed by the Italian Government in 2002. The CNAO will be built in Pavia to start clinical activity in 2007. The equipment will include a synchrotron and 3 treatment rooms mainly devoted to carbon ions but able to deliver also protons. The Centre should be able to deliver up to 20,000 fractions / year. The realization of CNAO is part of a more ambitious project to set up an integrated national network. The need of hadrontherapy centres is defined by epidemiological studies based on Italian tumour registries showing that almost 900 patients can be electively treated with protontherapy and about 10,000 could be included in clinical trials. Considering that ions could be used for radioresistant tumours that affect about 25,000 new patients/year, we estimate that 10-15%, i.e. 3000-4000 patients would benefit from ion therapy. The realization of a nationwide network possibly linked to a larger European network will be very helpful in making available hadrontherapy for a large part of the population.

Proton radiation and TNF-alpha/Bax gene therapy for orthotopic C6 brain tumor in Wistar rats

High-grade tumors of the brain remain virtually incurable with current therapeutic regimens, new approaches to augment existing therapies need to be explored. The major goal of this pilot study was to evaluate the feasibility of gene therapy using plasmid DNA encoding tumor necrosis factor-alpha and bax together with proton radiation in an immunocompetent animal model with orthotopic brain tumor. C6 glioma cells were stereotactically implanted into the left hemibrain of Wistar rats (day 0). On day 5, the appropriate groups received intratumoral pGL1-TNF-a and pGL1-Bax (10 microg each), parental plasmid pWS4 (20 microg), or PBS. Hemibrain proton irradiation (10 Gy, 90 MeV, single fraction) was delivered 18-20 hr later. Rats were euthanized when signs of illness appeared. In addition, a subset of animals from each group was euthanized on day 9 for immune and other assays. By day 9, 25%, 20%, and 10% of rats treated with PBS, pWS4, or pGL1-TNF-alpha/pGL1-Bax, respectively, had been euthanized due to weight loss or other signs of illness, whereas all rats treated with pGL1-TNF-alpha/pGL1-Bax + radiation or radiation alone were healthy (P<0.05). At this same time, the pGL1-TNF-alpha/pGL1-Bax + radiation group had significantly elevated lymphocyte percentages (P<0.005 or less) and a relatively high level of lymphocytic infiltrate within tumors. Although the rats treated with pGL1-TNF-alpha/pGL1-Bax had the highest levels of activated T helper (CD4+/CD71+) and T cytotoxic (CD8+/CD71+) cells, the values were not significantly different compared to the pWS4-injected control group. Splenocytes in all tumor cell-injected groups had higher mean values for DNA and protein synthesis compared to the non-tumor cell injected control group, whereas oxygen radical production by phagocytes was consistently higher in groups injected with plasmid or treated with radiation. Body, hemibrain, and spleen masses, white blood cell, red blood cell and platelet counts, hemoglobin, hematocrit, and transforming growth factor-beta1 levels in plasma were similar among groups. The results demonstrate that treatment with pGL1-TNF-alpha/pGL1-Bax combined with proton hemibrain irradiation is safe under the conditions used. Overall, these data support further investigation of this unique combination therapy.

The current and potential role of cryoablation as a primary therapy for localized prostate cancer

Targeted cryoablation of the prostate has evolved significantly since its reintroduction in the early 1990s. This evolution stems from engineering advancements, procedural refinement, introduction of temperature monitoring, and greater understanding of cryobiology. Recent publications demonstrate durable efficacy for cryoablation, equivalent to other therapies for low-risk disease and possibly superior for moderate- and high-risk prostate cancer. Morbidity following the procedure is mild in comparison with other therapies, with the exception of sexual function impairment. However, longer-term quality-of-life studies show that a significant number of patients return to having intercourse, and late-onset morbidities are not observed. These results contrast with those for radiotherapy--specifically brachytherapy--for which several recent studies document a decline in sexual function, protracted morbidity, and the emergence of late-onset morbidity. Cryoablation is an effective therapy with acceptable morbidity that should be offered as a treatment option to all patients with localized prostate cancer. Furthermore, cryoablation has the potential ability to be tailored to an individual patient's disease. As diagnostic tools and methods continue to advance, it may become possible to target the less aggressive forms of prostate cancer. Focal cryoablation may prove to be an ideal treatment modality in this setting.

Review article: current therapeutic options for radiation proctopathy

Radiation proctopathy is a common unfortunate complication following radiation therapy of pelvic malignancies. Symptoms of chronic radiation proctopathy include haematochezia, urgency, constipation, tenesmus, diarrhoea and rectal pain. Currently, a wide variety of pharmacological options, endoscopic cautery techniques and surgical procedures have been proposed for the treatment of chronic radiation proctopathy. Although these have been proposed primarily as treatment for rectal bleeding, the control of other symptoms has been noted with some of these agents. Pharmacological options include 5-aminosalicylic acid preparations, coticosteroid enemas, sucralfate (oral, enemas), formalin, short chain fatty acid enemas, oestrogen/progesterone, hyperbaric oxygen, antioxidants, sodium pentosan polysulphate and misoprostol rectal suppositories. Of these, sucralfate and formalin therapy appear to be effective for bleeding control. Misoprostol rectal suppositories and oral sucralfate may be useful in the prevention of acute and chronic symptoms of radiation proctopathy. Endoscopic cautery techniques have included the use of Nd:YAG laser and argon laser for coagulation of bleeding neovascular telangiectasias. Argon plasma coagulation offers a safe non-contact method of delivering haemostasis which has proven to be particularly useful in targeting difficult to reach lesions tangentially. Surgery is generally reserved for severe refractory cases involving ongoing haemorrhage, obstruction, stricture formation, fistulas and perforation. Given that formal randomized placebo-controlled studies are lacking for most treatments, the management of these patients is often challenging and unclear. Hence, there is a need for more research and education on radiation proctopathy.