Stereotactic radiotherapy for the treatment of pituitary adenomas.

PURPOSE: The aim of this study was to retrospectively review local control and morbidity following stereotactic radiotherapy (SRT) for pituitary adenoma. METHODS: Between 1997 and 2004, 39 patients with pituitary adenomas received SRT. Median age was 56 years (range: 13 to 90 years). Thirty-three patients underwent incomplete transsphenoidal surgery prior to SRT and six had unresectable tumors. The largest tumor dimension varied from 1.7 to 6 cm (median: 3 cm). Tumor volume varied from 1.2 to 56 mL (median 10.5 mL). Thirty-five tumors were < or = 1 mm from the optic chiasm/nerve. Thirty-three tumors were non-functional. SRT was delivered by a dedicated linear accelerator (Novalis, Heimstetten, Germany). Beam collimation was achieved by a fixed circular collimator (five patients) or a micro-multileaf collimator (34 patients). Total dose varied from 4500 to 5040 cGy (median: 4860 cGy) and was prescribed at the 90 % isodose line. RESULTS: After a median follow-up of 32 months (range: 12 to 94 months), the local control rate was 100 %. Tumor size was stable in 26 patients and decreased in 13 patients. Hormone normalization did not occur following SRT. New endocrine deficiency occurred in six patients. No patient developed cranial nerve injury or second malignancy following treatment. CONCLUSIONS: SRT achieves a high rate of local control and a low rate of treatment-induced morbidity. SRT is applicable to pituitary adenomas in close proximity to the optic apparatus and tumors in excess of three centimeters in the greatest dimension. Further follow-up is necessary to establish the long-term outcome following SRT for pituitary adenomas.

Linear accelerator stereotactic radiosurgery for the treatment of gelastic seizures due to hypothalamic hamartoma.

PURPOSE: There are reports of successful gamma-knife stereotactic radiosurgery (SRS) for the treatment of gelastic seizures associated with a hypothalamic hamartoma. The authors reviewed the results of linear accelerator (LINAC) radiosurgery for patients with medically refractory gelastic seizures due to a sessile hypothalamic hamartoma. METHODS: Three patients with gelastic seizures received SRS between 2003 and 2004. All patients had associated partial complex and/or generalized seizures. One patient demonstrated aggressive behavior. Sessile hamartomas varying in diameter from 6 to 14 mm were identified by MRI. SRS was delivered to a single isocenter by a dedicated LINAC equipped with either a circular beam collimator or a micromultileaf collimator. Patients received 1500 to 1800 cGy prescribed at the 90 to 95 % isodose line. Seizure outcome was scored according to Engel's classification. RESULTS: Two patients became free of gelastic and partial complex/generalized seizures seven and nine months after radiosurgery. These patients remain free of seizures at 17 and 15 months, respectively, after treatment (Engle Class IA). One patient experienced a decline in gelastic seizure frequency nine months after treatment (Engle Class II) without significant reduction in aggressive behavior. Follow-up MRI demonstrated no change in the size or signal characteristics of any tumor. No patient developed post-treatment cranial neuropathy or hypothalamic-pituitary suppression. CONCLUSIONS: LINAC SRS represents a safe and effective therapeutic alternative for patients with medically refractory gelastic seizures due to unresectable hypothalamic hamartomas. Radiosurgery is associated with a latency of several months from treatment to reduction in seizure frequency. Further follow-up is required to establish the duration of seizure control following radiosurgery.

Dynamic arc radiosurgery field shaping: a comparison with static field conformal and noncoplanar circular arcs.

PURPOSE: Recent advances in field-shaping technology and linac multileaf collimator (MLC) integration have resulted in new approaches to performing stereotactic radiosurgery. We present a modeling study comparing the absolute dose distributions from three radiosurgery delivery techniques: a conventional approach utilizing noncoplanar circular arcs, a static field conformal approach, and a dynamic arc field-shaping approach. In the latter, the MLC leaves more in a continuous fashion, conforming to the beam's-eye-view projection of the target at every increment along the path of an arc. METHODS AND MATERIALS: For the analysis, we devised a simulated target consisting of three overlapping spheres. This was chosen because it offered a straightforward planning approach for all three techniques, primarily the multiple isocenter approach. In addition, three representative cases were selected from the prior radiosurgery experience. These range in increasing size, from 0.50 to 9.79 cm(3), and in complexity, requiring from 3 isocenters to 16 in the case of circular arcs. In each situation, the goals were twofold: (1) to cover the entire volume with as high an appropriate isodose level (90% in the case of the conformal and dynamic arc techniques, 50% in the case of circular collimators) while (2) minimizing the dose to normal brain and where applicable, any adjacent radiation-sensitive structures. Because of the latter requirement, a single isocenter circular arc approach was ruled out for the analysis. RESULTS: In the case of large or irregularly shaped lesions, the circular arc technique requires multiple isocenters, producing a high level of dose heterogeneity within the target volume. Both the static field and dynamic arc conformal techniques, as with all single isocenter approaches, produce a highly homogeneous dose throughout the target region. For a given large dose, peripheral dose is decreased as additional beams or arc degrees are added with either of the conformal approaches. Dose--volume histogram analysis evaluating the peripheral dose shows that, in many cases, dose to surrounding structures can be reduced through the use of a conformal static or dynamic arc approach over the conventional multiple isocenter, circular arc techniques. CONCLUSIONS: Dynamic arc shaping is an efficient and effective method for accurately delivering a homogeneous target dose while simultaneously minimizing peripheral dose in radiosurgery applications.

Radiosurgery and stereotactic radiation therapy of skull base meningiomas: proposal of a grading system.

OBJECTIVE: The development of a grading system to guide treatment selection, and predict treatment difficulty and outcome of skull base meningiomas infiltrating the cavernous sinus which are managed by stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT), based on an 8-year experience with stereotactic radiation of skull base meningiomas. METHODS: T1 gadoliniun-enhanced magnetic resonance imaging (MRI) of 40 patients with skull base meningiomas, with or without prior surgery, who underwent radiosurgery or stereotactic radiation therapy from 1991 to 1998 at the UCLA Medical Center were reviewed, and the result of treatment was related to the tumor grade. Grade was based on tumor infiltration of the cavernous sinus and extension into adjacent structures. Treatment was performed with a linac-based system. The dose prescribed to the periphery of the tumor for SRS patients (n = 34) ranged from 12 to 22 Gy, and the maximum dose delivered to the tumor ranged from 24 to 46 Gy. SRT (n = 6). Treatment was planned using a single isocenter, usually prescribed to the 90% isodose volume, bringing the fractionation scheme to the maximal tolerance of the optic apparatus. The periphery dose ranged from 24 to 46 Gy with a maximum dose of 45 to 51 Gy. Clinical and MRI follow-up was performed every six months for the first 3 years and every year thereafter. RESULTS: Grade I meningiomas were restricted to the cavernous sinus (n = 12). Grade II cavernous sinus meningiomas extended to the clivus and/or the petrous bone, without compression of the brainstem (n = 9). Grade III meningiomas had superior and/or anterior extension with compression of the optic nerve or tract (n = 9). Grade IV tumors compressed the brain stem (n = 8), and Grade V were bilateral lesions (n = 2). Tumor control rates were 90% for Grade I, 86% for Grade II, 86% for Grade III, 42% for Grade IV and no control for tumors Grade V. Complications were not related to tumor grade. CONCLUSION: This grading system correlated with outcome and difficulty in planning radiosurgery. Failure of treatment was more likely to occur in patients with higher Grade tumors.

Gangliogliomas: experience with 34 patients and review of the literature.

Ganglioglioma is an uncommon central nervous system tumor. The role of adjuvant postoperative radiation therapy is undefined. The authors retrospectively reviewed the clinicopathologic features and results of therapy for 34 patients with ganglioglioma treated at the University of California at Los Angeles. There were 18 women and 16 men. Median age was 18 years. Twenty-five tumors were low grade. Twenty-one patients underwent gross total resection. Three patients received adjuvant radiotherapy. The 4-year actuarial progression free and overall survival rates were 67% and 75%, respectively. The median time to progression was 14 months and all relapses were local. Factors significantly influencing progression-free or overall survival according to univariate analysis included degree of resection and tumor grade. Survival and relapse were not significantly influenced by any factor according to multivariate analysis. The progression-free survivals after gross total resection of low- and high-grade tumors were 78% and 75%, respectively. Respective rates after subtotal resection were 63% and 25%. Review of the literature demonstrates no role for radiotherapy after total resection of ganglioglioma or after partial removal of low-grade tumor. Radiation therapy appears to reduce the relapse rate after partial removal of high-grade lesions. A dose in excess of 5,000 cGy is necessary for ganglioglioma.

Treatment results of unresected or partially resected desmoid tumors.

The authors compare the progression-free survival of patients with unresected or partially resected desmoid tumors treated with radiotherapy with those not given radiotherapy. A retrospective analysis and pathologic review was performed on 14 patients treated at the University of California Los Angeles School of Medicine from 1965 through 1992. Median follow-up was 6 years. The 6-year progression-free survival for irradiated patients was 100%, compared with 50% for those not irradiated (p = 0.04). Of the seven patients irradiated, only two had a complete response and one had a partial response. There was no difference in disease-specific survival between patients irradiated and those not irradiated, because only 1 of 14 patients died of desmoid tumor progression, which caused airway obstruction. This data suggest that radiotherapy may improve the progression-free survival of patients with unresected or partially resected desmoid tumor; however, the number of patients in this series is small. Most patients did not have a complete response to radiotherapy. For patients with tumor adjacent to the airway in the neck or upper thorax, the authors recommend radiotherapy because of the potential for mortality. Otherwise, because tumor progression rarely causes death, one must consider whether the morbidity of treatment would outweigh the morbidity of disease progression.

Fractionated stereotactic radiotherapy: rationale and methods.

Stereotactic radiosurgery (SRS) has become a widely accepted technique for the treatment intracranial neoplasms. Combined with modern imaging modalities, SRS has established its efficacy in a variety of indications. From the outset, however, it was recognized that the delivery of a single large dose of radiation was essentially "bad biology made better by good physics." To achieve the accuracy required to compensate for this biological shortcoming, the application of SRS has required that a neurosurgical head frame of some sort be rigidly attached to the patients head. Historically, this prerequisite has, primarily for practical reasons, precluded the delivery of multiple fractions over multiple days. With recent improvements in immobilization and repeat fixation, the good biology of fractionated delivery has been realized. This technique, which has come to be known as stereotactic radiotherapy (SRT), has significantly expanded the efficacy of the technique through the use of accurate physical targeting coupled with the basic radiobiological principles gleaned from decades of clinical experience.

The role of adjuvant radiotherapy in the treatment of resectable desmoid tumors.

PURPOSE: Desmoid tumors have a high propensity for local recurrence with surgical resection. There are many reports describing good responses of desmoid tumors to irradiation, but none have clearly established the indications for adjuvant radiotherapy in treating resectable desmoid tumors. METHODS AND MATERIALS: A retrospective analysis was performed on 61 patients with resectable desmoid tumor(s) who were treated at our institution from 1965 to February of 1992. Five patients had multifocal disease and are analyzed separately. Fifty-six patients had unifocal disease, of which 34 had positive surgical margins. Forty-five of the 56 patients with unifocal disease were treated with surgery alone, while 11 were treated with surgery plus adjuvant radiotherapy. Median follow-up was 6 years. Local control was measured from the last day of treatment, and all cases were reviewed by our Department of Pathology. RESULTS: Multivariate analysis of the 56 patients with unifocal disease revealed that positive margins independently predicted for local recurrence (p < or = 0.01). Only 3 of 22 patients with clear margins experienced a local recurrence, with a 6-year actuarial local control of 85%. Multivariate analysis of the 34 patients with positive margins revealed that adjuvant radiotherapy independently predicted for improved local control (p = 0.01), and patients with recurrent disease had a slightly higher risk of local recurrence (p = 0.08). The 6-year actuarial local control determined by Kaplan-Meier for patients with unifocal disease and positive margins was 32% (+/-12%) with surgery alone, and 78% (+/-14%) with surgery plus adjuvant radiotherapy (p = 0.02). Subgroup analysis of the patients with positive margins and recurrent disease revealed that those treated with surgery alone had a 6-year actuarial local control of 0% vs. 80% for those treated with surgery plus radiotherapy (p < or = 0.01). Patients with positive margins and primary disease had a trend towards improved local control with adjuvant radiotherapy, but this was not statistically significant. None of the patients treated with radiotherapy developed serious complications or a secondary malignancy. CONCLUSIONS: Margin status is the most important predictor of local recurrence for patients with resectable, unifocal desmoid tumor. Adjuvant radiotherapy is indicated in the treatment of patients with positive margins following wide excision of recurrent disease. The role of adjuvant radiotherapy in patients with positive margins following resection of primary disease is controversial, and should be based on a balanced discussion of the potential morbidity from radiotherapy compared to the potential morbidity of another local recurrence. Adjuvant radiotherapy is less likely to benefit those with clear margins due to the excellent results for these patients treated with surgery alone. The local control of desmoid tumor in the adjuvant setting is excellent with total doses ranging from 50-60 Gy, with acceptable morbidity. Field sizes should be generous to prevent marginal recurrences, and large volume MRIs of patients with extremity lesions should be used to identify those patients with multifocal disease.

Craniopharyngioma: treatment in the CT and MR imaging era.

PURPOSE: To determine optimal treatment in patients with craniopharyngiomas. MATERIALS AND METHODS: In 1977-1990, 49 patients (age range, 3-67 years; median age, 35 years; 25 female, 24 male) with craniopharyngiomas were examined. Follow-up was 5-17 years (median, 8 years). Fifteen patients were aged younger than 18 years. RESULTS: All patients underwent surgical resection. Complete resection was achieved in 19. Seven patients underwent additional surgery for recurrent disease. Rate of mortality due to surgical complications was 10% (n = 5). Eight patients had marked perioperative or long-term morbidity. Twenty-five patients judged to have undergone subtotal resection underwent postoperative radiation therapy (RT). RT doses were 4,600-6,287 cGy administered in fractions of 180-200-cGy/d. Actuarial 5-year progression-free survival in patients who underwent complete resection was 63% (12 of 19 patients) versus 96% (24 of 25 patients) in patients who underwent subtotal resection followed by RT (P = .04). No RT dose response was observed. Patient functional status has not been substantially affected by adjuvant RT. CONCLUSION: RT achieves excellent tumor control after subtotal resection of craniopharyngiomas.

Outcome of children with brain stem gliomas after treatment with 7800 cGy of hyperfractionated radiotherapy. A Childrens Cancer Group Phase I/II Trial.

BACKGROUND: Brain stem gliomas remain the childhood brain tumors most resistant to treatment. Treatments with hyperfractionated radiotherapy at doses as high as 7560 cGy have been fairly well tolerated. This study was undertaken to determine the toxicity and possible efficacy of hyperfractionated radiotherapy in children with brain stem gliomas using 100 cGy of radiation twice daily, to a total dose of 7800 cGy. METHODS: Sixty-six children (mean age at diagnosis, 7.5 years) with diffuse intrinsic brain stem gliomas were treated. Patients were evaluated for potential toxicity of treatment, progression-free survival, survival, and response to treatment. RESULTS: Objective response to treatment was documented in 20 of 58 (34%) evaluable patients, with 8 (14%) patients having a greater than 50% reduction in tumor size. Overall survival was 35% plus or minus 6% at 1 year and 11% plus or minus 6% at 3 years. Intralesional cystic/necrotic radiographic changes developed in nine patients 6 weeks after radiation, and three of these patients subsequently improved without antitumor intervention. Six of 14 autopsied patients had evidence of probable radiation-induced intralesional necrotic damage, and in 1, necrosis may have played a role in death. Thirty-three of 66 patients were treated with steroids for prolonged periods. CONCLUSIONS: The results of this treatment regimen demonstrate that hyperfractionated radiotherapy, as delivered in this study to a total dose of 7800 cGy, is relatively well tolerated, but may result in prolonged steroid-use dependency and possible radiation-associated damage. Objective responses to treatment were seen in 34% of patients, but these results were not better than those seen at lower doses of hyperfractionated radiotherapy. There is no evidence that radiation to 7800 cGy results in improved survival for patients with diffuse intrinsic brain stem gliomas.

Primary central nervous system lymphoma. Results at the University of California at Los Angeles and review of the literature.

The authors report 24 patients with primary central nervous system lymphoma (PCNSL) treated from 1977 to 1992. There were 13 females and 11 males. Median age was 57 (range: 17-84). Patients were symptomatic for a median of 3 months. Headache was the most common complaint. Median Karnofsky performance score was 70. There were 19 patients with solitary PCNSL, and 5 had multiple deposits. Disease was confined to the supratentorium in 23 patients. Cerebrospinal fluid cytology was positive in 5 of 22 patients examined. All patients received whole-brain irradiation with or without supplemental tumor boost. Tumor doses ranged from 10 to 60 Gy. Intrathecal chemotherapy was administered to 16 patients and 7 received systemic agents. After follow-up ranging from 1 to 66 months, median survival and progression-free survival were each 8 months. One- and 3-year actuarial survival rates were 50% and 36%, respectively. One- and 3-year actuarial progression-free rates were 41% and 15%, respectively. Relapse occurred in 18 patients, and in 17 there was a component of local progression. Lesions recurred in the spinal meninges in 1 patients and in the vitreous in 1. Patients with Karnofsky performance status > or = 70 demonstrated median progression-free survival of 27 months, compared to 4 months for patients < 70 (p = .024). No other significant patient or treatment-related prognostic factors were identified. Clinical dementia occurred in 2 of 11 patients surviving at least 1 year. Review of the literature indicates PCNSL demonstrates relative radioresistance. The most immediate improvement in prognosis for patients with PCNSL can be achieved by properly sequencing systemic and intrathecal chemotherapy with radiation therapy.

Postirradiation sarcomas. A single-institution study and review of the literature.

BACKGROUND: With improvement in survival after cancer treatment, it is becoming increasingly important to examine treatment-related morbidity and mortality. Sarcomas can develop in the irradiated field after radiation therapy (RT). The authors undertook a study to estimate the risk, and compared the risk of postirradiation sarcoma (PIS) with other treatment modalities used against cancer. METHODS: Since 1987 the authors have reviewed the records of 1089 patients with head and neck, gynecologic, gastrointestinal, and extremity sarcomas. Of these 1089 patients, 37 had a prior history of RT. RESULTS: Conditions for which these patients received RT included: Hodgkin's disease (2 patients), retinoblastoma (3), non-Hodgkin's lymphoma (2), acne (1), astrocytoma (1), multiple recurrent mixed parotid tumor (1), laryngeal cancer (1), papillary adenocarcinoma of the thyroid (1), bony fibrous dysplasia (1), lymphangioma (1), squamous cell carcinoma of the nasopharynx (1), Ewing's sarcoma (1), choriocarcinoma (1), menorrhagia (4), cervical cancer (6), ovarian cancer (2), breast cancer (7), and hypoplasia (1). RT doses ranged from 3000 to 12,440 cGy. Latency time from RT to the development of PIS averaged 12 years. More than 15,000 patients have received RT for various conditions at our institution since 1955. CONCLUSIONS: From our data and a review of the literature, we estimate the risk of PIS with long-term follow-up to be 0.03-0.8%. From a review of the literature that compared mortality risks of chemotherapy, general surgery, and anesthesia, the risk of PIS appears no worse. Thus, given the large number of patients who can be cured or receive palliative treatment with RT, concern regarding PIS should not be a major factor influencing treatment decisions in patients with cancer.

Clinical trial of Serratia marcescens extract and radiation therapy in patients with malignant astrocytoma.

PURPOSE: A clinical trial was undertaken to determine the safety and efficacy of combining a biologic response modifier derived from the bacterium Serratia marcescens (ImuVert) and radiation therapy (RT) in patients with newly diagnosed anaplastic astrocytoma (AA) or glioblastoma multiforme (GBM). PATIENTS AND METHODS: Fifteen patients who had undergone either a gross total resection, a partial resection, or a biopsy were treated concurrently with ImuVert and RT. Safety and tolerance were examined by assessment of symptomatic reactions recorded at each ImuVert treatment. Efficacy of treatment was examined in terms of time to progression of tumor and survival. RESULTS: All patients experienced local reactions at the injection sites that consisted of erythema and induration. The majority of patients experienced flu-like symptoms. Hypotension was responsible for the most significant morbidity (which required fluid resuscitation and extended observation) and dose deescalation. No patients were removed from the study because of toxicity. There were no on-study deaths related to ImuVert treatment. Median time to progression was 33.4 weeks, and median survival was 78 weeks. CONCLUSION: These results compare favorably with those of recent studies in patients with malignant astrocytomas who received multimodality therapy.

Primary lymphoma of female urethra: long-term control by radiation therapy.

We report a case of primary urethral lymphoma successfully managed by external beam radiation therapy. Long-term freedom from recurrence in this case suggests irradiation is a viable treatment option for this rare malignancy.

Hyperfractionated radiation therapy (72 Gy) for children with brain stem gliomas. A Childrens Cancer Group Phase I/II Trial.

BACKGROUND: Most children with brain stem gliomas (BSG) die within 18 months of diagnosis. Early experience suggested that hyperfractionated radiation therapy (RT) at a dose of 72 Gy, administered in 1-Gy fractions twice daily, possibly improved disease-free survival for children with BSG. METHODS: To better characterize the toxicity and possible efficacy of this dose and fractionation of RT, 53 assessable children with diffuse intrinsic or malignant BSG were treated. Survival figures also were combined with outcome in 36 patients treated in a previous pilot study. RESULTS: An objective response to treatment was observed in 28 of 53 (53%) patients; a partial response occurred in 7. No child died of treatment-related brain necrosis, although 7 of 53 did have intralesional cystic/necrotic changes within 6 weeks of completion of RT. The overall survival rate for patients in the study was 38% (+/- 6.5) at 1 year, 14% (+/- 5.4) at 2 years, and 8% (+/- 6.5) at 3 years. Leptomeningeal dissemination was observed in 4 of 48 (8%) children who had relapses. A greater than 2-month duration of symptoms before diagnosis was related to a better prognosis. There was no statistical association between any other clinical parameter, neuroradiographic finding, or pathologic finding and outcome. Combined with that in 35 patients treated in the pilot study, the survival rate in 88 children was 14% (+/- 5) at 3 years. CONCLUSIONS: The radiographic response rate is encouraging; however, it cannot be concluded that hyperfractionated RT, at this dose schedule and total dose, is superior to conventional RT.

Management of oligodendrogliomas.

To define optimum treatment and delineate recurrence patterns and prognostic factors in oligodendrogliomas, the authors reviewed the records of 49 patients who received treatment for these rare tumors between 1957 and 1990; 41 patients had at least 5 years follow-up. Age, race, gender, performance of computed tomography (CT), tumor location and grade, histologic findings, calcifications, surgery with or without postoperative radiation therapy, and the doses and fields used in radiation therapy were evaluate for prognostic relevance by means of chi 2 and Wilcoxon log-rank tests. Metaanalysis of relevant literature was also performed. Actuarial survival at 5, 10, and 15 years was 61%, 41%, and 24%, respectively. The pattern of recurrence was predominantly local alone (30 of 31 patients [97%] with recurrence). Age younger than 40 years, low-grade tumor, calcifications, and performance of CT were statistically significant prognostic factors. A trend existed toward improved 5-year survival in patients who underwent postoperative radiation therapy (P = .067); at stratification for subtotal resection, this improvement became significant (74% vs 25%, P = .019). Metaanalysis demonstrated a survival advantage for surgery with radiation therapy versus surgery only (56% vs 42%, P < .01).

Conservation therapy for invasive lobular carcinoma of the breast.

Earlier literature suggests a high incidence of multicentricity and bilaterality, with an overall poor prognosis, in patients with invasive lobular carcinoma of the breast. Consequently, there is considerable disagreement regarding appropriate local management of this disease. To determine the influence of invasive lobular histologic findings on local tumor control, disease-free survival, and overall survival, the authors reviewed 60 patients with Stage I and II invasive lobular breast carcinoma treated with local tumor excision and radiation therapy between 1981 and 1987 (mean follow-up, 5.5 years; range, 2.5 to 10 years). The 5-year actuarial risk of locoregional recurrence was 5%, with two of three failures occurring in the regional lymphatics. The mean time to locoregional failure was 28 months. The 5-year actuarial disease-free survival (84%) and overall survival (91%) were comparable to those seen in several large series of similarly treated patients with invasive ductal carcinoma. Contralateral breast cancer occurred at a rate of approximately 0.6% per year. This study and a review of the literature suggest that breast conservation, with local resection and radiation therapy, is appropriate therapy for invasive lobular breast cancer.

Technical considerations in the use of prophylactic radiation therapy to prevent heterotopic bone formation.

The UCLA Department of Radiation Oncology radiated 97 hips at high risk for heterotopic bone (HTB) formation from 1980 through 1988. Adequate follow-up (minimum of 2 months, median, 10 months) is available in 92 hips (82 patients). These hips were treated with a variety of doses, fractionation schedules, and shielding techniques as treatment evolved over time. There was a total of 49 hips with porous coated ingrowth prostheses. These were all shielded with custom blocks. There were no untoward complications in this subgroup. Only 6 of the 92 hips evaluable developed clinically significant HTB. Five of these 6 failures can be attributed to initiating treatment after postoperative day (POD) 5 or block malposition. Of the 78 hips that initiated radiation therapy before POD 6 (with proper shielding), only 1 (1.3%) developed clinically significant HTB. Radiation therapy is very effective at preventing HTB formation following hip surgery when treatment is initiated within 4 days of surgery. To assure an optimal outcome, close attention to the technical aspects treatment is critical.