Transmission block technique for the treatment of the pelvis and perineum including the inguinal lymph nodes: dosimetric considerations

Organ sparing by conformal avoidance intensity-modulated radiation therapy for anal cancer: dosimetric evaluation of coverage of pelvis and inguinal/femoral nodes

PURPOSE

To describe a novel and straightforward conformal avoidance intensity-modulated radiation therapy (IMRT) technique for coverage of pelvis and inguinal/femoral nodes and to compare the dosimetry of the new method with that of other traditional methods of radiation treatment.

METHODS AND MATERIALS

Data of 2 patients with anal cancer were used as example cases to illustrate details and advantages of conformal avoidance IMRT technique. Conventional photons with enface electrons design was created first, thereby providing "outermost boundaries" defined as planning target volume (PTV) for subsequent conformal avoidance IMRT design. Organs at risk (OARs), including femoral head and neck and external genitalia, were contoured as conformal avoidance structures. A step-and-shoot inverse IMRT planning was subsequently generated. For dosimetric comparison, a recently published technique by modified segmental boost was also generated. These treatment techniques were evaluated by dose-volume histogram (DVH) of PTV and OARs. Dose profiles at four different depths from each treatment planning were generated for comparison.

RESULTS

The DVH of PTV showed that coverage of the PTV was comparable among three treatment techniques. Percent volume of PTV receiving more than 90% prescription dose was in the range 94-98% for the three treatment techniques, and all had only 0-2% of PTV receiving more than 110% of prescription dose. The DVH of OARs confirmed that both femoral head and neck and external genitalia could be spared well by conformal avoidance IMRT as compared with the other two techniques. Although greater inhomogeneity of dose distribution within the PTV was noted by conformal avoidance IMRT technique, as shown by dose profiles at four different depths, the maximum doses at different depths were less than 115%, which was comparable to those planned by modified segmental boost technique. Planning by photons and enface electrons technique, however, showed a greater dose variation up to 134% of the prescription dose at 1.5 cm depth along photon-electron match-line.

CONCLUSIONS

To cover pelvis and inguinal/femoral nodes, conformal avoidance IMRT is technically simple to simulate, plan, and execute. Dosimetric study has demonstrated that it achieves comparable PTV coverage compared with other approaches while at the same time significantly sparing the surrounding OARs.

Irradiating the groin nodes without breaking a leg: A comparison of techniques for groin node irradiation

The purpose of this study was to determine the optimal technique for delivering postoperative radiotherapy for vulvar cancer and other tumors requiring treatment of the inguinal nodes. This project compared tumor coverage and normal tissue sparing for the 5 main radiotherapy techniques that are used to treat vulvar cancer. The intensity-modulated radiation therapy (IMRT) plan was undesirable because it resulted in an excessive dose to portions of the central pelvic structures. The photon thunderbird with skin match was unacceptable because it underdosed a portion of the groin region. The electron thunderbird was ideal for thin patients but was not applicable for most patients because of excessive dose to the skin and subcutaneous tissues. The photon through-and-through and the photon thunderbird with deep match were acceptable in most situations. In thin patients, where the depth of the inguinal vessels is less than 3 cm, the electron thunderbird is the technique of choice. In the average-sized patient, both the photon through-and-through and the photon thunderbird with deep match are reasonable options. The available literature suggests that the risk of femoral neck fracture or necrosis of the femoral head is approximately 11% at 5 years using the photon through-and-through technique. In our opinion, this is an acceptable price to pay for reliable node coverage, setup simplicity, and zero risk of overdose at field junctions.

Irradiation of the inguinal lymph nodes in patients of differing body habitus: A comparison of techniques and resulting normal tissue complication probabilities

The treatment of the inguinal lymph nodes with radiotherapy is strongly influenced by the body habitus of the patient. The effect of 7 radiotherapy techniques on femoral head doses was studied. Three female patients of differing body habitus (ectomorph, mesomorph, endomorph) were selected. Radiation fields included the pelvis and contiguous inguinal regions and were representative of fields used in the treatment of cancers of the lower pelvis. Seven treatment techniques were compared. In the ectomorph and mesomorph, normal tissue complication probability (NTCP) for the femoral heads was lowest with use of anteroposterior (AP) and modified posteroanterior (PA) field with inguinal electron field supplements (technique 1). In the endomorph, NTCP was lowest with use of AP and modified PA field without electron field supplements (technique 2) or a 4-field approach (technique 6). Technique 1 for ectomorphs and mesomorphs and techniques 2 and 6 for endomorphs were optimal techniques for providing relatively homogeneous dose distributions within the target area while minimizing the dose to the femoral heads.

Improved treatment of pelvis and inguinal nodes using modified segmental boost technique: dosimetric evaluation

PURPOSE

To describe a novel, yet simple, modified segmental boost technique (MSBT) and to compare the dosimetry of our method with that of other traditional methods of treatment for the pelvis and inguinal nodes.

METHODS AND MATERIALS

We developed a radiotherapy technique that uses linear accelerators with multileaf collimators to treat the pelvis and sequentially boost the inguinal regions, while minimizing "hot spots" across the match-line. This was achieved by angling the gantry for the inguinal fields so that their medial borders aligned with the divergence of the posterior pelvic field. Film dosimetry was performed to compare the MSBT with the traditional segmental boost technique, partial transmission block, and photon/electron combination techniques. These treatment techniques were scored on the basis of the dose homogeneity index, defined as the ratio of match-line maximum dose to the average dose at a given depth in the groin treatment area.

RESULTS

The values of the dose homogeneity index were the same (1.04) for MSBT and partial transmission block, and 1.21, 1.39, and 1.18 for the segmental boost technique, photon pelvis with electron tags, and photon pelvis with electron boost, respectively.

CONCLUSION

The MSBT proved to be technically simple while optimizing dose homogeneity compared with the other techniques and allows for maximum use of the features of modern linear accelerators.

A technique for inguinal node boost using photon fields defined by asymmetric collimator jaws

A technique is described for treating inguinal nodes when using radiotherapy in the control of pelvic malignancies. A posterior photon field treats the pelvis. A wider anterior photon field treats pelvis and inguinal nodes. An anterior photon boost to nodes is delivered using asymmetric collimator jaws moved across center line. Advantages of this technique include simplicity of setup and treatment (a single isocenter is retained, and no transmission block is needed), minimal dose inhomogeneity, reduced dose to femoral necks reducing the risk of femoral fracture, low risk of nodal underdose, and elimination of dosimetric difficulties inherent in electron beam boosts.

Assessment of target dose delivery in anal cancer using in vivo thermoluminescent dosimetry

PURPOSE

To measure anal dose during external beam radiotherapy (EBRT) using in vivo dosimetry, to study the difference of measured from prescribed dose values, and to evaluate possible associations of such differences with acute and late skin/mucosal toxicity and anorectal function.

MATERIALS

Thirty-one patients with localized anal carcinoma underwent in vivo measurements during the first EBRT session. Themoluminescent dosimeters (TLD) were placed at the center of the anal verge according to a localization protocol. No bolus was used. Patients received a median dose of 39.6 Gy (range: 36-45 Gy) by anteroposterior opposed AP/PA pelvic fields with 6 or 18 MV photons, followed by a median boost dose of 20 Gy (range: 13-24 Gy). Concomitant chemotherapy (CCT), consisting of 1-2 cycles of continuous infusion 5-fluorouracil (5-FU) and bolus mitomycin-C (MMC), was usually administered during the first weeks of the pelvic and boost EBRT courses. Acute and late skin/mucosal reactions were recorded according to the Radiation Therapy Oncology Group (RTOG) toxicity scale. Anal sphincter function was assessed using the Memorial Sloan Kettering Cancer Center (MSKCC) scale.

RESULTS

TLD anal doses differed by a mean of 5.8% (SD: 5.8) in comparison to the central axis prescribed dose. Differences of at least 10% and at least 15% were observed in eight (26%) and three (9.7%) patients, respectively. TLD doses did not significantly correlate with acute or late grade 2-3 skin or mucosal toxicity. However, patients having good-fair MSKCC anal function had a significantly greater mean difference in anal TLD dose (10.5%, SD: 5.9) than patients having excellent function (3.8%, SD: 4.6) (P = 0.004). Prescribed dose values, length of follow-up, and age at diagnosis did not correlate with late sphincter function.

CONCLUSIONS

These data show that AP/PA fields using megavoltage photons deliver adequate dose to the anal verge. However, in about one quarter of patients treated with this technique the anal dose varied from the prescribed dose by at least 10%. The observed correlation of TLD values and late sphincter function suggests that direct measurement of the dose delivered to the anal verge might be clinically relevant.

Use of segmental boost fields in the irradiation of inguinal lymphatic nodes

En face electron fields to boost inguinal lymphatics have been used by oncologists for many years. With the introduction of multileaf collimators (MLC) and independent jaws, the practice of creating segmental fields to boost areas of interest has expanded. Typical anterior-posterior opposing field treatment of the pelvis may now be enhanced to include additional anterior segments to boost lymphatic tissue at a predetermined depth. This report illustrates the clinical implementation of one such segmental boost technique. Computer generated isodose plans utilize manual contour and CT-generated data for analysis of inguinal lymphatic depths. Potential areas of field overlap are discussed as well as the use of combined 6 and 15 MV photon energies to reduce areas of inhomogeneous dose. Technical details associated with MLC field size limits and other clinical factors are also discussed in relationship to smooth treatment delivery.

Transmission blocks for lower neck and inguinal lymph node radiotherapy

We evaluate techniques for radiotherapy to low neck and inguinal lymph nodes. Partial transmission blocks (PTBs) simplify treatment planning, daily setup, and improve reproducibility and dose homogeneity. PTBs minimize the risk for dose misadministration to critical organs. Disadvantages include doses that are potentially lower to the medial cervical lymphatics and higher to the femur. PTBs can surmount common treatment planning problems.

Prophylactic chemoradiation of inguinofemoral lymph nodes in patients with locally extensive vulvar cancer

OBJECTIVE

Primary surgical resection of locally advanced squamous cancer of the vulva may compromise the integrity of important midline structures such as the anus, clitoris, urethra, and vagina. Chemoradiation (synchronous radiation and cytotoxic chemotherapy) has been used as alternative initial treatment which may serve as definitive management for some patients, or may reduce the scope and functional sequelae of subsequent surgery in others. Inguinofemoral node dissection is associated with substantial risk of both acute and late morbidity, prompting consideration of elective inclusion of groin nodes within the irradiated volume and deletion of subsequent groin surgery. Concern that disease relapse in the groins is potentially fatal suggested the prudence of formal outcome assessment of our recent experience with prophylactic treatment of clinically uninvolved groin nodes in the context of concurrent chemoradiation for locally advanced primary vulvar cancer.

METHODS

A review was conducted of 23 previously untreated patients with locally advanced squamous cancer of the vulva (2 T2, 20 T3, 1 T4) and clinically uninvolved groin nodes (1969 FIGO stages 14 N0, 4 N1, and 5 N2 with negative node biopsies) who were treated since 1987 with chemoradiation administered to a volume electively including bilateral inguinofemoral nodes. These patients did not undergo subsequent groin surgery.

RESULTS

With follow-up from 6 to 98 months (mean, 45.3 months; median, 42 months), no patient has failed in the prophylactically irradiated inguinofemoral nodes. No patient has developed lymphedema, vascular insufficiency, or neurological injury in a lower extremity, and no patient has experienced aseptic necrosis of a femur.

CONCLUSIONS

Elective irradiation of the groin nodes in the context of initial chemoradiation for locally advanced vulvar cancer is an effective therapy associated with acceptable acute toxicity and minimal late sequelae. It constitutes a sensible alternative to groin dissection in this patient population.

A simple technique for fabrication of transmission block for concomitant treatment of bilateral anterior inguinal lymphatics and pelvic/perineal structures

The efficacy of transmission block technique with contiguous photon irradiation of inguinal as well as pelvic and perineal structures has been reported in literature. In this paper, a simple and accurate method for the proper fabrication of transmission block has been described and also demonstrated to be effective and useful. The procedures for a precise geometrical alignment and dose verification are also detailed.

Radical vulvectomy with postoperative irradiation for vulvar cancer: therapeutic implications of a central block

PURPOSE/OBJECTIVE

To report the long-term results of vulvectomy, node dissection, and postoperative nodal irradiation using a midline vulvar block in patients with node positive vulvar cancer.

METHODS AND MATERIALS

From 1971 through 1992, 27 patients with carcinoma of the vulva and histologically involved inguinal lymph nodes were treated postoperatively with radiation therapy after radical vulvectomy and bilateral lymphadenectomy (n = 25), radical vulvectomy and unilateral lymphadenectomy (n = 1), or hemivulvectomy and bilateral lymphadenectomy (n = 1). Federation Internationale de Gynecologic et d'Obstetrique stages were III (n = 14), IVA (n = 8), and IVB (n = 5) squamous cell carcinoma. Inguinal lymph nodes were involved with tumor in all patients (average number positive = 4, range 1-15). Postoperative irradiation was directed at the bilateral groin and pelvic nodes (n = 19), unilateral groin and pelvic nodes (n = 6), or unilateral groin only (n = 1). These 26 patients had the midline blocked. In addition, one patient received irradiation to the entire pelvis and perineum. Doses ranged from 10.8 to 50.7 Gy (median 45.5) with all patients except 1 receiving > or = 42.0 Gy.

RESULTS

Actuarial 5-year overall survival and disease-free survival estimates were 40% and 35%, respectively. Recurrences developed in 63% (17/27) of the patients at a median of 9 months from surgery (range 3 months to 6 years) and 15 of these have died; two patients with recurrences are surviving at 24 and 96 months after further surgery and radiation therapy. Central recurrences (under the midline block) were present in 13 of these 17 patients (76%), either as central only (n = 8), central and regional (n = 4), or central and distant (n = 1). Additionally, three patients developed regional recurrences and one patient developed a concurrent regional and distant relapse. One patient developed a squamous cell cancer of the anus under the midline block 54 months after the initial vulvar cancer and an additional patient developed transitional cell carcinoma of the ureter (outside the radiation field) 12 months after diagnosis. Factors associated with a decreased relapse-free survival included increasing Federation Internationale de Gynecologic et d'Obstetrique stage (p = 0.01) and invasion of the tumor into the subcutaneous (SC) fat or deep soft tissue (p = 0.05). Chronic lower extremity edema developed in four patients, but there have been no other complications.

CONCLUSIONS

Radical vulvectomy has often been considered sufficient central treatment for vulvar carcinoma, with postoperative irradiation directed only to the nodes. Although designed to protect the radiosensitive vulva, use of a midline block in this series resulted in a 48% (13/27) central recurrence rate, much higher than the 8.5% rate previously reported with this technique. Routine use of the midline block should be abandoned and, instead, postoperative irradiation volumes should be tailored to the individual patient.